Why analog inputs have negative values

Why do my analog inputs have negative values?

Seeing negative analog values reported by the WRTU is most often caused by a current loop device whose output dips below 4 mA. Unlike other instrumentation products, the AlarmAgent WRTU does not clamp or hard-limit the current loop input to a minimum of 4 mA. This allows greater flexibility of input types, e.g. 0-20 mA or 0-5 VDC in voltage mode.

Common Causes of Unexpected Negative Analog Input Readings:

  • The input may be wired backwards.
  • The scaling in AlarmAgent.com Analog Scaling can be incorrect.
  • The transducer may have failed or lost loop power.
  • The control loop is not properly grounded. It may be grounded somewhere else besides the AlarmAgent WRTU.