• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 3 answers
  • Subscribers 32 subscribers
  • Views 526 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

FDC1004: Application method and Calibration steps

Maggie Tan
Prodigy 10 points
Part Number: FDC1004


The sensor is used in Coffee machine, and have some question in FDC1004DGSR. Look forward to your reply~

  1. Does this IC requires calibration or not during our PCBA or product production?
  2. We’d like to use cap-sense IC in a plastic water tube to sense if there is water flowing through the tube (no need detect water level). Water tube will be surrounded by copper foil and we plan to use 1 channel to detect water. What is the accuracy of the sensing at different ambient temperature or different water temperature? Is calibration needed for application in different environment?
  3. In the cap-sense IC application note, it is suggested to use 2 more channels to detect water tank bottom and upper area as a reference capacitance offset. Do you think we should use 2 more channels or 1 more channel to detect water existence in water tube?
  4. If calibration is needed, please advise the steps for calibration.
  • 0
    TI__Mastermind 18545 points

    Hello, 

    Using a reference sensor can help your system offset any environmental impacts and reduce the need to calibrate or offset these with other methods. Temperature can have an impact on the sensor data but if you are just doing a simple yes/no detection for the state of the water, you may not care about the change you get from temperature variation. 

    Here are a few things to consider when deciding if you need to implement any calibration in this application: 

    • What is the measurements dynamic range between having water and no water present? 
    • What is the minimum resolution you need? For detecting presence vs no presence, I expect you do not need a fine resolution
      • If you need high resolution, can you use the FDC1004 calibration registers to offset for parasitic capacitances in your system
    • What variation do you get testing your system over temperature? If it is a large change relative to your resolution, you may need a reference sensor or temperature calibration in your system

    The existence of the reference sensors in our application note are to help provide references for level detection. Since the main concern here is presence detection of the liquid, I do not think you will need the additional sensor unless you expect environmental factors to be able to impact your sensor. 

    Best Regards, 

    Justin Beigel

  • 0 in reply to Justin Beigel
    Prodigy 40 points

    Dear Justin,

    In our application, temperature is low and stable because  tap water flow is detected. May I ask should we use 3 channels in the design? 1 for detect water, 1 for ambient reference, 1 for water tube? Thanks

    Best Regards,

    James Lo

  • 0 in reply to james lo
    TI__Mastermind 18545 points

    Hello James, 

    Based on the information provided, I think you are fine to just use one channel to determine if there is water present. 

    Best Regards, 

    Justin Beigel

  • 0 in reply to Justin Beigel
    Prodigy 40 points

    Dear Justin,

    Thanks for your comments. Attached is the schematic for using 1 channel. May I ask if it is ok? Thanks

    cap_sens.pdf

  • 0 in reply to james lo
    TI__Mastermind 40295 points

    James,

    Justin is out today.
    Your schematic looks fine. 
    You can most likely remove the 51pF cap from the SHLD connection that will be used in your set-up.
    If you see ringing on your I2C lines, you might consider making the pull-ups 5k.

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Prodigy 40 points

    John & Justin,

    Thanks for your comments. 

    If we want to calibrate C level (0) when IC is start-up. Please advise if below procedure is ok. Thanks

    Procedure:
    1. Water tube is empty
    2. Machine plugged AC mains and cap-sense IC energize
    3. Read C level (0)
    4. Store C level (0) in the IC or MCU. This value is a parasitic capacitance reference point.

    Best Regards,

    James Lo

  • 0 in reply to james lo
    TI__Mastermind 40295 points

    James,

    It looks to me like your procedure is sound.
    Please let me know if you have any more questions.

    Regards,
    John