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haideralibutt

Industry signals in instrumentation

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haideralibutt
, 07-08-2010 at 09:58 AM (1461 Views)
It would be highly appreciated if some one could let me know these questions regarding the signals.
Why we use 3-15 psi why not other limits i.e 0-15 psi?
Why we use 4-20 mA why not other values i.e 0-20 mA?

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Instrumentations

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  1. dinil's Avatar
    the answer s simple in case we use 0-20 mA the zero stands for zero process variable, any damage happens to the connection also shows the zero even if there s some process variable presents, and the another reason is some current flow ll show by the system due to stray emf in the field. in second case we use 4-20mA, 4mA stands for 0% PV and the 0mA stands for broken lines or some dagage happened to lines or instrument... the reasons are same for pneumatic signals too......... hope u understand wat i explained
    dinil: dinilmurukesan@gmail.com
  2. dinil's Avatar
    the 4- 20 scale s linear too.......
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