WEG CFW-10 - Special Functions Parameters - P500 to P599; Introduction; Description

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CHAPTER 6 - DETAILED PARAMETER DESCRIPTION
6.3.4 Special Functions Parameters – P500 to P599
6.3.4.1 Introduction
Other application examples: level control, temperature, dosing, etc.
The CFW-10 is fitted with PID regulator function that can be used
for closed loop process control. This function works as a
proportional, integral and derivative regulator which superimposes
the normal inverter speed control.
The speed will be changed in order to maintain the process variable
(the one that want to be controlled – for example: water level of a
reservoir) at the desired value, set at the reference (set point).
For instance, a motor connected to a pump and driven by an inver-
ter makes a fluid circulate into the piping. The inverter itself can
make the flow control into the piping by means of the PID regulator.
In this case, for example, the set point (flow) could be given by the
input (HMI Potentiometer) or through P525 (digital set point) and
the flow feedback signal would come to the analog AI1 input.
Other application examples: level control, temperature, dosing, etc.
6.3.4.2 Description
Figure 6.23 shows a schematic representation of PID regulator
function.
The feedback signal must come in the analog input AI1.
The set point is the process variable value which desires to operate.
This value is entered as percentage, and it is defined by the following
equation:
Setpoint (%) =
setpoint (UP)
x P234
full scale of used sensor (UP)
Where both set point and full scale of the used sensor are given by
the process unit (i.e., °C, bar, etc.).
Example: A pressure transducer (sensor) with 4 - 20 mA output and
25 bar full scale (i.e., 4 mA = 0 bar and 20 mA = 25 bar) and
P234 = 200. If 10 bar is desired to control, the following set point
should be entered:
Setpoint (%) =
10
x 200 = 80 %
25
The set point can be defined via:
- Keypad: digital set point, P525 parameter.
- Input (HMI potentiometer) (only available in the CFW-10 Plus):
the percentage value is calculated based on P238 and P240
(see description of these parameters).