CAPSENSE Stuck at same value

Tip / Sign in to post questions, reply, level up, and achieve exciting badges. Know more

cross mob
Patfahy
Level 1
Level 1
First question asked Welcome!

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.

Patfahy_0-1654606288338.png

Patfahy_1-1654606304028.png

Patfahy_2-1654606322654.png

 

 

Many thanks,

Pat

0 Likes
1 Solution
ncbs
Moderator
Moderator
Moderator
500 replies posted 50 likes received 250 sign-ins

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

View solution in original post

0 Likes
1 Reply
ncbs
Moderator
Moderator
Moderator
500 replies posted 50 likes received 250 sign-ins

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

0 Likes