Electronic Timing Relays - Circuit Check?

Lakee911 · Feb 4, 2012

Hi All,

I know this is a *PLC* forum, but I'm trying to create a hardwired circuit using one timer that will shutdown a motor when it fails to get a close-open-close cycle of a limit switch every two minutes. In addition, I'd like for it to illuminate a lamp that shows we have zero speed. There is no chance of the device stopping with the limit open.

Can someone look at logic attached and see if I've designed this correctly?

Thx,
Jason

Mickey · Feb 4, 2012

I think you might want to take a look at the timer symbols you are using. See picture below. If I understand what you want the circuit to do, correctly.

shooter · Feb 5, 2012

It looks fine, but the light should be on a delay close contact.

moggie · Feb 5, 2012

Depends on the type of timer is being used.
If a delay on timer, then the circuit will only check if the limit switch stays "closed" for a given time - what happens if the limit switch "sticks" in the open position.
To monitor the Opening - closing function of the limit switch you should check the Eaton TMR5 series timers with the "watchdog" function.

iant · Feb 6, 2012

as you are dealing with relay logic, you still need to make allowance for the 'Air Gap'. when a switch operates it is allways takes time to open and reclose.
Your current cct will, when the timer times out, stop the motor then reclose the motor contact every 2 mins.

You need to take the timer contact out of the motor rung - put it to an aux relay, at least double pole.
use one aux contact in series with the motor.
let the relay be held by in itself, until the selector is turned off.
that should fix the problem.

Lakee911 · Feb 6, 2012

moggie said:
Depends on the type of timer is being used.
If a delay on timer, then the circuit will only check if the limit switch stays "closed" for a given time - what happens if the limit switch "sticks" in the open position.
To monitor the Opening - closing function of the limit switch you should check the Eaton TMR5 series timers with the "watchdog" function.

Well, according to my original post the chance that it sticks in the open need not be considered.

I did investigate the relay and so far I like it! Thanks.

iant said:
as you are dealing with relay logic, you still need to make allowance for the 'Air Gap'. when a switch operates it is allways takes time to open and reclose.
Your current cct will, when the timer times out, stop the motor then reclose the motor contact every 2 mins.

You need to take the timer contact out of the motor rung - put it to an aux relay, at least double pole.
use one aux contact in series with the motor.
let the relay be held by in itself, until the selector is turned off.
that should fix the problem.

The timer is likely to be open for 5sec and closed for 120sec. I don't see how it's going to open/close every two mins when timed out. Won't the NCTO stay closed until it times out and then open and stay open until power is removed?

iant · Feb 6, 2012

You gave no info as to the 5 secs open time
But is there is a timing error and the motor is still rotating the switch will reset the timer causing the motor to restart as stated,

If you didnt want advice on what may happen dont ask

Lakee911 · Feb 6, 2012

iant said:
You gave no info as to the 5 secs open time

I realize that I didn't state that it would be open for 5seconds, and that is why I clarified it in my earlier post.

iant said:
But is there is a timing error and the motor is still rotating the switch will reset the timer causing the motor to restart as stated,

I'm not sure I follow what you're saying here. Can you elaborate?

Lakee911 said:
Well, according to my original post the chance that it sticks in the open need not be considered. I did investigate the relay and so far I like it! Thanks.

Instead of the TMR5, is the Eaton TRW27 a better model perhaps? http://datasheet.octopart.com/TRW27-Eaton-datasheet-9671653.pdf

Thx

iant · Feb 6, 2012

you have a rotating load - if it is slower than the shutdown timer for some reason the timer could timeout to stop the motor contactor.
then the switch could open and reset the timer which will allow the contactor to re-energise and start the motor.

Your cct works in a perfect world.
as you want to catch the fault and stop the motor from re-starting.
it it wrong on two accounts.
1. your stopping a motor by keeping a device energised
2. If the motor is stopped and someone touches the switch the motor will start automatically.

Even the suggestion I made is technically incorrect.
but at least the operation of the switch won't restart the motor.

it is dangerous to use your current method,

Lakee911 · Feb 6, 2012

iant said:
you have a rotating load - if it is slower than the shutdown timer for some reason the timer could timeout to stop the motor contactor.
then the switch could open and reset the timer which will allow the contactor to re-energise and start the motor.

Your cct works in a perfect world.
as you want to catch the fault and stop the motor from re-starting.
it it wrong on two accounts.
1. your stopping a motor by keeping a device energised
2. If the motor is stopped and someone touches the switch the motor will start automatically.

Even the suggestion I made is technically incorrect.
but at least the operation of the switch won't restart the motor.

it is dangerous to use your current method,

I see, I see. Ok. Thanks, Ian.

iant · Feb 6, 2012

Sorry for being a bit harsh - it is 12:30 AM here
I have 35 year of Circuit knowledge - cut my teeth on complex relay logic.
PLC's here were in their infancy - Square D or Texas Instruments.

Lancie1 · Feb 7, 2012

2. If the motor is stopped and someone touches the switch the motor will start automatically.

Well, yes, that is generally the whole purpose of a switch labeled "ON - OFF". How else could anything be started without turning on a switch? If the intent is not to energize a motor when a switch labeled On-Off is turned to On, then how else to get it on safely? This arguement seems to call for some logic that can read minds. It's coming down the road, but not yet widely available.

Ian, were you talking about touching the Limit switch? Still the circuit is ON, so the motor should be able to start at any time. Probably for safety, a running light is needed to show ON when the On-Off switch is on.

moggie · Feb 7, 2012

A self "latching" fault circuit could be included so that the motor switch has to be turned off to reset the fault.

iant · Feb 8, 2012

Lancie1 said:
Well, yes, that is generally the whole purpose of a switch labeled "ON - OFF". How else could anything be started without turning on a switch? If the intent is not to energize a motor when a switch labeled On-Off is turned to On, then how else to get it on safely? This arguement seems to call for some logic that can read minds. It's coming down the road, but not yet widely available.

Ian, were you talking about touching the Limit switch? Still the circuit is ON, so the motor should be able to start at any time. Probably for safety, a running light is needed to show ON when the On-Off switch is on.

yes of course, not the selector, it was late I was trying to answer quickly.
The motor has no stop/start cct as such - only the selector.
So if the timer is slightly faulty or set wrong - which can happen.
the motor can be locked out until the timer de-energises.
should the limit switch be operated by hand the timer contact will allow the motor to restart.

- The selector switch is not the problem -

iant · Feb 8, 2012

moggie said:
A self "latching" fault circuit could be included so that the motor switch has to be turned off to reset the fault.

This is what I was suggesting Thanks for doing the drawing
- BUT -
It is still not correct -

Since you want to do the drawing - do it with the reverse logic in mind.
The relay K2 should be energised to allow the motor to run.
not de-energised.
Then the logic will be correct.

Electronic Timing Relays - Circuit Check?

Lakee911

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