Transcript
TIDE STATION USERS’ MANUAL Chapter 6
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6.1
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REDUNDANT (BACKUP) GAGE ISSUES
REQUIREMENTS
The National Ocean Service (NOS) uses a backup water level measuring system will all tide gages. However, there is NO standard configuration for the backup system. The backup system for the legacy Sutron Model 9000 based tide stations is a Sutron Model 8200 data recorder equipped with (typically) a pressure transducer. In some instances the pressure transducer is replaced with other sensors such as a quadrature shaft angle encoder. In any case, the typical legacy backup system is a data logger, no telemetry, and some type of water level sensor. At the time of this writing (March, 2005), NOS is moving toward a different concept to provide backup data at tide stations. NOS is now considering the concept of a redundant gage. The redundant gage would duplicate the instruments and functionality of the primary gage in every way except for telemetry. The primary gage would still have the responsibility for telemetry, although even that is under debate. Regardless of the concept – backup gage, redundant gage, there is a common set of principles regarding how the two gages are set up. The purpose of this chapter is to present these principles. Specifically, this chapter discusses:
Communications between the primary tide station and the backup/redundant station Example of software setups to transfer data from the backup/redundant gage to the primary gage
NOTE: At the time of this writing there is NO standard backup/redundant gage setup. This chapter discusses ONLY setup issues on the primary gage. The user is responsible for determining an appropriate backup/redundant gage setup and for making use of the examples here to create an appropriate backup/redundant setup on the primary gage.
6.2
COMMUNICATIONS BETWEEN THE PRIMARY AND BACKUP/REDUNDANT GAGE
The communications between the two gages is, in almost all cases, a hard-wired, RS-232 serial communications link. The user must provide a null modem-configured DB-9 cable for the connection. Any of the XPert COM ports except COM 1 can be used. COM 1 can also be used, but this normally conflicts with other applications and also may require use of a straight cable, depending on what port is used on the backup/redundant gage.
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The communications protocol used for the data exchange is Sutron Standard Protocol (SSP). SSP is supported by all Sutron data loggers and RTUs. It is explicitly assumed here that the backup/redundant gage is a Sutron XPert or Model 9210 Xlite. Communications with older backup gages (Model 8200, 8210) is possible because the protocol is SSP. However, the appropriate setup for older backup gages is not discussed here.
6.3
COMMUNICATIONS CONCEPTS – GET TAG/SEND TAG PAIRS
The term “tag” comes from the process control industry. It is commonly used to mean a named value that is available in real time within an RTU or data logger. The RTU creates and maintains the tag so that it is available to other RTUs and processes in a system. The Sutron SSP communications protocol provides the ability to get and send tags. In the case of a backup/redundant tide station, the backup will be using a function called SEND TAG to post water levels and other values for recovery by matching GET TAG functions on the primary gage. Figures 6.1 and 6.2 illustrate the backup/redundant gage part of a GET TAG/SEND TAG pair. (Note the there is no specific SEND TAG block. SEND TAG is incorporated into the functionality of a COMS block.)
Figure 6. 1 SEND TAG Setup on Backup/Redundant Gage
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Figure 6. 2 COMS Tag Properties Note that the backup/redundant gage does not have to specify a COM port. SSP “knows” where to post the values for BWL and how to find them when requested to do so. The absolutely critical part of the setup is to make the name of the tag match on both of the gages. If the COMS tag on the backup gage is named BWL then the matching GET TAG on the primary gage must also be set to look for BWL. Figures 6.3 and 6.4 illustrate the matching main gage setup for the SEND TAG in Figures 6.2 and 6.2.
Figure 6. 3 GET TAG Setup on Primary Gage
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Figure 6. 4 GET TAG Properties Note that GET TAG needs to know what COM port is used for communications with the backup/redundant gage. In the example in Figures 6.3 and 6.4 the COM port is 4. The COM port also has to be set to handle SSP communications. This is done by changing COM port settings in the XPert Setup tab, as illustrated in Figures 6.5 and 6.6.
Figure 6. 5 COMS Setup in XPert
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Figure 6. 6 COM Port Setup Window The SSP4 condition was obtained by clicking on Edit with Coms selected to obtain the COM Port setup window shown here. Note that COM 4 has been set to SSP at 9600 bits per second. If other ports are set up for SSP then they will appear as options in the Port drop-down illustrated in Figure 6.4. Be sure to select the correct SSP port if more than one is defined.
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TIDE STATION USERS’ MANUAL Chapter 6
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EXAMPLE PRIMARY GAGE SETUP
Figure 6.7 illustrates the setup rows required to obtain a backup water level (BWL), BWL standard deviation (BWSIG), BWL outlier count (BOUT), and the backup gage battery voltage (BBAT). Note that the setup blocks (icons) on the left are all GET TAG blocks. They have been renamed in the setup to make it clear which GET TAG obtains which value. This setup file is provided as BackupExample.SSF on the CD.
Figure 6. 7 GET TAG Setup for Reading Multiple Backup Gage Values
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TIDE STATION USERS’ MANUAL Chapter 6
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EXAMPLE REDUNDANT/BACKUP GAGE SETUP
Figure 6.8 illustrates the matching setup rows required to match the Primary Gage setup illustrated in figure 6.7. . This setup file is provided as Backup Pair Example.SSF on the CD. Note that no setup is required on the backup/redundant gage for the time synchronization.
Figure 6. 8 GET TAG Setup for Reading Multiple Backup Gage Values
6.6
OTHER ISSUES – SYNCHRONIZING TIME
It is always good practice to keep the clocks synchronized between the primary and backup/redundant gage. The primary gage, because it GOES telemetry, has access to GPS time. GPS time is accurate to small fractions of a second. XPert loggers provide a special setup block called SendTime to allow the primary gage to reset the clock on the backup gage. A Send Time block is illustrated at the bottom of Figure 6.7. The SendTime block has to be configured to send the time synchronization command to the appropriate place. Figure 6.9 illustrates the SendTime properties.
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Figure 6. 9 Send Time Block Properties The Time property is NOT the current clock reading. Time is an offset from midnight each day at which the Send Time block begins sending time synchronization messages. The Interval property tells SetTime how often to send time synchronization messages. This particular block is set for every 6 hours, which is sufficient for GOES operations. Note the Port property. This MUST be set to the SSP port to which the backup gage is connected. Here it is set to SSP4 (SSP over COM 4), to be consistent with the other examples. The Path property is only used for systems using radios, telephones, or other communications with multiple paths. The * setting simply means ,”Use any available path.”
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