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Published byChelsey Notley Modified over 2 years ago

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Salinity Sensor

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Calibrated Solution and Electrode - 50,000uS/cm from YSI Incorporated - 50,000uS/cm from YSI Incorporated - Electrode apart - 1.3cm - Electrode apart - 1.3cm - 65000uS/1.3cm - 65000uS/1.3cm - Electrode Cross sectional Area (A) - 1.5mm^2 - Electrode Cross sectional Area (A) - 1.5mm^2 - Length of Electrode (L) - 1/5cm - Length of Electrode (L) - 1/5cm - Resistivity (P) = (1/50000uS) *1.3cm - Resistivity (P) = (1/50000uS) *1.3cm = 20ohm *1.3cm = 26ohm*cm = 20ohm *1.3cm = 26ohm*cm - Resistance = (P*L)/A - Resistance = (P*L)/A - Estimated Resistance = 344963ohm - Estimated Resistance = 344963ohm

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Electrode NOTE: Epoxy would be put on electrode to make it about 1/3cm long.

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Circuit Diagram

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WheatStoneBridge and Differential Amplifier

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WheatStone Bridge Vin = Vabc = Vadc Iabc(R3+Rx) = Iadc(R1+R2) Vab = IabcR3 = Vin *R3 R3+Rx Vad = Iadc*R1 = Vin *R1 R1+R2 Vg = (V1 – V2) Vg = Vab – Vad = VinR3 - VinR1 R3+Rx R1 +R2 Vg = ( R3 - R1 ) Vin R3+Rx R1+R2 Vg = Rx - R1 Vin Rx+R3 R1+R2 Vg + R1 = 1 Vin R1 +R2 (1+ R3/Rx) Rx = R3/ ( 1 -1 ) (Vg/Vin + R1/(R1+R2))

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Differential Amplifier Vg = V1 – V2 Vout = -Ra (Vg) Rb Vg = - (Vout*Rb) Ra

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Actual Vs Meausured Resistance Actual R1 = R2 = R3 = 4.3Kohms Ra = Rb = 220kohms Measured - R 1 = 4.2560; R3 = 4.2827; R2 = 4.2967 - R 1 = 4.2560; R3 = 4.2827; R2 = 4.2967 - RA1 = 218.10K; RA2 = 220.50K; RB1 = 2204.8K RB2 = 217.05K - RA1 = 218.10K; RA2 = 220.50K; RB1 = 2204.8K RB2 = 217.05K

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Calculation and Diagram Set Vg of the bridge and amplifier to equal each other Vout = -Ra( (RX/(RX+R3)) – (R1/(R1+R2))) Rb

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Test and Procedure 1. Connect the circuit 1. Connect the circuit 2. Pour the 50,000uS/cm calibrated solution in the beaker up to 200ml (make sure the temperature is about 25C to avoid worring about specific conductivity.) 3. Record the DC output Voltage (V1 – V2) and solve for Rx (the electrode impedances) 4. Pour the Solution out of the beaker until it reaches about 100ml in the beaker. 5. Add some distilled water in the beaker to reach 200ml. (This basically reduces the conductivity by half.) 6. Measure the DC output voltage. 7. Repeat procedure (4 – 6) until around measurements are made. 8. Plot the Data: The concentration of Salt in the water, VS electrode impedances. NOTE: PPM = (Electrical Conductivity(EC)) * 500.

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Data and Graph Data and Graph ConductivityV1 - V2Temperature 50,0005.815 +-25C 250005.843 Time Elasped per sample 125005.8511minute 62505.8605 31255.8866 1562.55.8685 781.255.8737 390.6255.8746 195.31255.8781 97.656255.88 48.828155.8819 48.828155.8834 24.41406255.8845 12.20703135.8852 6.103515635.8864 3.051757815.8865 1.525878915.8862

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Data and Graph 5.8822 ConductivityV1-v2 50,0005.8814 250005.8823 125005.8822 62505.8831 31255.8831 1562.55.8848 781.255.8859 390.6255.8868 195.31255.8876 97.656255.8881 48.828155.888

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Using Wheatstone Bridge Formula Rx = R3/( 1 -1 ) (Vg/Vin + R1/(R1+R2)) Rx at Vg = 5.8814 = 344963.4187 Compared to Estimate It is similar It is similar

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