3. Study the ladder logic program in Figure 8-41, and answer the questions that

Question

3. Study the ladder logic program in Figure 8-41, and answer the questions that follow: a. What type of counter has been programmed? b. What input address will cause the counter to increment? c. What input address will cause the counter to decrement? d. What input address will reset the counter to a count of zero? e. When would output O:6/2 be energized? f. Suppose the counter is first reset, and then input I:2/6 is actuated 15 times and input I:3/8 is actuated 5 times. What is the accumulated count value? Ladder logic program 126 coUNT-UP COUNTER C52 Preset Accumulated 0 ON 13/8 COUNT-DOWN COUNTER 5:2 25 0 Preset 5:2 0:6/2 DN 141 C5.2 RES Figure 8-41 Program for Problem 3

Explanation / Answer

Solutions:

a) From the figure ,

i) In first rung UP-Counter is used with I:2/6 as input and preset value as 25.

ii) In the second rung DOWN-Counter with I:3/8 as input and preset value as 25 are present .

So, in the figure UP and DOWN counter programmed.

b)UP conuter will get increment by one count for every positive input pulse at the counter input port , similarly Down counter will get decrement by one count for every input positive pulse at the conter input port.

For every positive pulse from the input address I:2/6 causese the one increment of the up-counter.

c) For every positive pulse from the input address I:3/8 causes the one decrement of the Down-Counter.

Note :

i)If the UP counter Count value crosses the accumulated value, then overflow will occur.

ii) Down conter will never go the negative count.

For using above conter properly first increment the up-Conter then you use the downcounter , if not mal-operations may takes place

d) We need to make the counter reset to high state , for restting the counter accumulated value to zero.

In the rung 4 , by giving a positive input pulse at I:4/1 (i.e.on the NO switch I:4/1) , as input to the Reset coil with address C5:2, that leads to the count value becomes zero of the counter C5:2  

e)The coil O:6/2 will become energised, when the C5:2 DN (done bit) will becomes high, this will happen only when the counter C5:2 's accumulated value becomes equal to the preset value.

f) For every positive input pulse at I:2/6 leads to one count increment of the UP Counter . so, for 15 times , the value of the accumulated value will reach to a value 15. For every positive pulse at the I:3/8 leads to to one count down of acculated value, so after 5 countdowns , the accumulated value will get count down by 5 values i.e. from 15 it count down to 10. So , the counter value will becomes 10 .

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