3-Electrode sensor potentiostatic circuitry

[timkoers]

I'm designing a circuit to read out the C2H4-CA10 sensor (datasheet http://www.membrapor.ch/sheet/Ethene-Gas-Sensor-C2H4-CA-10.pdf).

Following the typical applications document (https://www.membrapor.ch/sheet/Application_Note_MEM1.pdf)
I designed the following:



To verify the schematic, I created a new TINA simulation:



When probing VM1, I get a output value of 999,952953mV with IG1 @ 350nA (which equals the starting current for the sensor.)

When the sensor is at 10ppm, the current value should be 1550nA, and the voltage over VM1 rises to 1,000000V.

I've got a few questions.

• Do both OP1 and OP2 need to have a power supply connected? It's not part of the schematic in the MEM1 document.
• If yes, how do I need to connect them? I've searched around on Google and didn't find a single potentiostatic circuit with an external power supply connected.
  If I remove the power supply from OP2, the output value drops to 20uV, so I suppose OP2 does need it.
• Why is the output voltage limited to 1V@1550nA? I connected it to a 5V supply.

When realising the circuit once the design process has been completed, I want to make Rgain disconnectable from C2 to allow for better tweaking, is the circuitry affected if I use two headers with jumpers to connect/disconnect Rgain?

EDIT:

I just noticed that changing the simulation to the schematic listed below, generates an output voltage which complies to I = Isensor * Rgain
OP1 and OP2 both receive a supply voltage of -1V at it's negative pin and 1V at it's positive pin