# Need help finding sensor



## CFL (Jan 28, 2009)

I need a way to sense when a rotating drum has stopped rotating. The drum contains a slurry mix that will harden if it's not continously mixed. The sensor or other device is just going to control a stobe light above the drum to alert the operator.

I was thinking of using a pulse generator on the shaft below the drum to signal a plc. There are several drums for 1 robot station and there are several robots in all. I would like to things simple and cost efficient. Thanks in advance.


----------



## MDShunk (Jan 7, 2007)

Do you already have a PLC? 

If not, I've used a delay timer that gets pulses from a 120V photoreflective sensor recently, for that purpose. The sensor cycled the power on and off to the delay timer. If the sensor stayed made, the timer would cycle through the time period, and the contacts would switch condition. 

In my case, this was for the outfeed conveyor out of a packaging machine. If the conveyor was full, it would stop the packaging machine and keep it from jamming up. If the conveyor's sensor saw a continuous flow of packages (pulses from the sensor), the timer would not make and the packaging machine kept running. If the sensor stayed made (package in front of sensor, meaning full conveyor), the packaging machine would shut down. 

In your case, I'd put a bolt or something sticking out of a portion of the agitator mixer shaft, coupler, or gearbox and use a prox switch to sense the bolt head passing. If the prox switch does not make at least one time every certain time period (or stayed made, in case the agitator stopped when the bolt was over the prox), some output gets set on the PLC. Pretty simple to accomplish, actually. You could do this with timers and relays too, if you don't already have a PLC or spare I/O points on your PLC.

I'm not so sure I like your encoder idea, mostly due to cost. Make your own "pulse generator" from a bolt and a prox. 

Get on Banner or Turck's website for sensor selection. There's a million of them that will do the trick. Banner has interactive sensor tutorials on their site.


----------



## MDShunk (Jan 7, 2007)

A little more dirty way to do this is with a current sensing relay. Assuming that the tank of product causes the motor to draw more current than the motor running with no product, a current sensing relay would work also. If the motor stopped, shaft coupler broke, belt broke, etc, the contacts on the current sensing relay would switch condition. You just "dial in" the current that the motor normally draws when mixing product, and anything less than that will make the contacts switch. This is a bit "dirty" because the motor spinning the empty drum might draw too close to the same amount of current as a drum with product in it, so it might not work. You'll have to pull some amp draws to check.

Maybe your beacon is just to assure that no one intentionally shut off the motor or that the motor didn't trip a breaker? If so, the current sensing relay is probably your easiest and most economical solution to turning on a beacon.


----------



## John Valdes (May 17, 2007)

Take a look at this. http://www.speedswitch.com/
You could put the motor starter interlock (contact) in parallel with one of the contacts provided on this rotation control to signal the operator if required.

Marcs suggestion no doubt will cost less. Why not call one of your suppliers and get another opinion? That is what I would do today. Good luck.


----------



## B4T (Feb 10, 2009)

Marc.. you have to be the "MacGyver" of the electrical world.

You always find some way of fixing a problem that many of us have to ask.. What? :blink:

I personally would walk away from most of the stuff you take on because it is not in my "skills" department.

Sure I could figure it out in time, but I could never make money doing it, and that is the goal.


----------



## CFL (Jan 28, 2009)

MDShunk said:


> Do you already have a PLC?
> 
> If not, I've used a delay timer that gets pulses from a 120V photoreflective sensor recently, for that purpose. The sensor cycled the power on and off to the delay timer. If the sensor stayed made, the timer would cycle through the time period, and the contacts would switch condition.
> 
> ...


Thanks Marc, I think that's just the solution I was looking for. I do already have the PLC as well as a good selection of prox. sensors. Your other idea, with the current sensor, I also like. I have those in stock as well (don't know why), and the drums are always kept full so amperage should be consistent. They are controlled by VFD's and I was originally hoping to use those to monitor amperage, but I don't believe they have that feature(broken belt). Thanks again.:thumbsup:


----------



## CFL (Jan 28, 2009)

John Valdes said:


> Take a look at this. http://www.speedswitch.com/
> You could put the motor starter interlock (contact) in parallel with one of the contacts provided on this rotation control to signal the operator if required.
> 
> Marcs suggestion no doubt will cost less. Why not call one of your suppliers and get another opinion? That is what I would do today. Good luck.


Thanks John. That is exactly what I would like to use. I reread Marc's post and realize this is what he was referring to. I'm anxious to get a price on one, but worst case I'll use Marc's solution of timer relays.


----------



## John Valdes (May 17, 2007)

CFL said:


> Thanks John. That is exactly what I would like to use. I reread Marc's post and realize this is what he was referring to. I'm anxious to get a price on one, but worst case I'll use Marc's solution of timer relays.


This suggestion IMO is the fastest and easiest way to accomplish your task. It is specifically designed for the purpose. Please let us know what the price is. I have no idea.


----------



## MDShunk (Jan 7, 2007)

John Valdes said:


> This suggestion IMO is the fastest and easiest way to accomplish your task. It is specifically designed for the purpose. Please let us know what the price is. I have no idea.


$650 up to a couple thousand.


----------



## TheRick (Apr 13, 2008)

I have used these in the past, they are easy to set up and work great!


----------



## CFL (Jan 28, 2009)

TheRick said:


> I have used these in the past, they are easy to set up and work great!


Do you remember what you paid for them? I had no time today to call suppliers, too many emergencies. $650 is probably out of the price range if I can accomplish the same thing using a timer and relay (as mentioned in MDShunk's post). I will need to install about 30 in all. 

I know it's difficult to say with the limited info I've given, but can anyone give me good reasons to justify going with the purpose built zero speed switch. This is a learning experience for me. This is not a safety issue, but they do stand to lose alot in downtime, labor and damage to equipment.

Thanks guys for all the responses.


----------



## Mr.C (Dec 20, 2009)

You say you got 30 of these to install, and you are using VFD's and a PLC hooked up to them already or you have the PLC laying around not hooked up yet? There has got to be one drive running dry contact on these VFD's somewhere what are the make and model of the drives?


----------



## TheRick (Apr 13, 2008)

CFL said:


> Do you remember what you paid for them?


 
It's been a couple of years since I put one in, but I want to say around $300


----------



## CFL (Jan 28, 2009)

Mr.C said:


> You say you got 30 of these to install, and you are using VFD's and a PLC hooked up to them already or you have the PLC laying around not hooked up yet? There has got to be one drive running dry contact on these VFD's somewhere what are the make and model of the drives?


I'm sorry, I don't understand what you mean by drive running dry contact. This system is all up and running and I am now adding this in. This facility has to stay running 24/7 so I'm only able to do things one step at a time. It's pretty much design as you go. The VFD's are Motortronics, VCM series. There is a robot controller that controls the VFD's.


----------



## John (Jan 22, 2007)

Something along the lines of what john was talking about is a speed sensing switch that is mounted to the shaft, motor that needs to be monitored. I have use an AB speed switch for plugging motors and also to sense when a machine has come to a stop. An example that I did a while ago was to sense when the commercial washing machine (very large!) was stopped. The door was interlocked to stay shut until the drum had stopped rotating for safety reasons.

http://www.torq.com/ESSspeedswitch.htm


----------



## CFL (Jan 28, 2009)

John said:


> Something along the lines of what john was talking about is a speed sensing switch that is mounted to the shaft, motor that needs to be monitored. I have use an AB speed switch for plugging motors and also to sense when a machine has come to a stop. An example that I did a while ago was to sense when the commercial washing machine (very large!) was stopped. The door was interlocked to stay shut until the drum had stopped rotating for safety reasons.
> 
> http://www.torq.com/ESSspeedswitch.htm


In your case I can see using a purpose built device for safety reasons. A homemade solution wouldn't fly. In my case safety is not our concern so I'm not convinced that I should use a speed switch. I'm going to make calls first thing this morning and I'll post the prices for anyone who cares.


----------



## Introyble (Jul 10, 2010)

Positional transducer , abosolute rotational sensor, or even an encoder.

You can get any with digital or analog input/outputs.

Program a plc or a red lion process control meter. Maybe the red lion CUB5 would work (going from memory). You can visit red lion to look up the exact controller you need.


----------



## John (Jan 22, 2007)

CFL said:


> In your case I can see using a purpose built device for safety reasons. A homemade solution wouldn't fly. In my case safety is not our concern so I'm not convinced that I should use a speed switch. I'm going to make calls first thing this morning and I'll post the prices for anyone who cares.


It's called ROI.....Cost of sensor versis the cost of product/production lost. :whistling2:
Say if the sensor installed costs $300 and the potential loss of product or production costs $1,000. It would not take to much to get this type of a project on the fast track with this type of a scenario. Bean counters and production people just love these types of numbers.


----------



## John Valdes (May 17, 2007)

John said:


> It's called ROI.....Cost of sensor versis the cost of product/production lost. :whistling2:
> Say if the sensor installed costs $300 and the potential loss of product or production costs $1,000. It would not take to much to get this type of a project on the fast track with this type of a scenario. Bean counters and production people just love these types of numbers.


I am in agreement with John here. How important is your process to your bottom line? There are many options and we have provided some for you. Call the salesman. (motor shop, drive guy, supply guy ect...) He would love a reason to visit.


----------



## John (Jan 22, 2007)

Old technology from Allen Bradley, simple and tried and true. There is also a lockout soleniod for the switch and the price is going to be around what Marc said.....

http://www.ab.com/conditionsensing/speed/808.html

I have always called a motor plugging switch...........


----------



## CFL (Jan 28, 2009)

My supply guy never found anything for me, but I did talk to a local company that has what looks likes a decent speed switch. Their switch is $250 and will do what I need it to do. However, the plant electrician has decided to go a different route and use a limit switch held open by the current of the liquid. As usual he is totally opposed to any of my suggestions. He always wants a "simple" solution to everything which sometimes turns out being more complicated. I also have to try to keep things as cheap as possible. In this case the speed switch is $250, and his limit switch was $280! But it was his idea so it wins. The switch company is Phares Electronics. I think it's a new company and still small, and the switch is not UL listed.

Thanks for all yall's help. Feel free to give your 2 cents on this limit switch idea, keeping in mind that it's a slurry mix which builds up and hardens.


----------

