How to Troubleshoot the 4 – 20mA Output of Rosemount 3051 Transmitter

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One of the most versatile and commonly used transmitters is the Rosemount 3051 pressure transmitter. This transmitter can be used to measure pressure, differential pressure, gage pressure, absolute pressure or a liquid level. The Rosemount 3051 transmitter provides an analogue output (4 – 20mA) with a superimposed HART signal on the 4-20 mA output.

The most common problems with the Rosemount 3051 transmitter are adapted from the transmitter manual and can be used to troubleshoot the 4 – 20mA output whenever the symptoms in the table below are observed during transmitter service:

Symptom	Corrective Actions
Transmitter miliamp is Zero	Verify power is applied to the signal terminals Check power wires  for reverse polarity Verify terminal voltage is 10.5 to 42.4 Vdc Check for open diode across test terminal
Transmitter Not Communicating with Field Communicator	Verify the output is between 4 and 20mA or saturation levels Verify terminal voltage is 10.5 to 42.4 Vdc Verify clean DC power to transmitter (Max. AC noise is 0.2 volts peak to peak Check loop resistance, 250 ohms minimum (PS Voltage - transmitter voltage/loop current Have field  communicator poll for all addresses
Transmitter milliamp reading is low or high	Verify applied pressure Verify 4 and 20mA range points Verify output is not in alarm condition Verify if 4 - 20mA output trim is required
Transmitter will not respond to changes in applied pressure	Check test equipment Check impulse piping or manifold  for blockage Verify the transmitter is not in  multi-drop mode Verify applied pressure is between 4 and 20mA set points Verify output is not in alarm condition Verify transmitter is not in loop test mode
Digital pressure variable reading is low or high	Check the accuracy of test equipment Check impulse piping for blockage or low fill in wet leg Verify transmitter is calibrated properly Verify pressure calculations for application
Digital pressure variable reading is erratic	Check application for faulty equipment in pressure line Verify transmitter is not reacting to equipment turning on/off Verify damping is set properly for application
Milliamp reading is erratic	Verify power source to transmitter has adequate voltage and current Check for external electrical interference Verify transmitter is properly grounded Verify shield for twisted pair is only grounded at one end