Instruction manual

36 RFT9739 Field-Mount Transmitter Instruction Manual
Output Wiring
continued
Control output in open
collector mode
The RFT9739 provides current to the control 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 control output circuit can be used in open collector mode.
If the frequency/pulse output is configured for constant current (see
"Configuration for open collector mode," page 33), the control output is
rendered inoperable. To reconfigure the control output to function
properly, independent of this frequency/pulse output configuration, the
control output circuit can be configured for open collector mode.
To configure the control 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 R15 (R2 on models with enhanced EMI immunity) and add
an external DC power supply and a pull-up resistor. See
Figure 5-11
,
page 37.
• 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.
• Resistor R15 (R2) is located on the RFT9739 output board, behind the
output terminal blocks, as illustrated in
Figure 5-12
, page 37. To
access resistor R15 (R2), unplug the output terminal blocks from the
transmitter.
CAUTION
Clipping resistor R15 or R2 will eliminate the internal
voltage source from the transmitter.
After clipping resistor R15 or R2, an external power supply
is required to use the transmitter’s control output.
Before permanently altering any equipment, contact the
Micro Motion Customer Service:
• In the U.S.A., phone [phone]
• Outside the U.S.A., phone [phone]
• In Europe, phone [phone]
• In Asia, phone [phone]