FDC1004-Q1: FDC1004 capacitance accuracy problem

Sathya,

Thank you for your post and your interest in TI products.

Could external noise be a factor in your measurements?
Are you using the FDC1004's active shields to reduce EMI impact on the sensors?

Do you see the same behavior with the tank filling and emptying?

More information on the FDC1004 and its applications can be found at the FDC1004 Capacitive Sensing FAQs,
and two blogs cover active shielding, part 1 and part 2.

Regards,
John

Thanks for your reply.

Could external noise be a factor in your measurements?

Not sure, how to filter external noise.

Are you using the FDC1004's active shields to reduce EMI impact on the sensors?

yes, am using Sheid 2 as a reference 

Do you see the same behavior with the tank filling and emptying?

Yes, same behavior for full and empty bottle.

Sathya,

Depending on your system, you might be able to shield from EMI/noise by using the active shield feature in the FDC1004.
The active shields can frequently be configured to protect your sensors from EMI/noise, without loading the sensors as a grounded shield would.

As I mentioned before, we have a comprehensive list of app notes and blogs at the FDC1004 Capacitive Sensing FAQ page.
One of the app notes - Capacitive Sensing: Ins and Outs of Active Shielding - gives guidance on how to configure & use sensors and active shields.

Another app note - Capacitive Sensing: Out-of-Phase Liquid Level Technique - provides guidance on configuring the FDC1004 sensors and active shields so the liquid being measured is electrically neutral, which makes the system more robust against external, grounded objects.

If external noise is the problem, then there's very little that can be done to make it better with just the device settings.

If this info doesn't address what you are seeing, we will need to work through the details of your implementation for the application you want to support.

Regards,
John

PFA image of FDC section.

If external noise is the problem, then there's very little that can be done to make it better with just the device settings

- Can you plesae elabrote the above point.

Sathya,

My last statement was not clear or helpful. Apologies for that.

Could you show a layout of how your sensors, active shields and any grounded shields are positioned in your application?

Also, how are the sensors and active shields provisioned? You mentioned SHLD2 is being used as a reference.

Is the FDC1004 positioned close by the sensors and shields, or are they connected by long wires?

Regards,
John