User`s guide

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CHAPTER 6 - DETAILED PARAMETER DESCRIPTION
setpoint (%) =
setpoint (UP)
x P234 x 100 %
full scale of the used sensor (UP)
6.3.5
Special Function Parameters - P500 to P599
6.3.5.1
Introduction
CFW-08 is fitted with the PID regulator that can be used
for closed loop process control. This function acts as a
proportional, integral and derivative regulator,
superimposed on the normal inverter speed control.
Thespeed will be changedin order to maintain the process
variable (the variablethatshould becontrolled - forinstance:
water level of a container) at the desired value, set in the
setpoint.
This regulator can, for instance, control the flow in a piping
system.The setpoint (flow) can be given bytheanaloginput
AI2 or through P525 (digital setpoint), and theflowfeedback
signal is given at analog inputAI1.
Other application examples: level control, temperature
control, dosing control, etc.
Figure 6.27 shows the block diagram of the PID regulator.
The feedback signal must be sent to the analog inputAI1.
The setpoint is the value of the process variable at which
the operation is desired. This value is entered as a
percentage and is defined by the following equation:
6.3.5.2
Description
Both the setpoint and the full scale value of the sensor are
given by the process unit (°C, bar, etc.).
Example: a pressure transducer (sensor) with output 4 -
20 mA and full scaleof 25bar (i.e., 4 mA = 0 bar and 20 mA
= 25 bar) and P234 = 2.00.If the controlof 10bar is desired,
you should enter the following setpoint:
setpoint (%) =
10
x 2 x 100 % = 80 %
25
The setpoint can be defined via:
-
Keypad: digital setpoint, parameter P525.
-
Analog inputAI2 (onlyavailable in the CFW-08 Plus):
the percentage value is determined by considering
P238, P239 and P240 (refer to description of these
parameters).