Voltage adjustment in cyclic voltammetry circuit

[ecaits1]

This is a circuit of cyclic voltammetry in which all three electrode i.e. WE (Working Electrode), CE(Counter Electrode) & RE (Reference Electrode) are dipped in electrolyte solution.

The source voltage is -1V to +1V (mentioned in circuit) but generally we are using -0.2V to +0.6V as scanning voltage. During scanning (-0.2V to +0.6V), I have measured the voltage between working electrode (WE) and reference electrode (RE) which is -0.4 to +0.8V (approx.) which should be -0.2V to +0.6V and this is happened due to electrolyte (solution resistance).

The circuit may need to improve by taking feedback from WE & RE to make it exact -0.2V to +0.6V.

I want few suggestion for circuit improvement.

 

[KlausST]

Hi,

there are a lot of issues ... or maybe i don´t understand how you expect it to work.

* no power supply and no power supply capacitors. Yes, I know that some simulation run without them, but a real circuit will have problems..
* No naming of the parts makes it difficutl to discuss a circuit.
* 100uF directly connected at the ouput of the most right OPAMP. Usually OPAMPs are not made to drive that large capacitance.
* non_inverting input to most right OPAMP is named with "1V ref for shifting".
But it is not 1V, it rather is "PIN3_DAC / 5" --> it shifts with PWM.
* RE input has no ESD protection.... it´s easy to kill the OPAMP by handling of the electrodes.
* while CE and WE are less prone for ESD problems, I still recommend to add ESD protection.
* lower_LT1097 has no local feedback. You risk oscillation and noise pickup.
* add capacitors to the DC nodes to stabilize them and reduce noise.

The overall function is not clear to me.

Klaus

 

[ecaits1]

Hi,

there are a lot of issues ... or maybe i don´t understand how you expect it to work.

* no power supply and no power supply capacitors. Yes, I know that some simulation run without them, but a real circuit will have problems..
* No naming of the parts makes it difficutl to discuss a circuit.
* 100uF directly connected at the ouput of the most right OPAMP. Usually OPAMPs are not made to drive that large capacitance.
* non_inverting input to most right OPAMP is named with "1V ref for shifting".
But it is not 1V, it rather is "PIN3_DAC / 5" --> it shifts with PWM.
* RE input has no ESD protection.... it´s easy to kill the OPAMP by handling of the electrodes.
* while CE and WE are less prone for ESD problems, I still recommend to add ESD protection.
* lower_LT1097 has no local feedback. You risk oscillation and noise pickup.
* add capacitors to the DC nodes to stabilize them and reduce noise.

The overall function is not clear to me.

Klaus

Hello Klaus,

I have not mentioned the power supplies in op-amps otherwise +/-12V is provided.
100uF op-amp is not connected direct to op-amp. The output of op-amp is given to ADC module.
1V reference IC is used for voltage shifting from (0V to 5V) range to (-1V to +1V) using voltage divider method.
RE is just reference electrode to provide the fix reference voltage for WE(working electrode) so in this application, i think no need of ESD protection and same way for CE & WE.
For, lower_LT1097 has no local feedback but it has feedback through electro-chemical cell. You can suggest for that.

The main issue is that the voltage between WE & RE should be same to voltage of linear sweep generator.
If the voltage of linear sweep generator is -0.2V to +0.6V then voltage between WE & RE is approx. -0.4 to +0.8V (approx.)