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Hi,
I have a capsense sensor to sense liquid level in a tank. I have thresholds that move according to temperature which seems to work fine. I am having a problem where the capsense output gets stuck at ~49151 on some sensors.
Has anyone ever seen this before or know how to rectify it ? I am performing resets of the capsense board every 30 seconds, but I have also tried without the resets, same problem.
Many thanks,
Pat
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Hi @Patfahy,
I believe your scan resolution is set to 16 bits. You are observing a constant level at 49151 because this region corresponds to the "flat spot" region of the sigma-delta converter used in the CapSense block. Flat spot is an inherent characteristic of the sigma-delta converter. In this region, the raw counts do not increase with increase in capacitance, thus creating a "dead-zone". These regions occur at 25%, 50% and 75% of the maximum raw count. Mathematically,
Scan resolution = 16 bits
Max. raw count = (2^16)-1 = 65535
75% of max raw count ≈ 49151
One way to overcome these regions is to set the baseline to 85% (which is more than 75%) of max. raw counts. You can eliminate the flat spots by using PRS. I would suggest you to go through the following thread too: https://community.infineon.com/t5/PSoC-4/Why-do-flat-spots-occur/m-p/240827. Additionally, refer to the section 5.3.2.1.2 Flat-spots in PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide. For 5th generation CapSense devices, refer to section 5.3.4.1.2 of the same document.
Best regards,
Nikhil
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Hi @Patfahy,
I believe your scan resolution is set to 16 bits. You are observing a constant level at 49151 because this region corresponds to the "flat spot" region of the sigma-delta converter used in the CapSense block. Flat spot is an inherent characteristic of the sigma-delta converter. In this region, the raw counts do not increase with increase in capacitance, thus creating a "dead-zone". These regions occur at 25%, 50% and 75% of the maximum raw count. Mathematically,
Scan resolution = 16 bits
Max. raw count = (2^16)-1 = 65535
75% of max raw count ≈ 49151
One way to overcome these regions is to set the baseline to 85% (which is more than 75%) of max. raw counts. You can eliminate the flat spots by using PRS. I would suggest you to go through the following thread too: https://community.infineon.com/t5/PSoC-4/Why-do-flat-spots-occur/m-p/240827. Additionally, refer to the section 5.3.2.1.2 Flat-spots in PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide. For 5th generation CapSense devices, refer to section 5.3.4.1.2 of the same document.
Best regards,
Nikhil