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Help with sensing a stopped sprocket

craig forcht

Sep 20, 2016
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Hi all. I am somewhat familiar with electronics, meaning I know what most components do. but I am not an electronics engineer by any means. In fact I probably know just enough to be dangerous. so I am seeking more experienced help for this little project.

The application is a simple low speed mechanical machine that has an electrical motor with a VFD controlling rpm. The VFD has an external fault circuit (open/closed) to interrupt the motor operation when triggered. The machine uses a mechanical friction clutch that overrides in the event of a machine jam.

I would like help designing a simple circuit that will control a relay or similar to trip the fault circuit in the VFD should the machine jam and the sprocket stops turning. I have a Cherry GS1005 gear tooth speed sensor I bought hoping to figure this out myself. but alas. Its outside my capabilities. Any help would be greatly appreciated. thank you.
 

Minder

Apr 24, 2015
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The Prox sw has a open collector NPN output so you should be able to interface direct to the VFD depending of whether the input is sink or source, see pdf.
What is the part No. of the VFD?
But if you need to detect a stopped condition only then you will need a missing pulse detector that can be made from a 555 IC very simply.
Also known as a Watchdog timer.
M.
 

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craig forcht

Sep 20, 2016
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Thanks for the reply. the VFD is an Automation direct GS2-10P2

Yes I need to detect a stopped only condition. where a relay or what not will trigger the fault circuit to stop the motor.
 

Minder

Apr 24, 2015
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You could use the output of the 555 direct into the DI3 which is External Fault input and is a sourcing input so when pulses are present the 555 will be high and will output a low on pulse fail, Google 555 missing pulse detector.
You should not need a relay.
It also looks like you have access to the internal 10v+ supply so you can power any circuit from the VFD itself.
You probably will need a override some how to ignore or open the input on start up. As it will detect missing pulses at that point.
Have you ever built any small circuits?
M.
 

craig forcht

Sep 20, 2016
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Minder,
Yes I have built small circuits before. not many but enough to be comnfortable with this. Just alcking the know how. soldering etc are no problem. and yes I figured I would need some way to "override" it during start up. I am planning on using a push button or something of that variety to keep the fault circuit closed on start up.

I already have other things on the fault circuit, all are in series so that any one of them will trip the fault circuit. those are just simple micro switches.

I did look on google for missing pulse detectors, there are many to choose from. but not sure which would be the best one for my application using this sensor. since I have the other micro switches in place that is why I was looking to control a relay so it would be on the same concept as the switches. simple open/closed operation
thanks again for the help so far.
 

Minder

Apr 24, 2015
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I can whip up a simple 555 circuit if you want to pursue that method, the inputs appear a s N.O. so if you place a N.C. P.B. in series with the input it will open up during start up.
You will have to decide on a elapsed time period where it is considered stopped.
M.
 

craig forcht

Sep 20, 2016
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Minder,
That my kind sir would be awesome.
yes I think the 555 route is the way I would like to proceed. the elapsed time would be around 2-3 seconds or so which would be plenty for this application. I think I might even have a couple of those laying around somewhere.
as for the pushbutton. whichever place you think it would work best.
the VFD fault circuit works as NC during normal operation. meaning when the circuit opens the VFD sees it as a fault and stops.
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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Minder, this is just a Re-Minder. It's now tomorrow. :)

Sorry, I couldn't resist!
Chris
 

Minder

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Minder, this is just a Re-Minder. It's now tomorrow. :)

Chris
I didn't know there was a penalty??:p

Craig measure from DCM to the +10v terminal, if OK then you should be able to supply from the VFD, if not just connect the circuit common to DCM and the DI3.
If a separate supply just use 12v supply.
Note: R1 is connected to pin 3 not PWR.
The P.B. sw should be N.C..
Adjust R1 and the 10mfd accordingly for length of delay.
If the logic is not correct, (the manual is a little vague) you can add a bi-polar or mosfet (2n7000) on the output of the sw
M.
 

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craig forcht

Sep 20, 2016
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Nope I dont believe there is a penalty either. but as I have found on other forums someones always bustin yer chops.

Minder, thank you very much for the schematic, I do appreciate it. I will give it a try.
 

craig forcht

Sep 20, 2016
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CDdrive, I noticed your avatar. I once saw a guy hauling 20 foot lengths of steel material strapped to the underside of his Geo Metro. If that wasnt comical to see.
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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Wow, that was fast response! Imagine how different the world would be if it was that easy to tweak a contractors butt! :p

Chris
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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Ha, so was I. Electronics contractor at a hospital. I have to confess that my favorite pacification lines were...

Yup, I'm on it. Waiting for an obsolete part that can only be procured from the remote regions of Siberia.

Yeah, I know you needed this last week but the ER has priority. Your complaining to the wrong guy.

This is the first time I'm hearing this. Did you submit a work order?

You did!

Well, I didn't receive a PO. :D

Chris
 

craig forcht

Sep 20, 2016
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I do contract machining for the pharmaceutical industry among others.
Yeah I can see that. I've used a couple myself.
Like the material didn't come in when it was supposed to.
had to order special tooling
the machine is broke down and waiting on those parts from Siberia etc.
every industry has them.
but sometimes those are real excuses not just fictitious pacification's
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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Yes, sometimes it isn't pacification.

Anyway, let us know how Minder's circuit works out for you. We always hear from OP's when things aren't working out but when they do work they disappear like the relative you lent money to. :)

Chris
 
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craig forcht

Sep 20, 2016
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LOLOL yeah Im sure thats exactly how it works. itll be a couple days before I round up all the stuff and have a go at it. will let you know how it works. thanks again for the help and the laughs
 

craig forcht

Sep 20, 2016
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Minder, bad news man. it does not work like it should. finally got it put together and had a chance to try it. connected to its own 12v power supply (wall plug) put my multi-meter across pin 3 and ground and it pulses the meter. but couldnt really figure out what it was doing this way so I hooked a 12v led strip with 3 led's on it across the output and with the sprocket not moving it pulses the led strip about once per sec.as the speed increase on the sprocket the pulsing of the led's slows down but never become constant on or off. or at least within the speed range im working with on the sprocket. any ideas? thanks
 
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