Instruction manual
78
RFT9739 Rack-Mount Transmitter Instruction Manual
Troubleshooting
continued
7.6 Wiring
For transmitter wiring instructions, refer to
Chapter 4
, page 17, and
Chapter 5
, page 25. Wiring problems are often incorrectly diagnosed as
a faulty sensor. At initial startup of the transmitter, always check the
following:
1. Proper cable, and use of shielded pairs
2. Proper wire termination
a. Wires on correct terminals
b. Wires making good connections at transmitter terminals
c. Wires making good connections at the sensor terminals
d. Wires properly connected at any intermediate terminal junction,
such as the user-supplied junction box between a Model DT
sensor and transmitter.
If a fault condition is indicated, follow these instructions:
1. Disconnect the transmitter's power supply.
2. Unplug the terminal blocks from the transmitter back panel.
3. Use a digital multimeter (DMM) to measure resistance between wire
pairs at the transmitter terminals:
-
Drive coil, check terminals CN1-Z2 and CN1-B2 (brown/red)
-
Left pickoff coil, check terminals CN1-Z8 and CN1-B8
(green/white)
-
Right pickoff coil, check terminals CN1-Z10 and CN1-B10
(blue/gray)
-
RTD, check terminals CN1-Z6 and CN1-B4 (violet/yellow)
4. If the measured resistance is outside the range listed in
Table 7-6
,
repeat the measurements at the sensor terminals.
5. Reinsert the terminal blocks and restore power to the transmitter.
6. Use the DMM to troubleshoot the flowmeter.
Table 7-6. Nominal resistance ranges for flowmeter circuits
Notes
• Temperature sensor value increases 0.38675 ohms per
°
C increase in temperature
• Nominal resistance values will vary 40% per 100
°
C. However, confirming an open coil or shortened coil is more impor-
tant than any slight deviation from the resistance values presented below.
• Resistance across terminals 6 and 8 (right pickoff) should be within 10% of resistance across terminals 5 and 9 (left
pickoff).
• Resistance values depend on the sensor model and date of manufacture.
Circuit Wire colors
Sensor
terminals Transmitter terminals Normal resistance range
Drive coil Brown to red 1 to 2 CN1-Z2 to CN1-B2 8 to 2650
Ω
Left pickoff Green to white 5 to 9 CN1-Z8 to CN1-B8 15.9 to 300
Ω
Right pickoff Blue to gray 6 to 8 CN1-Z10 to CN1-B10 15.9 to 300
Ω
Temperature sensor Orange to violet 3 to 7 CN1-B6 to CN1-Z6 100
Ω
at 0
°
C + 0.38675
Ω
/
°
C
Lead length compensator Yellow to violet 4 to 7 CN1-B4 to CN1-Z6 100
Ω
at 0
°
C + 0.38675
Ω
/
°
C