96
P a r r I n s t r u m e n t C o m p a n y
Output Modules:
The analog
outputs are 0-20 mA. A suitable
dropping resistor can be used
to convert this to 0-5 or 0-10
VDC. Analog outputs are com-
monly used to set stirrer motor
operating speeds, position
control valves, or drive mass
flow controllers or pumps.
Each analog output is capable
of controlling four separate
devices or functions.
The digital outputs are
open collector type capable of
sinking up to 300 mA . They
are commonly used to control
heaters, solenoid valves for
cooling or other flow control,
system safety shut down,
visual and/or audible alarms,
and similar devices. Each digi-
tal output module is capable
of controlling sixteen separate
devices or functions.
Control Loops
The controller can provide
any number of PID or ON/OFF
control loops, limited solely by
the available CPU memory.
The PID control algorithm
includes auto-tuning and fuzzy
logic overshoot suppression for
each control loop. For heating
and cooling control, the PID
control loops provide time
proportioning of the associated
digital output.
Many temperature control
applications utilize two sepa-
rate time proportioning ouputs
with one PID controller; one for
heating and one for cooling.
Control loops can be linked
together to provide cascade,
feed forward or ratio control
for difficult or advanced control applications.
Both high and low limit values can be entered
for each control loop to sound alarms or initiate
safety control schemes.
Set Point Programming
Recipes for controlling the entire process of a
reactor can be written using the setpoint profiler
incorporated into the control firmware. A single
profile may be from 2 to 50 segments in length.
A typical profile might be a ramp and soak
of the reactor temperature but, in addition, the
4871 Process Controller Input/Output Diagram.
Parr 4871
Process
Controller
Parr 4875
Power Controller
Data Logging
Alarms
Temperature
Pressure
Stirrer Speed
Flow Rate
Safety Links
Other
Heating Control
Cooling Control
Stirrer Control
Safety Interlock
PC Graphical
User Interface
Multiple 4875 Power Control Modules
can be controlled, with individually
isolated inputs and outputs, with one
4871 Process Controller.
Thirty-one 4871 Controllers can be
controlled by a single PC operating
the SpecView software.
4871 Process Controller
analog and digital outputs can be tied to the basic
profile to start and stop flows, activate stirrers
or accessories, or change alarms. Any of the set-
points within the profile can be protected with the
setpoint guarantee function that assures that the
process variable will be within the entered limits
before the profile can proceed.
The number of set point programmers is lim-
ited by the amount of available memory in
the controller CPU. Typically, at least eight
separate profiles can be running independently
(8 reactors each on their own program, for
example) simultaneously.
