AI CHARM Diagnostic - Primary Variable Inaccurate

AI CHARM with HART enabled, E&H Promag connected and auto-sensed correctly.

No diagnostics are indicated at the meter.  Instrument is functioning normally.

CHARM diagnostics indicate OInteg = BAD, and Primary Variable Inaccurate.

HART Device alarms are disabled.  Can someone tell me what is triggering this? Not sure how to diagnose. 

4 Replies

  • Sim,

    There are a couple of possibilities I can think of. Check the CHARM configuration and make sure the UNDERRANGE_PCT hasn't been set to zero (default is -3). That can trigger an uncertain status. The other is that the status is coming over the HART status from the device. There may be a "calibration required every xx" type of setting configured in the device.
  • In reply to Scott Thompson:

    Interesting. I'm wondering if the device Voltage drop is exceeding the fields side limit of 15 Volts, and is not able to drive the mA signal to match the actual PV value, hence a discrepancy between the analog signal and the HART PV value.

    This usually manifests at the higher end of the mA range as the voltage drop on the Input resistor (and some voltage drop in the Current Limiter circuit).

    I would compare the analog signal to the PV and if there is a discrepancy, figure out at what % value this happens at. Check the device specifications to see if there are some start up loads that might prevent proper initialization.

    One solution for higher startup or runtime power is to use the new DeltaV 3 wire Analog Terminal block. This block provides fused Injected power to the device, which bypasses the internal current limiting circuit of the CHARM and will provide full 24 volts at the field terminal. This can add up to 3 Volts of head room on the circuit. This terminal block was released with v13 and can be used on SIS or BPCS IO. It is strictly a hardware option so the DeltaV version does not matter. ( it works on any version).

    Not sure yet what the issue is, but if you have a second device in series in the current loop, the sum of voltage drops could affect the device's ability to drive the mA signal.

    Andre Dicaire

  • In reply to Scott Thompson:

    Hello Scott!  Underrange_pct is at -3, default.

    Device is posting no current diagnostics, but I'll keep digging -

    I was thinking a hidden HART status as well


  • In reply to Andre Dicaire:

    Thanks Andre, will check voltage.