Delta-electronics Programmable Logic Controller DVP-PLC Manuel d'utilisateur télécharger pdf (Page 397)

100

101

7 Application Instructions API 50-99

DVP-PLC APPLICATION MANUAL

7-113

Example 3: Diagram of using PID instruction in temperature control (S

+ 4 = 1)

PID

Temperature instruction (SV)

Heating (MV)

Actual temperature

(PV)

Heater

Temperature

detection

device

Example 4: How to adjust PID parameters

Assume that the transfer function of the controlled device G(S) in a control system is a first-order function

()

(most models of motors are first-order function), SV = 1, and sampling time (T

) = 10ms, we

suggest you to follow the steps below for adjusting the parameters.

Step 1: Set K

and K

as 0 and K

as 5, 10, 20 and 40. Record the SV and PV respectively and the results

are as the figure below.

1.5

0.5

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

K =40

K =20

K =10

SV=1

K =5

Time (sec)

Step 2: From the figure, we can see that when K

= 40, there will be over-reaction, so we will not select it.

When K

= 20, the PV reaction curve will be close to SV and there will not be over-reaction, but due to its

fast start-up with big transient MV, we will consider to put it aside. When K

= 10, the PV reaction curve will

get close to SV value more smoothly, so we will use it. Finally when K

= 5, we will not consider it due to the

slow reaction.

Step 3: Select K

= 10 and adjust K

from small to big (e.g. 1, 2, 4 to 8). K

should not be bigger than K

Adjust K

from small to big (e.g. 0.01, 0.05, 0.1 and 0.2). K

should not exceed 10% of K

. Finally we

obtain the figure of PV and SV below.

1 2 ... 392 393 394 395 396 397 398 399 400 401 402 ... 585 586

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