Chapter 7 Usage of Various Functions
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(b) PID8AT instruction parameter setting and explanation.
① Scan time
S_TIME is the period of reading data (sampling), and 10 times scaled up for more precious operation.
The range of sampling time is 0.1 ~ 10 seconds, and actual input range is 0 ~ 100.
② Control target(SV)
SV (set value : the designated value) and PV (process value : present value) of MASTER-K120S PID operation
have the range 0 ~ 4000. The range is set with the consideration of the resolution of A/D and D/A module of
MASTER-K120S series (12 bits) and offset value. When setting the SV or PV, please be careful convert the
analog value of control object (temperature, velocity, etc.) to digital value that are the output of A/D convert
module.
ⓐ When using sensor and A/D conversion module
Assume that PID control is used for temperature control with Pt100 (operation range : -200 °C ~ 600 °C),
and the goal value is 100 °C. The equivalent digital output of A/D module (current input range : 4 ~ 20mA) is
1500 if the A/D module outputs 0 (4mA) with -200 °C, and 4000(20mA) with 600 °C. Therefore, the input of
SV should be 1500, not 100.
ⓑ When using sensor and RTD module(G7F-RD2A)
Assume that PID control is used for temperature control with Pt100 (operation range : -200 °C ~ 600 °C),
and the goal value is 100 °C. The digital output of RTD module is calculated as below.
2
200010. +×
=Temp
putDigitalOut
Therefore, SV should be 1500,
③ Tuning method
The MASTER-K120S perform auto-tuning operationin two methods. One is rela
y
response method and the
other is process reaction curve method.