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# AD5940 (Ramp example & Calcuration Rtia in Amperometry)

Dear all,

I have a little problem during testing the Ramp example. I used ad5940,adicup3029 (Evaluation board)  and crocodile clip cable.

I  configured hardware by referring to this site(AN-1563 (Rev. 0) (analog.com))

I constructed the circuit & coding like a picture

and the result is the following picture.

This is the same result as connecting resistance only.

I think this is a problem caused by cap and diode or ad5940's hardware configuration.

How this could be fixed?

+ The link mentioned earlier contains the Rtia formula for all examples except amperometry. What should I refer to?

Parents
• Hi,

Can you ensure the jumpers JP9, JP10 and JP11 are connected in position C to connect the USB to the AD5940. What is the value of the dummy network?

The formula is the same for amperometry.

• Hi,

Can you ensure the jumpers JP9, JP10 and JP11 are connected in position C to connect the USB to the AD5940. What is the value of the dummy network?

The formula is the same for amperometry.

Children

This circuit is intended to ensure proper operation before proceeding with the cyclic voltammetry with a solution.

as you advised, I moved the jumpers JP9,10,11 at position C. There have been some changes.

It works well when there's only resistance. Also, although the signs are the opposite, I was able to get results similar to simulation with that circuit.

simulation(Green is voltage, Blue is current)

test

But there were many noise and I got similar but different results every time .

I think Rtia should be chosen appropriately, but I don't know how. So I'm trying to change it one by one.

How this could be fixed?

+ When I envisioned that circuit through a simulation program, the maximum current was 66nA.

Can I recover this much current accurately with the ad5940?

Thank you again for your kindness.

• Set the RTIA to 512K. It is the largest available gain resistor internal in the AD5940. If the data is still noisy an external resistor (10MOhm) can be connected to RC0_0 and RC0_1 to increase resolution.

• Thank you for your response!!

I set the RTIA to 512K, but it was still very noisy.

How can i connect an external resistor (10MOhm) to RC0_0 and RC0_1 to increase resolution? does external resistor mean LPTIARloadSel?

+Do you also think this is a problem caused by the wrong Rtia setting?