3 Replies Latest reply on Apr 13, 2020 5:47 AM by BragadeeshV_41

    Are high accuracy capacitance sensors available or could they be created?

    BrHo_4675206

      I’m interested in the capacitance technology used for the CapSense liquid level sensing 12 sensor flex PCB sensor contained in the liquid level sensing kit (CY8CKIT-022).  I noticed that of the two sensors (2 sensor & 12 sensor) supplied in the kit, one was more precise than the other.  I’m interested in finding out if this sensor could be manufactured with even more precision and if the technology could be manufactured with a width close to half what is currently in use (1.81”) for the 12 sensor flex PCB sensor. 

       

      I’ve got an application in which a similar sensor could be employed if the width could be adjusted (~1.00” width) to allow attachment to a 25 ml buret while still allowing use of the graduations on the buret.  In addition, the precision would need to be adjusted to provide a minimum resolution equaling half the minimum graduation on the buret (a linear distance of 0.027”).     

       

      The application mentioned would involve a total of between 25 and 50 sensors.

        • 1. Re: Are high accuracy capacitance sensors available or could they be created?
          BragadeeshV_41

          Hi BrHo_4675206,

           

           

          1. You can increase the number of sensors and decrease the width of the segments to achieve higher accuracy in terms of resolution. The maximum number of sensors you can have is only limited by the no of  GPIOs of the selected device.

           

          2. We highly recommend you to shield all the ground electrodes from the sensing electrode and the sensor traces to avoid high parasitic capacitance. To achieve this, we recommend you to connect the inactive sensors connection to shield and connect the hatch pattern to shield. This will also help in achieving good temperature compensation.

           

          3. You can have ground electrode on either side of the sensing electrode as given in the 12 RX sensor pattern. But make sure that the distance between the ground electrode and the sensing electrode is atleast 2 to 3 times the container thickness (overlay) and have shield electrode in-between the two if possible. This will help if the liquid can get accidentally shorted to ground.

           

          4. Some questions:

          a. Is your liquid conductive? What is the liquid used?

          b. Does it have a large connection to ground (resistive/ capacitive)?

          c. Are there chances for your liquid to be accidentally grounded?

          d. Is much variation in liquid temperature expected?

           

          Regards,

          Bragadeesh

          • 2. Re: Are high accuracy capacitance sensors available or could they be created?
            BrHo_4675206

            4. Some questions:

            a. Is your liquid conductive? No What is the liquid used?  Tap water

            b. Does it have a large connection to ground (resistive/ capacitive)? It's not connected to ground at all.

            c. Are there chances for your liquid to be accidentally grounded? No

            d. Is much variation in liquid temperature expected? No, it's in climate controlled facility.

            • 3. Re: Are high accuracy capacitance sensors available or could they be created?
              BragadeeshV_41

              BrHo_4675206,

               

              We believe that tap water is conductive. Please confirm.

              We recommend you to go for CSD + Shield configuration for your application.

              It is also recommended to have a ground electrode with area greater than the sensing electrodes (combined) on either side of the sensing electrode, just like the 12 RX flex pattern. But make sure that the ground electrodes are at least 2 to 3 times the thickness of the container away from the sensing electrodes.

              For better accuracy, ensure that the tilt in the electrodes is around 1.3 - 1.5 times the pitch size of the electrodes.

               

              The gap between the electrodes can be maintained at 0.5 mm with adjacent electrodes to the electrode being sensed connected to shield for minimum Cp.

              You can have the Rx electrodes as wide as possible to increase SNR.

               

              If there are no chances for the liquid to get accidentally grounded, we also recommend you to test the same pattern for CSX sensing as well. For this, the ground electrodes on either side of the sensing electrodes is connected to Tx of the CSX sensing. But it is important to have at least 2 to 3 times of container wall thickness gap between Tx and Rx electrodes. CSX technique has higher SNR compared to CSD technique. In this case, the rawcounts will decrease with increase in water level and this has to taken care in firmware.

               

              Let us know if you have further questions.

               

              Regards,

              Bragadeesh