Dear mister Pete Samig and mister Bruce Trump,
Thank you for your answers, this clears up a lot of things. Unfortunately I cannot easily use another connector than BNC because the pH electrode already has a coax cable with a BNC connector attached. As an addition, I plan to use some other electrodes including an industrial ORP probe to measure the redox potential. This one has a lower internal resistance than the pH probe, and is able to produce voltages from -2000 to 2000 mV (according to the datasheet). It has a S8 head, but I already have a proper S8-to-BNC adapter cable ready. The specs for the two electrodes can be found here:
pH: Hanna Instruments HI 1230B
http://www.hannainst.com/usa/prods2.cfm?id=030&ProdCode=HI%201230B
ORP: Hamilton Oxytrode Pt 120
http://www.hamiltoncompany.com/products/sensors/c/764/
While accidentally shorting the BNC shield with the ground may not damage the opamp itself, it can easily damage the reference/pseudoground circuitry. This is why I originally wanted to include a resistor (i.e. 10 MOhm) between the reference/vground terminal and the opamp negative input. My electrodes offer only two connections, so there does not seem to be any grounding. The ORP is an industrial probe, but the pH probe was from a handheld pH meter (HI 83141), which was battery-powered.
I currently only have a +12VDC 2Amp single supply from a mains switching adapter. The reason I decided to use it was due to simplicity, however, switching to a bipolar supply would likely require me to invest into a custom power supply circuitry. I will also need the 12VDC to power a bipolar stepper motor for a peristaltic dosing pump. There's also a microcontroller that will drive the motor, and read/send the measurements to a PC. I will consider having separate power supplies for analog/motor/digital parts.
P.S. would the circuit above still work, if I disconnect the +6VDC reference/vground terminal from the opamp input?
Kind regards!
