Transcript
SCHERING BRIDGE AB13
Analog Lab Experiment Board Ver. 1.0
QUALITY POLICY To be a Global Provider of Innovative and Affordable Electronic Equipments for Technology Training by enhancing Customer Satisfaction based on Research, Modern manufacturing techniques and continuous improvement in Quality of the products and Services with active participation of employees.
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94-101, Electronic Complex, Pardesipura INDORE-452010, India.
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Tel.: 91-731-2570301 Fax: 91-731-2555643 Email:
[email protected] Web: www.scientech.bz
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SCHERING BRIDGE AB13 TABLE OF CONTENTS 1.Introduction
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2. Theory
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3.Schering Bridge
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4.Experiment
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To measure the value of unknown capacitance with the help of Schearing Bridge
5.Observation table
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6.Datasheet
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7.Warranty
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8.List of service centers
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9.List of accessories with AB13
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INTRODUCTION AB13 is a compact, ready to use SCHERING BRIDGE experiment board. This bridge is the simplest way to determine the value of unknown capacitance; by comparing the branch impedance of the bridge. It can be used as stand alone unit with external DC power supply or can be used with SCIENTECH ANALOG LAB, ST2612; which has built in DC power supply, AC power supply, function generator, modulation generator, continuity tester, toggle switch and potentiometer. List of boards : Model
Name
AB01 AB02 AB03 AB04 AB05 AB06 AB07 AB08 AB09 AB10 AB11 AB12 AB14 AB15 AB16 AB17 AB18 AB19 AB20 AB21 AB22 AB23 AB25
Diode characteristics (Si, Zener, LED) Transistor characteristics (CB NPN) Transistor characteristics (CB PNP) Transistor characteristics (CE NPN) Transistor characteristics (CE PNP) Transistor characteristics (CC NPN) Transistor characteristics (CC PNP) FET characteristics Rectifier Circuits Wheatstone Bridge Maxwell’s Bridge De Sauty’s Bridge Darlington Pair Common Emitter Amplifier Common Collector Amplifier Common Base Amplifier Cascode Amplifier RC-Coupled Amplifier Direct Coupled Amplifier Class A Amplifier Class B Amplifier (push pull emitter follower) Class C Tuned Amplifier Phase Locked Loop (FM Demodulator & Frequency Divider / Multiplier) Multivibrator ( Mono stable / Astable) F-V and V-F Converter V-I and I-V Converter
AB28 AB29 AB30
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AB31 AB32 AB33 AB39 AB41 AB42 AB43 AB44 AB45 AB51 AB52 AB53 AB54 AB56 AB65 AB66 AB67 AB68 AB80 AB81 AB82 AB83 AB84 AB85 AB88 AB89 AB90 AB91 AB92 AB93 AB96 AB97 AB101 AB102 AB106
Zener Voltage Regulator Transistor Series Voltage Regulator Transistor Shunt Voltage Regulator Instrumentation Amplifier Differential Amplifier (Transistorized) Operational Amplifier (Inverting / Non-inverting / Differentiator) Operational Amplifier (Adder/Scalar) Operational Amplifier (Integrator/ Differentiator) Schmitt Trigger and Comparator Active filters (Low Pass and High Pass) Active Band Pass Filter Notch Filter Tschebyscheff Filter Fiber Optic Analog Link Phase Shift Oscillator Wien Bridge Oscillators Colpitt Oscillator Hartley Oscillator RLC Series and RLC Parallel Resonance Kirchoff’s Laws (Kirchoff’s Current Law & Kirchoff’s Voltage Law) Thevenin’s and Maximum power Transfer Theorem Reciprocity and Superposition Theorem Tellegen’s Theorem Norton’s theorem Diode Clipper Diode Clampers Two port network parameter Optical Transducer (Photovoltaic cell) Optical Transducer (Photoconductive cell/LDR) Optical Transducer (Phototransistor) Temperature Transducer (RTD & IC335) Temperature Transducer (Thermocouple) DSB Modulator and Demodulator SSB Modulator and Demodulator FM Modulator and Demodulator ………… and many more
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THEORY An A.C. Bridge, in its basic form, consists of four arms, a source of excitation and a balance detector. In an A.C. bridge each of four arms are impedance, and the A.C. source and a detector sensitive to small alternating potential differences. The usefulness of A.C. bridge circuits is not restricted to the measurement of unknown impedances and associated parameters like inductance, capacitance, storage factor etc. These circuits find other application in communication system and complex electronics circuits. A.C bridges are commonly used for phase shifting, providing feedback paths for oscillators and amplifiers, filtering out undesirable signals and measuring the frequency of audio signals. For measurement at low frequencies, the power line may act as the source of the supply to bridge circuits. For higher frequencies electronic oscillators are universally used as bridge source supplies. These oscillators have the advantage that the frequency is constant easily adjustable and determinable with accuracy the waveform is very close to a sine wave and their power output is sufficient for most bridge measurements. Detectors most commonly used for A.C. bridges are 1.
Head phones
2.
Vibration galvanometers
3.
Tunable amplifiers detectors
Head phones are widely used as detectors at frequencies of 250 Hz and up to 3 or 4 kHz. They are most sensitive detectors for this range When working at a single frequency a tuned detector normally gives the greatest sensitivity and discrimination against harmonics in the supply .Vibration galvanometer are extremely use for power and low audio frequency ranges .Vibration galvanometers are manufactures to work at various frequencies ranging from 5 Hz to 1000 Hz but are most commonly used below 200 Hz as below this frequency they are more sensitive that the head phones. Tunable amplifiers detectors are the most versatile of the detectors .The transistors amplifiers can be tuned electrically and thus can be made to respond to a narrow bandwidth at the bridge frequency .The output of the amplifier is fed to a pointer type instrument this detector can be used, over a frequency range of 10 Hz to 100 kHz.
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General equation for bridge balance : Basic A.C. bridge circuit is shown below the four arm of the bridge are impedance Z1, Z2, Z3, Z4.The condition for balance of bridge require that there should be no current through the detector .this requires that the potential difference between points ‘b’ and ‘d’ should be zero. This will be the case when the voltage drop from a to b equals the voltage drop from a to ‘d’ both in magnitude and phase. In complex notation we can, write: E1 = E2 I1Z1 =I2Z2 Also at balance,
I1=I3 =E/Z1+Z2 I2=I4=E/Z2+Z4
Substituting the Eq. We Get Z1Z4=Z2Z3 Eq. states that the product of impedances of one pair opposite arms must equal the product of impedance of the other pair of opposite arms in complex notation .This means that both magnitude and phase angle of the impedance must be taken into account. Two conditions must be satisfied simultaneously when balancing the A.C. Bridge The first condition is that the magnitude of impedances satisfies the relationship: Z1 Z4=Z2Z3 The second condition is that the phase angles of impedance satisfy the relationship: θ1+θ4=θ2+θ3 The phase angles are positive for inductive impedance and negative for capacitance impedance.
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SCHERING BRIDGE This Bridge is the simplest method of comparing two capacitance and to determine unknown capacitance. Figure 1 shows the basic Schering Bridge circuit configuration. Its first arm ZX consisting of an unknown capacitor Cx in series with the resistance Rx and second arms are consisting of capacitor C 3 and third arm consisting of variable resistance R2 and fourth arm consists a parallel combination of resistance R1 and capacitor C1. The balance can be obtained by varying the resistance R2 of third arm. CX = capacitor with unknown capacitance, RX =Effective resistance, C3 = standard capacitor, R1, R2 = non-inductive resistance. At balance,Z1ZX=Z2Z3 The value of Rx can be calculated by the formula: Rx = R2C1 C3 The value of Cx can be calculated by the formula: Cx=R1C3 R2 The Dissipation factor for the capacitor is given by the formula: D=ωCxRx Where Cx is the value of unknown capacitor and Rx is effective resistance. The value of D is the reciprocal of the quality factor Q i.e. D=1/Q D indicates the quality of the capacitor. This bridge is widely used for measurement of small valued capacitors at low voltages with high Precision.
Schering Bridge Scientech Technologies Pvt. Ltd.
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EXPERIMENT Objective : To measure the value of unknown capacitance with the help of Schearing Bridge. Apparatus required :
1.
Analog Board, AB13
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DC power supplies +/–12V from external source ST-2612 Analog lab
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Function generator
4.
2 mm patch cords.
5.
Digital multimeter
Circuit diagram : Circuit used to measure the value of unknown capacitance is shown
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Procedure :
• 1.
Connect +/–12V dc power supply at their indicated position from external source or ST-2612 Analog lab. Connect function generator probes between Vin terminals.
2. Connect 2mm patch chord between sockets ‘d’ and ‘a’ to calculate the value of Cx1 and Rx1. 3.
Switch ON the power supply and function generator.
4. Set the 5Vpp, 1 KHz input sinusoidal signal of function generator. 5. Rotate the potentiometer R2 to find a condition where null or minimum sound is obtained. The null point should be such that beyond or below that point sound gets starts gradually increasing. 6.
Switch off the power supply and function generator
7.
Take the reading of potentiometer resistance at test-point ‘e’ and ‘f ’.
8.
Calculate the value of capacitance Cx and Rx by their formulae.
9. Calculate the value of dissipation factor for capacitor CX1 10. Connect 2mm patch chord between point‘d’ and ‘b’ to determine the capacitance of capacitor Cx2. 11. Repeat the above step from 4 to 10.
12. Connect 2mm patch chord between point‘d’ and ‘c’ to determine the capacitance of capacitor Cx3. 13. Repeat the above step from 4 to 10.
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OBSERVATION TABLE Sr. no.
R1 Ω
C1 µf
C3 µf
R2 Ω
Rx=R2C1/3 Ω
Cx=R1C3/R2 µf
D
1 2 3
Note : Values of C1 , C3, and R1 are indicated on the front of the board. Calculation : Measured value of R2 is. ………. Ω/kΩ Now measure the value of Cx by the formula : Cx=R2C1/C3 Now measure the values of Rx by the formula : Rx=R1C3/R2 Now calculate the value of dissipation factor by the formula : D = ωCxRx The dissipation factor D i.e. wCxRx should be approximately equal to ω*C1*R1. Result : The capacitance of capacitor Cx = ……… µf The effective resistance Rx = ………….
Ω/KΩ
The dissipation factor D = …………..
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DATASHEET
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WARRANTY 1.
We guarantee the instrument against all manufacturing defects during 24 months from the date of sale by us or through our dealers.
2.
The guarantee covers manufacturing defects in respect of indigenous components and material limited to the warranty extended to us by the original manufacturer, and defect will be rectified as far as lies within our control.
3.
The guarantee will become INVALID. a)If the instrument is not operated as per instruction given in the instruction manual. b)If the agreed payment terms and other conditions of sale are not followed. c) If the customer resells the instrument to another party. d)Provided no attempt have been made to service and modify the instrument.
4.
The non-working of the instrument is to be communicated to us immediately giving full details of the complaints and defects noticed specifically mentioning the type and sr. no. of the instrument, date of purchase etc.
5.
The repair work will be carried out, provided the instrument is dispatched securely packed and insured with the railways. To and fro charges will be to the account of the customer. DISPATCH PROCEDURE FOR SERVICE
Should it become necessary to send back the instrument to factory please observe the following procedure: 1)
Before dispatching the instrument please write to us giving full details of the fault noticed.
2)
After receipt of your letter our repairs dept. will advise you whether it is necessary to send the instrument back to us for repairs or the adjustment is possible in your premises.
Dispatch the instrument (only on the receipt of our advice) securely packed in original packing duly insured and freight paid along with accessories and a copy of the details noticed to us at our factory address.
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LIST OF SERVICE CENTERS 1. Scientech Technologies Pvt. Ltd. 90, Electronic Complex Pardesipura, INDORE – 452010 2. Scientech Technologies Pvt. Ltd. First Floor, C-19, F.I.E., Patparganj Industrial Area, DELHI – 110092 3. Scientech Technologies Pvt. Ltd. New no.2, Old no.10, 4th street Venkateswara nagar, Adyar CHENNAI – 600025 4. Scientech Technologies Pvt. Ltd. 202/19, 4th main street Ganganagar, BANGALORE- 560032 5. Scientech Technologies Pvt. Ltd. 8,1st floor, 123-Hariram Mansion, Dada Saheb Phalke road, Dadar (East), MUMBAI –400014 6. Scientech Technologies Pvt. Ltd. 988, Sadashiv Peth, Gyan Prabodhini Lane, PUNE – 411030 7. Scientech Technologies Pvt. Ltd SPS Apartment, 1st Floor 2, Ahmed Mamoji Street, Behind Jaiswal Hospital, Liluah, HOWRAH-711204 W.B. 8. Scientech Technologies Pvt. Ltd Flat No. 205, 2nd Floor, Lakshminarayana Apartments ‘C’ wing, Street No. 17, Himaytnagar, HYDERABAD- 500029 Scientech Technologies Pvt. Ltd.
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LIST OF ACCESSORIES
1.
2 mm Patch cords (Red) .............................................................3 Nos.
2.
2 mm Patch cord (Black) ...........................................................2 Nos.
3.
2 mm Patch cord (Black) ...........................................................1 Nos.
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