# Help with proximity sensor in wwtp



## buddhakii (Jan 13, 2011)

I'm working on a wwtp upgrade and they changed out the grit auger which is in a chamber about 20 feet deep. The vendor of the system supplied their own proximity sensor that looks at the auger as it spins and there is also an existing proximity sensor that looks at the teeth of the sprocket up top. Both are hooked up to the same kind of instrinsically safe relay. When the auger turns the existing one toggles the relay on and off as it should because it only picks something up as a tooth of the sprocket passes it. The sensor that looks at the auger though energizes the relay as a vane passes the sensor but the sensor stays energized even after the vain passes and it's looking at nothing. I can de-energize the relay by disconnecting one of the wires to the sensor and it doesn't re-energize until a vain passes and then it stays energized. Wondering if I need some kind of resistor in parallel with it. Contacted the supplier of the equipment and they didn't even really understand what intrinsically safe is. Talked to the engineer and he really didn't even understand the concept of intrinsically safe. So that brings me here for this question. I'm sure one of you industrial wwtp guys can give me some help on this.


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## wildleg (Apr 12, 2009)

sounds like the sensor is "latching". need more info. you sure they didn't give you the wrong sensor.


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## nolabama (Oct 3, 2007)

I hate to ask , but why intrinsically safe in wwtp?


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## buddhakii (Jan 13, 2011)

They classified the entire headworks as a class 1 div. 2 and anything in the channels is class 1 div 1. Pretty common around here. All our lift stations are class 1 div 1. As for the sensor, it was supplied with the new grit auger. The cable on the sensor is definately designed for intrinsically safe wiring. Tried to get more info on it but I'm not even sure the supplier knows what they gave us. But it's up to us to make it work.


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## John (Jan 22, 2007)

nolabama said:


> I hate to ask , but why intrinsically safe in wwtp?


Same idea as conduit seals except that it's for sensors......So a sensor will not make things go boom.


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## nolabama (Oct 3, 2007)

John said:


> Same idea as conduit seals except that it's for sensors......So a sensor will not make things go boom.


I have done an intrinsically safe job at the gasoline plant. I did not know the poo plant used that stuff too.


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## wildleg (Apr 12, 2009)

nolabama said:


> I have done an intrinsically safe job at the gasoline plant. I did not know the poo plant used that stuff too.


put a lighter next to your butt next time you been eating too many beans


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## Jlarson (Jun 28, 2009)

wildleg said:


> need more info.


Agreed, manufacture and model of the ISR's


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## JohnR (Apr 12, 2010)

It certainly sounds as if the sensor is wired with a latching contact or is inherently latching itself. Sounds like the wrong sensor?


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## JRaef (Mar 23, 2009)

Is it working differently than it used to? Or are you just trying to figure it out? The intrinsic safety issue is separate and technically unrelated unless there is a problem with the ISR. 

Usually, these sensors are used to make sure the auger is rotating. The one looking at the teeth is counting them into a PLC or something that is timing them to determine speed. The one looking at the vane blade may just be there as a zero speed detector. It could be that the ISR has an off delay timer built in. When the vane passes, the timer is initiated and changes state immediately. If the vane passes again before the timer times out, The timer stays initiated and indicates no problems. If the auger jams or gets overloaded and slows down, the timer times out and causes the starter to drop out.

They may have both because a sprocket means a chain drive, so if the sprocket sensor is happy but the vane sensor times out, you know you have a broken chain.


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## Jabberwoky (Sep 2, 2012)

I just ran into a similar problem a couple weeks ago. Come to find out the ground on the prox we were using was bad. Some proxes use case ground as a discharge path. Well after a technician kept replacing a prox with two others with bad grounds I showed him the discharge path on the prox's data sheet. If it is a three pin or more then I would verfiy the ground pin is actually getting grounded. The time it would take the charge to leak to ground is probably significantly longer than the time between fins of the auger.

The discharge time on our prox was more than a minute with a bad ground.


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## buddhakii (Jan 13, 2011)

As far as I know the prox is all plastic. And to answer your questions JRaef the relay doesn't have an off delay timer in it. I installed two relays exactly the same with one going to the sprocket and the other to the auger. The one for the sprocket toggles on and off as it should but the one for the auger just stays on. And yes, that is exactly what it is for. A couple years back I guess their chain broke and no one new about it for a couple of days and they ended up with grit backing up. Like I said this sensor was supplied with the auger and it's looks a little different than the existing one looking at the sprocket.


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## ace24wright (Jul 10, 2012)

Is there a sensitivity adjustment on the sensor?


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## buddhakii (Jan 13, 2011)

There is no sensitivity adjustment. It actually has to be within about a 1/4 of an inch of the material you are monitoring. As for the ISR, I'm not sure the model number but it is a Turck. The only settings on it is three dip switches on the front to monitor for open circuit, short circuit, and NO or NC. Doesn't matter what position dip switches are in as far a changing how this thing is not working properly.


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## ace24wright (Jul 10, 2012)

I would change it


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## MDShunk (Jan 7, 2007)

Scrap the sensors and monitor it with a current transducer or monitor that parameter in the VFD.


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## buddhakii (Jan 13, 2011)

Unfortunately it's not my decision to scrap the sensor. Sounds like it's either I make this one work or they go back to the original design that has a stainless steal rod going down to a cam on the end of the auger and put the original sensor that was submitted looking at the top of the rod. Piss poor design if you ask me. I would be very surprised if there was no way to make this one work somehow. I'm sure the supplier of this equipment has used it before. They just need to tell me what I need to make it work.


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## SCG (Oct 28, 2012)

buddhakii said:


> Unfortunately it's not my decision to scrap the sensor. Sounds like it's either I make this one work or they go back to the original design that has a stainless steal rod going down to a cam on the end of the auger and put the original sensor that was submitted looking at the top of the rod. Piss poor design if you ask me. I would be very surprised if there was no way to make this one work somehow. I'm sure the supplier of this equipment has used it before. They just need to tell me what I need to make it work.


 Did you get the turd mixer working?


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## buddhakii (Jan 13, 2011)

Yes it's working. The proximity sensor is not working at this time though. Still waiting on the solution.


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## LogixElectrician84 (Dec 7, 2012)

buddhakii said:


> I'm working on a wwtp upgrade and they changed out the grit auger which is in a chamber about 20 feet deep. The vendor of the system supplied their own proximity sensor that looks at the auger as it spins and there is also an existing proximity sensor that looks at the teeth of the sprocket up top. Both are hooked up to the same kind of instrinsically safe relay. When the auger turns the existing one toggles the relay on and off as it should because it only picks something up as a tooth of the sprocket passes it. The sensor that looks at the auger though energizes the relay as a vane passes the sensor but the sensor stays energized even after the vain passes and it's looking at nothing. I can de-energize the relay by disconnecting one of the wires to the sensor and it doesn't re-energize until a vain passes and then it stays energized. Wondering if I need some kind of resistor in parallel with it. Contacted the supplier of the equipment and they didn't even really understand what intrinsically safe is. Talked to the engineer and he really didn't even understand the concept of intrinsically safe. So that brings me here for this question. I'm sure one of you industrial wwtp guys can give me some help on this.


Hi buddhakii,

I'm not sure if you're still working on this, but I wanted to find out more out of curiousity. As another member asked earlier, do you have the manufacturer part numbers for the relays and sensors? Is this a two wire or three wire sensor? Also, out of curiousity, do you have a copy of the PLC program for this device (if it's PLC controlled)?

I am guessing that if it is two wire, it is leaking enough and latching on after it picks up a vane and not unlatching after the vane passes. Possibly not anything simple like debris stuck to the head? Just having a copy of the program would also help to understand the operational logic behind it.

Also, I like the idea of possibly trying a resistor in parallel, BUT, am not sure if this is a good idea to void the Intrinsically safe rating of the sensor?

What kind of prox switch is this? Inductive I assume? The more info the better, I would enjoy finding out the what the solution is to this.


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## buddhakii (Jan 13, 2011)

LogixElectrician84 said:


> Hi buddhakii,
> 
> I'm not sure if you're still working on this, but I wanted to find out more out of curiousity. As another member asked earlier, do you have the manufacturer part numbers for the relays and sensors? Is this a two wire or three wire sensor? Also, out of curiousity, do you have a copy of the PLC program for this device (if it's PLC controlled)?
> 
> ...


I tried to find the part # for the sensor but no one can seem to come up with one. I don't have a copy of the program but if I understand it correctly it is a discreet input into the plc from the iso. relay from N.C. contacts. The plc looks for a pulsed siglnal from the relay and if it doesn't see a pulsed signal in a certain amount of time it shuts the motor down and sends an alarm. As far as the kind of prox switch it is I couldn't even tell you that. It looks magnetic to me but don't know for sure. I tried to get more info on it but at this point I am just leaving it up to the engineer. I know the engineer and GC are in a bit of a battle over the whole thing on how they are going to make it right and this is a battle I am staying out of. Wish I could give you more info but at this point I am pretty much done with it. I've already spent too much time on a design flaw that needs a design fix and I am not a designer.


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## LogixElectrician84 (Dec 7, 2012)

buddhakii said:


> I tried to find the part # for the sensor but no one can seem to come up with one. I don't have a copy of the program but if I understand it correctly it is a discreet input into the plc from the iso. relay from N.C. contacts. The plc looks for a pulsed siglnal from the relay and if it doesn't see a pulsed signal in a certain amount of time it shuts the motor down and sends an alarm. As far as the kind of prox switch it is I couldn't even tell you that. It looks magnetic to me but don't know for sure. I tried to get more info on it but at this point I am just leaving it up to the engineer. I know the engineer and GC are in a bit of a battle over the whole thing on how they are going to make it right and this is a battle I am staying out of. Wish I could give you more info but at this point I am pretty much done with it. I've already spent too much time on a design flaw that needs a design fix and I am not a designer.


Hahaha, okay, I guess sometimes people get stuck in the middle of bad decisions. Thanks for the response though.


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## Netree (Sep 3, 2011)

Could there be a protrusion issue with this new sensor? Some for example cannot be flush-mounted in metal because the sides of the sensor will pick up the surrounding metal as well. Is it possible to observe the state of the sensor as you slowly put it in place?

Is the sensor of the wrong type? NPN vs PNP? Many questions yet need answers.


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## buddhakii (Jan 13, 2011)

Old thread but still an ongoing issue. I guess I do have to be the design team on this one. So I found a rotational speed monitor that seems like it will work. It is a turck mk21-122. I hooked this up at the beginning of all this and it seemed like it would have worked, but after asking my pm to do a little research to see if it was rated to be in a class 1 div 2 area he came back and said no, rip it out, the engineer will figure it out. Well, now that that pos pm quit I did my own research and found that this apparatus is rated for the area. The only problem I'm having is figuring out exactly how to program it. This auger runs on a timed mode and when it runs the plc wants to see an input to know that the auger is turning. If it is not turning it should send an alarm so someone has to come check it. This thing seems to have all sorts of functions but I don't think I need to worry about a lot of them. Cmon Jraef, I need your help on this one buddy


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## Jlarson (Jun 28, 2009)

Does it have an underspeed set point? Set that, when the auger is not turning the monitor will be outputting an alarm with whatever output the thing has to the PLC, if the PLC is calling for the auger and the alarm from the monitor is still true it isn't turning. Not perfect but ok.


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## sparkywannabee (Jan 29, 2013)

The sensor they supplied you with is the best design for this kind of setup, you really need to get the make and part# from the supplier, find the manual online, when you say dip switches are for open/short circuit, what does that mean. I have come across sensors that have a time delay depending on how you use those switches. If you have a scope, the signal wire should have a sq. wave or pretty close to it, and this should drop out when the sensor sees nothing. If you had npn or pnp mixed up, it should'nt work at all. Good luck.


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