Rockwell Automation 1771-PD PID MODULE (+DU) - Manual (Page 25)

Assembly and Installation
Chapter 2
2Ć12
External Connections
Terminal identification of the PID module’s field wiring arm and general
connections are shown in Figure 2.4. Typical I/O connections for a single
closed loop configured in current mode are shown in Figure 2.5. The
remaining three figures show typical connections to input and output
devices and control mode connections to a manual control station.
Figure 2.6 shows typical connections to input devices without a manual
control station. When an input loop is configured in current mode, the
input impedance of all devices connected in series must be considered
when selecting the input power supply. the input loop could contain one
or more recording devices (250 ohms) and/or a manual control station
(100 ohms) in addition to the PID module (250 ohms) and the current
transmitter. Current transmitters typically require at least 18V dc.
Voltage transmitters, if used, draw their power from a supply independent
of the input circuit.
Figure 2.7 shows typical connections to actuators when the output is
monitored by the tieback input. Note that when a tieback input is not used
to monitor a voltage output, the jumper to the TIEBACK INPUT terminal
is not connected. When the tieback input is not used to monitor a current
output, the return from the actuator is connected to MODULE
COMMON, not to the TIEBACK INPUT terminal. The module monitors
tieback inputs only when you enable manual mode of the manual control
station described below.
Figure 2.8 shows the connections from the PID module to a manual
control station required for switching control automatically to the station
or manually at the station. The wiring is the same for PID module outputs
configured in current or voltage mode.
The MANUAL REQUEST terminal permits the PID module, upon
detecting a hard fault or when under PC processor control, to switch the
manual control station from automatic to manual mode. The MANUAL
MODE terminal is used to inform the PID module when the station is in
manual mode. The TIEBACK INPUT terminal monitors the station
output and allows a bumpless transfer of control from the manual control
station to the PID module.