Op amp used in cyclic voltammetry application

ecaits

Joined Jan 6, 2014
56
In cyclic voltammetry application (as per circuit design given in image), the voltage difference between reference electrode (RE) and working electrode (WE) will be constant.

As per REDOX process (Reduction & Oxidation), the current will flow between counter and working electrode.

The circuit given in image, is looks open loop circuit. To maintain the constant voltage between RE & WE, the circuit must be close loop.

We have used I to V convertor, to convert the working electrode's current into voltage.

How do I take voltage difference between RE & WE and give back to control the current flow between CE & WE? I need support to understand how to make close loop circuit.

Thanks,

Nirav

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MisterBill2

Joined Jan 23, 2018
11,598
In cyclic voltammetry application (as per circuit design given in image), the voltage difference between reference electrode (RE) and working electrode (WE) will be constant.

As per REDOX process (Reduction & Oxidation), the current will flow between counter and working electrode.

The circuit given in image, is looks open loop circuit. To maintain the constant voltage between RE & WE, the circuit must be close loop.

We have used I to V convertor, to convert the working electrode's current into voltage.

How do I take voltage difference between RE & WE and give back to control the current flow between CE & WE? I need support to understand how to make close loop circuit.

Thanks,

Nirav
To control the voltage difference between the RE and the WE requires a summing junction with another opamp will require another op amp monitoring the voltage difference between the U6 output and the U4 output, with the output of that opamp adjusting the control voltage applied to R18, the control for the current source. The magnitude and polarity of the gain are variables I have not calculated. You will also need an adjustable voltage to set the required current.
The arrangement will close the feedback loop.

Delta Prime

Joined Nov 15, 2019
1,326
Hello there I have used these for years in the lab and still do today, Your voltamagram function generator contains a Potentiostat.
potentiostats contain feedback circuitry between the output and measured potential.You're three electrodes should be put in a electrochemical cell containing the electrolyte solution and a reference solution. All you should really have to do is flip a switch and your chemical solution either loses an electron (oxidation) or gains an electron (reduction) depending on the direction of this current sweep to get your duck shape plot

MisterBill2

Joined Jan 23, 2018
11,598
Hello there I have used these for years in the lab and still do today, Your voltamagram function generator contains a Potentiostat.
potentiostats contain feedback circuitry between the output and measured potential.You're three electrodes should be put in a electrochemical cell containing the electrolyte solution and a reference solution. All you should really have to do is flip a switch and your chemical solution either loses an electron (oxidation) or gains an electron (reduction) depending on the direction of this current sweep to get your duck shape plot
There is no feedback in the circuit presented in post #1, except for within the voltage source circuit. The We is not part of any feedback loop, and to have feedback there must be some connection. Thus something is missing. Evidently DP is an expert, so DP can explain what connection must be added, using language thet others can understand.

Delta Prime

Joined Nov 15, 2019
1,326
The We is not part of any feedback loop, and to have feedback there must be some connection. Thus something is missing.
My response was a supplement to your post. An addition to your analysis I should have stated that. apologies it was no attack on you or your intellect,
To the thread starter.Make ,Model serial number of your Voltamogram function generator. As @MisterBill2 pointed out the circuit was not engineered for your application you're missing the feedback which is provided by what is known as a Potentiostat.

MisterBill2

Joined Jan 23, 2018
11,598
My response was a supplement to your post. An addition to your analysis I should have stated that. apologies it was no attack on you or your intellect,
To the thread starter.Make ,Model serial number of your Voltamogram function generator. As @MisterBill2 pointed out the circuit was not engineered for your application you're missing the feedback which is provided by what is known as a Potentiostat.
No apology needed as there was no offense taken. The whole discussion, as far as the chemistry aspect goes, is a few levels past my chemistry studies, which were adequate for an engineering career, mostly. Strictly the inorganic portion, relative to material stability and physical properties of materials.
I had presumed the circuits were the work of a senior level student hoping to achieve some research goal using "created instrumentation." I had not considered that this might be manufactured equipment. Interesting.

Wolframore

Joined Jan 21, 2019
2,533
I‘m curious, what is being measured? There are various projects out there to build cheap stats. What sort of voltage and current are we talking about?

ecaits

Joined Jan 6, 2014
56
To control the voltage difference between the RE and the WE requires a summing junction with another opamp will require another op amp monitoring the voltage difference between the U6 output and the U4 output, with the output of that opamp adjusting the control voltage applied to R18, the control for the current source. The magnitude and polarity of the gain are variables I have not calculated. You will also need an adjustable voltage to set the required current.
The arrangement will close the feedback loop.
Hello MisterBill2,

As per your suggestion, I have modified the circuit as per attached here.

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ecaits

Joined Jan 6, 2014
56
There is no feedback in the circuit presented in post #1, except for within the voltage source circuit. The We is not part of any feedback loop, and to have feedback there must be some connection. Thus something is missing. Evidently DP is an expert, so DP can explain what connection must be added, using language thet others can understand.
As per your input, I have prepared schematic given below.

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MisterBill2

Joined Jan 23, 2018
11,598
Hopefully Delta Prime will be able to verify that the revised circuit is what they are used to working with.
My chemistry education is a bit limited, although I did very well in the two courses required for non-chemical engineering students. I did get the organic chemistry text and at that point realized that organic chemistry is incredibly complex. Oh Well.