Understanding timers

I am wondering if anyone out there can help, I have a situation where I need to activate a timer and the input that starts the timer is a contactor. After every activation of the contactor the timer needs to reset regardless of whether or not the timer has timed out. Any info would be a great help, thanks

Welcome to the Forum !

It would help with syntax and instruction specifics if you could specify which make and model of PLC you are working with.

I think that the basic timing logic you are describing is:

1. When the Contactor is energized, the Timer begins timing.
2. If the Contactor is still energized when the Timer reaches its Preset, the Timer stops timing.
3. If the Contactor is de-energized, the Timer will continue timing until it reaches its preset.
4. If the Contactor is re-energized before the Timer reaches its preset, the Timer will start over at zero and return to Step 2.

In an Allen-Bradley PLC (with which I am most familiar), I would use a rising-edge one-shot instruction tied to the contactor input to perform a Reset (RES) of the Timer instruction.

But you may be thinking of a different controller or a different function, so go ahead and explain in more detail what you want.

Thanks for the welcome Ken

What I am trying to achieve is conveyor speed control via a VSD and PLC, The controller is a Moeller 'Easy Relay" range.

What needs to happen is the conveyor to run at constant speed say 100% until an external signal is recieved that will start the timer, the timer needs to time for 'x' amount of seconds and then switch the VSD to 15% speed, however if the input signal is turned off before the timer has timed out, then the timer needs to be reset before the next input signal is switched on and the conveyor is to carry on at 100% speed. If the timer has achieved 'x' amount of seconds and switched the conveyor to 15% then it should only run like this until the original signal is removed and the conveyor then returns back to 100%

I am not familiar with your PLC, however, in an AB PLC a simple TON Timer would do what you describe. If the Moeller has a similar Timer, it should do the job.

AB TON Timers Reset automatically when the Input Conditions go False. If the Timer reaches Preset, the Done Bit will stay True until the Input Conditions go False.

Can you provide a Link to the Moeller Instruction Reference Manual?

Stu....

Thanks for the info Ken, I have looked at the Moeller data shetts and manuals but there is nothing specific in there regarding timer types, it is only a simple low budget PLC so I am expecting it to be of the Tmer On (TON) type, the brochure link I have is http://www.moeller.net/binary/w_brochures/w7557en.pdf

Thanks again buddy

According to the description given here besides Figure 19 you can achieve what you want by programming like this:

I1-----TT1



-

I1-----RT1

The I1 in the second rung is a Negated I1

There are typically different varieties of timers available in a PLC. There are "On Delay" and "Off Delay" timers. With an "On Delay" timer, the accumulator increments when the timer's input is on and the timer's output (or Done Bit) is set whenever the accumulator equals the preset.

With an "Off Delay" timer, the timer's output (or Done Bit) is set when the input line becomes true, and the accumulator increments when the timer's input returns to an off state. The timer's output (or Done Bit) then returns to an off state when the accumulator equals the preset.

Both of these types of timers reset their accumulator to zero based upon the state of their single control input. With an "On Delay" timer, the accumulator resets when the input is false. With an "Off Delay" timer, the accumulator resets when the input is true.

There are also "Retentive Timers". These timers have two inputs. One input enables incrementation of the accumulator, but does not reset the timer accumulator if the input returns to an off state. The second input is used to reset the timer instead. This allows accumulated timing of intermittent events, while allowing separate reset control based upon a different event or condition.

Hope that helps.

Let me untangle this and break it down:

simonmusson said:

What needs to happen is:
1. the conveyor to run at constant speed say 100%
2. an external signal is recieved that will start the timer,
2a. if the input signal is turned off before the timer has timed out, then the timer needs to be reset
3. the timer needs to time for 'x' amount of seconds and then switch the VSD to 15% speed

Click to expand...

Basically you want the conveyor to run at two speeds:
15% only after the timer is done.
100% if the timer is not done.

so the timer done bit serves as the speed select switch in your relay program.

Some timers will reset if the conditions preceding them in ladder logic go false (assuming your relay uses ladder logic). Some controllers require that you explicitly reset the timer with a separate input branch or instruction, which merely amounts to one more line of code to reset the timer at all times when the input from the contactor is false.

Basically you want the conveyor to run at two speeds:
15% only after the timer is done.
100% if the timer is not done.

Click to expand...

I agree with Paul. Here is a little Eaton Moeller EZ-Soft Version 6 program that should do the trick. I set the timer for 30 seconds as a guess, change as needed. I can post a ZIPped copy of the Eaton *.e60 program if you want it. I think that the software is available from the Eaton-Moeller site. If not, you can get a Demo version from www.Eaton.com
http://www.moeller.net/en/products_solutions/motor_applications/control/easy/software.jsp

http://www.eaton.com/Eaton/Products...ownloads/index.htm?litlibtarget=1162919213810

Thanks for all the feedback guys, im sure with all this information i'll get it sorted out, its a project thats in the pipeline thats not been given the go ahead yet, just trying to get all the prep work done to impress the boss, Thanks again everyone

I know this is a PLC forum but wouldn't it be much simpler to use a hardwired type On-Delay relay similar to one in the link below if this is all that is needed?
Different coil voltages are available besides the one shown in the link.
Link:
http://www.zorotools.com/g/00062846...kw={keyword}&gclid=CKGWnqOZt7UCFckx4AodihwAug

jrwb4gbm said:

I know this is a PLC forum but wouldn't it be much simpler to use a hardwired type On-Delay relay similar to one in the link below if this is all that is needed?
Different coil voltages are available besides the one shown in the link.
Link:
http://www.zorotools.com/g/00062846...kw={keyword}&gclid=CKGWnqOZt7UCFckx4AodihwAug

Click to expand...

It would be, if this single control function is all that's required. If you wind up needing 3 timers for some reason, then you would have saved money with a small PLC instead.