My end goal is to create a digital read-out and interlock logic circuit of pressure as a function of voltage from an auxiliary signal of an electrometer ion gauge. Here the arduino needs to measure a DC voltage from an ion gage controller accessory cable in which the electrometer signal (0 to -2.5 V, 2Kohm impedance) corresponds to meter information in the controller, a pressure between 10^-8 and 10-4 Torr.
My issue is that the arduino uno does not handle negative voltage. I'm open to suggestions on how to obtain this signal.
I've attached a relevant .pdf section of the ion gauge controller manual that describes the signal I'd like to collect with the arduino (pins 2 & 9, signal & ground respectivly).
I can only see page 3 of 6. Do you have the entire document. From this restricted glympse, I get the impression that you may have access to -5v
If so you could connect this to your arduino GND then make your readings relative to this. (assuming your arduino and the other equipment have independent power sources)
My first thought was to ground the negative signal to the arduino and measure the controller's ground as you've suggested KenF. I didn't know if this would damage the arduino but I'll try it after the inverting op-amp method. Thanks Grumpy_Mike and KenF. I'll follow up when I have the solution. Best.