Reference electrode input bias current return path
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.0
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.0
