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Match the functions to the appropriate types of counters. 1. Count the total number of parts made during each shift. 2. There are 10 parts in a full hopper. As parts leave, keep track of the number of parts remaining in the hopper. 3. Keep track of the current number of parts in a stage of a process as they enter and exit.
1 Up-counter 3 Up/Down-counter 2 Down-counter
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? Round the final answer to the nearest whole number.
10
What is the accumulated count of counter CTU? Round the final answer to the nearest whole number.
15
Suppose the accumulated value is 24 and the ac line power is lost to the controller. When power is restored to the controller, what will the accumulated value be? Round the final answer to the nearest whole number.
24
Match the PLC counter instructions to their descriptions. 1. Down-counter 2. Up/down-counter 3. Up-counter
3 This counter will increment by 1 each time a counted event occurs. 1 This counter will decrement by 1 each time a counted event 2 This counter will either increment or decrement by 1, depending on which count input is triggered, each time a counted event occurs.
Output A is in an on state.
False
Output B is in an on state.
False
Provided that rung 4 is false, each false-to-true transition of rung 1 decreases the counter's accumulated value by 1.
False
Rung 4 goes true and while it is true, rung 1 goes through five false-to-true transitions of rung conditions. The accumulated value of the counter after this sequence of events will be 5.
False
The counter instructions of PLCs are normally retentive, that is, the count contained in a counter at the time of a processor shutdown will be erased.
False
The output O:6/2 will be energized when the accumulated count is less than the preset count.
False
The output of a PLC counter gets energized when the accumulated count becomes more than the preset count.
False
What input address will cause the counter to increment?
I:2/6
What input address will cause the counter to decrement?
I:3/8
What input address will reset the counter to a count of zero?
I:4/1
Suppose the input pushbutton is now released to the normally off position and remains off. How will the status of output B3:0/9 be affected?
It remains off during this transition.
Suppose the input pushbutton is actuated from off to on and remains held on. How will the status of output B3:0/9 be affected?
It stays on for one scan and then goes off.It stays on for one scan and then goes off.
Identify the common applications of counters.
Keeping track of the number of items moving past a given point Determining the number of times a given event occurs
Will the output O:2/0 be energized when the accumulated count is less than the preset count?
No
Will the output O:2/1 be energized when the accumulated count is equal to or greater than the preset count?
No
Identify the basic programming processes involved in the cascading of two counters.
The output of the first counter is programmed into the input of the second counter.
What determines the maximum speed of transitions that a PLC counter can count?
The program's scan time
Compare the operation of a standard examine-on contact instruction with that of an off-to-on transitional contact.
The transitional off-to-on contact will close for only one program scan whenever the trigger signal goes from off-to-on, even though the triggering signal may stay on. A standard EXAMINE IF CLOSED contact will stay on as long as the trigger signal is on.
What is the accumulated count of counter CTD? Round the final answer to the nearest whole number.
15
Identify the four pieces of information usually associated with a PLC counter instruction.
Counter type Counter address Preset count Accumulated count
A PLC counter instruction increments or decrements its current count whenever the count input transfers from an on state to an off state.
False
What is the normal function of a transitional contact used in conjunction with a counter?
Resetting the counter
Output C is in an on state.
True
What type of counter has been programmed in the ladder logic program?
Up-counter
Identify the three forms of PLC counter instructions.
Up-counter Down-counter Up/down-counter
What type of counter has been programmed?
Up/down-counter
When is the underflow bit of a down-counter set?
When the down-counter has exceeded the lower limit
When is the overflow bit of an up-counter set?
When the up-counter has exceeded the accumulated upper limit
When will the count be reset?
Whenever rung 4 is true
Can an OSR (one-shot rising) instruction be used to freeze rapidly changing data?
Yes
In a PLC counter instruction, are the addresses of the counter and the reset instructions the same?
Yes
