Chapter 15. The PID functions
15-20
1) SV (setting value : the designated value) and PV (process value : present value)
of GM6 PID operation have the range 0 ~ 4000. The range is set with the
consideration of the r esolution of A/D and D/A module of GM6 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. For e xample, assume that PID control is used for
temperature control with Pt100 (operation range : 0
°
C ~ 250
°
C), and the goal
value is 100
°
C. The equivalent digital output of A/D module (voltage output
range : 1 ~ 5V) is 1600 if the A/D module outputs 0 (1V) with 0
°
C, and 4000(5V)
with 250
°
C. Therefore, the input of SV should be 1600, not 2.
2) S_TIME is the period of reading data (sampling), and 10 times scaled up for more
precious operation. Generally, it should be synchronized with external trigger input
(EN input of function block) to perform proper PID operation. The range of
sampling time is 0.1 ~ 10 seconds, and actual input range is 0 ~ 100.
3) The GM6 -CPUB and GM6-CPUC module perform auto-tuning operation based on
the frequency response method. PID parame ters are obtained by On/Off operation
during 1 cycle of PV variation. The RIPPLE parameter shows at which cycle the
CPU module will perform auto -tuning operation. If 0 is selected, the CPU will get
PID parameters during the first cycle of PV variation. If 1 is selected, the second
cycle will be used. (refer Fig. 12-15 for detailed information) Other choice of
RIPPLE parameter is not allowed. In general case, select 1 for proper auto -tuning
operation. The On/Off operation will be occur at the 80% of PV value.
80% of PV
Perform A/T operation at the 1
st
cycle
(When the RIPPLE = 0)
Perform A/T operation at the 2
nd
cycle
(When the RIPPLE = 1)
