Chapter 7. Usage of Various Functions
7-30
(10) Delta MV
This is useful to limit maximum change of manipulation value. For example, ifΔMV is set to 500, the MV value
in the operation scan does not change more than 500. The value should be set with proper value because the
speed could be reduced. Setting range is 0 ~ 4000 and default value is 4000.
(11) Bias (%MW4810)
The Bias data is used for the compensation of offset in the proportional control. The range of input is 0 ~ 4000.
Be cautious that The actual range of Bias is –2000 ~ 2000. namely, 0~2000 represents 0 ~ +2000 and 2001 ~
4000 represents -1 ~ -2000.
Example) If offset (SV-PV) is 100 → Bias should be 100.
If offset (SV-PV) is -100 → Bias should be 2100.
(12) SV(Target) and PV(Current)
SV (setting value: the designated value) and PV (process value: present value) of GM7U 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 GM7U
series (12bits) and offset value.
(13) Forward and reverse action
PID control has two kinds of action, forward action and reverse action.
- Forward action makes PV reach SV by outputting MV when PV is less than SV, the heating system is an
example of the forward action.
- Reverse action makes PV reach SV by outputting MV when PV is more than SV, the air cooling systems is an
example of the reverse action.
A diagram in which forward and reverse actions are drawn using MV, PV and SV is shown as below.
Forward and reverse action with MV, PV and SV
SV Ramp is designates
Time
Current SV
Changed SV
SV Ramp = 1
SV Ramp * Scan time
Forward action
Reverse action
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