To study the working of Up Counter PLC program in Allen Bradley Programmable Logic Controller (PLC).
In the above picture, there are totally three parameter,
COUNTER: C4:0 – Counter File name (TimerC5:0, C5:1,C5:2…)
PRESET – PRE : Limit value of COUNT-Up to how much it should count
ACCUMULATOR – ACC : Running Value of counter when condition turn ON.
From the data file,along with preset and accumulator, we have few more bits,
CD: Countdown Bit-whenever the counter is enable makes this bit to go ON.
DN: Done Bit-When accumulator value equals preset value, done bit turns to ON.
UA: Counter Underflow – When accumulator value reached the limit value (-32767),it rolls back to +32767 for the upcoming counter operation, underflow bit turns ON, in this condition.
Notes:
UA – Update Accumulator Value-Only used when high speed counters are used in the program.
CU & OV – Used for Up Counter Function.
I:0/0 is used to give input to counter and Preset value and accumulator value set to 5.
In the below Ladder logic,
Having condition input I:0/0 which gives input to counter to perform counter down function.
Having Counter CU Bit which enable only when counter is in function or when input to the counter turns ON and accumulator value counted down.
Counter done bit turns on when accumulator value equals preset value.
In the below Ladder logic,
Having condition input I:0/0 which gives input to counter to perform counter function.
Having Counter CU Bit which enable only when counter is in function or when input to the counter turns ON and accumulator value counted down.
In the below Ladder logic,
Having condition input I:0/0 which gives input to counter to perform counter function. Accumulator value goes to negative if I:0/0 goes ON for 6th time in the below case,
In the Below Ladder Logic,
Counter accumulator value under flows when accumulator value reaches -32767 in Allen Bradley PLC Programming.
In the below ladder Logic,
When we turn ON the I:0/0 ,accumulator value rolls back to 32768 and start counting down from 32767 to -32767.Counter underflow bit turns ON when this condition happen (Rung 003).
We can use this explanation to understand the working of Down Counter function in Allen Bradley Programmable Logic Controller (PLC).
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View Comments
Hello Hema,
Please, is there a way to hinder the countdown of the counter from reaching the negative count values without using a limits or comparison instructions?