Rosemount 644 temperature transmitter's four troubleshooting methods

Instrument workers often encounter four failures: Rosemount 644 temperature transmitter does not communicate with the field communicator, 4-20mA output is too high, 4-20mA output is unstable, 4-20mA output is too low or no output, Changhui instrument Summarized the troubleshooting methods of Rosemount 644 temperature transmitter for your reference.

Trouble phenomenon 1: Rosemount 644 temperature transmitter does not communicate with the field communicator

Possible cause:  There is a problem with the circuit wiring

Troubleshooting:

① Check the version of the device description information (DD) of the 644 temperature transmitter stored in the communicator. The communicator should report Dev v4, DD v1 (improvement) or refer to the previous version of "Field Communicator". Please contact Emerson Process Management Customer Center for assistance.

② Check whether there is at least 250 ohm resistance between the power supply and the field communicator connection.

③ Check whether the power supply voltage of Rosemount 644 temperature transmitter is sufficient. If the field communicator is connected and the resistance in the loop is 250 ohms, then the terminal voltage of the transmitter must reach at least 12.0V to work (within the entire 3.5 to 23.0mA working range), and at least 12.5V to perform digital communication.

④ Check for intermittent short circuit, open circuit and multiple grounding conditions.

Trouble phenomenon 2: Rosemount 644 temperature transmitter 4-20mA output is too high

Possible cause 1:  The output is too high, the temperature sensor input or connection failure

Troubleshooting:

① Connect the field communicator and enter the 644 temperature transmitter test mode to check the temperature sensor failure.

② Check whether the temperature sensor is open or short-circuited.

③ Check the process variable to see if it is out of range.

Possible cause 2: There is a problem with the circuit wiring.

Troubleshooting: 

Check whether the terminals, interconnect pins or sockets are dirty or defective.

Possible cause 3: Power failure

Troubleshooting: 

Check the output voltage of the power supply on the terminal of the Rosemount 644 temperature transmitter. The value should be 12.0 to 42.4Vdc (within the entire 3.75 to 23mA operating range).

Possible cause 4: The circuit board is faulty

Troubleshooting:

① Connect the field communicator and enter the Rosemount 644 temperature transmitter status mode to isolate the module failure.

② Connect the field communicator and check the sensor limit to ensure that the calibration adjustment value is within the sensor range.

Trouble phenomenon 3: Rosemount 644 temperature transmitter 4-20mA output is unstable

Possible cause 1: There is a problem with the circuit wiring

Troubleshooting:

① Check whether the power supply voltage of Rosemount 644 temperature transmitter is sufficient. The voltage on the transmitter terminals should be 12.0 to 42.4Vdc (within the entire 3.75 to 23mA operating range).

② Check whether there are intermittent short circuits, open circuits and multiple grounding conditions.

③ Connect the field communicator and enter the loop test mode to generate 4mA, 20mA signals and the value selected by the user.

Possible cause 2: Circuit board failure

Troubleshooting: 

Connect the field communicator and enter the Rosemount 644 temperature transmitter test mode to isolate the module failure.

Trouble phenomenon 4: Rosemount 644 temperature transmitter 4-20mA output is too low or no output

Possible reason 1: temperature sensor element failure

Troubleshooting:

① Connect the field communicator and enter the Rosemount 644 temperature transmitter test mode to isolate the temperature sensor failure.

② Check the process variable to see if it is out of range.

Possible cause 2: There is a problem with the circuit wiring

Troubleshooting:

① Check whether the power supply voltage of Rosemount 644 temperature transmitter is sufficient. The value should be 12.0 to 42.4Vdc (within the entire 3.75 to 23mA operating range).

② Check whether there is a short circuit and multiple grounding conditions.

③ Check whether the polarity of the signal terminal is correct.

④ Check the circuit resistance.

⑤ Connect the field communicator and enter the loop test mode.

⑥ Check the wiring insulation to detect whether there is a short circuit to the ground.

Possible cause 3: Circuit board failure

Troubleshooting: 

Connect the field communicator and check the sensor limit to ensure that the calibration adjustment value is within the sensor range.