Rockwell Automation 1771-PD PID MODULE (+DU) - Manual (Page 4)

Chapter
1
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Introduction
The Proportional/Integral/Derivation Control (2-loop) Module Assembly
(cat.no.1771-PD) is an intelligent I/O module that performs closed loop
PID control. The PID module is a process controller. The PID module
monitors the analog input process variable, compares the input to the
desired set point, and calculates the analog output control variable based
on the control algorithm programmed in the module. The PID module has
the hardware inputs and outputs and microprocessor to perform PID
control.
The PID module assembly consists of:
1 Proportional/Integral/Derivation Control (2-loop) Module (cat. No.
1771-PD)
1 Field Wiring Arm (cat. No. 1771-WF)
The PID module can control up to two closed loops such as flow,
temperature, pH, and level. Advanced control features include cascade,
feedforward, scaling, square root, error squared, digital and led/lag
filtering. The PID module can directly interface with an optional user
supplied manual control station. Transition from manual to automatic
control can be performed with bumpless transfer.
[1] Input and output
ranges can be selected for each loop to either +1 to +5V DC or +4 to
+20mA.
The PC processor uses block transfer programming to communicate with
the module. The PC processor writes loop configuration parameters such
as gain constants, set points, digital filter values, limits, alarm points to
the PID module and reads status information such as analog input values,
analog output values, limit alarms and diagnostics from the PID module.
The PID module can be used with any Allen-Bradley PC processor that
has block transfer capability and uses the 1771 I/O structure.
When using the Mini-PLC-2 and PLC-2/20 processors, programming will
be more lengthy because these processors do not have the block format
instructions which permit shorter programs and easier data monitoring.
[1] Bumpless transfer, as defined in Fundamentals of Process Control Theory by Paul W. Murril,
means a smooth transition from manual to automatic control.
General