Answer the questions regarding the program in Figure 3. For what value of the ac

Question

Answer the questions regarding the program in Figure 3.

For what value of the accumulated count will the LOT FULL LIGHT come on?

During normal operation of the program, the accumulated value of CTU would always be:

A. the same as that of CTD.         B. 150.           

C. between 50 and 100.                D. between 0 and 100.

Assume the accumulated count is 100 and the following order of events then occurs: Exit switch input is actuated 20 times, Reset input is actuated 10 times, and Enter switch input is actuated 5 times. After this sequence, what is the accumulated count?

Ladder logic program ENTER L1 inputs Output 12 SWITCH CTU CU LOT FULL COUNT UP COUNTER ENTER LIGHT Counter C5:1 SWITCH DN Preset 150 Accumulated EXIT SWITCH CTD EXIT COUNTDOWN COUNTER CD Counter SWITCH DN 150 Preset Accumulated 0 LOT FULL C5:1/DN LIGHT -o RESET RESET C5:1 RES

Explanation / Answer

Solution - Accumulated value should be more than 150 or equal to 150 to turn the DN bit on, which which turn on the LOT FULL LIGHT. Because in the count up timer if the accumulated value is less than preset value , then it will disable the DN bit. Hence to enable the DN bit it should be greater than or equal to preset value.

#During normal operation of program the DN bit of Count up timer operates the lot full light. But the DN bit is enable only when the Accumulator value is 150 or mote. Hence the value of accumulator should be equal to 150 during normal operation.

# when the accumulated count is 100. Now if you press the exit switch it will actuate the CTD counter and decrement the Accumulator value by one. So everytime it will decrement by 1. Hence after 20 times the Accumulator value will be 100-20= 80.

But when we actuate the RES input it will reset the Accumulator value to zero. As the RES instruction is used to reset the counters value to zero. No matter how many times reset is actuated, it will reset the accumulator to zero. Hence after 5 times the Accumulator value will still be zero.

Now if we actuate the enter switch , it will increment the accumulator value by 1 everytime it is actuated. Hence after actuating 20 times the accumulator value will increment by 20. So it will increment from 0 to 0+20= 20.

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