Emerson Exchange 365

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Trouble Reading RPM with and I.S. DI NAMUR CHARM

We are having problems reading the basket speed (RPM) of a centrifuge. The speed pickup is a Hall Effect sensor as described in attached pdf. Speed gear has 72 teeth so our PCI/PULSE_VAL is set at 0.01388 and max speed is 1500 RPM. Frequency (1800hz) at max speed is well within the operating range of the probe and the CHARM DI. The DI Input (using diagnostics) did not appear to be reading until the RPM is above 500. Once there or above, it appears to read ok until the RPM drops below 500. The diagnostics show 0hz below 500 RPM. What gives?  

Speed pickup for CE1701.pdf

putelism

• 5 Dec 2017 6:24 PM
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4 Replies

• Rune Reppenhagen

  

  • 7 Dec 2017 1:33 PM

  From Books Online:

  

  Please check if you have the HIGH_FREQ_ENA parameter enabled. If so, please disable it.

  Regards,

  Rune

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• putelism

  

  • 7 Dec 2017 3:36 PM

  In reply to Rune Reppenhagen:

  Rune, thank you for this tid-bit! It will make a difference in our results.

  The parameter meaning in DeltaV Explorer HELP is misleading. Our top speed 1500 RPM generates a probe frequency of 1.5 kHz. By interpreting the HIGH_FREQ_ENA parameter use below, this value should be set to TRUE because we are reading above 500 Hz. This is what caused or reading to drop off.

  

  I also noticed the default FILTER time is set to 1.3 sec (1sec period of control) for a PCI discrete. Why is this? Do speed probes have a noisy signal?     

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• Rune Reppenhagen

  

  • 20 Dec 2017 5:24 PM

  In reply to putelism:

  Here is a little more detailed information on this issue:
  
  The ENAB_HIGH_FREQ parameter does not affect the frequency of whatever is measured. If a user is measuring frequency as in the this example, it does not matter what the parameter is set to. If the user however is counting pulses and accumulating that value, the point at which the reported count rolls over will change from either:
  
  (2^16) - 1 = 65,536 total pulses - If ENAB_HIGH_FREQ = FALSE
  (2^32) – 1 = 4,294,967,295 total pulses - If ENAB_HIGH_FREQ = TRUE
  
  The very next count on either of the above values will roll the counter back to zero.

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• putelism

  

  • 20 Dec 2017 5:35 PM

  In reply to Rune Reppenhagen:

  Thank you!
  BOL could improve the parameter explanation.

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