During our lab testing with pH and reference electrodes provided by Dr. Hintz, we found the reference electrode to be very sensitive to any movement around it even though the electrodes were enclosed inside a Faraday box . Thus, causing output signal to shift up/down. Per our group conversation with Mr. Marc Hebert at Microelectrodes, he recommended to place a MOhms resistor from the reference electrode to ground for the input bias current to have return path to ground. The figure below shows our contemporary amplifier circuit with the addition of 132 MOhms of resistance.

After placing a MOhm resistor we noticed that even though our output reading were linear for pH (4, 7 & 10) buffer fluids, the output of pH 4 was ( – 1.80 Volts), pH 10 was (- 5.0 Volts) and pH 7 was was (- 3.44 Volts). We are not sure why the output reading changed after placing a MOhms resistor connected from reference electrode to ground.

ASTEC AA16130 power supply provided by Dr. Hintz for our senior design project is being used to power up Dr. Hintz’s alkalinity measurement protoytpe and also our INA116 amplifier. During our lab testing we found out that the (-12 V) outputted by the power supply had a AC ripple as to clean DC signal. In order to get rid of the AC ripple, we installed 2200uF electrolytic capacitor on the (-12 V) of the power supple and got rid of the AC ripple. On the positive 12 volts we saw clean DC signal on the oscilloscope.