Firstly – First post so let me know if I have done anything wrong.
Okay, so I am tying to get this biased potentiostat to work. I have attached the circuit below. I am using the following sensor:
http://www.alphasense.com/WEB1213/wp-content/uploads/2016/03/NO-A4.pdf
For the purposes of this example, you can ignore the Aux electrode, I am only taking into account the change on the working electrode.
When placed on zero gas, the reading settles, and appears good.
After zeroing, the sensor is placed on span gas (5ppm), and the reading initially quickly climbs, as you would expect. However the reading does not settle, instead it drifts upwards slowly.
After moving back to zero gas, the reading is much higher, almost that of when initially placed on span gas. I cannot figure out where this drift is coming from, and could do with a second look at my circuit.
The 3v3Bat rail is continuously maintained, and therefore the sensor bias is maintained too. All voltages look good, and the general noise floor is very low.
Main Potentiostat:
Bias / virtual ground generation here:
Thanks!
Best Answer
Now, granted I haven't thoroughly analyzed your circuit but I'm not seeing any extreme low passes or anything that would "store" a value for several seconds or minutes.
I have to assume there is some kind of problem with the sensor itself, or the way you're using it. Perhaps it takes minutes or hours to stabilize after a change in conditions?