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Jack H.Integration and automation of manufacturing systems.2001.pdf
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e.g. A Retentive Off Timer (RTF)

A

A

T4:0 EN

T4:0 DN

page 157

RTF

 

 

Timer T4:0

 

(DN)

Time Base 0.01

 

 

 

 

Preset 350

 

(EN)

Accum. 0

 

 

 

 

 

T4:0 Accum.

0

3

6

10

16

18

20

• When using timers (especially retentive) we must reset values when done. The (RES)

instruction does this.

7.8 COUNTERS

• Count up/count down counters will track input events.

page 158

• An allen Bradley PLC-5 counter is shown below

 

 

 

 

a count up counter

 

 

 

CTU

 

 

 

A

 

 

counter C5:0

 

 

(EN)

 

 

 

 

 

 

 

Preset 4

 

 

 

 

 

 

 

 

 

 

 

 

Accum. 2

 

 

(DN)

 

 

 

 

 

 

 

 

 

 

 

 

1.Each time A turns on (then off), the accumulated value increases (here from 2to3, then 3to4, and so on)

2.When the accumulated value reaches the preset value, the ‘DN’ flag is set.

C5:0

DN

3. We can set the accumulated value to zero with. C5:0

RES

Count down counters are similar.

Consider the example below,