Red Lion PCU - Manual (Page 9)

GENERAL DESCRIPTION
The PCU Controller accepts either a 0 to 10 VDC or a 4 to 20 mA DC input
signal, precisely scales the process signal according to programmable scaling
points, and provides an accurate output control signal (time proportional,
linear, or valve positioning) to maintain a process at the desired control point.
A comprehensive set of easy to use steps allows the controller to solve various
application requirements.
The controller can operate in the PID control mode for both the main output
and optional secondary output. On-demand auto-tune establishes the tuning
constants. The PID tuning constants may be fine-tuned by the operator at any
time and locked out from further modification. The controller employs a
unique overshoot suppression feature that allows the quickest response
without excessive overshoot. The unit can be transferred to operate in the
manual mode, providing the operator with direct control of the output. The
controller can also be programmed to operate in the ON/OFF control mode
with adjustable hysteresis.
Dual 4-digit displays allow viewing of the measured value and setpoint
simultaneously. Front panel indicators inform the operator of the controller
and output status. Replaceable and interchangeable output modules (Relay,
SSR Drive, or Triac) can be installed for the main control output, Alarm
output(s), Secondary output, and Valve Positioner outputs.
Optional dual alarms can be configured to activate according to a variety of
actions (Absolute HI or LO, Deviation HI or LO, Band IN or OUT, and Valve
Fail Detect) with adjustable hysteresis. A standby feature suppresses the
output during power-up until the process stabilizes outside the alarm region.
An optional secondary output is available (for processes requiring cooling,
pH balance, etc.) that provides increased control accuracy and response.
A linear 4 to 20 mA or 0 to 10 VDC output signal is available to interface
with actuators, chart recorders, indicators, or other controllers. The type of
Linear DC output is determined by the model ordered. (See
Ordering
Information, page 84, for available models.) The output signal can be
digitally scaled and selected to transmit one of the following: % output
power, measurement value deviation or setpoint value. For Linear DC control
applications, the adjustable output demand dampening, output deadband, and
output update time parameters expand the versatility of the PCU to final
control devices.
The optional Motorized Valve Positioner directly controls the position of a
valve by the use of twin outputs (open and close) to control the direction of
motor rotation. The motor position defines the opening position at the valve.
Two control modes are possible: position control, which makes use of the
slidewire feedback signal supplied with the positioner and velocity control, in
which no slidewire feedback signal is used. Parameters are provided to adjust
the operation of the valve. These include:
- Valve activity hysteresis
- Valve update time
- Variable control dampening
- Slidewire signal fail action
- Adjustable valve position limits
The Valve Positioner PCU achieves tight process control; yet minimizes
unnecessary valve activity. An alarm event output or display alarm can be
programmed under loss of slidewire feedback or under valve fail detection.
The optional Second Analog Input (0 to 20 mA DC) can be configured as a
Remote Setpoint signal or as a Secondary Process signal. Configuration of
the Second Analog Input as a Remote Setpoint signal allows ratio control,
master setpoint/multiple slave operation, and the ability to cascade the PCU
with another controller (External Cascade). Configuration of the Second
Input as a Secondary Process signal allows operation as a two-process
cascade controller within a single unit (Internal Cascade). In either control
mode, parameters are provided to scale, configure, communicate and monitor
the activity of both analog inputs. A square law linearizer function can be
used to linearize signals derived from flow transmitters.
The optional RS485 multi-drop serial communication interface provides
two-way communication between a PCU unit and other compatible
equipment such as a printer, a programmable controller, or a host computer.
In multi-point applications the address number of each unit on the line can be
programmed from zero to ninety-nine. Up to thirty-two units can be installed
on a single pair of wires. The Setpoint value, % Output Power, Setpoint Ramp
Rate, etc. can be interrogated or changed, by sending the proper command
code via serial communications. Alarm output(s) may also be reset via the
serial communications interface option.
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