# Looking for instrumentation reccomendations



## MWayne (Nov 8, 2010)

We are going to put the elevation of this sluice gate on SCADA and we're leaning toward some kind of radar. I don't have any experience with this specific application, the kind I've been involved with are for liquid level measurement in enclosed tanks. 









Another idea is to use some sort of encoder working off the small cable at the very edge of the gate, this cable goes up overhead to a pulley and is kept taut by a weight.
I would really appreciate hearing what y'all use in these kind of situations and how well it works (or doesn't).


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## bigdan1 (Jun 16, 2013)

Just a thought, but I have used magnets mounted on a sheet metal strip with a sensor mounted on the inside or out side of the door where ever works for your application with success. Similar to the ones you come across in elevator shafts. I am not exactly sure if this will work for this application, but may be worth looking into. It has been useful in managing heights of platforms, leveling, and very useful when trying to count operations at differing levels.


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## ScooterMcGavin (Jan 24, 2011)

I suppose you might be able to train a non-contact radar to track the gate, perhaps if you added a target to it or something. Never tries it for something like this. Also you could probably adapt a tape float transmitter to work on the gate. Thirdly, we had a conveyor that we needed to track the position of and we just ran a bolt through the shaft and mounted an inductive proximity sensor and used it as an encoder. Works really hood unless the bolt gets loose and breaks the sensor off.


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## Jlarson (Jun 28, 2009)

String potentiometer. Sorta like your cable idea but already built and ready to go.


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## ShaneDugas (Apr 24, 2010)

Good application for a string pot actually.

You could do a radar based level detector (Vega, etc)tuned for solids but that is likely to be the most expensive alternative. Another alternative that might work for your application is laser measurement. Something like http://www.astech.de/en/products-home/velocity-and-length-sensors-vlm/vlm320.html

Not sure what the rest of your setup looks like but most of those models have the ability to do 4-20 out so it could be interfaced to whatever controller you are using.

Only experience I have is with a similar unit used for velocity measurements, at much closer distances, several years ago.


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## varmit (Apr 19, 2009)

There are scale tapes (linear encoders) that are used on large machine tools. These consist of a sensing strip that is mounted to the stationary side of the equipment and an electronic sensor/transmitter that mounts to the moving piece. The mounting positions could be swapped if it would suit the application better so as not to need a traveling cable. i can't remember a brand, but will check if you are interested. These were not terribly expensive.


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## BT Electric (Feb 7, 2014)

Check out Magnescale (www.mgscale.com) we use them on the machinery where I work to measure position of tooling. They are very rugged and accurate and rarely give any problems. I have only had to cycle power on one of the units to reset it once in the past 2 years. They have all kinds of solutions for most any kind of application.


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## JRaef (Mar 23, 2009)

The biggest challenge in this application is going to be weather exposure. Most of the things that work great on machine tools will not be able to survive long when exposed to weather. Been there, done that. Cable pot with a SS cable is what you will end up with after a few failures anyway, just start there and do it once. The only ultrasonic sensor application I had any success with on a weir gate was a wave guided radar sensor, where the radar signal was confined to a tube and I could rig a system in which the target could move with the gate height inside the tube. But I was only able to do it because I had enough height below the tube to make a rod rise inside of it with the gate. That's unusual.

Tried it with magnetostrictive position indicators and absolute encoders, they don't survive outdoors for long. If you don't need extreme accuracy and are handy with a welder, you could attach a gear to the counterweight pulley and use an inductive prox to count pulses. The problem with this is that it is not an absolute position indicator, in that it never knows where it is after a power failure. So you either have to home it by running all the way closed after every power failure, then back to position, or you still need an analog sensor, which is back to square one. I did one for an irrigation ditch weir gate where they didn't mind closing it after every power failure, that was a cheap way out. But a lot of applications can't have that happen because it causes other problems.


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## MWayne (Nov 8, 2010)

JRaef,
I agree about the weather issue but was hoping to avoid moving parts altogether. A salesman was telling me about a radar system that uses a radar equivalent of an optical retro reflector target. Where the system "sees" the reflector and is able to accurately measure without the tube and target you described. We may have to be the Guinea pigs to find out if that new technology stand the test of time.


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## Nuzzie (Jan 11, 2012)

We use cable encoders on our gates. Reliable and survive in the weather.


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## MWayne (Nov 8, 2010)

Nuzzie said:


> We use cable encoders on our gates. Reliable and survive in the weather.


Do you have manufacturer info (model number etc.)?


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## sparky970 (Mar 19, 2008)

*Pepperl Fuchs. http://www.pepperl-fuchs.com/global/en/classid_364.htm?view=productgroupoverview*


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## oliquir (Jan 13, 2011)

there is also laser sensor that works great


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## MWayne (Nov 8, 2010)

oliquir said:


> there is also laser sensor that works great


Do you have a link to product?


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## JRaef (Mar 23, 2009)

oliquir said:


> there is also laser sensor that works great


My attempts at using laser or infra-red analog distance transducers outside exposed to weather is that eventually, a film builds up on the lens and causes it to fail. Some better ones offer what is called Automatic Gain Control that pumps up the energy level of the beam as that film develops, which helps to forestall the inevitable but not stop it. So if you go that route, you have to add a maintenance routine that has someone clean the lens. I have found that to always end up getting forgotten in short order as staff are cut back, reassigned etc.

My personal experience with P+F is not great, I never consider them any more. Difficult to understand the "Frenglish" instructions, then I have seen a high failure rate and poor customer service. YMMV.


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## JRaef (Mar 23, 2009)

I've used these string pots from BEI, very reliable. They use a nylon coated SS cable that holds up better than any others I had used. Not the cheapest, but you only do it once. The point I was making on all of this was that it's the call-backs that kill you. These things are never located close to home, you only want to go there when getting paid.

http://www.beisensors.com/draw-wire-sensor-transducer.html

Who is the radar sensor vendor?


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## MWayne (Nov 8, 2010)

JRaef said:


> Who is the radar sensor vendor?


 Hycontrol, I'll try to put up a link to their product brochure later.

http://www.hycontrol.com/level-measurement/products/level-measurement


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## IP-EI (Apr 7, 2014)

Go with a string pot. I use them for position indication on all the agitator rakes at my facility (rakes are raised and lowered according to torque). They last a very long time, they can handle bad weather and all the lime and H2S in the air here, where most things cannot. It's gonna be your best bet.


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## Big John (May 23, 2010)

I'll jump on the linear-encoder bandwagon, that seems to be very popular for gate position sensing, and I've used it successfully a bunch of times.

That said, on a gate with a really long travel where it gets difficult to install linear actuators, or on a gate where there's any risk of debris over-topping or ice interfering with the encoder, I'd use a rotary limit switch on the cable winch. Unlike a rotary encoder, these things are beefy as hell: Line power rated harsh-environment switches. Get a NEMA 4X and you'll be in like Flynn.


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## denny3992 (Jul 12, 2010)

Awesome ideas... I guess im spolied that All, i mean ALL of our gates have rotork mov's....Analog in and out and im done...

Older ones have cams for 0-25-50-75-100%

We have Lots of wwtp experience here guys... Nice to hear diff ways!


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## KennyW (Aug 31, 2013)

Absolute multi-turn rotary encoder coupled to one of the sheaves on that cable would be what I'd be looking at, like your original post. We mount these on winch drums for shiploaders and cranes all the time. 

Honestly though while I guess you'd need to clean it eventually, we also use "Sick" Distance measuring lasers in pretty dusty environments with pretty good success. 

What sort of PLC would it be going back to?


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## MWayne (Nov 8, 2010)

Big John said:


> I'd use a rotary limit switch on the cable winch. Unlike a rotary encoder, these things are beefy as hell: Line power rated harsh-environment switches. Get a NEMA 4X and you'll be in like Flynn.


 Do you have a link to these? Can they be set up to mark every half foot?
Edit: found one that had up to 40 contacts available, I couldn't figure out if they could be set up to where when the gate rose a half foot the first contact would close at one foot the second contact would close at a foot and a half the third contact would close etc. until eight feet and sixteen contacts closed. And on the gates way down the contacts would open in reverse order, like a mechanical absolute encoder.


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## MWayne (Nov 8, 2010)

KennyW said:


> Absolute multi-turn rotary encoder coupled to one of the sheaves on that cable would be what I'd be looking at, What sort of PLC would it be going back to?


Do you have a link for the encoders you use? Most of our PLCs are Modicon Quantums, we have a few Premiums, overheard that going forward we may start using Modicon M-580s.


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## don_resqcapt19 (Jul 18, 2010)

I was at the Sensors Show in Chicago yesterday, and DimetixUSA was showing a laser level transmitter for this exact application. I think it was the FLS series. The vendor rep said one of the applications they have been selling it for is the water control slide gate on a small hydro plant.


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