AD623 input signal offset compensation

Hi stoccarda,

Good day and thank you for reaching out to us about your query.
If I understood correctly the one giving the offset of 6mV are the temperature controllers  which is connected to V_ACT and 'false' triggering the voltage monitor MC33161D because this is being gained up by the inamp. I just want to make sure that all the AD623 works expectedly and I understand the scenario.

If this is the case will it be okay if you show us the circuitry that connects to V_ACT? This may show us what's causing the offset or if it is inherent with the device/s connected there. The only way I could think off for now is if we can calibrate the effect of the 6mV offset at the output of the AD623 going in to the voltage monitor but this will require doing it for all the temperature controllers.
Let's see first what we have on the initial stage stoccarda then we'll go from there.
Thank you.

Best Regards,
Dann

Hello,
will the OPAmp (or different) be a better forum to get ideas how to find a solution?

Hi Stoccarda,

Sincere apologies for the delay in response.
Since you mentioned that there's no problem with the AD623, I think we have to look at the actual circuit connected to the input pins of the AD623. 

As I requested from my previous response, will it be okay to show us the schematic at the input side of the AD623? or give us the actual temperature controller used.
I'm curious to look at the specification sheet of these temperature controllers and how they were connected to the AD623, since if the offset is inherent, we may be able to adjust the trip point of the MC33161 to accommodate the maximum offset we expect from the system. One more way is through system calibration, but since you're not using any microcontroller (based on what you showed here) we have to think about how to actually perform it based on the diagram.

Thanks stoccarda. Apologies again for the delay in response.

Best Regards,
Dann

Hi Dann,
thanks for coming back !

The temperature controller has two monitor outputs:
ACT: Temperature  voltage  monitor.    Buffered  measurement  of  voltage  across
Sensor+ & Sensor-.  [1 kΩ output impedance]
SET :Setpoint voltage monitor.  Buffered measurement of the setpoint input.
[1 kΩ output impedance].

They are directly connected to pin 2 and 3 of the AD623.

From data sheet:

Setpoint vs. Actual T Accuracy: 5 mV (negative as well as positive difference measured)
with Gain=213 -> more than 1.065 'offset error' at MC33161.

You are right, there is no MCU used in this circuit.

Thanks

Hi Dann,
thanks for coming back !

The temperature controller has two monitor outputs:
ACT: Temperature  voltage  monitor.    Buffered  measurement  of  voltage  across
Sensor+ & Sensor-.  [1 kΩ output impedance]
SET :Setpoint voltage monitor.  Buffered measurement of the setpoint input.
[1 kΩ output impedance].

They are directly connected to pin 2 and 3 of the AD623.

From data sheet:

Setpoint vs. Actual T Accuracy: 5 mV (negative as well as positive difference measured)
with Gain=213 -> more than 1.065 'offset error' at MC33161.

You are right, there is no MCU used in this circuit.

Thanks