Eaton ELC-PB, Руководство по программированию

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3 . I n s t r u c t i o n S e t
M N050 03003E F or mo re infor ma tio n vi sit:
w w w. e a t o n . c o m
3-263
Example 3:
Block diagram for a temperature control application (
S
3
+4 = 1)
PID
Temperature instruction (SV)
Heating (MV)
Actual temperature
(PV)
Heater
Temperature
detection
device
Example 4:
Adjusting PID parameters
Assume that the transfer function of the controlled device G(S) in a control system is a first-order
function
( )
a s
b
s G
+
=
(model of general motors), SV = 1, and sampling time (T
S
) = 10ms. Suggested
steps for adjusting the parameters are as follows:
Step1:
Set K
I
and K
D
as 0, and K
P
as 5, 10, 20, 40. Record the SV and PV respectively and the results are
per the figure below.
1.5
1
0.5
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
K =40
P
K =20
P
K =10
P
SV=1
K =5
P
Time (sec)
Step 2:
When K
P
is 40, response overshoot occurs, so we will not select it.
When K
P
is 20, PV response is close to SV and won’t overshoot, but transient MV will be too large
due to a fast start-up. A better curve is needed.
When K
P
is 10, PV response is close to SV and is smooth. We can consider using it.
When K
P
is 5, the response is too slow. So we won’t use it.
Step 3:
Select K
P
= 10 and increase K
I
gradually, e.g. 1, 2, 4, 8. K
I
should not be bigger than K
P
. Then,
increase K
D
as well, e.g. 0.01, 0.05, 0.1, 0.2. K
D
should not exceed 10% of K
P
. Finally we obtain the
curves for PV and SV below.