Deck 8: Programming Counters

Question 1

A down-counter output instruction will decrement by 1 each time the counted event occurs.

Answer 1

True

Question 2

The counter reset (RES)instruction,it is always given the same address as the counter it is to reset.

Answer 2

True

Question 3

In normal use,the down-counter is used in conjunction with the up-counter to form an up/down-counter.

Answer 3

True

Question 4

Programmed counters can serve the same function as mechanical counters.

Question 5

Some PLC counters operate on the leading edge of the input signal,while others operate on the trailing edge.

Question 6

A counter's input signal can come from an external device such as a sensor.

Question 7

Up and down counters may be programmed together to count up and down.

Question 8

All up-counters count only to their preset values,and additional counts are ignored.

Question 9

Every PLC model offers some form of counter instruction.

Question 10

Counters can count past their preset values.

Question 11

Encoder pulses can be counted to measure distance.

Question 12

A counter instruction is an input instruction.

Question 13

The counter accumulated value is the current count based on the number of times the rung goes from false to true.

Question 14

PLC counters are normally nonretentive.

Question 15

A transitional off-to-on contact will allow logic continuity for one scan and then open,even though the triggering signal may stay on.

Question 16

All PLC manufacturers require the reset rung or line to be true to reset the counter.

Question 17

The counter number C5:4 represents counter file 5,counter 4 in that file.

Question 18

Counters are similar to timers,except that they do not operate on an internal clock.

Question 19

The counter enable bit is true whenever the counter instruction is false.

Question 20

The output of the counter is energized whenever the accumulated count is less than or equal to the preset count.

Question 21

Normally counters are retentive.This means that if your accumulated count is up to 300 and power to your system is lost,when power is restored the accumulated count will be:

A)000
B)250
C)300
D)999

Question 22

The PLC counter instruction is similar to the:

A)internal relay instruction.
B)transitional contact instruction.
C)relay coil and contact instruction.
D)timer instruction.

Question 23

Programmed counters can:

A)count up.
B)count down.
C)be combined to count up and down.
D)all of these.

Question 24

A PLC down-counter (CTD)counts:

A)scan transitions.
B)true-to-false transitions.
C)false-to-true transitions.
D)both b and c.

Question 25

When the up-counter reset is set to true,the following happens:

A)the preset value is set to 0.
B)the preset value increments.
C)the accumulated value is set to 0.
D)the accumulated value is set to maximum.

Question 26

A counter is to be programmed to keep track of the number of parts coming off a production line.If you wanted to subtract the number of rejected parts so your counter would count only the good parts,you would program:

A)two up-counters.
B)two down-counters.
C)an up/down-counter.
D)a counter with a transitional contact input.

Question 27

The accumulated count of a CTD counter:

A)increments with each true-to-false transition.
B)decrements with each true-to-false transition.
C)decrements with each false-to-true transition.
D)increments with each false-to-true transition.

Question 28

A one-shot,or transitional,contact:

A)operates the same as an NO contact instruction.
B)operates the same as an NC contact instruction.
C)operates the same as a timed closed contact.
D)closes for only one program scan when actuated.

Question 29

A PLC up-counter (CTU)counter counts:

A)scan transitions.
B)true-to-false transitions.
C)false-to-true transitions.
D)both b and c.

Question 30

When the accumulated count exceeds the preset count,the:

A)accumulated value is set to zero.
B)preset is set to zero.
C)reset changes state.
D)counter done bit is true.

Question 31

The output of a PLC counter is energized when the:

A)accumulated count equals the preset count.
B)preset count is greater than the accumulated count.
C)counter input rung is true.
D)counter input rung is false.

Question 32

Which of the following is not usually associated with a PLC counter instruction?

A)Address
B)Preset value
C)Time base
D)Accumulated value

Question 33

The accumulated count of a CTU counter:

A)increments with each true-to-false transition.
B)decrements with each true-to-false transition.
C)decrements with each false-to-true transition.
D)increments with each false-to-true transition.

Question 34

The counter RES instruction:

A)is used to reset the counter.
B)is given the same reference address as the counter instruction.
C)decrements the count when actuated.
D)both a and b.

Question 35

For the counter table shown,word level addressing is used for:

A)CU,CD,DN,OV,UN,and UA
B)CU,CD,and DN
C)OV and UN
D)PRE and ACC

Question 36

Output PL1 will be energized:

A)until the accumulated value equals the preset value.
B)when the accumulated value equals the preset value.
C)only when the accumulated value is less than 10.
D)only when the accumulated value is 99.

Question 37

The counter instruction is found on:

A)all PLCs.
B)small-size PLCs.
C)medium-size PLCs.
D)large-size PLCs.

Question 38

In an up-counter,when the accumulated count exceeds the preset count without a reset,the accumulated count will:

A)set itself to zero.
B)start decrementing.
C)continue incrementing.
D)hold the accumulated value.

Question 39

For the PLC counter to reset,the counter reset rung must:

A)be true.
B)be false.
C)be either true or false,depending on the manufacturer.
D)undergo a true-to-false transition.

Question 40

Output PL2 will be energized:

A)until the accumulated value equals the preset value.
B)when the accumulated value equals the preset value.
C)only when the accumulated value exceeds 10.
D)only when the accumulated value is zero.

Question 41

The counter program shown is designed to:

A)count up and count down.
B)record the time of an event.
C)count beyond the maximum count allowed per counter.
D)count below the maximum count allowed per counter.

Question 42

For the 24-hour clock program,RTO is preset for a:

A)60-s time period.
B)2-min time period.
C)12-h time period.
D)24-h time period.

Question 43

For the 24-hour clock program,Counter C5:0 is preset for:

A)12.
B)24.
C)60.
D)120.

Question 44

Which instruction,when true,will preset the counter to a count of zero?

A)Enter switch input.
B)Exit switch input.
C)Reset input.
D)Lot Full Light output.

Question 45

Which instruction will cause the counter to decrement?

A)Enter switch input.
B)Exit switch input.
C)Reset input.
D)Lot Full Light output.

Question 46

When output PL is energized,how many counts have occurred?

A)4,000
B)32,000
C)64,000
D)99,999

Question 47

The 24-hour clock program shown uses:

A)3 timers and 3 counters.
B)2 timers and 2 counters.
C)1 timer and 2 counters.
D)2 timers and 1 counter.

Question 48

Counter C5:1 starts counting:

A)when the accumulated value of C5:0 reaches 32,000.
B)whenever input PB1 is actuated.
C)whenever input PB2 is actuated.
D)either b or c.

Question 49

Suppose the accumulated count is 60 before the Enter switch input is actuated 15 times and the Exit switch input is actuated 5 times.After this operational sequence,the accumulated count would be:

A)80.
B)65.
C)75.
D)70.

Question 50

For the 24-hour clock program,Counter C5:1 is preset for:

A)12.
B)24.
C)60.
D)120.

Question 51

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,the accumulated count would be:

A)100.
B)115.
C)5.
D)0.

Question 52

When input PB2 is actuated:

A)output PL is switched off.
B)counter C5:0 is reset.
C)counter C5:1 is reset.
D)all of these.

Question 53

If you wanted output PL to go on after a count of 40,000,you would change the preset count of C5:1 to:

A)9,999.
B)6,000.
C)8,000.
D)12,000.

Question 54

The output Lot Full Light will be energized when the accumulated count is:

A)0
B)150
C)100
D)300

Question 55

For the 24-hour clock program,a false-to-true transition of rung 002 increments the clock by:

A)1 ms.
B)1 s.
C)1 min.
D)1 h.

Question 56

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.

Question 57

The field device that will cause the counter to increment is:

A)input PB1.
B)input PB2.
C)output PL1.
D)output PL2.

Question 58

Output PL will be energized when:

A)the accumulated value of C5:0 reaches 32,000.
B)counter C5:0 is reset.
C)the accumulated value of C5:1 reaches 32,000.
D)the accumulated value of C5:0 and C5:1 reaches 32,000.

Question 59

The counter file for SLC 500 controllers is:

A)C2
B)C3
C)C4
D)C5

Question 60

The figure shown illustrates the operation of a

A)timer contact instruction
B)counter contact instruction.
C)one-shot contact instruction.
D)sensor contact instruction.

Question 61

For the 24-hour clock program,Rung 003 undergoes a true-to-false transition once every:

A)60 s.
B)2 min.
C)hour.
D)24 h.

Question 62

For the 24-hour clock program,assume the accumulated count of Counter C5:1 is 14 and that of C5:0 is 10.The correct time of day would be:

A)2:10 p.m.
B)10:14 a.m.
C)10:14 p.m.
D)2:10 a.m.