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3051 Pressure Transmitter range changed randomly

Hello,

We recently had a 3051 gauge pressure transmitter decide to change its range in the middle of the night.  The desired range and calibrated range is 0-1000 psig.  Typical operating pressure is ~300 psig.  A couple of nights ago, this transmitter decided to change its URV from 1000 to 315.7.  The tranmitter display indicated the proper pressure and the milliamp output calculated to be accurate at this range, but it was throwing our DCS control off.  The output was 19.1 mA as found.  I changed the URV back to 1000 and this fixed the issue.  Can anyone explain to me how this transmitter decided to change its URV in the middle of the night?  The ambient temp was about 100°F.  There was nobody in the area that would have changed the range and the cameras back that up.  The transmitter is not on a HART AI for the DCS, so I don't think there could be any input from the DCS that would affect it.

matt.wilson@johnsoncountypower.com
  • Tinh Phan
    Hi Matt, is this on a DeltaV DCS and are you sure the DCS channel is not HART enabled? Other than the DCS that can talk to the device via HART and someone download a new xdscale to the device. I can't see how the device can just change it's scale on it's own. I have not seen this situation in the 28 years working with instrumentation. This is a dangerous issue and I would like to follow this thread to see what happened.
    In the meantime not to say it has not happens. I suggest you enable the lock switch on the device to prevent any changes happen in the future. If you camera did not catch anyone near the transmitter, they can change it at the distribution panel or at the dcs connection. They don't have to be at the device using a handheld communicator to make this change.
  • Brad Burton
    Matt,

    Does your model code have the "D4" zero and span button option? This sounds like an issue with the span button activating unexpectedly. This could happen as a result of corrosion, contamination, or even magnetic interference. Your span was set near the operating point, so your symptoms indicate that the span button activated inadvertently and caused a change in URV.
    I would have a look at the buttons, or you can simply deactivate them using a HART configurator to avoid this moving forward.

    Feel free to contact me if you have questions.
  • matt.wilson@johnsoncountypower.com

    In reply to Brad Burton:

    Our model does not have a "D4", however, we had the same issue happen just now, and when we connected out HART communicator up, the alert said Stuck Zero/Span button. So we disabled the option and adjusted the URV back to where it should be. We looked for the Zero/Span pushbuttons, but we never saw any. I assume the circuitry is there, but the interface is not. Instead we have a display option.
  • Brad Burton

    In reply to matt.wilson@johnsoncountypower.com:

    Matt,
    If you put your security switch in the on position that will prevent any changes from happening. So update your URV as desired and then flip the security switch to on.
    The physical security switch is found on the electronics board of the transmitter. It can be seen on the lower right-hand side of the board in the 4-5 O'clock position, just below the display board. The switch can be flipped without removing the display with a small screwdriver.

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