Salinity SensorSalinity Sensor

Calibrated Solution and ElectrodeCalibrated Solution and Electrode

- - 50,000uS/cm from YSI Incorporated50,000uS/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

ElectrodeElectrode

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

Circuit DiagramCircuit Diagram

WheatStoneBridge and Differential AmplifierWheatStoneBridge and Differential Amplifier

WheatStone BridgeWheatStone Bridge

Vin = Vabc = VadcVin = Vabc = Vadc Iabc(R3+Rx) = Iadc(R1+R2)Iabc(R3+Rx) = Iadc(R1+R2) Vab = IabcR3 = Vab = IabcR3 = Vin *R3Vin *R3 R3+RxR3+Rx Vad = Iadc*R1 = Vad = Iadc*R1 = Vin *R1Vin *R1 R1+R2R1+R2 Vg = (V1 – V2)Vg = (V1 – V2) Vg = Vab – Vad = Vg = Vab – Vad = VinR3VinR3 - - VinR1VinR1 R3+Rx R1 +R2R3+Rx R1 +R2 Vg = ( Vg = ( R3R3 - - R1 R1 ) Vin ) Vin R3+Rx R1+R2R3+Rx R1+R2 Vg Vg = = RxRx - - R1 R1 Vin Rx+R3 R1+R2Vin Rx+R3 R1+R2 Vg Vg + + R1 R1 = = 11 Vin R1 +R2 (1+ R3/Rx)Vin R1 +R2 (1+ R3/Rx)

Rx = R3/ ( 1 -1 ) Rx = R3/ ( 1 -1 ) (Vg/Vin + R1/(R1+R2))(Vg/Vin + R1/(R1+R2))

Differential AmplifierDifferential Amplifier

Vg = V1 – V2Vg = V1 – V2 Vout = -Vout = -RaRa (Vg) (Vg) RbRb Vg = - Vg = - (Vout*Rb)(Vout*Rb) RaRa

Actual Vs Meausured ResistanceActual Vs Meausured Resistance

ActualActual R1 = R2 = R3 = 4.3KohmsR1 = R2 = R3 = 4.3Kohms Ra = Rb = 220kohmsRa = Rb = 220kohms

MeasuredMeasured

- 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

Calculation and DiagramCalculation and Diagram

Set Vg of the bridge and amplifier to equal Set Vg of the bridge and amplifier to equal each othereach other

Vout = Vout = -Ra( (RX/(RX+R3)) – (R1/(R1+R2)))-Ra( (RX/(RX+R3)) – (R1/(R1+R2))) RbRb

Test and ProcedureTest 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 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.)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)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.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 5. Add some distilled water in the beaker to reach 200ml. (This basically reduces the conductivity by half.)conductivity by half.) 6. Measure the DC output voltage. 6. Measure the DC output voltage. 7. Repeat procedure (4 – 6) until around measurements are made.7. Repeat procedure (4 – 6) until around measurements are made. 8. Plot the Data: The concentration of Salt in the water, VS electrode impedances. 8. Plot the Data: The concentration of Salt in the water, VS electrode impedances. NOTE: PPM = (Electrical Conductivity(EC)) * 500.NOTE: PPM = (Electrical Conductivity(EC)) * 500.

Data and GraphData and Graph

Conductivity

V1 - V2 Temperature

50,000 5.815 +-25C

25000 5.843Time Elasped per

sample

12500 5.851 1minute

6250 5.8605

3125 5.8866

1562.5 5.8685

781.25 5.8737

390.625 5.8746

195.3125 5.8781

97.65625 5.88

48.82815 5.8819

48.82815 5.8834

24.4140625 5.8845

12.2070313 5.8852

6.10351563 5.8864

3.05175781 5.8865

1.52587891 5.8862

Salinity Graph

5.75

5.8

5.85

5.9

50,0

00

6250

781.

25

97.6

56

24.4

14

3.05

18

COnductivity

V1-

V2 Series1

Data and GraphData and Graph

Salinity Graph

5.8785.88

5.8825.8845.8865.8885.89

50,0

00

1250

031

25

781.

25

195.

313

48.8

282

Conductivity

V1-

V2

ou

tpu

t

Series1

5.8822

Conductivity V1-v2

50,000 5.8814

25000 5.8823

12500 5.8822

6250 5.8831

3125 5.8831

1562.5 5.8848

781.25 5.8859

390.625 5.8868

195.3125 5.8876

97.65625 5.8881

48.82815 5.888

Using Wheatstone Bridge FormulaUsing Wheatstone Bridge Formula

Rx = R3/( Rx = R3/( 1 1 -1 ) -1 ) (Vg/Vin + R1/(R1+R2))(Vg/Vin + R1/(R1+R2))

Rx at Vg = 5.8814Rx at Vg = 5.8814 = 344963.4187= 344963.4187 Compared to EstimateCompared to Estimate

It is similarIt is similar