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IBRAHIM AL-ZUGHAIBI

COUNTERS

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Counters

Common applications of counters include keeping trackof the number of items moving past a given point, and determining the number of times a given action occurs.

A preset counter can control an external circuit when its counted total matches theuser-entered preset limits.

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Electronic CountersElectronic counters can count up, count down, or be combined to count up and down. They are dependent on external sources, such as parts traveling past a sensor or actuating a limit switch for counting.

CounterApplications

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Block-Formatted Counter Instruction

Type of counter

Preset value

Accumulated value

Count line

Reset line

Outputline

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The up-counter is incremented by 1 each time the rung containing the counter is energized.

Counter Counting Sequence

The counter will increment until the accumulated value is equal to or greater than the preset value, at which time an output will be produced.

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The down-counter decrements by 1 each time the rung containing the counter is energized.

Counter Counting Sequence

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Simple Up-counter Program

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Up-counter Program Timing Diagram

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1. One common application for a counter is keeping track of the number of items moving past a given point. (True/False)

2. Timers, like counters, are not dependent on external sources for counting. (True/False)

3. The down-counter increments by 1 each time the rung containing the counter is energized. (True/False)

10 points

10 points

10 points

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4. Normally, when power to your PLC system is lost, when power is restored the counter accumulated value will be:

a. zero

b. whatever it was preset for

c. maximum

d. Unchanged

10 points

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5. The output of a PLC counter is switch from “off” to “on” any time the count input rung is "true".(True/False)

6. A PLC up-counter normally counts true-to-falsetransitions. (True/False)

7. In order for the PLC counter to reset, the counter reset rung must be “false”. (True/False)

10 points

10 points

10 points

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8. The done bit of a counter is true whenever:

a. the accumulated value is equal to the preset

value

b. the counter instruction is true

c. the accumulated value is greater than the

preset value.

d. both a and c

10 points

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9. The _________ value of a PLC counter is the current count based on the number of times the rung goes from false-to-true.

a. preset c. accumulated

b. overflow d. underflow

10 points

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10. Count rung transitions can be caused by actuating:

a. a limit switch c. a pressure switch

b. a sensor d. any of these

10 points

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Down-Counter

Normally the down-counter is used in conjunction with the up counter to form an up/down counter.

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Up/Down Counter Timing diagram

Preset Value = 3

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Parking Garage Counter Program

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Parking Garage Counter Program

50

50

38

38

150

150

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Partner Work

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