PLC Function Part-2

 In This Article we are going to see PLC FUNCTIONS Part-2 (Counter and Timer)


PLC INSTRUCTION


Counters

No : 1

CTD : (Count Down)

Counter

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)

Counter

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)

Timer

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)

Timer

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)

RTO Timer

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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