Progress... but still need more help!
Hey all, I really appreciate the help that everyone has given me. My project is moving forward well, but I have hit another stumbling block, and I am hoping someone can help me diagnose the problem.
I have managed to get the triangular wave working, and I connected my entire circuit in Multisim and simulated it. Here is the basic circuit:
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Between the WE and RE, the circuit can be modelled as: R + R||C. The same is between CE and RE. I have measured these values with an impedance analyzer and have come up with a range of 1 uF to 10 uF for the parallel capacitors, and roughly 1k to 10k for the parallel resistors. The resistors in series have <100 ohm.
The circuit is works by passing the Vbias voltage across the WE and RE electrodes. My problem is when I simulate it, I can't get the inverting input of the transimpedance amplifier to stay at ground. Here are my circuit and simulations:
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----- Vbias from triangular oscillator
----- -Vbias set to reference electrode
----- Inverting input of transimpedance amplifier
----- Output of transimpedance amplifier
I am essentially trying to model my chemical solution based on the data that I measured. For this system to work, I really need the yellow signal (inverting input of the transimpedance amplifier) to be zero constantly.
Anyone have any ideas, this one's a toughy. Thanks!
JP