3 Replies Latest reply on Oct 6, 2015 9:21 PM by bharadhwajas_91

    Capsense raw value drift



      I have a more theoretical question regarding CapSense (implemented using a PSoC4 BLE device):


      My application uses CapSense generic sensors to measure the change of a liquid level within a cup (from the outside). The signal is quite weak, but after tuning a decent signal can be observed when the cup is filled. BUT:  the raw count value constantly decreases, kind of drifts down significantly. Can you give me a hint why this drifting occurs ? I am perfectly OK with it to happen, but need to know why.


      Please note the attached screenshot from the tuner GUI, I added black lines to make the decline visible. The sensor electrodes are made from flexible PCB, following the CapSense guidelines.


      Thank you for your help!

        • 1. Re: Capsense raw value drift

          Hi J,


          Since it is Capsense generic Sensors , the rawcount could vary because of change in Cp.So could you check your sensor construction once,Having Gnd around will help improve stability. What about the temperature of the liquid/Sensor ?Is is cooling down?


          You can try with the normal capsense sensors (use only scan sensors api and check the rawcount array) to compare with Generic sensors.

          • 2. Re: Capsense raw value drift



            thank you for the help. The sensor array is provided with hatched ground and the liquid is of constant temperature. I forgot to say that there is no drift in idle mode. But if I change the overall capacity (filling a before empty cup or emptying a before full one), the new raw count value drifts in direction of the state before (which was stable after some time).


            It seems a bit as if there an algorithm working in the background, trying to level out changes. Is it possible, that the "auto level" option of the CapSense component (which I do use) has this effect? 

            • 3. Re: Capsense raw value drift



              Do you mean sensor auto-reset?I think since the generic sensor just provides the rawcount it may not matter if auto reset is set or not.See




              However the capacitance could very because of temperature ,whenever there is change in liquid(emptying /filling), there is change in liquid temperature and takes sensor temperature takes some time to catch-up.This might be the reason for the   behavior you are observing.