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SMART Transmitters

Response time of SMART trasmitter = dead time + time constant. Another parameter called Damping is closely related to response time. What is the relation between response time & damping in SMART transmitters? Is there any mathematical relation?

avik_ic

• 4 May 2012 12:15 PM
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• CaitlinBreen

  

  • 18 Mar 2014 7:28 PM

  Hello avik_ic,

  The more a transmitter is damped, the slower the transmitter's response time.  In some applications, pumps or other process noise must be 'damped out' to get good control or indication.  Damping is the ability of an instrument to prevent rapid or excessive corrections in response to process noise that may result in measurement instability or oscillation.  Regarding your question of an equation - here is an example:

  Damping may be “adjustable between 0.2 and 255
  seconds.” In other words, the transmitter can be set to respond
  to changes in the process (i.e., reflect a change in output) every
  0.2 seconds, every 255 seconds, or at any interval in between.
  
  Figure 5.6 shows the time required to change a transmitter’s
  output reading with 5-second damping. The time before the
  output starts to change is called dead time. After the first
  5-second interval, 63.2% of the process variable’s true value is
  reflected in the transmitter’s output. This time interval is called
  the time constant (the time required [after dead time] for the
  output to reach 63.2% of the input’s true value). After 25
  seconds, almost 100% of the process variable’s true value is
  registered in the output. The dead time plus one time constant
  equals total response time.

  Hope that answers your question

  Regards,

  Caitlin

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