Instruction manual

Micro Motion
®
Model D and DT Sensors Instruction Manual 47
Troubleshooting continued
Checking for erratic flow rate at the transmitter
Before troubleshooting erratic flow rate, you must first determine
whether it is a result of the transmitter or a connected output device.
Check for an erratic flow signal at the transmitter using any of the
following methods. If necessary, refer to the instruction manual (or
on-line help for software) for the method you choose.
• Use the transmitter display, if it has one
• Use a HART Communicator, ProLink software, or AMS software
• Use a Modbus, fieldbus, or Profibus-PA host controller
• Use a DMM on the transmitter’s 4-20 mA or frequency output terminals
If the flow rate or output signal is not erratic at the transmitter outputs,
the problem is not with the transmitter.
Checking for faulty output wiring
Having already checked the output at the transmitter end (above), use a
DMM to check the signal at the other end (the receiving end) of the
output wiring. If the signal is not erratic, the problem is not with the
output wiring.
Checking for faulty flowmeter wiring
Wiring problems are often incorrectly diagnosed as a faulty sensor.
Examine wiring between the sensor and transmitter as follows:
1. Check the cable preparation. The flowmeter cable must be
prepared correctly. The most common problem is improperly
prepared drain wires. See illustration, below. The drains are clipped at
the sensor end. They should not be connected to any terminals in the
sensor junction box. See wiring diagrams, pages 22-32.
2. Check wire terminations. Check to be sure wires are secured tightly
in the terminal blocks, and making good connections. Make sure no
wires remain exposed at either end of the flowmeter cable.
3. Check ohm levels. If the cable was properly prepared and terminal
connections are good, check resistance across wire pairs to
determine whether the flowmeter cable is faulty. The procedure is
performed first at the transmitter, then at the sensor. Follow these
steps:
a. Disconnect the transmitter’s power supply.
b. Disconnect sensor wiring from the transmitter’s flowmeter
terminals.