No Frequency Found

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Nick Vandehey

• August 22, 2023 03:21

Are there limits (high/low) of the voltage measurement for the "measure frequency" command?

I have this block of code in my test plan that consistently results in "no frequency detected" failure, despite me being sure that there is a lovely square wave on the test point connected to PPC_CLK1

  - command: freq 1
  - command: sleepms 3000
  - command: measure frequency 31-34KHz

Pk-Pk voltage: 1.84v, Freq: 32.77kHz, duty cycle(+): 47.25%

Is the voltage too low to be detected?

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  Nick Vandehey

  • August 22, 2023 04:13

  Ok. So I got the measurement above working, but the question from above is still appropriate. But now I have even a more challenging signal to measure frequency on. 

  72mV pk to pk on a 1v DC offset. 32MHz sinusoidal-sawtoothy signal. 

  Should I expect the PLT-300 to pick up on the frequency on this type of signal?

  

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  Jeremy Wood

  • August 22, 2023 19:28

  Glad you got the first scenario working. For the second scenario, the PLT-300 cannot generally measure frequencies that high, because of signal limitations through the HD-78 cable and typical ICT fixture.

  The DMM module in the PLT can measure up to 60MHz, but we specify a real-world limit of 20MHz. Please note that reaching that 20MHz "limit" is dependent on the signal type, specific fixture design, and so on. In some setups it may be possible to measure higher, and some cases it might not be possible to clock the signal successfully.

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