CAV444-capacitance to voltage converter IC

Discussion in 'The Projects Forum' started by saifudeen rizal, Jun 26, 2018.

  1. saifudeen rizal

    Thread Starter Member

    Jun 5, 2018
    36
    2
    Hai.,
    i am working on the fuel level sensor project and i have used CAV444 IC .,
    The issue is that .,
    Even though i have followed the circuitry and values that was given in the below link

    https://www.analog-micro.com/_pages/ics/cav444/cav444_bb.pdf

    The Vout doesn't change and it gives a constant value and for the info i get the correct value of Vref as 2.5V.
    and for the input i use cap.probe .,

    Thank you in advance.,
    -saif
     
  2. jpanhalt

    Expert

    Jan 18, 2008
    6,290
    1,173
    Many years ago, I used the CAV414 as a proximity detector, which may be somewhat similar to your application.

    Have you done any tests with known ways to affect capacitance to determine whether your circuit works? If so, then address the application. Otherwise, I would focus on getting the circuit to work.

    Are you using the factory evaluation board or one of your own making? If the latter, please post your schematic.

    If you are using the factory board, please describe how your application is set up.
     
  3. saifudeen rizal

    Thread Starter Member

    Jun 5, 2018
    36
    2

    No.,i have jst followed the circuit that was given by them(that link).,and i m using one of my own making.,

    and i m getting vref as 2.5 V as exactly and thats the reason i m sure that my cicuit works.,
     
  4. jpanhalt

    Expert

    Jan 18, 2008
    6,290
    1,173
    Have you changed Cm to verify the output change? For example, use a small trimmer capacitor as Cm and determine whether the output changes as expected? If the output doesn't change as expected, then the first problem is probably your circuit.

    Be sure to report the capacitance of the test capacitor and what you expect the capacitance of your fuel level detector to be. That is why I asked for you to show that design.
     
  5. saifudeen rizal

    Thread Starter Member

    Jun 5, 2018
    36
    2

    No.,will check it and reply to u,

    The other issue that i am facing is normally the capacitance value(i/p)is from 0.24 nf to 0.46 nf but when i connected to the cav444 IC the I/P capacitance value increases to 165nf(I don't know wat would be the reason for the Cap.energizing issue?)(i measured it with the help of Cap. Meter)

    The Input Range for the cav444 is between 10pf to 10nf
     
  6. saifudeen rizal

    Thread Starter Member

    Jun 5, 2018
    36
    2
    i have changed the Cm but value didnt change and the circuit also i have checked.
     
  7. jpanhalt

    Expert

    Jan 18, 2008
    6,290
    1,173
    upload_2018-6-28_10-37-15.png

    How are you measuring Vout? Wha voltage are you observing? I used a buffer on Vref and measured the output as a differential voltage between Rref and Vout (I wanted it to act as a proximity detector rather than give an analog measure of capacitance) . If you are not seeing a change, either your component values are wrong so the range of Cm doesn't affect Vout or your layout has an error.

    Please post your exact schematic with component values and the values you used for Cm.
     
  8. saifudeen rizal

    Thread Starter Member

    Jun 5, 2018
    36
    2
    Hai.,

    sry i have just misunderstod the whole circuit.,

    i didnt realised the KAli_cav444 thing which itself calculates and gives the resistive value according to our need and input and thank u for replying to my post.,

    and i have one doubt.,
    It says to enter the Current value of Cm and Cw., but how do i measure it .,
     
  9. JanikaS

    New Member

    Jul 20, 2018
    2
    2
    Hello Saifudeen,

    did you use the following Excel Sheet (https://www.analog-micro.com/_pages/ics/cav444/cav444_cali.xls) to calculate the capacitors and resistors needed to make CAV444 work?

    The best starting point for the converter and CM charge current is 20 uA. For CM,min and CM,max you can enter the capacitance values measured using your capacitance meter. If you want a voltage output of 1 to 4 V you can keep the preset values for VDiff,min and VDiff,max. After entering these values the excel sheet should give you all the information you need to assemble your circuit.
     
    absf and saifudeen rizal like this.
  10. saifudeen rizal

    Thread Starter Member

    Jun 5, 2018
    36
    2
    Hai.,

    Thanks for helping me out in this project and i got the output as expected
    Thank you again.,

    -Saif
     
    JanikaS likes this.
  11. JanikaS

    New Member

    Jul 20, 2018
    2
    2
    You're welcome. I'm glad I was able to help you.
     
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