Table Of Contents Pulse))))air V7, Sw 7.2.0

Transcript

Table of Contents Pulse))))Air V7, SW 7.2.0 1.0 Introduction. Pulse))))Air_V7, Software Version 7.2.0 .................................................................... 3 1.1 Description .......................................................................................................................................... 3 1.2 Specifications ...................................................................................................................................... 7 2.0 Probe Installation........................................................................................................................................... 8 2.1 Requirements for Installation into Pipes or Tanks ............................................................. 8 2.2 Installation in External Flow Pipe ......................................................................................... 12 3.0 Operator Interface Installation .............................................................................................................. 13 4.0 Wiring .............................................................................................................................................................. 13 4.1 AC Input......................................................................................................................................... 14 4.2 Pulse Sense and Actuator Wiring .................................................................................................. 14 4.3 Probe Earth Ground ...................................................................................................................... 14 4.4 Analog Outputs ............................................................................................................................. 15 4.5 Process Interlock ...................................................................................................................... 15 5.0 Operating Screens ....................................................................................................................................... 16 5.1 Startup Screen ............................................................................................................................... 16 5.2 Default Operating Screens ................................................................................................................ 16 5.2.1. Softkeys .................................................................................................................................. 18 5.2.2 “CTRL VALUES” Softkey for PID Screen ............................................................................. 18 5.3 Additional Operating Screens ........................................................................................................... 19 5.3.1 DETAIL RESULT Screen: Air Calculations .................................................................................... 19 5.3.2 DETAIL RESULT Screen: Input/Output ............................................................................. 22 5.3.3 ALARMS ................................................................................................................................... 23 6.0 Change Parameters ..................................................................................................................................... 27 6.1 Initial Setup ....................................................................................................................................... 28 6.2 Calibrate Air ..................................................................................................................................... 29 6.3 Pulse)))Air Parameters ...................................................................................................................... 32 6.3.1 Pulse))))Air On/Off ..................................................................................................................... 32 6.3.2 Process Interlock ........................................................................................................................ 33 6.3.3 Test Frequency ........................................................................................................................... 33 6.3.4 Test in Averaging ....................................................................................................................... 33 1 6.3.5 Minimum Air Out, Maximum Air Out ...................................................................................... 34 6.3.6 Minimum Bubble Index, Maximum Bubble Index .................................................................... 34 6.3.7 Demo Mode ............................................................................................................................... 34 6.4 Pressure Compensation .................................................................................................................... 35 6.5 Solubility Compensation ................................................................................................................... 35 6.5.1 Solubility Compensation On/Off ............................................................................................... 36 6.5.2 Gas/Liquid Combination ............................................................................................................ 36 6.5.3 Temperature .............................................................................................................................. 37 6.6 Calibrate Pressure ............................................................................................................................. 38 6.7 Change Screen Contrast .................................................................................................................... 38 6.8 Analog Output Channel Assignment ................................................................................................. 38 6.9 Process Controller Parameters ......................................................................................................... 40 6.9.1 Activating or Removing the Controller ...................................................................................... 40 6.9.2 Description of Controller Algorithm .......................................................................................... 41 6.9.3 Setting Gain, Reset, and Derivative............................................................................................ 41 6.9.4 Setpoint Tracks Air when in Manual Mode................................................................................ 43 6.9.5 Controller Output Limits in Auto................................................................................................ 43 6.9.6 Deadband ................................................................................................................................... 43 7.0 Maintenance .................................................................................................................................................. 44 7.1 Seals .................................................................................................................................................. 45 8.0 Wiring Diagrams (Pulse))))Air_V7.2) .................................................................................................. 47 2 1.0 Introduction. Pulse))))Air_V7, Software Version 7.2.0 1.1 Description Operator Probe Interface Figure 1.1. Pulse))))Air_V7tm Entrained Air Sensor. Sensor includes Insertable Probe and Operator Interface. . Fig. 1.1 shows the two components of the Pulse))))Air: the insertable “Probe” and the “Operator Interface”. Fig. 1.2 is an open section drawing of the Probe, with key components identified. Referring to the Figures, the operation is as follows: The “Piston Housing” portion of the Probe is preferably inserted into the fluid in the “Process Pipe” through a pipe nipple and valve arrangement. The Process Pipe refers to the user’s process 3 piping, vessel wall, or other process fluid containment. In the case of process piping, the diameter of the process piping can be as small as 2” diameter. There is no upper limit on pipe diameter. The Process Pipe may be part of an external flow loop (i.e., the probe insertion does not need to be “invasive” to the process). The probe can also be installed through the wall of a tank, or simply suspended from above, with the end of the Piston Housing submerged in the process liquid. Figure 1.2. Open Section Drawing of Probe The solid-state “Actuator” is connected to the “Compression Piston”. At the end of the Compression Piston, is a flush-diaphragm “Pressure Transducer” which is in contact with the process fluid. Not shown is Fug. 1.2 is the provision for making the connection of the Piston Housing to the Process Pipe both sealed and detachable. This is explained further in Section 2.0. Upon command from the Operator Interface, the Actuator rapidly moves the Compression Piston into the process fluid. This rapid movement causes the fluid at the face of the Pressure Transducer to be compressed. (Note: Never touch the pressure transducer.) The resultant pressure “Pulse” which occurs at the face of the Pressure Transducer due to this movement is related to the entrained air content of the fluid. The magnitude of the pressure Pulse decreases with increasing entrained air content. Fig. 1.3 shows a typical relationship between entrained air content and the magnitude of the pressure Pulse. The Pulse is converted to the equivalent entrained air content by logical calculations in the microprocessor in the Operator Interface. It should be apparent from this description that it is NOT necessary to collect and isolate a process sample. Because the movement of the Compression Piston is so rapid, the process fluid does not have time to move away from the advancing face of the Pressure Transducer. Consequently, the fluid itself serves as a dynamic containment vessel. 4 The Actuator utilizes the principle of “magnetostiction”, wherein magnetically susceptible crystallites will reorient in an applied magnetic field. When a brief high voltage pulse is applied to the coil in the Actuator, the resulting magnetic field causes the magnetically susceptible crystallites to reorient such that the Actuator rod length increases by approximately 140 microns (0.005”) over a time of approximately 200 microseconds. The structural change in the crystal structure is within elastic deformation limits of the relevant materials, In other words, all stresses are small enough that material life is very long. In addition, although the Compression Piston moves across the “Seal”, the movement is so small that the Seal does not rub. Rather, the Seal simply deforms slightly. The consequence of these small elastic movements is that the Probe falls into the class of “solid-state” devices with a correspondingly long lifetime. Figure 1.3. Entrained Air vs. Pulse The Operator Interface incorporates a Digi International (formerly Rabbit Semiconductor and before that, Zworld) model OP7200 microprocessor, operating at 22.5 MHz. All calculations and decisions are controlled by the OP7200. Two isolated 4-20 ma signals are software configurable to transmit the entrained air and other process measurements, such as bubble size distribution, to remote devices. The software also includes a selectable process controller which can be used to drive an output device, such as a defoamer pump, in order to automatically control entrained air to a setpoint. All of the signal conditioning is not done on the analog conditioning board located in the Operator Interface. Additional preconditioning is also done on the Amplifier Board, shown in 5 Fig. 1.4. This board is mounted at the sensor in the junction box closest to the mounting flange. The Amplifier Board amplifies the low-level millivolt differential voltage that is produced by the Pressure Transducer and converts it into a higher level single-ended signal that is passed to the Operator Interface. This procedure reduces noise in the Pressure Transducer signal. The board also includes a high frequency RFI filter to reduce unwanted noise from radio transmitters and other sources. J1 Position 1 J2, Position 1 Figure 1.4. Amplifier Board. The board is located at the Probe, in the junction box closest to the mounting flange. 6 1.2 Specifications Performance Measurement Range: 0.05 to 20% Accuracy, in % air units: Between 0.05 and 5%: +/-0.005 at 0.05%, increasing to +/-0.1 at 5%. Between 5% and 20%: +/-0.1 at 5%, increasing to +/-0.5 at 20%. Drift: Approximately 2% of reading per year. Calibration: Initial calibration is completed at factory. Startup calibration is completed by PAPEC on-site. Subsequent calibrations are completed by customer in the actual installed location by entering manual entrained air measurement results into the microprocessor using the Operator Interface touchscreen. Mechanical/Electrical (Insertable Probe) Material: Wetted parts are 316 SS. Probe Weight: 11.8 kg (26 lbs). Temperature Limits: Inserted portion of Probe: 0-94C (32-200 F). Electronic Components: 065C (32-148 F). Pressure Limits: 3.4 bar (50 psig). Pressure Transducer damaged above 6.8 bar (100 psig). Suspended solids: No limit to concentration. Solids should be non-abrasive. Viscosity: Viscosity changes of < +/-20% have negligible effect. Mechanical Life, as cycles and years at 5 seconds per cycle: Actuator 108 cycles (9 years). Pressure Transducer 5*107 cycles (4.5 years). Seals 106-107 cycles (0.5 to 1 year), depending upon fluid-material compatibility. Pipe/Vessel Installation: Minimum 2” (5cm) pipe diameter, no limit on maximum size. Process Fluid Flow Rate: 3 ft/sec (1 m/sec) minimum flow. No limit on maximum flow. Mechanical/Electrical (Operator Interface) Environmental Isolation: Nema 4X (IP65) Power: 100-240 VAC, 50-60 Hz, single-phase at 50 watts. Temperature Limits: 0-44 C (32-110 F). Analog Outputs: 4-20 ma into 800 ohm max. 24 VDC loop power is provided by the Operator Interface electronics. Analog outputs are isolated up to1500 volts. Interlock Digital Input: Open circuit is logical high, switch closure is logical low. Microprocessor: Dgi International OP7200. Display: Graphic 320x240 LCD with resistive touch screen. Backlight life 8.5 years to 50 % intensity. Real Time Clock Battery Life: 3-5 years. Program Code: Code in EEPROM, parameters in battery-backed SRAM. 7 2.0 Probe Installation The procedures for proper installation of the Probe and Operator Interface are explained in this section. Close attention to the procedures is important in order to obtain best performance. Pay attention to the label on the side of the Actuator Housing: The pressure transducer is not to be touched! When the Probe is first unpackaged, there is also a warning label on the Piston Housing. That label needs to be removed before installation. Do not remove the warning label on the side of the Actuator Housing. Relevant dimensional data for the Probe are shown in Fig. 2.1. Two junction boxes are provided for connections to the Probe. The ports are ½” NPT. The boxes are Nema4 rated, provided that the top covers are securely in place and good water-tight fittings are used for wire passage. The boxes are powder-coated aluminum. 2.1 Requirements for Installation into Pipes or Tanks Extension into pipe or tank. The end of the Probe should extend well into the process fluid in order to ensure that a representative fluid sample is tested. The extension of the Probe into the process fluid should be at least 5 mm (1/4"). Avoid stagnant fluid. There must be adequate flow of fluid around the end of the Probe in order to ensure that the Probe is not looking at a stagnant sample. In a pipe installation, the minimum fluid flow past the end of the Probe is 0.5 m /sec (1.6 ft/sec). The flow in the pipe must be turbulent (Reynolds number greater than 3,000 is recommended). If the Probe is installed vertically in an open tank, it is especially important to ensure that there is enough flow around the end of the Probe so that there will be no bubbles held against the end of the Probe by buoyancy forces. If the Probe must be installed in an open tank where there is not a great deal of turbulence, then the Probe should be mounted at as much of an angle away from vertical as possible. Orientation relative to flow. The Probe should preferably be installed perpendicularly to the direction of the process stream flow. It should normally not be installed with the end facing downstream because pressure pulsations caused by eddies shedding off the end of the probe can interfere with good measurement. However, if the process fluid is abrasive, it may be necessary to place the end of the probe facing slightly downstream. The Operator Interface automatically analyzes the magnitude and frequency of process noise caused by the shedding of turbulent eddies, and it provides a warning if the noise is excessive. In such a case, another orientation of the Probe is necessary. 8 Figure 2.1 Probe Dimensions and Installation Notes 9 Avoid pressure pulsations. Pressure pulsations with a frequency of between 500 Hz and 6000 Hz, and with an amplitude of more than 0.07 bar (1 psi) will interfere with best measurement when entrained air contents are less than approximately 2%. The best way to avoid the possibility that pressure pulsations will interfere with accurate air measurement is to install the Probe upstream of valves or pumps. The Probe should be installed no less than 5 pipe diameters upstream and no less than 10 pipe diameters downstream of valves or pumps. The Operator Interface automatically analyzes the magnitude and frequency of process pressure pulsations, and it provides a warning if the noise is excessive. Dealing with air stratification. When selecting a position on a tank or pipe, keep in mind that entrained air in process fluids can often stratify very quickly. For example: Entrained air tends to collect along the inside of pipe walls; Entrained air will rise to the top of the pipe in a long horizontal pipe run; Entrained air will move to the inside of pipe elbows. Therefore, if the Probe is installed by insertion into a process pipe or tank (the preferred installation method), then attention must be paid to the location and insertion depth of the sensor into the pipe or tank. Always consider the following guidelines when installing the Probe: -Insert the Probe a minimum of 5mm (1/4") into the process pipe or tank. -Install the Probe in or just after a process section in which there is considerable turbulence and mixing taking place, such as in a well-mixed tank, or after a pump. (However, observe the cautions regarding the adverse effects of pressure pulsations explained in the preceding paragraph.) -In a horizontal process pipe installation, install the Probe between the 1 o’clock and 6 o’clock position relative to the top of the pipe. -Picture how the air may stratify in any given situation and attempt to locate the Probe so as to minimize the effects of any stratification. Position relative to obstructions. If the Probe is installed in a pipeline, install the Probe no less than 10 pipe diameters downstream or 5 pipe diameters upstream of obstructions such as valves and elbows. Pressure. The Pulse))))Air_V7tm will operate satisfactorily at up to 3.6 bar (50 psig) of process line pressure. In many situations, it may be convenient to take advantage of this and install the sensor in a pressurized pipe or vessel. However, it is very important to take into account the effect of pressure on the solubility of the entrained gas in the process stream. At increased pressure, some or all of the entrained air which would be present at atmospheric pressure will be dissolved and not directly measureable at the elevated pressure. In most cases, the entrained air content at atmospheric pressure is the important information. For example, pulp drainage on drum washers is at atmospheric pressure, and pulp drainage on paper machine tables is at atmospheric pressure. Virtually without exception, all manual entrained air measurements are made at atmospheric pressure. Because of solubility effects, there is a minimum entrained air content required at atmospheric pressure in order to still have some free entrained air available to be measured at the pressurized location. This is illustrated in Figure 2.2, for the case of air in water. Consider, for example, that the sensor is installed in piping at a pressure of 15 psig and at a process temperature of 80C. Under these conditions, all entrained air below 1.4% at atmospheric pressure will be completely dissolved (and not directly measureable) at the 10 pressurized condition. Therefore, it is much preferred to perform the entrained air measurement at the process pressure that is of interest. Yet a further issue with regard to the effect of pressure on dissolved/entrained air is the rate of solution or dissolution as the pressure changes. The equilibrium solubility of air in process fluid is not reached instantaneously. Therefore, another consideration, in addition to the pressure itself, is how long the process fluid is subjected to the pressure. The Pulse))))Air can make compensating calculations of both equilibrium air solubility and the rate of air solution/dissolution. Therefore, if the Probe must be installed at a pressure other than the process pressure that exists at the problem point (again, such as on a drum washer or a paper machine table), it may be appropriate to make certain parameter settings in order to perform the necessary calculations. These procedures are explained in Sections 6.4 and 6.5. Minimum Possible Air at atm Pressure 6 5 4 3 2 T=20 T=80 1 0 0 10 20 30 40 50 Pressure in process vessel (psig) Figure 2.2. Minimum measureable air at atmospheric pressure vs. pressure at installed location of sensor. Process limits and safety cable. Observe the temperature and pressure limits shown in the Specifications. Always utilize the provided safety cable to prevent the Probe from pulling out completely before the valve is closed. Note that the PAPEC-provided adapter flange incorporates an o-ring seal so that it is not necessary to install an additional gasket between the faces of the mounting flanges. 11 2.2 Installation in External Flow Pipe Because the Probe can be inserted into process piping as small as 2”, in some cases it may be most convenient to install the Probe into an external flow loop using an external flow chamber as diagrammed in Fig. 2.3. The tank is easily assembled by the customer using standard piping. Figure 2.3. External Sample Pipe 12 Due to air stratification issues, attention needs to be paid to using good methods to obtain the sample flow from the process. These are explained in Section 2.1. In addition, never draw more than one sample flow from a single sample tap. The two (or more) flows obtained by splitting the flow from a single sample tap will usually contain different entrained air contents due to air stratification. If there is a need to pull a single sample from one location on the process pipe and then pass it to two or more test devices, then set the flow up in a series fashion with the flow first passing through one device and then continuing on to the next device(s). Although the external flow chamber shown in Fig. 2.3 is designed to minimize air stratification, the flow disturbances caused by the threads and shape to the 2” tee can still cause some air stratification. To minimize these effects it is important to maintain the sample flow at 10-20 gpm, and to configure feed valves and procedures so that the flow remains steady. 3.0 Operator Interface Installation The Operator Interface enclosure is Nema4X (IP65) and it can therefore be mounted in corrosive and wet environments. However, because the enclosure will be occasionally opened for service, and because someone will invariably fail to properly close the panel or to install good watertight wire seals, installation in the cleanest area possible is good practice. If there is any possibility that water may drip on the Operator Interface when it is opened for service, then a protective shield must be installed. The maximum distance of the Operator Interface from the Sensor is based on the acceptable amount of electrical noise that may be picked up by the Pressure Transducer electrical signal. With proper shielding of the signal lines to the Probe, a maximum distance of 50’ (15 m) from the Probe is recommended. A longer distance may be acceptable on a case-by-case basis. If the electrical noise is excessive, the Pulse))))Air is designed to detect that circumstance. Note that the ambient temperature at the Operator Interface must be greater than 0 C and less than 44 C (32-110 F). The cabinet outer dimensions are 13.5” high by 9” by 6” deep. The mounting hole pattern is 11.75” by 8” and the hole size is 5/15” . The door hinges on the left and four ½” NPT conduit hubs are provided on the right side for wire entry. 4.0 Wiring The wiring connections are shown in Fig. 8.1. The terminal connections shown on the right side of Fig. 8.1 represent connections on the processor board in the Operator Interface enclosure .The terminal connections shown on the left side of Fig. 8.1 represent connections on the terminal strips in the two junction boxes located at the Probe. Fig. 1.4 identifies the terminal position on the Amplifier Board that is located at the Probe in the junction box closest to the mounting flange. The number 1 position is identified in that Figure. Further detail is provided below. 13 4.1 AC Input Connect the AC power to the Operator Interface at terminal J3. The L1, L2, and Earth positions are identified on the silkscreen. Note that "Earth" may also be called "ground" by some electrical standards. Note also that some electrical standards may refer to “L1” as “live” and to “L2” as “neutral”. For the purposes of this system, L1 and L2 are interchangeable. AC power is 100-240 VAC, 50-60 Hz, single-phase at 50 watts. Power must be from a clean source. If a clean power source is not available, a power conditioner must be installed. Be certain to provide a good earth (ground). A good earth (ground) is necessary not only for safety, but also as a voltage sink to reduce power transients that develop on the board power busses as a consequence of the high voltage transients that are generated by the actuator components. 4.2 Pulse Sense and Actuator Wiring Wiring details are shown in Fig. 8.1. The Pulse Sense and Actuator connections are located at terminal strips J2 and J3, respectively, on the processor board in the Operator Interface enclosure. Connect J2 to the Amplifier Board terminal strip J2 (Fig. 1.4) in the lower junction box on the Probe (the one closest to the mounting flange). Be certain that the wires are connected as shown in Fig. 8.1 (Position 1 to 1, 2 to 2, etc.) as the connections are not protected against reverse polarity. Connect J3 to the terminal strip in the upper junction box on the Probe. Note the specification for the use of flexible metal conduit. The flexible metal conduit must make electrical contact with the metal junction box at the probe end. Make the flexible portions of the conduits long enough so that the Probe can be removed from the installed location without needing to disconnect any wires. Note that the Pulse Sense wiring is shielded and that the shield is landed at the Operator Interface end. The shield must not touch the Probe or the conductive wall of the conduit.. 4.3 Probe Earth Ground The Probe must be independently connected to an earth ground. Connect a conductive strap from any convenient location on the Probe to a local earth ground. To avoid the possibility of galvanic corrosion of the Probe, the electrical potential at the local earth ground must be as close as is practical to the electrical potential of the process fluid at the installed location of the Probe. 14 4.4 Analog Outputs The 4-20 ma analog output connections are located at terminal strip J1 in the Operator Interface enclosure (See Fig. 8.1). The Operator Interface provides the 24-volt loop power. Never connect an additional power supply to the analog output loops. Positions 1-2 on J1 provide the analog output for channel 1 (1 plus, 2 return), and positions 4-5 on J1 provide the analog output for the channel 2 (4 plus, 5 return). Positions 3 and 6 provide an optional position for landing the cable shields. However, note as specified in Fig. 8.1, that the preferred locations for landing the shields are at the customer's end. The shields must never be landed at both ends. The two analog output channels can be programmed to output any two of four process variables, including entrained air, bubble size, pressure, and process controller output (Section 6.8). The analog outputs are isolated from the Operator Interface and from each other at up to 1500 VDC. The analog outputs can drive up to 800-ohm loads. 4.5 Process Interlock Positions 7 and 8 on J1 (Fig. 8.1) provide an interlock capability. By connecting a switch between these two positions the customer can signal to the Pulse))))Air when the process is down, so that the Pulse))))Air can shut itself down during those times. Switch open signals that the process is running and switch closed signals that the process is down. 15 5.0 Operating Screens 5.1 Startup Screen When the Operator Interface is powered up, a general information display is first shown (Fig. 5.1). This display provides information on the model version, software version, and PAPEC contact information. After 60 seconds, this display times out automatically. The user may also press any key on the keypad to complete the startup before the 60 seconds is completed. Figure 5.1. Startup Screen 5.2 Default Operating Screens Upon startup, after the information screen has been displayed, one of two different default operating screen will be displayed, depending upon the status of the PID process controller. If the user has specified that the controller is not to be available for use (Section 6.9.1), then a screen is shown that provides a short summary of the air measurement (Fig. 5.2). Conversely, if the user has specified that the PID process controller is to be active, then the information screen shows additional information including entrained air setpoint and controller output (Fig. 5.3). 16 Figure 5.2 Default Operating Screen, PID Controller not Specified Figure 5.3. Default Operating Screen, PID Controller Specified 17 5.2.1. Softkeys Several “buttons” appear across the bottom of the default operating screens, as can be seen on Figs. 5.2 and 5.3. Those buttons which are outlined in boxes with round corners define the action of the keyboard keys under each button (”softkeys”). Pressing a softkey causes the display to change to show the requested information. The single button labeled "STATUS" is not touch-responsive. The STATUS button shows the status of the sensor at the current moment. The following information can be displayed in this button: -IDLE. This indicates that the sensor is active but at the moment is not running a test. The idle time is user specified to between 5 and 15 seconds. -TEST. This indicates that the sensor is running a test. The actual test time is only a few milliseconds. However, the TEST message is shown for one second so that the user can see it. -OFF. This indicates that the user has turned the sensor off by software configuration. -LOCK. This indicates that the user's process is down and that the Pulse))))Air is turned off by interlock action. 5.2.2 “CTRL VALUES” Softkey for PID Screen When the PID controller has been specified as active by the user, the “CTRL VALUES” softkey (Fig. 5.3) becomes available. The setpoint, defoamer output, and the control status can be changed at any time by selecting the “CTRL VALUES” softkey. When the key is pressed, the screen shown in Fig. 5.4 is displayed. Fig. 5.4 Changing PID A/M, Setpoint, and Defoamer 18 If the controller mode is currently in MANUAL mode, and the operator wants to change the controller to AUTO, move the cursor up or down using the up and down arrow keys as needed to highlight the item “AUTO/MANUAL:”, select it with the diamond enter key, and the mode will change to AUTO. Setpoint and defoamer are changed in similar fashion. When either of these is highlighted and selected, then a numerical entry screen appears. The new value is keyed in and returned, and the controller now uses that value. Note, however, that if the mode is MANUAL and setpoint tracking is specified ON (Section 6.9.4), then the setpoint cannot be changed; In that case, it is forced to always follow the current entrained air value. Note that when the controller is in the AUTO mode, the defoamer cannot be set above or below the defoamer limits allowed in the AUTO mode (Section 6.9.5). Also, if the mode has been MANUAL, and the mode is changed to AUTO, and, in addition, if the defoamer at the time of the change is out of the acceptable limits for AUTO mode, then the defoamer will be automatically reset to the allowed limit for the AUTO mode. 5.3 Additional Operating Screens The buttons across the bottom of the operating displays are used to select optional screens that show additional operating information. These optional screens are explained below. 5.3.1 DETAIL RESULT Screen: Air Calculations The first press of the “Detail Result” softkey brings up a screen that shows certain details about the air calculations. (Continued presses of the softkey cause the display to alternate between the air calculation details and a screen that shows analog and digital I/O details, described in Section 5.3.2). The air calculation details are shown in Fig. 5.5. 19 Figure 5.5. Air Calculation Details The items that are displayed on the air calculations screen are explained as follows: -"Background volts". This is the measure of background noise. It includes normal board-level noise, pulsations in static pressure in the process, and the effects of RFI in the area. Normal board-level noise is quite small, on the order of 0.05 volts. If pressure pulsations are low frequency and/or low magnitude compared with the pressure Pulse measurement obtained during a normal test, the background volts number will remain small. Pressure pulsations with a frequency close to the pressure Pulse frequency (about 3 kHz), and with an intensity of over approximately +/-1 psi relative to the background pressure, will start to interfere with the pressure Pulse measurement. This can be indicated by a background voltage number reaching or exceeding 0.4 volts. Radio frequency interference (RFI) can also drive the background volts high. It is not possible from this measurement to determine whether pressure pulsations or RFI are driving the background volts high. The Pulse))))Air compares the background volts measurement with an allowable limit (typically 0.5 volts) and turns on a alarm to indicate the discrepancy. To the right of the Background volts is a number shown in parentheses. As the Pulse))))Air prepares to run a test, it first checks the background noise. If the noise is too high, it pauses for 2 ms and then tries again. The number in parentheses is the number of attempts before the test was actually run. In a good installation, a value of 0 or 1 is typical. In a noisy environment, the value increases. A value consistently over 6 indicates a need to redesign the installation. -"Pulse Measured". This is the pulse voltage that has just been measured in the most recent test. -"Pulse Averaged". This is the running average of the Pulse Measured readings. The averaging is based upon a user-specified number of preceding measurements to keep in the running average. The averaging also utilizes a proprietary “statistical averaging” procedure 20 which automatically differentiates between real process changes and process noise. The statistical averaging procedure is not user-adjustable. -“Pulse to History” This is a one-minute average of the Pulse Averaged number. This number is kept minute by minute for a 2-hour period for use in calibration. The number shown is the progression in the one-minute average during the current one-minute period. The number in parentheses to the right represents the progression of time in the current one-minute accumulation. Due to bookkeeping and multitasking considerations, this number will not always be exactly 60 (seconds) at the time that the moving average is written to memory. -“Pulse Calibrated”. The air calculation logic passes this number to the look-up table (“LUT”) that provides the amount of entrained air that corresponds to the Pulse value. In the absence of recalibration of the LUT in the field by the end-user, the Pulse Calibrated value is the same as the Pulse Averaged value. If a calibration has been done in the field, then the Pulse Averaged is appropriately converted to Pulse Calibrated, and this value is used to enter the LUT. -“Newest Air”. This is the air value obtained from the LUT using the Pulse Calibrated value. It is the air value that is present at the actual pressure and temperature conditions for the sensor installation. Note that if this value is negative, then there is no entrained air present, and the entrained air cannot be determined at atmospheric conditions. This may indicate one or a combination of three conditions: the installed location may be unsuitable, the system may need to be calibrated, or the pressure measurement may be in error. -“Air at atm ref”. This is the Newest Air value adjusted to the air that would be present at atmospheric conditions based on the process pressure, temperature, and the specific gas/liquid characteristics (e.g., air/water, or CO2/water). The default configuration assumes that the sensor is installed into the process at essentially atmospheric pressure. If the sensor is installed into the process at a pressure other than atmospheric, then the user has the option to so indicate, and compensating calculations will be made to take the entrained air value actually measured in the pressurized location and correct it to the value which would be present at atmospheric pressure. “HV_SP”. The two values shown on this line refer to the voltage to be applied to the actuator. The first number is the high voltage setpoint. This number is initially factory-specified at 120 V. Following a setup by the user (Section 6.1) in the actual installed location, this value will usually differ from the factory specification. The second number is actual voltage applied to the actuator. This number is the high voltage setpoint adjusted if necessary for the Pulse voltage too high (Section 5.3.3, “Pulse Voltage too High” alarm). 21 -”Air Range”. The two values show the two sigma (2*standard deviation) range for the “Air at atm ref” number. This provides an indication of the precision of the entrained air measurement. It can indicate the amount of noise that goes into the determination of the entrained air value. It can also indicate how stable or unstable the process is. High variability in the entrained air measurement also makes calibration more difficult. -“Factors 1,2” and “Left =, Right =”.. These are the factors that convert Pulse Averaged to Pulse Calibrated. 5.3.2 DETAIL RESULT Screen: Input/Output The first press of the “Detail Result” softkey brings up a screen that shows certain details about the measurement of the entrained air (Section 5.3.1, above). Continued presses of the softkey cause the display to alternate between the air details and a screen that shows analog and digital I/O details (Fig. 5.6). The screen shows the analog input and analog output values for the active channels, and it shows the status of the digital input used for control of the interlock action. Also shown are the specified value for the high voltage output to the actuator, and the expected value for the voltage to the actuator. The second value in the CH2 (Actr V) line should be in close agreement with the third value in the HV_SP line in the entrained air details screen (Fig. 5.5). Figure 5.6. Input/Output Details . 22 5.3.3 ALARMS The ALARMS button shows if any alarms are active with the text "ON" or "OFF". When alrarms are active, the text in the alarms button ( “ALARMS **ON**”) blinks on and off once per second. Pressing the ALARMS button shows a list of the alarm and warning messages that are currently on. The complete list of messages which may be displayed include: "Might need to Calibrate" “Pulse Voltage too High” "Low Process Pressure " "High Process Pressure " "High Background Noise" "Low Background Noise " "Short or Bad Actuator/HV" "Bad Wiring to Actuator (J4)" "Bad Wiring to Pres Trans (J2)" "Henrys Law Parameter Error" "Backup Battery may be Dead" The conditions which cause these messages and possible corrective action are provided below. The conditions that cause alarm messages to be displayed are not completely independent of each other. Therefore, if more than one alarm message is displayed, then the conditions and corrective actions for all of the alarms that are on should be studied. “Might need to Calibrate”. Cause: The last entrained air calculation returned a value for entrained air of less than 0. Mathematically, this can occur because of the setup of the LUT. Correction: If the Pulse))))Air has been recently started up, allow it to run for 2-3 hours before taking action on this warning. If the message is still present after the 2-3 hour startup/stabilization time, then corrective action is to recalibrate the Pulse))))Air_V7 (Section 6.1 ). Note that if solubility compensation is active (Section 6.4.1), and the message “Henrys Law Parameter Error” is also displayed, then that issue must be corrected first. “Pulse Voltage too High”. Cause: The voltage being applied to the Actuator is too high. Correction: The Pulse))))Air will automatically reduce the voltage being applied to the Actuator. This can be followed by accessing the Detailed Results screen (Section 6.3.1) and looking at the three values shown on the “HV_SP” line. The first value is the factory-specified voltage value. The second value is the factory value adjusted for the process temperature. If the process 23 temperature has not already been specified , then now would be a good time to do so (Section 6.6). The third value is the final voltage applied to the Actuator. This is the value that the Pulse))))Air will automatically adjust as needed to eliminate the error condition. The action is slow. Two to three hours may be required to complete the adjustment. The progress can be followed by monitoring the third value on the “HV_SP” line (one correction every 1-5 minutes). This value will slowly decrease as long as the “Pulse Voltage too High” message is displayed. If this value reaches 80% of the second value on the HV_SP line, then no further correction can be made. In that event, contact PAPEC. “Low Process Pressure” Causes: If the indicated process pressure is less than 2 psia (-12.7 psig), then this message will be displayed. Corrections: If the Probe is installed in a high vacuum line (which some customers will do when they want to determine dissolved air) then the gauge pressure can be negative. If the pressure is indeed less than 2 psia, then it is necessary to move the sensor to a higher pressure location. If it is known for a fact that the process pressure is not this low, and the message "Bad Wiring to Pres Trans (J2)" is not displayed, then recalibrate the pressure transducer (Section 6.5). If the message "Bad Wiring to Pres Trans (J2)" is also be displayed then refer to that message for corrective action. “High Process Pressure” Causes: If the indicated process pressure is greater than 50 psig, then this message will be displayed. Corrections: If it is known for a fact that the process pressure is not this high, then this condition would require moving the Probe to a lower pressure location. Conversely, if it is known for a fact that the process pressure is not this high, and the message "Bad Wiring to Pres Trans (J2)" is not displayed, then recalibrate the pressure transducer (Section 6.5). If the message "Bad Wiring to Pres Trans (J2)" is also be displayed then refer to that message for corrective action. "High Background Noise" Causes: High pressure pulsations and /or RFI (radio frequency interference) in the area can cause this alarm. Before each pressure Pulse measurement, the processor measures the noise on the analog input channel corresponding to the Pulse measurement, but without firing the actuator. If this noise exceeds a factory-specified value, then the processor repeats the measurement. When this background voltage measurement does not exceed the limit, then the processor continues by firing the actuator and measuring the pressure Pulse. The severity of the problem can be assessed by looking in the DETAIL RESULT screen (Section 5.3.1) on the first line, called “Background Volts”. At the far right is a number in parentheses. This value is the 24 number of attempts needed to find a quiet period for the Pulse measurement. Normal values are 0-2. A value greater than 6 trips the alarm. If 10 attempts are reached, then the processor will take one of two actions: It will go ahead and measure the Pulse as is, or it will skip the present measurement and use the last good value. The action is factory-specified. The default specification is to use the last good value. Corrections: If the current installation has high pipe wall vibration or pump pressure pulsations or if the Probe is located too close to pumps, valves, or other obstructions, then the sensor must be moved. If the area is close to a radio transmitter, then the area will need to be marked as off limits to use of radio transmitters (for both the Probe and the Operator Interface) Typically, communication radio use closer than 5 feet to the Pulse))))Air will cause RFI. “Low Background Noise’ Causes: Before each pressure Pulse measurement, the processor measures the noise on the analog input channel corresponding to the Pulse measurement, but without firing the actuator. A noise level less than a factory-specified value triggers this alarm message. Corrections: This is usually an indication of wiring or component problems. The message "Bad Wiring to Actuator (J4)" will also normally be displayed. “Short or Bad Actuator HV” Causes: The high voltage supply to the actuator is monitored by means of an independent analog channel. The expected voltage based on this analog signal is compared to the system-specified voltage to the Actuator (5.3.1 Detailed Results, line HV_SP, third number displayed). If the expected and commanded values do not agree, then the alarm message is displayed. Corrections: Indications are an Actuator failure, a DC-DC convertor failure, or a short in wiring connections between the operator interface and the sensor. Check interconnecting wiring first. Check for water intrusion into the Actuator housing. Then contact PAPEC. "Bad Wiring to Actuator (J4)" Causes: When the Actuator is triggered, the processor expects a brief drop in the high voltage to the Actuator. If that does not happen, then the alarm is triggered. Corrections: Check the wiring connections between terminal strip J4 in the operator interface and the terminal strip in the top junction box on the sensor. 25 "Bad Wiring to Pres Trans (J2)" Causes: The processor checks the voltage input from the pressure transducer in the probe. If the voltage is too low, the message is displayed. Corrections: Check the interconnecting wiring between terminal strip J2 in the operator interface and the lower junction box (next to the mounting flange) on the sensor. Check that the amplifier board in the lower junction box is clean and dry. "Henrys Law Parameter Error" Causes: The message will display only if solubility compensation is on (Section 6.4.1). If the temperature is high enough, or if certain parameters have been entered incorrectly, then the indication is that process fluid is flashing, and the solubility corrections cannot be completed. Corrections: Check that the process temperature has been properly specified (Section 6.6). If the “User” option in the solubility parameters menu has been selected and used to enter parameters, check that proper parameters have been entered. "Backup Battery may be Dead" Causes: An artificial value is stored in SRAM after bootup. The next time that the operator interface is powered up, the value of this parameter is checked, and if it is not in agreement with the expected value, then the message is turned on. Correction: Replace the battery with a Panasonic BR2330 or equivalent, + sign up. The battery is held in place with a spring clip. Be sure to turn the power off while changing the battery. After the battery is changed, it will be necessary to reenter all of the user-parameters. The default factory parameters will reload automatically. Battery life is 3 years with the operator interface unpowered and 7 years with the operator interface powered. 26 6.0 Change Parameters Except for the PID controller running parameters (Setpoint, Auto/Manual, and Defoamer output explained in Section 5.2.2), all parameter changes start by pressing the “CHANGE PARAMS” softkey. The various menus are accessed by using the up and down arrows to highlight the desired action and then selecting that action with the center diamond-shaped button. While parameter changes are being made, the Pulse))))Air continues to operate in the background. All parameter changes are stored into a buffer and do not affect the Pulse))))Air operation until CHANGE PARAMS is exited (with the sole exception of the parameter which is used to shut down the actuator cycling, which takes effect immediately). From all menus, the user has the option to select “DONE” or “ESCAPE”. Selecting DONE signals the processor to move the buffer values into run-time parameters when CHANGE PARAMS is exited. Selecting ESCAPE signals that none of the changes are to be kept. The menus are nested, so that in some cases it may be necessary to select DONE or ESCAPE from more than one menu as the user backs out of the CHANGE PARAMS routine. The first menu that is displayed when the CHANGE PARAMS button is pressed is shown in Fig. 6.1. Each of these items is described in the following sections. Figure 6.1. Change Parameters Main Screen 27 6.1 Initial Setup An initial setup will normally be done following the startup after a first installation. However, if the Pulse))))Air is providing a measurement that is in good agreement with manual measurements of the entrained air, then this step may be skipped. Although a setup is normally run only on a new installation, a setup can still be run at any time. Note, however, that when a setup is run, the existing calibration (Section 6.2) is cancelled out. Therefore , recalibration will required whenever an initial setup is performed on a previously calibrated Pusle))))Air. The quality of the initial setup is only as good as the manual air measurements used for the initial setup. It is very important to be sure that the manual measurements are of high quality. It is best to perform the initial setup when the process is very stable. Do not do a setup when the process air is highly variable. The procedure is as follows: 1. Allow the Pulse))))Air to run for several hours in order to stabilize. Note that if the alarm message “Pulse Voltage too High” is on, then the initial setup cannot be done until the Pulse))))Air has corrected for that condition. 2. Start by obtaining and averaging a group of manual air measurements. 3. Start the initial setup within the next 5 minutes. Select CHANGE PARAMS and then highlight and select “1. Initial Setup” in the menu (Fig. 6.1). If the Pulse voltage is too high at this time (as would be indicated on the ALARMS menu) a message is displayed that the setup cannot be started until the actuator power has been automatically adjusted to correct for the high Pulse voltage. 4. A menu is displayed asking for the manual air measurement (Fig. 6.2). Enter the manual air value. Note that if the “Escape” choice is selected from any menu, then the setup will be terminated with no effect on the Pusle))))Air operation. Figure 6.2. Data Entry for Initial Setup 28 5. Select “Start Setup Calcs”. An information screen is displayed that shows the progress of the first step. This runs for 2 minutes, except for the rare case where convergence occurs in the first step. Immediately following completion of the first step, the information screen displays the status of the second step, which also runs for 2 minutes. When the second step is completed, the information screen notifies that the process is done, and asks the user to press any key. If during the setup the actuator voltage has been driven to either a high or low limit, then a notice of that event will be displayed first. Again, at any time selecting escape cancels the process. When the setup is complete, the change parameters menu is redisplayed. Note that at this point, escape no longer will cancel out the setup calculations. 6.2 Calibrate Air The characteristic shape of the pressure Pulse vs. entrained air differs somewhat from one sensor to another. A typical response curve is shown in Fig. 1.3. The characteristic shape is determined under ideal conditions at the factory, and the results are stored in a look-up table (LUT). In the installed location at the customer’s facility, the Pulse))))Air measures the intensity of the pressure Pulse. This measurement provides the entry point into the LUT, and the result is the entrained air. As described Section 1.1, the Pulse))))Air does not isolate and compress a precisely-defined volume of sample. In addition, the change in volume upon compression is also not precisely known, and the volume that is compressed is not large. Present experience indicates that the fluid layer which is compressed is on the order of 2-5 mm. The thin layer limits the size of the bubbles that can be measured (although bubbles greater than 2-5 mm diameter are large and typically not an issue in most processes). These factors require that the fluid adjacent to the end of the probe must be well mixed. This becomes even more important when the fluid contains fibrous solids. In this case, the probe measures not only the compressibility of the entrained air bubbles, but also the strength of the fiber structure surrounding the bubbles. Because of these circumstances, actual field use usually requires further calibration in place. The general procedure of the calibration is to manually measure the entrained air when the process is operating in a normal condition, and to also manually measure the entrained air at process conditions of both higher air contents and lower air contents. These values are entered into the calibration routine as described below. The calibration point that results for the normal condition is referred to as the “coarse” calibration. The other two calibration points represent “fine” calibration. The coarse calibration is always needed. The fine calibrations are not mandatory but a much better overall calibration will be obtained when all three conditions are included. 29 Process conditions are changed as appropriate to arrive at one of the three conditions: normal air, high air, or low air. Manual measurements are taken and the times of the tests are noted. The manual measurements are entered into the Operator Interface. The microprocessor retrieves from the historian the “Pulse for History” value (Section 5.3.1 Detail Results) that the Pulse))))Air measured at the specified sample time. In addition, values of the process pressure and temperature at the sample time, and the status of the user-specified flags that indicate if pressure and solubility compensation were active, are also obtained. The Pulse))))Air then calculates one of the three calibration factors. The process is repeated at the other conditions. The results of the manual tests are entered into the Operator Interface within two hours (The historian is two hours in size). When the "Calibrate Air" option from the main parameters menu (Fig. 6.1) is selected, the following menu shown in Fig. 6.3 appears: Figure 6.3. Initial Air Calibration Screen This screen is used to enter the data for the calibration sample. The asterisked values mean no numbers are yet available for those items. This first choice (Do Coarse Calib?”) deals with the fact that for a complete calibration, three conditions are needed: a normal condition and conditions deviating above and below the normal condition. The calibration logic needs to know how to categorize the calibration data that is being entered. If the Pulse))))Air sensor has just been installed, or if configuration changes have 30 been made, then the logic needs to treat the data as the coarse calibration point. Note that if the logic does treat the new data as a coarse calibration, then the fine calibration(s), if they have previously been run, do not change; a fine calibration changes only after a good coarse calibration is available and good data are entered for the fine calibration. These logical decisions are made automatically by the processor. One additional decision is made by the processor before proceeding: If the data which are being entered are very close to the existing coarse calibration point from an earlier calibration, then the coarse calibration is redone even if the user has specified that a coarse calibration is not to be done. Next highlight and select “Manual Air %”. Enter the manual air measurement. Last, highlight and select “Mins Since Sample”. Enter the minutes since the sample was taken (120 minutes maximum). The screen will show the values that have been entered, as illustrated in Fig. 6.4. Figure 6.4 Calibration Data Screen with Values Entered When satisfied with the values, highlight and select “Do Calculations”. If the values that were entered are not useable, then various messages will be displayed to indicate what the problem was with the entered data. The data may need to be entered again, or entirely new samples may be required. If the values entered were useable, then the processor does the necessary calculations and displays a screen summarizing the results. The information line “Did coarse (or fine) calibration” advises which type of calibration was run. Any values which have been changed as a result of the calibration are indicated by “(New)” to the right of the value. The “Pulse from history” is the 31 Pulse value which was stored at the specified sample time. The “Pulse for manair” is the corresponding value in the factory LUT. The calculated calibration factors are the values needed to adjust the Pulse value to the Pulse for manair. At times, it may be useful to discuss the displayed results with PAPEC. However, the main purpose of the screen is simply to indicate that the calculations have been completed. When done viewing the results, press any key to exit. The preceding procedure completes the calibration calculations for one calibration sample. If desired, process conditions can next be changed to generate higher or lower air and the calibration procedure can be repeated for a second or third calibration point. Those calculations will normally be specified as NOT coarse calibration. 6.3 Pulse)))Air Parameters Highlight and select “Pulse))))Air Parameters” in the main change parameters screen (Fig. 6.1). The changeable parameters listed in Fig. 6.5 are displayed. Figure 6.5. Parameters which may be set in the Pulse)))Air Parameter Selection 6.3.1 Pulse))))Air On/Off The user may elect to shut down the Pulse))))Air Probe while it is not needed, such as during a maintenance downtime. Note that the Pulse))))Air can also be shut down automatically if the process interlock is used (Section 6.3.2). Use the Pulse))))Air, On/Off selection to stop or start the Actuator cycling. Highlighting and selecting the item causes the Pulse))))Air Actuator to be 32 turned On/Off. This is the only user parameter which is not held in a buffer. The user choice is set immediately. 6.3.2 Process Interlock Highlighting and selecting "Process Interlock" determines if a process interlock is to be active. The value toggles between NO and YES. When the status is NO, it makes no difference whether or not an interlock switch is connected at J1, positions 7 and 8, on the Operator Interface terminal board (Section 4.5). If the status is YES, then switch closure causes the Pulse))))Air to stop testing. 6.3.3 Test Frequency Highlight and select “Test Frequency (sec)” to change the Pulse testing rate. The time between tests can be changed to between 5 and 15 seconds. Longer times result in somewhat longer equipment life, while shorter times provide more rapid response to changing conditions. Typically on pulp washer applications fast cycle times are preferred, while on paper machines slower cycle times provide enough information. PAPEC recognizes that some customers may require faster cycle times than the standard 5 seconds. Contact PAPEC if your application requires faster cycle times. Times up to 1 second are possible. 6.3.4 Test in Averaging Highlight and select "Tests in Averaging" to change how many samples are carried in the averaging of the individual tests. The limits are 5-30. The values in the array are summed and then divided by the number of readings in the array. A lower number allows faster response to rapid process changes, while a higher number smoothes out process noise. In addition to this “arithmetic” averaging, the Pulse))))Air also automatically carries out “statistical” averaging. In statistical averaging, the standard deviation of the entrained air readings carried in the array is used to determine if the current entrained air reading is likely to belong to the population of readings in the array. If the current reading is statistically different from the population average, then this reading is ignored, and is not added to the array. However, if three consecutive entrained air measurements do not belong to the population, yet they all 33 deviate in the same direction above or below the population average, then the current reading is added to the population. 6.3.5 Minimum Air Out, Maximum Air Out Highlight and select "Minimum Air Out" or "Maximum Air Out" as desired to set the analog output range for the Pulse))))Air. The maximum output is limited to 20% air. The value selected as minimum air corresponds to 4 ma output, and the value selected as maximum air out corresponds to 20 ma. The digitally displayed values on the front panel of the operator interface are unaffected by these settings. Note that the user must set the input 4-20 ma range on the receiving device to the same range using whatever procedures are necessary for that device. 6.3.6 Minimum Bubble Index, Maximum Bubble Index Highlight and select “Min Bubble Index” or “Max Bubble Index” as desired to set the analog output range for the bubble size distribution. Bubble size distribution is the relative deviation of the entrained air measurements (standard deviation divided by the average air). An increase in the bubble distribution at an otherwise unchanged average entrained air content is an indication of generally larger air bubbles. Typically, at the same entrained air content, larger air bubbles will have less effect on drainage. Said another way, when the entrained air measurement is staying almost constant, but the bubble size index is increasing, then process performance in terms of fluid drainage (pulp washers, paper machines, etc.) can be expected to improve. Conversely, for this same scenario, quality issues may increase, such as spots and formation on paper machines. 6.3.7 Demo Mode Infrequently, it may be helpful for training and marketing purposes to demonstrate the use and operation of the Operator Interface without installing the Operator Interface in the field or connecting the Operator Interface to the Probe. This can be done by selecting the demo mode. This mode writes an artificial value to the pressure Pulse. This allows various operating features to be studied and learned. When in demo mode, a message “DEMO MODE IN USE” is displayed on the standard operating interface as a reminder that the Pulse))))Air is providing no real control information while the demo mode is active. 34 6.4 Pressure Compensation When the Probe is installed in a pressurized pipe but the entrained air of interest is the air at atmospheric pressure, then the Pulse))))Air can correct the measured air value to the air that will exist at atmospheric pressure. This choice is made in the change parameters main screen (Fig. 6.1). Highlight and select "Pressure Compensation". The current value to the right changes to the opposite condition. If pressure compensation was OFF, then it becomes ON, and vice versa. If the Probe is installed in a location that is close to atmospheric pressure, then it is preferred to set pressure compensation OFF. When this is done, errors in calibration of the pressure transducer are not an issue. Pressure compensation utilizes an ideal gas law calculation to adjust the air volume measured at the actual process pressure to the value that would exist at atmospheric pressure. This calculation is quite accurate for nonpolar gases such as air and nitrogen. It's use is more questionable for polar, reactive gases such as CO2 in water. Note that temperature is not used in the ideal gas law calculation since the process fluid, whether at the process pressure in the process piping, or released from the process piping to atmospheric pressure, can be assumed to be at the same temperature in either case. 6.5 Solubility Compensation The Pulse))))Air can take into account the amount of gas that may be dissolved or released from solution as the static pressure changes. Whether or not to utilize the solubility compensation depends on several interactive factors, including: the pressure change from the Probe location to the process pressure at the actual point of process impact; the amount of entrained air at the actual point of process impact; the inherent solubility of the gas in the process fluid (e.g., air is sparingly soluble in water-based systems, but air is highly soluble in oil-based systems); the rate at which air dissolves or releases from the liquid. As previously explained in Section 2.1 (Pressure item), the effects of pressure are complex. Therefore, it is always recommended to install the Probe into the process flow at essentially the same pressure that exists where the process fluid is impacting the process performance. Because that is not always possible, the Pulse))))Air does include the ability to estimate the contribution of dissolved air. 35 The gas solubility is estimated using Henry’s Law. Therefore, the gas must be only slightly soluble in the liquid. If the pressure at the installed location of the Pulse))))Air sensor is quite high or the gas is highly soluble in the liquid phase, then estimates of gas solubility are less accurate. In most cases, the liquid phase is water and the gas phase is air (nitrogen and oxygen) and the assumption of sparing solubility is easily met. In some cases on paper machines the liquid phase is water and the dissolved gas is CO2, which to an extent reacts with the water as part of the solubilization process. To make changes in the solubility parameters, highlight and select Solubility Compensation in the change parameters main menu (Fig. 6.1) to obtain the solubility pull-down menu shown in Fig. 6.6. Each of the items in this menu is explained in the following sections. Figure 6.6. Solubility Compensation Main Menu. 6.5.1 Solubility Compensation On/Off Highlight and select this option to turn it on or off. The current status is shown to the right. 6.5.2 Gas/Liquid Combination The default gas/liquid pair is air in water. A second standard option is for CO2 in water. If either of these is selected as YES in the pull-down menu, then the appropriate parameters are automatically loaded and no further action needs to be taken. The user parameters can be 36 changed only if the Gas/Liquid pair is selected to be "User". To change the status, highlight the gas/liquid pair that is desired to be active, and then select it. That will change the status from NO to YES, while toggling the other two to NO. If the User pair is required, then after “Gas/Liquid = User” is set to “YES”, then the parameters need to be set by highlighting and selecting "Set User Parameters". In that case, the menu shown in Figure 6.7 appears. It is necessary to obtain and enter the appropriate values for the gas and liquid from technical references of component physical properties. Figure 6.7. User Parameters for Solubility Calculations. 6.5.3 Temperature Temperature is used for only solubility compensation calculations. The Pulse))))Air_V7 does not include a temperature sensor. It is the responsibility of the user to specify the process temperature. Note that the units are degrees C. 37 6.6 Calibrate Pressure To calibrate the pressure, highlight and select "Calibrate Pressure" in the get parameters main menu (Fig. 6.1). The following menu appears: Figure 6.8. Calibrate Pressure Screen. The screen shows the current pressure measurement. Highlight and select "Enter Calibration Pressure" and then enter the correct pressure using the numeric entry keyboard. The pressure is gauge, and the units are lbs/in2. 6.7 Change Screen Contrast The screen contrast is temperature sensitive. A menu for changing contrast is obtained from the main parameters menu (Fig. 6.1) by highlighting and selecting “Change Screen Contrast”. Highlight either "INCREASE CONTRAST" or "DECREASE CONTRAST" and then press the selection button repeatedly until the screen readability is improved. Experiment with the two choices as it is not immediately apparent which choice will give the best result. 6.8 Analog Output Channel Assignment There are two 4-20 ma analog output channels available. These are isolated to 1500V and they can drive 800 ohms. The 24 volt loop power is provided by the Operator Interface. Any two of four variables can be assigned to these two channels. These include air, bubble size distribution, pressure, and defoamer. If the PID controller is not specified to be active (Section 38 6.9) then the menu lists air, bubble size, and pressure. Conversely, if the PID controller is active, then the menu also includes defoamer. The analog output assignment screen for the case of no PID controller is shown in Fig 6.9. Fig. 6.10 shows the analog output assignment screen for the case of the PID controller specified active. To change an assignment, highlight the appropriate variable and then select it one or more times, The assignment changes between “1”, “2”, and “NONE”. A message displays at the bottom of the screen to warn if more than one variable is assigned to either of the channels. Adjust the assignments as necessary to ensure that only one variable is assigned to each channel. Figure 6.9. Analog Output Assignment Screen, no PID Controller. Figure 6.10. Analog Assignment Screen, PID Controller Active. 39 6.9 Process Controller Parameters Throughout the following description, the controller is called a “defoamer controller” because that is almost always how this controller is used. However, it should be apparent that the controller can control an output which is other than defoamer. Selecting “Controller Parameters” from the main parameter menu (Fig. 6.1) causes another menu to be displayed with a parameter list for the process controller, as shown in Fig 6.11. The various items in that list are explained as follows. Figure 6.11. Process Controller Parameters. 6.9.1 Activating or Removing the Controller The controller can be activated or removed by highlighting and selecting the “Defoamer Controller” item. After the status of the controller is changed, the analog output assignments normally will need to be changed. The analog output assignment screen is automatically displayed. Make the appropriate changes as described in Section 6.8. The availability of the defoamer controller affects which basic operating screen which is displayed during normal operation (Section 5.2). 40 6.9.2 Description of Controller Algorithm The algorithm used for the defoamer controller is in the following form: Defoamer += (Gain*error + Reset*sum_error + Derivative * deriv_error) (1) Where: “+ =” means that the results of the calculation are added to the existing defoamer value. error = Setpoint – Air sum_error = sum of error values from all preceding passes through calculation deriv_error = error - Prev_error Prev_error = error from the preceding pass. Gain, Reset, Derivative are user-specified parameters. This calculation is run every 5 seconds. 6.9.3 Setting Gain, Reset, and Derivative For users needing some assistance in deciding how to configure the controller response, Equation (1) in Section 6.9.2 is useful for developing a qualitative understanding of the relative contributions of Gain, Reset, and Derivative. Gain. Gain is also frequently called “Proportional Band”. It affects the increment added to or removed from the existing defoamer due to the error that exists at the time that the algorithm is run. A Gain of 1 means that all of the current error is added to or removed from the existing defoamer. If the error is also 1, then the increment is Gain*error = 1. Note that an increased Gain value results in an increased effect on defoamer. Also note that setting Gain = 0 does not turn off the defoamer controller as can be seen from Equation (1). The controller can only be turned off by setting Gain, Reset, and Derivative all to 0. (Or the controller can be deactivated). If the Gain is specified as 1.0, and the Reset and Derivative are specified as 0, and the error between setpoint and air is 1%, unchanged from pass to pass, then in one minute (12 passes at 5 seconds between each pass) the defoamer will increase by 12%. This would likely be far too large a correction as the air will not respond to such a defoamer change within just one minute. However, a Gain value of 0.1 would result in an increase in defoamer of 1.2% over 1 minute. Intuition and experience says this rate of increase in defoamer would be more reasonable. 41 Reset. Reset is also frequently called “Integral”. This reflects the fact that this part of the algorithm is a progressive, integral, type of action. The error term in this case is the progressive sum of all of the individual errors. The individual errors are both positive and negative, so over the long run the summed error is close to zero. Over shorter times, if errors are tending to be consistently positive (or negative), then the effect of the reset term in the algorithm is to move the defoamer more and more rapidly in the desired direction over time. Some additional tests are applied to determine if the reset term should be zeroed early. Thus, if the defoamer has reached a specified limit, then the sum_error is zeroed. This is referred to as “anti-reset-windup”. Also if the error drops to a small value, called the “Deadband”, then the sum_error term is zeroed. If the error is 1%, unchanged from pass to pass, then sum_error starts at 1 in the first pass and increases to 12 by the end of the 12th pass. If the Gain and Derivative are specified as 0, and the Reset is specified as 0.1, then the effect of Reset alone after one minute is to increase the defoamer by 7.8%. Again, this would likely be too large a correction. However, a Reset value of 0.01 would result in a defoamer increase of 0.8%, a more reasonable number. This indicates that a starting point for reset would be about 1/10 of the Gain value. If the Gain is set at 0.1, then a starting point for the Reset would be 0.01. Derivative. If the error is constant from pass to pass, then deriv_error = 0. Thus Derivative will have an action only when fairly large changes in error are occurring from pass to pass. An example of when this effect is useful is as follows: Assume that the entrained air has been less than the setpoint for some time. The effects of Gain and Reset will have been to steadily reduce the defoamer. Now suppose that the entrained air suddenly starts to increase, yet it is still less than the setpoint. Gain and Reset will still continue to remove defoamer. However, the deriv_error will be positive, and the Derivative action will actually work to increase the defoamer. This effect is normally most useful in systems with rapid changes in entrained air, and in systems in which the entrained air responds very quickly to changes in defoamer. In the pulp and paper industry, neither of these conditions is common. The entrained air changes are usually slow, and the entrained air responds quite slowly to defoamer changes. One way to set the Derivative is by observing the entrained air measurement over time. If long periods of slowly-changing entrained air are occasionally interrupted by short periods of rapid increases or decreases in entrained air, then some Derivative control might be appropriate. 42 6.9.4 Setpoint Tracks Air when in Manual Mode The user can specify whether or not the setpoint is to track the air when the controller is in Manual mode. This is commonly referred to as “bumpless transfer”. The advantage is that if the controller is in Manual mode and the process is running well at the current air content, then when a switch is made to Auto mode, the control starts right off with the setpoint matched to the air at that point. If the bumpless transfer is not selected, then the user needs to verify that the setpoint at the time that the change is made to Auto mode is a suitable value. Either way works. It is a matter of user preference. 6.9.5 Controller Output Limits in Auto When the controller is used to control defoamer, it is virtually always the case that the user should limit the defoamer output to safe and reasonable values. This is especially true at the low end of the output. If the output is allowed to go to zero, then not only does this become dangerous for process stability, but also the defoamer pump may stall and fail to restart or burn out. The limits are set by highlighting and selecting the appropriate item and then entering the desired value from the numeric pad. The software ensures that the lower defoamer limit is always less than the upper defoamer limit. Note that if the controller has been operating in Manual and the defoamer output at the time of a switch to Auto mode is outside of the acceptable limits for Auto operation, then the defoamer will be clamped at the appropriate limit. Also note that when operating in Auto mode, adjustments to the defoamer output outside of the defoamer limits are not allowed. 6.9.6 Deadband The controller logic endeavors to reduce the difference between the setpoint and the air (the “error”) to zero. In the real world, this is not practical because there is always inherent variability in the air measurement. By not forcing the controller to try to take the error all the way to zero, control is improved. The Pulse))))Air continually calculates the variability in the air measurement. This value is available in the Details Screen (Section 6.3.1 “Air Range”). Start 43 with the Deadband specified at half of this value. For example, if the Air Range is shown as 4.85.2%, , then use (5.2-4.8)/2 = 0.2 for the Deadband. The Deadband is set by highlighting and selecting “Deadband” and then entering the desired value from the numeric pad. 7.0 Maintenance 44 7.1 Seals For a new installation, the seals should be changed on a preventative basis according to the schedule below. If the seals appear to be undamaged and there is no process fluid inside, then the replacement schedule may optionally be extended. Otherwise, the seals will need to be changed more frequently. If the seals show signs of chemical attack, contact PAPEC to discuss alternate elastomers. Pressurized(1) Abrasive T>170F Change Seals(2) No Yes No No Yes No No No Yes Yes No No Yes Yes Yes 12 months 6 months 6 months 3 months 2 months (1) Greater than 5 psi (2) Initial schedule, increase or decrease as appropriate Fig 7.1 is an open cross section showing the seals. To change seals: -Remove the dust cover bolt over the Setscrew (Fig 7.1) that holds the connector rod housing in place. Loosen the setscrew and pull the Connector Rod Housing out. -Remove and replace the End Seal(s), the Bearing Seal, and the Connector Rod Seal. Do not replace the Pressure Transducer Seal. The Pressure Transducer Seal is to be replaced only in the event that the pressure transducer is being replaced. Do not remove the pressure transducer without first contacting PAPEC. 45 -Slide the Connector Rod Housing back into place. Some Probes utilize an internal spring which will necessitate pushing the housing into place with some force. Lock the housing in place with the setscrew. Use just enough force to keep the connector rod housing from rotating. Overtightening will cause a burr to be formed on the connector rod housing, and the housing will be difficult to remove the next time. -Put a new seal on the dust cover bolt, and reinstall the dust cover bolt. The seals may be purchased from PAPEC (part number S21). However, the standard seals are commonly available buna rubber o-rings, and the customer may elect to purchase them directly from a seal supplier. The part numbers are: Dust cover #2-012 Bearing #2-213 End #2-123 Housing #2-027 (Some models have two end seals) These are all 70 durometer. Figure 7.1 Seals 46 8.0 Wiring Diagrams (Pulse))))Air_V7.2) Figure 8.1. Interconnections Between Probe and Operator Interface 47 Figure 8.2. Interconnections Between Processor Board and Backside of Computer. Provided for reference only. These are factory connections. 48