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measuring beyond 20v — Parallax Forums

measuring beyond 20v

HumphreybasHumphreybas Posts: 4
edited 2011-12-07 05:25 in Accessories
Is it correct that I can't measure a 24 volt signal with the propscope?
And if yes, how would I proceed to measure anyway? Does a voltage divider change my measurements?

Comments

  • Dr_AculaDr_Acula Posts: 5,484
    edited 2011-12-07 04:12
    Yes a voltage divider should work. Why not try two 10k resistors in series - input =>10k resistor => 10k resistor => ground. Measure the volts in the middle and it will be half so your voltage now goes zero to 12V.
  • HumphreybasHumphreybas Posts: 4
    edited 2011-12-07 04:35
    Thank you!

    Am I the only one who thinks 20V is a bit silly to put the maximum for the propscope since so many PLC and other automation components run on either 12V or 24V?
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2011-12-07 04:46
    Maybe, but two 10k resistors might set you back two cents, and I guess the designers figure that because they understand voltage dividers and Kirchhoff's laws, you do too! You can divide by other ratios as well if you want - eg a 30k and a 10k in series will divide by four. The ratio is the lower resistor (10k) over the total (10k+30k) = 1/4. In reality, you might not be able to find a 30k resistor so you could use three 10k resistors in series, or a near value like 27k, and then work out your ratio of 10k/37k and do some maths to get the correct value.

    In your case, divide by 2 will work. You might want to think about using 1% 10k resistors instead of 5% resistors to get a more accurate reading.
  • hover1hover1 Posts: 1,929
    edited 2011-12-07 04:52
    If you put your probes to 10X, and adjust the software for 10X), you can measure to 200 volt PP.

    http://www.parallax.com/Portals/0/Downloads/docs/prod/prop/32220GettingStartedv1.0.pdf
  • HumphreybasHumphreybas Posts: 4
    edited 2011-12-07 05:19
    So no need to use a voltage divider then. That makes more sense, Thank you!
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2011-12-07 05:25
    Even better hover1!

    Very clever.
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