Fisher-Rosemount 3095FT, Manual

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Rosemount Model 3095FT HART Flow Transmitter
5-6
Unexpected Process
Variable (PV) Readings The Model 3095FT User Interface Software provides a means to
continuously display the current process variables and flow calculations
(see Page 4-42.) Unexpected process variable readings may also be
detected when reading the audit trail logs.
Symptom High PV Reading Potential Source and Corrective Action
Orifice Plate
• Check for restrictions at the orifice plate.
• Check the installation and condition of the orifice plate.
• Note any changes in process gas properties that may affect
output.
Impulse Piping
• Check to ensure that the pressure connection is correct.
• Check for leaks or blockage.
• Check to ensure that blocking valves are fully open.
• Check for entrapped liquid in the gas lines.
• Check for sediment in the transmitter process flange.
The following performance limitations may inhibit efficient or
safe operation. Critical applications should have appropriate
diagnostic and backup systems in place.
Pressure transmitters contain an internal fill fluid. It is used
to transmit the process pressure through the isolating
diaphragms to the pressure sensing element. In rare cases,
oil loss paths in oil-filled pressure transmitters can be
created. Possible causes include: physical damage to the
isolator diaphragms, process fluid freezing, isolator
corrosion due to an incompatible process fluid, etc.
A transmitter with oil fill fluid loss may continue to perform
normally for a period of time. Sustained oil loss will
eventually cause one or more of the operating parameters
to exceed published specifications while a small drift in
operating point output continues. Symptoms of advanced oil
loss and other unrelated problems include:
• Sustained drift rate in true zero and span or operating
point output or both
• Sluggish response to increasing or decreasing pressure or
both
• Limited output rate or very nonlinear output or both
• Change in output process noise
• Noticeable drift in operating point output
• Abrupt increase in drift rate of true zero or span or both
• Unstable output
• Output saturated high or low.