MoTeC Global Forum

I have some sensors that vary their conductance (1.0/resistance) linearly with pressure.
The resistance range is ~30k-Ohms to ~1M-Ohm.
How do I get this into an ACL?
Do the standalone thermocouple amps (I think #58008??) have the same/identical amplification as the circuits in an E888?
And what are the technical specs for the thermocouple circuits in gain, offsets, etc? Is there a math equation for the response with respect to resistance? Or is it a gain with respect to current (I think that they are current devices).
Either way I would like to understand the circuit behaviour.

For my particular resistance/conductance logging, will I need to precondition the signals with an OP-amps?

The thermocouple amplifiers are high input impedance, high gain voltage amplifies. Thermocouples can not supply much current and have a very low resistance across the terminals. I don’t think this sort of amplifier would be suitable with your sensor.

If you are using a VIM with your ACL I would try using an analogue input with a weak pull up (perhaps 100K) to 5v. The inputs on the VIM have very high resolution so you don’t need to use the full range of the input (0-5v) to have useful data. One side of the sensor needs to go to 0v and the other to the input on the VIM with the pull up.

David