Q8: How do I know, if a mA signal is active or passive?

 

Example 1: Your device outputs a 4…20 mA signal which is measured by a PR module.

 

  1. Disconnect the two current loop wires from the PR module input terminal.
  2. Using a voltmeter, measure for DC voltage present on the wires.
  3. If no voltage is present, then your device is creating a passive current signal. This means a loop excitation source, (typically 12...24 VDC), must be used to power the current loop and measure the signal. Many PR modules have an input excitation source which powers a passive current loop, allowing our module to both measure and energize your device.
  4. If you measure voltage on the wires, (typically 12...24 VDC), then the current signal created by your device is active. Do NOT use our loop excitation source when measuring an active current signal.

 

Example 1 (1)

 

 

Example 2: A PR module outputs a 4…20 mA signal which is measured by your device.

  1. Disconnect the two current loop wires from our output terminal.
  2. Using a voltmeter, measure for DC voltage present on the wires.
  3. If no voltage is present, then your device has a passive input. Therefore, the PR module must provide the excitation source needed to power and regulate current flow on the loop.
  4. If you measure voltage on the wires, (typically 12...24 VDC), then your device has an active input. Therefore, the PR module should only regulate the level of current flowing through the loop, it should NOT power the loop.

 

Example 2