Hello all,
The skinny on what I am trying to do is pass a triangular wave (4 Vp-p, 500 mHz) into my op-amp control system and use it to bias a certain electrode in solution with respect to another electrode. To clear things up here is my schematic with what I have worked out so far, with the generous help of others as well, specifically BrownOut:
**broken link removed**
Basically, I am biasing the working electrode at virtual ground and holding the reference voltage at the triangular voltage signal. My final goal is to measure the current flowing from solution through the working electrode to the counter electrode. The counter electrode simply provides a pathway for the current to flow in and out of the system and back into solution. The reference electrode passes no current, but merely holds its voltage signal.
The troublesome thing about this is that depending on the triangular voltage level, different amounts of ions will react on the working electrode, thus the capacitive and resistive natures of the electrodes change. The electrochemical model presented has been used for a long time now and gives a very good interpretation for what is going on in solution. Using an impedance analyzer, I figured out for my purposes, Rcounter and Rworking range from 10k to 50k and Ccounter and Cworking range from 1 uF to 10 uF.
The system operates reasonably well when Rcounter and Rworking are the same, but if they are relatively different, the reference voltage begins to become curved and distant from the triangular wave that it should be.
I have figured out the frequency response of the U3A amplifier but I don't know how to choose values for components based on my requirements for the system to work, in terms of bandwidth, phase, and delay, because I have never dealt with triangular waves only sinusoids...
Here is a transient response plot for a number of the labeled traces to give you a visual:
**broken link removed**
If you noticed, the red trace V(reference) should be equal in magnitude to the blue trace V(tri) but 180 degrees out of phase. In this simulation the phase difference is correct, but it is scaled down when it shouldn't be...
JP
The skinny on what I am trying to do is pass a triangular wave (4 Vp-p, 500 mHz) into my op-amp control system and use it to bias a certain electrode in solution with respect to another electrode. To clear things up here is my schematic with what I have worked out so far, with the generous help of others as well, specifically BrownOut:
**broken link removed**
Basically, I am biasing the working electrode at virtual ground and holding the reference voltage at the triangular voltage signal. My final goal is to measure the current flowing from solution through the working electrode to the counter electrode. The counter electrode simply provides a pathway for the current to flow in and out of the system and back into solution. The reference electrode passes no current, but merely holds its voltage signal.
The troublesome thing about this is that depending on the triangular voltage level, different amounts of ions will react on the working electrode, thus the capacitive and resistive natures of the electrodes change. The electrochemical model presented has been used for a long time now and gives a very good interpretation for what is going on in solution. Using an impedance analyzer, I figured out for my purposes, Rcounter and Rworking range from 10k to 50k and Ccounter and Cworking range from 1 uF to 10 uF.
The system operates reasonably well when Rcounter and Rworking are the same, but if they are relatively different, the reference voltage begins to become curved and distant from the triangular wave that it should be.
I have figured out the frequency response of the U3A amplifier but I don't know how to choose values for components based on my requirements for the system to work, in terms of bandwidth, phase, and delay, because I have never dealt with triangular waves only sinusoids...
Here is a transient response plot for a number of the labeled traces to give you a visual:
**broken link removed**
If you noticed, the red trace V(reference) should be equal in magnitude to the blue trace V(tri) but 180 degrees out of phase. In this simulation the phase difference is correct, but it is scaled down when it shouldn't be...
JP
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