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#128171 - 09/05/02 12:46 PM Help... Virgil's baffled by control work again...
sparky66wv Offline
Member

Registered: 11/17/00
Posts: 2339
Loc: West Virginia
This will take a while to load... Sorry to rob your bandwidth there, Bill, but as they say, a picture is worth a thousand Q's, or something like that...

This first drawing basically shows what I've got:



Here's the real thing, it will be replaced with a PVC dust proof box and new controls as soon as I can figure out how it works:



Here's the original schematic:



Here's how I think it would be hooked up according to above schematic:



Here's one of the limit switches:


I haven't seen the motor, gate, or any other parts.

The more I study it, the less it makes sense.

In a nutshell, the crowd gates push the cows towards the milk parlor door, stop when it hits a cow, waits a few minutes and cycles again. There doesn't seam to be a reverse to reset the whole works, I guess you have to move the gates back by hand?

The schematic given just doesn't make sense to me... Especially how the timer controls, and the connection between the timer NC and the relay NO, seams like it'll just be energized from opposite directions and stops, depending on the relay position and timer.. Am I just goofy?

Any help at all is greatly appreciated.

Hey, if y'all say it'll work just fine like that, I'll go for it and chalk my misunderstading up due to ignorance...

_________________________
-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI

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#128172 - 09/05/02 01:58 PM Re: Help... Virgil's baffled by control work again...
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
Virgil,
It appears that the motor starts to run as soon as you turn on the switch and continues to run until one of the limits is tripped. The limits pick up the time delay relay coil and the motor relay coil. The motor relay coil is sealed in through the normally closed time delay contact and the normally open motor relay contact. It appears that the time delay relay is of the pneumatic type. The timing will start after the limit switch returns to the open position. After the timer times out its contact will open and this will in turn drop out the motor relay and the motor will again be powered through the normally closed motor relay contact.
Don

[This message has been edited by resqcapt19 (edited 09-05-2002).]
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Don(resqcapt19)

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#128173 - 09/05/02 02:11 PM Re: Help... Virgil's baffled by control work again...
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Virgil,

The original schematic (and your re-drawing of it) should be fine.

The limit switches must be physically installed such that the "normally closed" contacts are actually held open during normal running and close when the gate hits an obstruction.

Here's how it will work:

Assuming no obstruction is present when the power is turned on, the only complete path for current is through the relay's N/C contacts to the motor. The relay will remain released and there will be no power to the timer control.

When the gate hits an obstruction (like a cow, or an electrician!) one of the limit switches will close and apply power directly to the relay coil. Power will also be applied to the timer control to start the delay cycle.

When the relay energizes, the N/C contacts open and immediately stop the motor. At the same time, the N/O contacts close. The timer N/C contacts are also closed at this point, so the two sets of contacts effectively bridge the limit switches to insure that power remains applied to the relay and timer even after the limit switch opens again.

The circuit will remain in this state with the relay energized until the timer completes its cycle. At that time, the timer N/C contacts open and break the path that was keeping power applied to the relay coil. The relay will drop out, thereby closing the N/C contacts to restart the motor. Power will also be removed from the timer control, causing its contacts to close again, but this will not have any immediate effect because the relay's N/O contacts will have already opened again. The circuit is now back in its original state, ready to be triggered again if/when either limit switch operates.

Hope that makes sense --

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#128174 - 09/05/02 02:21 PM Re: Help... Virgil's baffled by control work again...
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Don,
The timing will have to start when the limit switch closes, not when it opens. As soon as the relay energizes the series combination of the relay N/O and timer N/C contacts are paralleled across the limit switches. The latter can then have no effect on the circuit until the path holding the relay opens again.

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#128175 - 09/05/02 02:50 PM Re: Help... Virgil's baffled by control work again...
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
Paul,
I made the assumption that the time delay relay was of the pneumatic type and if so the timing won't start until the time delay relay is deenergized.
Don
_________________________
Don(resqcapt19)

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#128176 - 09/05/02 02:52 PM Re: Help... Virgil's baffled by control work again...
sparky66wv Offline
Member

Registered: 11/17/00
Posts: 2339
Loc: West Virginia
Thanks guys!

Now I've got a better mental picture of the whole works...

Boy, what did I do without you guys (besides scratching my head and looking puzzled a lot!)



The server with my pix is down at the moment...
_________________________
-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI

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#128177 - 09/05/02 03:02 PM Re: Help... Virgil's baffled by control work again...
sparky66wv Offline
Member

Registered: 11/17/00
Posts: 2339
Loc: West Virginia
Don,

I don't think it is pneumatic, I believe it is an electric (mechanical) timer.

My plan is to use a standard Ice Cube relay and a digital timed delay relay, with a new switch, terminal bar, and box (and new wire ans stacons too). I don't think the motor has more than say 1/2 hp, so a contactor would be unneccesary, wouldn't it? The limit switches are in bad shape too, very corroded.

Anyway, thanks again!
_________________________
-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI

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#128178 - 09/06/02 05:07 AM Re: Help... Virgil's baffled by control work again...
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
"...Picture's worth a thousand words" applies quite well here. Based on the rust, looks like maybe the crowd of cows [and/or guys] over the years may have had full bladders, and had to “break loose” waiting for the gate timer a few times.

As far as controls, the timer and limit switches have some states that understanding can simplify troubleshooting. Here’s a basic lesson, applied to the crowd gate. Normally-Open [NO] and Normally-Closed [NC] contacts are usually well understood, and are the basis for initiating most machine controls. Being able to describe operation in terms used by many helps an electrician visualize operation, and, {dare we say} explain it to others

Limit switches can be visualized as NO or NC, but sometimes as-found or powered-down states are different. NOHC is a Normally-Open\Held-Closed condition. NCHO is a Normally-Closed\Held-Open condition.

Time-delay relay contacts can often be described as having four states. “On delay” [most common] can be described as Normally-Open\Timed-Closed [NOTC] state, or it can be in a Normally-Closed\Timed-Open [NCTO] state. “Off delay” [less common] can be described as Normally-Open\Timed-Open [NOTO] state, or it can be in a Normally-Closed\Timed-Closed [NCTC] state.

Lesson Two will cover: Tape—Friction or Plastic? Take two aspirin now.

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#128179 - 09/06/02 03:12 PM Re: Help... Virgil's baffled by control work again...
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Glad you've managed to figure it out Virgil, and I was assuming that the timer is a mechanical type as well.

Don,
I don't see how a pneumatic relay of the type you described would work in this circuit. If you installed one in which the time delay didn't start until after power is removed, then the first operation of a limit switch would just lock up the relay and stop the motor from running until the whole lot was switched off and back on.

As soon as a limit switch closes, you have power on the relay and timer. The relay N/O contacts latch it on via the timer N/C contacts, after which the limit switch opening again can have no effect.

Other than switching off, the only way for power to be removed from the relay (and thus the timer) at that time is for the timer's N/C contacts to open after the appropriate delay. The timing cycle has to start when power is applied to the timer (whatever type it is), otherwise it just won't work.

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#128180 - 09/06/02 04:41 PM Re: Help... Virgil's baffled by control work again...
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
Paul,
I'm assuming that the limit switch will open when the animal moves away from the gate even if the motor is not running. By the looks of the spring on the limit switch, I believe that this is possible. If the timing starts when the limit switch is closed, then the timer can time out and start the motor again with the animal still in the way. At this point with the limit switch still closed, there is no way to stop the motor other than the on/off switch. This could cause the motor to trip out on its overload contact, if it has one, because it will be trying to move the gate against the cow. If the timing starts after the limit switch has opened, then the gate will have some more space to move. When the timer has timed out, the timing contact will open and the motor will start again because with the limit switches open and the timer contact open, the motor relay is denergized and the normally closed motor relay contact will start the motor.
Don
_________________________
Don(resqcapt19)

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