Micro Motion Fisher Rosemount RFT9739, Instruction Manual

Page: 43 / 130

Output Wiring
continued
RFT9739 Rack-Mount Transmitter Instruction Manual
33
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Configuration for open
collector mode The RFT9739 provides current to the frequency/pulse output circuit. In
applications where this current must be permanently suspended, and for
receiving devices that require input voltage higher than approximately
10 volts, the frequency/pulse output circuit can be used in open collector
mode.
To configure the output for open collector mode, a resistor must be
clipped as described below.
This procedure will permanently alter the
transmitter and cannot be reversed.
• Clip resistor R5 and add an external DC power supply and a pull-up
resistor. See Figure 5-8, page 34.
• The pull-up resistor must be of sufficient value to limit loop current to
less than 0.1 ampere, depending on the total loop resistance at the
transmitter.
• To prevent damage to the optocoupler and dual-channel frequency
output circuits, the external voltage must not exceed 15 V.
• Resistor R5 is located on the inside of the RFT9739 back panel.
To access resistor R5, refer to Figure 5-9, page 34, and follow these
steps:
1. Remove the bottom cover of the transmitter housing.
2. Remove the back panel, and carefully pull it loose from the power
board and the control board.
3. Locate and clip resistor R5 on the inside of the RFT9739 back panel.
See Figure 5-10, page 35.
4. Reinstall the bottom cover.
5. Reinstall the back panel, carefully aligning the connector pins with the
connectors on the power board and the control board.
CAUTION
Clipping resistor R5 will eliminate the internal voltage
source from the transmitter.
After clipping resistor R5, an external power supply is
required to use the transmitter’s frequency/pulse output.
Before permanently altering any equipment, contact the
Micro Motion Customer Service:
• In the U.S.A., phone 1-800-522-6277, 24 hours
• Outside the U.S.A., phone 303-530-8400, 24 hours
• In Europe, phone +31 (0) 318 549 443
• In Asia, phone 65-770-8155