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Shaft speed sensing #188449 08/09/09 05:00 PM
Joined: Jan 2004
Posts: 171
M
Merlin Offline OP
Member
I am looking for a source of a shaft speed sensor. I want to sense the rotation of a shaft on a bucket elevator. I want to be able to drop out the control circuit to this elevator if the shaft speed drops as in the case of the belt slipping. Does anyone have a source for this type of sensor? I would like to keep it simple without using plc's or the such. Anyone got any suggestions on this situation?Thanks, Merlin

Work Gear for Electricians and the Trades
Re: Shaft speed sensing [Re: Merlin] #188468 08/10/09 04:43 PM
Joined: Jan 2005
Posts: 5,316
renosteinke Offline
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Such sensors are made by nearly every control maker. A typical arrangement has you add a small wheel to the shaft. Part of this wheel has a magnet. The wheel, and the magnet, rotate through a piece that senses the magnet each time it passes.

Re: Shaft speed sensing [Re: renosteinke] #188470 08/10/09 05:22 PM
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WESTUPLACE Offline
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Automation Direct at www.automationdirect.com

Re: Shaft speed sensing [Re: WESTUPLACE] #188474 08/10/09 11:00 PM
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T
twh Offline
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I worked with a type that would maintain state between pulses so it was on steady instead of blinking off and on every time the shaft turned. It had an adjustment so it could be tuned to the rotation speed. I suppose you could do the same thing with a time delay relay but it might be hard to adjust.

If you don't use a plc, you'll need to bypass the sensor on start-up and it's a bear to trouble-shoot.

Re: Shaft speed sensing [Re: twh] #188478 08/11/09 01:06 AM
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NORCAL Offline
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Re: Shaft speed sensing [Re: NORCAL] #188479 08/11/09 01:31 AM
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gfretwell Offline
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Way back in the olden days we did stuff like this with some sort of pulse generator on the shaft (optical, Hall Effect or magnet/coil) and a pretty simple logic circuit that compared the pulses to a time base. It could be as simple as a 555 timer set up as a missing pulse detector. If the motor pulse didn't reset it within the window it triggered the alarm.
Usually they would just suppress errors for a second or so to let the motor speed stabilize.
An even older scheme used a small DC generator on the end of the shaft. If the output voltage dipped, the motor was slowing down. That was really more of an adjustment tool than a monitor though. We used them to set up the hydraulic motor/spool valve assembly on line printers (looking at it with a scope).


Greg Fretwell
Re: Shaft speed sensing [Re: Merlin] #188490 08/11/09 04:39 PM
Joined: Jul 2004
Posts: 272
A
A-Line Offline
Member
Originally Posted by Merlin
I would like to keep it simple without using plc's or the such. Anyone got any suggestions on this situation?Thanks, Merlin

I would consider using one of the Teco controllers. They can be programmed without software or you can download their free software and order a cable to program them. They're cheap and work well.

http://www.factorymation.com/s.nl/sc.2/category.22/.f

http://www.factorymation.com/s.nl?it=A&id=841&sc=2&category=44

A simple prox switch wired to an input of this controller with a timer programmed into the controller would work for what you're wanting to do.

Last edited by A-Line; 08/11/09 04:44 PM.
Re: Shaft speed sensing [Re: A-Line] #188492 08/11/09 06:08 PM
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Posts: 9,569
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gfretwell Offline
Member
That looks like a nice controller. I might order me one just to play with. I am thinking about a solar controller and this might do the trick.


Greg Fretwell
Re: Shaft speed sensing [Re: gfretwell] #188498 08/12/09 12:48 AM
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Posts: 947
T
twh Offline
Member
The controller is an excellent idea.

Greg, get the software. It's way more interesting than the actual controller. You can always get the controller when you need it.

Re: Shaft speed sensing [Re: twh] #188508 08/12/09 11:12 PM
Joined: Jan 2004
Posts: 171
M
Merlin Offline OP
Member
Thanks guys for all the information. The information is helpful. I was told by another EC that you can put a sensor on the shaft and simply wire it through the #2 on start-stop button. He said the only hang up is you will have to hold the start button until the shaft is up to speed. That is all OK but i guess i'm a little cloudy on how this would work. Can someone point me in the right direction? I understand the cocept but how will that hold the coil in without a timing relay. This is going to be on a shaft with only about 100 rpm. Thanks again

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