PLC Function Part-2
In This Article we are going to see PLC FUNCTIONS Part-2 (Counter and Timer)
Counters
No : 1
CTD : (Count Down)
Description
- The Counter accumulator will decrease once each time the input goes from false to ture.
- If the accumulator value reaches the preset the done bit, DN, will be set.
- The accumulator value will still decrease even when the done bit is set.
Status Bits :
CU : Not used for this instruction
CD : Will be ture when the input is ture
DN : Will be set when ACC < PRE
OV : Not used for this instruction
UN : Will be set if the counter value has gone below 32,768
Registers :
ACC : The time that has passed since the input went ture.
PRE : The maximum time delay before the timer goes on
Available on : Micrologix , PLC-5
No : 2
CTU : (Count Up)
Description
- The Counter accumulator will increase once each time the input goes from false to ture.
- If the accumulator value reaches the preset the done bit, DN, will be set.
- The accumulator value will still increase even when the done bit is set.
Status Bits :
CU : Will be ture when the input is ture
CD : Not used for this instruction
DN : Will be set when ACC < PRE
OV : Will be set if the counter value has gone above 32,767
UN : Not used for this instruction
Registers :
ACC : The Total count
PRE : The maximum count before the counter goes on
Available on : Micrologix , PLC-5
Timer
No : 1
TOF : (Timer OFF)
Description
- This timer will delay turning off (the done bit , DN , will turn on immediately).
- Once the input turns off the accumulated value (ACC) will start to increase form zero.
- When the preset (PRE) value is reached the DN bit is turned off and the accumulator will reset to zero.
- If the input turns on before the off delay is complete the accumulator will reset to zero.
Status Bits :
EN : This bit is ture while the input to the timer is ture
TT : This bit is ture while the accumulator value is increasing
DN : This bit is ture when the accumulator value is less than the preset value and the input is ture, or the accumulator is changing.
Registers :
ACC : The time that has passed since the input went false.
PRE : The maximum time delay before the timer goes Off.
Available on : Micrologix , PLC-5
No : 2
TON : (Timer ON)
Description
- This timer will delay turning ON (but will turn off immediately).
- Once the input turns ON the accumulated value (ACC) will start to increase form zero.
- When the preset (PRE) value is reached the DN bit is set.
- The done bit will turn off and the accumulator will reset to zero if the input goes false.
Status Bits :
EN : This bit is ture while the input to the timer is ture
TT : This bit is ture while the accumulator value is increasing
DN : This bit is ture when the accumulator value is equal the preset value.
Registers :
ACC : The time that has passed since the input went True.
PRE : The maximum time delay before the timer goes ON.
Available on : Micrologix , PLC-5
No : 3
RTO : (Retentive Timer ON)
Description
- This timer will delay turning ON.
- When the input turns on the accumulated value (ACC) will start to increase from zero.
- When the preset (PRE) value is reached the DN bit is set.
- If the input goes false the accumulator value is not reset to zero.
- To reset the timer and turn off the timer the RE5 instruction should be used.
Status Bits :
EN : This bit is ture while the input to the timer is ture
TT : This bit is ture while the accumulator value is increasing
DN : This bit is ture when the accumulator value is less than the preset value.
Registers :
ACC : The time that has passed since the input went True.
PRE : The maximum time delay before the timer goes ON.
Available on : Micrologix , PLC-5
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