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Automating Manufacturing Systems - Process Control and ...

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plc timers - 9.15<br />

CTU<br />

A Counter C5:0<br />

Preset 4<br />

Accum. 2<br />

(CU)<br />

(DN)<br />

C5:0/DN<br />

X<br />

B<br />

RES<br />

C5:0<br />

Figure 9.15<br />

An Allen Bradley Counter<br />

Count-down counters are very similar to count-up counters. And, they can actually<br />

both be used on the same counter memory location. Consider the example in Figure 9.16,<br />

the example input I/1 drives the count-up instruction for counter C5:1. Input I/2 drives the<br />

count-down instruction for the same counter location. The preset value for a counter is<br />

stored in memory location C5:1 so both the count-up <strong>and</strong> count-down instruction must<br />

have the same preset. Input I/3 will reset the counter.

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