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Simple circuit to indicate rotation has stopped

Simple circuit to indicate rotation has stopped

Simple circuit to indicate rotation has stopped

(OP)
I need a simple circuit that will indicate when a gear has stopped rotatong. This is a polypropylene gear that has one or more short metal rods imbedded in it.

In the past I have used the metal with a proximity switch to count the gear speed by an output to a PLC.

On the current project, there will be no output to a PLC, everything will be self contained. So I need a circuit that would run on 12 VDC and light a LED or sound a horn when the gear stopped.

Any ideas?

RE: Simple circuit to indicate rotation has stopped

There are many ways to do this. And they are all over the place on effort and cost.

Are you up for circuit boards?
Have you got embedded controller skills?
Is this a one-off or for many?

Keith Cress
kcress - http://www.flaminsystems.com

RE: Simple circuit to indicate rotation has stopped

centrifugal switch is one option

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RE: Simple circuit to indicate rotation has stopped

(OP)
Actually simple and cheap.

I have no imbedded controller skills, (I don't even know what it means).

This will be for 15 units.

RE: Simple circuit to indicate rotation has stopped

(OP)
The gear moves too slow for a centrifugal switch, but good idea.

RE: Simple circuit to indicate rotation has stopped

Timer continuously reset by a pulse from the rotating wheel? Wheel stops, timer runs to end of period, indication triggered. Should be able to build that from off-the-shelf control components.
  

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If we learn from our mistakes I'm getting a great education!
 

RE: Simple circuit to indicate rotation has stopped

Well that precludes something pricey and off-the-shelf.

I can find nothing on a brief web search.

All the remaining solutions, I can think of, are too technical or evolved to ever get across a thread.

I'd use a hall-effect sensor and microcontroller to monitor it and provide the filtering and timing desired to provide your signal.  But like all these things once you bother with a micro there are often many other thing you can toss on it that makes the systems better with only minor incremental cost increases.

Then you have the board shape.  Sometimes you want a strange shape to fit amongst the gears or in the surrounding spaces.

You also want the mounting of the board to utilize existing screws or available mounting holes.

Maybe you should hunt up an engineer to design these for you and get a quote.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Simple circuit to indicate rotation has stopped

Assuming you can arrange things so that the system provides rotation output pulses of some sort, then the good old fashioned 555 timer chip can be made to work as a 'missing pulse detector'.

 

RE: Simple circuit to indicate rotation has stopped

ScottyUK hit upon my first thought. Since you already had a pulse-type speed sensor, just connect the speed sensor into what is sometimes called a "missing pulse detector", or some other type of pulse detector circuit. This type of circuit is frequently made from 555-type timer chips or from 4538B or similar monostable multivibrator ICs.

RE: Simple circuit to indicate rotation has stopped

Why do you say he, "has a pulse-type speed sensor"??
I don't see where he said that.(?)

Off-the-shelf prox sensors are not inexpensive and he needs fifteen..

Keith Cress
kcress - http://www.flaminsystems.com

RE: Simple circuit to indicate rotation has stopped

A weighted & sprung lever attached to a micro-switch, driven by a cam.  

Oops, sorry, that's a mechanical answer. :)

RE: Simple circuit to indicate rotation has stopped

Allen Bradley used to make nice zero speed switches but they were big and pricey.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Simple circuit to indicate rotation has stopped

That describes Allen Bradley perfectly!

roy & ComcoKid: yes, we're thinking on the same lines. Rather than a roll-yer-own timer circuit there are plenty inexpensive ones which are designed for DIN rail mounting which would avoid getting involved in making boards and the like. I hesitate to suggest anything like Veroboard (stripboard) because I really don't like the stuff, even for a simple circuit like that 555 example.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Simple circuit to indicate rotation has stopped

I don't work with DIN rail or similar industrial control components, but I'm sure there are 'equivalents' to the circuits I described.

I assume the control in it's PLC version is a pulse-type pickup since it consist of metal rods in a plastic gear sensed by a proximity pickup.

I suggest looking for a time-delay relay/control module with a reset input. Connect the proximity pickup to the reset input. If the delay module does not get a pulse on the reset input (speed=0) then after a quick delay, the module will output a signal indicating that there is no rotation. This is the module equivalent to the missing pulse/monostable circuit I suggested earlier.

RE: Simple circuit to indicate rotation has stopped

you can weld a small gear to the rotating gear then we can couple it by a chain to another gearbox which rotates a potentiometer that gives a signal to a comparator which determine if there's no signal (gear stopped)

RE: Simple circuit to indicate rotation has stopped

Quote (melghazaly):

you can weld a small gear to the rotating gear then we can couple it by a chain to another gearbox which rotates a potentiometer that gives a signal to a comparator which determine if there's no signal (gear stopped)
Isn't that going around your elbow to get to your rear end?

Dan - Owner
http://www.Hi-TecDesigns.com

RE: Simple circuit to indicate rotation has stopped

Two circuits are parts of the solution:
1 - a movement/rotation sensor;
2 - a retriggerable timer/monostable.

For the first circuit I'd use either one of this:
- hall sensor; with a small magnet attached/glued to one of the rods
- optical sensor:
  - reflective sensor - and you need to glue a piece of reflective foil (like the one used to pack chocolate) on the top of the rod, or
  - photo interrupter - with a small piece of opaque foil (metal sheet?) attached to the rod...
 
For the second circuit I'd go with the good old 555 configured as a retriggerable monostable. I prefer this over the 4528/4538 for reliability, availability and output capabilities.
The whole thing will cost under $5 and, while still demanding basic electronic skills, you don't have to program anything in assembler, C# or other .NET horrors. I know there are many here that would happily replace the 555 (or even a resistor!) with anything from a microcontroller to a mainframe computer, just because is close to their hearts, but is really not the case here...

RE: Simple circuit to indicate rotation has stopped

Although they're not explicitly mentioned, there are probably other bits of hardware that are also rotating. It's safe to assume that the gear in question isn't rotating all by itself.
 

RE: Simple circuit to indicate rotation has stopped

If there is an AC or DC motor involved, that signal can be fed into an op amp. Any voltage and a relay closes. Op amp input can be protected by back to back diodes and a several hundred K resistor.

Even a missing pulse detector can be made with an op amp. Any input signal charges a cap with a long discharge. A second op amp switches when the voltage on the cap goes near zero.  A neophyte may have more luck with an op amp than a 555.    

RE: Simple circuit to indicate rotation has stopped

PRW, if you still have a proximity switch, consider one of the watchdog timers available for such purposes. Maxim makes several.

http://www.maxim-ic.com/view_press_release.cfm/release_id/143

One thing to consider is that the watchdog must be edge-triggered. Otherwise, if the gear stops on one of the prox. switch targets, a simple 555 reset scheme will be held off indefinitely. The app notes for these parts may have some other insights into possible design issues.   

RE: Simple circuit to indicate rotation has stopped

(OP)
I must offer my apologies for not looking at this post for a long time. I was on another project and could not take the time. I do value your inputs, now I just need to figure out how to use them.

I have investigated the 555 circuits ( missing pulse detector ) that were mentioned and also looked into hall effect sensors. I would like to use both, but have no experience with actual circuit design.

Terms like when triggered, the output goes low, what does that mean? Would I need a relay at the output to turn on a light of the relay is de-energized?

Then there is the problem one of you mentioned about where or not the gear stopped next to the sensor. Since the repetition stops, will the missing pulse detector not perform as designed?

I think I need to find a "Circuits for Dummies" Book!

 

RE: Simple circuit to indicate rotation has stopped

PRW, there are a couple of issues to address. What are the consequences of not detecting the cessation of rotation? Life safety, damage to equipment, cost of having an operator run over and punch the reset button occasionally? The more serious the consequences, the more I'd suggest an off-the shelf solution.

Then, there's the issue of latency. How many pulses per second (RPM, whatever) does this device run at? What is the minimum speed under which a 'no rotation' signal must be generated and how soon after it drops below this threshold must a signal be produced?

The behavior I mentioned in a previous post applies to some of the simplest 555 circuits, which are timers that will run to completion if not periodically reset. If the pulse which resets the timer is based on a sensor level (high or low), what happens if the gear stops directly under the sensor, holding the 555 'off' and incapable of generating its output indefinitely? These are all things that have been addressed by designers of things like watchdog circuits. You'll still have to do some soldering, but the application notes will probably cover a case close enough to yours that re-inventing the wheel will be unnecessary.  

RE: Simple circuit to indicate rotation has stopped

If the motor stops when the gear stops then you could use a current switch. see ACS150 Series from automationdirect.

RE: Simple circuit to indicate rotation has stopped

Look at an Omron H3CR-A AC24-48/DC12-48 timer set to mode E - interval. Use a proxy switch as the start signal. It will keep the output contacts energized when there is a pulsing start signal. If the start signal goes away or stays on it will time out and de-energize the output contacts.

Nice thing is that one will run on 24VDC and the NPN from the proxy switch can connect directly to the start input. Y?You should just require the proxy sensor, 24VDC power supply and timer to make the circuit. It also has contact outputs which make it easy to use the output.
 

RE: Simple circuit to indicate rotation has stopped

(OP)
Lionel,

This looks like any excellent solution, except for the cost. I was hoping to do this for a lot less money, but I don't know how. I design mechanical stuff, and although I can put together some simple electronic parts, I have no idea of how they connect.

I will keep your suggestion in mind, but I am sure the "counters of beans" will shoot it down.

Thanks,

Paul

RE: Simple circuit to indicate rotation has stopped

Well, I really don't see any cheaper way to do it. If you were to ask me to design something for 15 units I could not spend the time to design and build the circuit cheaper than those timers would cost. But then, I might get a price for that timer which is a lot less than you found.

If you can change to magnets instead of steel in the gear then you could find some cheaper sensors.

 

RE: Simple circuit to indicate rotation has stopped

(OP)
Lionel, I can use magnets, in fact I have some round neodimium magnets that I have used with a reed switch. The problem is the reed switch fails, maybe the contacts are welding, who knows.
In any earlier post I mentioned looking a hall effect sensors, and was thinking of using the Allegro switch on this page: http://www.allegromicro.com/en/Products/Part_Numbers/3245/
Based on my very limited knowledge, I thought this would work.
Someone mentioned earlier in the post that there would be a problem if the input stayed high. How do I overcome that? Would that be a problem if I used the timer you mentioned?

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