Allen Bradley Timer Trouble

[pr_wainwright]

Hi,
I am looking to achieve the following using a timer in a ControlLogix project.

The input to the timer when true should not start the timer. when the input is false the timer should start timing down. If the input becomes true again the timer should stop timing and reset the accumilator to zero.

I have used Siemens in the past and feel sure one of the timers could do this but I am struggling with Allen Bradley.

Any help appreciated.
Thanks
Paul.

 

[Marc_U]

If I am reading your description correctly, what you are wanting is a normally closed contact (XIO) of the Input to the Timer.

AB timers count up from zero to the preset time.

If you want a decreasing value, then you will need to add an additional rung, which subtracts the Accumulated time (ACC) from the Preset time (PRE), which would effectively give you a countdown.

I hope that helps.

 

[nettogrisen]

Try this.
Note that the timers count in milliseconds.

 

[MarkNightingale]

Paul,

Like this..........

 

[jstolaruk]

Try this.
Note that the timers count in milliseconds.

Rung 3 (timer reset) is redundant - only needed if the timer was retentive (RTO vs TON)

 

[pr_wainwright]

Hi,
Thanks for the suggestions. Managed to get the code working as I wanted.

Thanks
Paul.

 

[nettogrisen]

Rung 3 (timer reset) is redundant - only needed if the timer was retentive (RTO vs TON)

You're absolutely right

 

[OkiePC]

Also, note that the ACC can overrun the PRE, so you may want to CLR the DEST of the SUB when the timer is DN to avoid a negative DEST.

 

[passwordg]

Hi,
I am looking to achieve the following using a timer in a ControlLogix project.

The input to the timer when true should not start the timer. when the input is false the timer should start timing down. If the input becomes true again the timer should stop timing and reset the accumilator to zero.

I have used Siemens in the past and feel sure one of the timers could do this but I am struggling with Allen Bradley.

Any help appreciated.
Thanks
Paul.

Please correct me if I am wrong, but this seems like the operation of a TOF isn't it ?
I've rarely ever used TOF so not completely sure of its operational an I'm away from the work computer to verify.

 

[dmargineau]

You are absolutely correct.

"The input to the timer when true should not start the timer. when the input is false the timer should start timing down. If the input becomes true again the timer should stop timing and reset the accumilator to zero."


This will be a TOF application.
Be careful when examining the .DN bit of a TOF timer though; it will be true at all times except when the .ACC = .PRE