Salinity Sensor

Calibrated Solution and Electrode - 50,000uS/cm from YSI Incorporated - 50,000uS/cm from YSI Incorporated - Electrode apart - 1.3cm - Electrode apart - 1.3cm uS/1.3cm uS/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 = ohm - Estimated Resistance = ohm

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

Circuit Diagram

WheatStoneBridge and Differential Amplifier

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))

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

Actual Vs Meausured Resistance  Actual  R1 = R2 = R3 = 4.3Kohms  Ra = Rb = 220kohms Measured - R 1 = ; R3 = ; R2 = R 1 = ; R3 = ; R2 = RA1 = K; RA2 = K; RB1 = K RB2 = K - RA1 = K; RA2 = K; RB1 = K RB2 = K

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

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.

Data and Graph Data and Graph ConductivityV1 - V2Temperature 50, C Time Elasped per sample minute

Data and Graph ConductivityV1-v2 50,

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