IDEC MicroSmart Pentra - Manual (Page 95)

C ONFIGURING PID M ODULE USING W IND LDR
6-30 FC5A MicroSmart PID Module User’s Manual FC9Y-B1283
Input Parameters when External SP Input is Selected
The input CH1 parameters when External SP input is selected as the Input CH1 Function are described here.
(1) Control Register+55: Input Range
Select input type for the external SP input. Current (4 to 20mA DC or 0 to 20mA DC) or voltage (0 to 1V DC or 1
to 5V DC) can be selected.
(2) Control Register+62: PV Correction
If the sensor cannot be installed to the location of the control target, the temperature measured by the sensor
may deviate from the actual temperature of the control target. When a target is controlled with multiple PID
modules, the measured temperatures may not match due to the differences in sensor accuracy or dispersion
of load capacities even though the set points (SP) of those PID modules are the same. In such cases, the
process variable (PV) of the PID module can be adjusted to the desired temperature by using the PV
Correction.
The process variable (PV) after PV correction can be calculated using the following formula.
Process variable (PV) after PV correction = Process variable (PV) + (PV correction value)
(3) Control Register +63: PV Filter Time Constant
The PV filter function is a software filter to stabilize the process variable (PV) affected by fluctuating processes
such as pressure or flow rate by calculating first-order lag of the process variable (PV). Even if the process
variable (PV) changes as shown in the Figure 1, when the PV filter time constant is configured, the process
variable (PV) changes as shown in the Figure 2. After the PV filtering process, the process variable (PV)
reaches 63% of the process variable (PV) in T seconds.
If the PV filter time constant is too large, it adversely affects the control results due to the delay of response.
Example: If the least significant digit of the process variable (PV) is fluctuating, the fluctuation can be
suppressed by using the PV filter time constant.
Figure 1. Process variable (PV) Figure 2. Process variable (PV)
before PV filtering process after PV filtering process
(10)
(1)
(2)
(3)
(4)
(8) (9)
(5)
(6)
(7)
T
Time (Second)
Process
Variable
(PV)
Time (Second)
Process
Variable
(PV)