Temperature control switch

Discussion in 'The Projects Forum' started by Bigcountry, Aug 15, 2010.

  1. Bigcountry

    Thread Starter Active Member

    Jul 4, 2008
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    I think doing this project I have learned more than I ever learned in college. But I am getting there. So far I learned a lot but still have more to learn. Plus this is fun for me.

    I have found the temperature control switch.

    http://www.mtmscientific.com/tempkit.html

    I am wondering how I can make it programmable. I am trying to set or vary the temperature in pipe of water. I am already controlling the water flow in by other valves. But when the water reaches lets say 95 degree F ( + -2 degrees F). I want the circuit to open the valve. I was trying to figure out how I could sent this information back to my PLC. Or would I just have to keep this separated? i found a valve that will actually do this without all the circuits from Johnson Controls but it is $280. So I am working on new route.
    I think I am going in the right direction just need little guidance to keep me straight. thanks for all the help.
     
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
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    How big of a pipe does the valve go on? JCI is expensive on a lot of items that can be replaced with alternates.

    I monitor and switch a lot of things on our systems with a simple temp control circuit built using an LM335 temeprature sensor IC but you may want to look into these from (you guessed it) JCI. You can find them for around $55, often locally or on eBay or Amazon.

    http://cgproducts.johnsoncontrols.com/MET_PDF/125188.PDF

    It's got totally open relay contact outputs so you could rig up about any interface circuitry you wanted, alternately you can use the method I use in some situations by hooking one of these up to an op amp circuit: http://www.st.com/stonline/books/pdf/docs/2158.pdf

    I've buried them in thermo-wells or attached them directly to fittings using MasterBond thermally (but not electrically) conductive epoxy, they make some really good stuff. Top that off with some insulation and you can get some fairly accurate readings.
     
  3. Bigcountry

    Thread Starter Active Member

    Jul 4, 2008
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    The pipe is small only around .5 inch. I do like the A419. It seems to fit its purpose in my project. But what I am suppose to do. Just drill a hole in the pipe and seal the probe in the pipe. I could make the part of the pipe larger. I found a lot of different temp controls on ebay. thank you. But I was looking for a digital one of some sort. I was thinking maybe a hot tub would have some controls that might fit my needs. Do you know anything about them?
     
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
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    I know that you won't find anything cheaper than the 419 for all the features it offers. I've found them to be quite accurate and quite frankly don't know how they can sell them for that low of a price.

    Prices do vary, I bought my last one from a large industrial HVAC supplier. Sometimes they're cheap on eBay or Amazon but sometimes not as they've become the "in thing" for controlling home built wine coolers and greenhouse fans.

    If the pipe is easy to separate and not operating under much pressure just put a tee into it and epoxy the sensor into that. If you don't want to disturb the pipe simply attach it with some thermally conductive epoxy or smear on a glob of heat transfer compound and wrap it closely in contact to the pipe with tape, then insulate the area all around it. Despite what you think, if properly insulated you'll get a pretty accurate reading of the temp of what's flowing through the pipe.

    Probably the best tape to use would be that nasty pure rubber Scotch electrical tape that bonds to itself, it's also sold as a pipe sealing tape for small leaks. Home Depot carries both types.
     
  5. Bigcountry

    Thread Starter Active Member

    Jul 4, 2008
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    Wow! That is some good information. I hadn't thought about the tee to put in it. That also gives me another idea for something else. Thank you.

    http://www.pexsupply.com/Johnson-Co...age-Digital-Temperature-Control-120-240v-SPDT

    I found one there for 55 dollars. I am pretty sold on that now. You are right that is cheap for the all it can do. It is funny you put that in there about it being on the outside of the pipe would be accurate readings of what is in the pipe. I wouldn't think it would be that close but then again if it is was well insulated that would sure do the trick.

    I think my project is coming together. Now all I need is a vacuum pump that will pump some liquid soap. any suggestion? I found some but they either too small or too big but then again I haven't had any experience with vacuum pumps. I just need to pump some liquid soap about 3 or 4 feet. It needs to be able to turn it on via PLC.

    This one seems like it will work but it is still in development stages.

    http://www.dynaflopumps.com/products/4122x.html

    At the same time I will be sure to get one that pumps fast enough because of the viscosity of liquid soap is different.

    Thanks again for all your help. I feel like I am light years ahead now.
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    You may need a more positive displacement type pump that still gives a predictable flow - http://en.wikipedia.org/wiki/Peristaltic_pump
     
  7. marshallf3

    Well-Known Member

    Jul 26, 2010
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    You won't even have to pay shipping if you can find it locally but then theres the tax ....

    Vacuum pumps abound. I've seen some that work by blowing air pressure across an orifice to create a vacuum.
    http://www.harborfreight.com/air-vacuum-pump-with-r134a-and-r12-connectors-96677.html

    I've seen people modify those cheap tire inflator compressors from Harbor Freight. Depending on how often you need to do this you could even set up a 5 gallon plastic water bottle full of water with a drain on the bottom, as the water flows out it creates a vacuum at the top.

    Here's where it will pay to do a little math - how much does X square feet of water weigh and what amount of vacuum will it take to move it up Y feet? Don't be surprised if it turns out to be a higher number than you think.

    A shop vac will work to some extent, Harbor Freight sells electric drill driven or self-powered plastic pumps that will draw a vacuum. This one will pull 10' if it's primed but that might defeat your purpose: http://www.harborfreight.com/1-inch-clear-water-pump-1479.html

    If it has to pull fast you're looking at some $ outlay. If it can be a slowly building vacuum even the compressor salvaged from an old refrigerator will work.
     
  8. Bigcountry

    Thread Starter Active Member

    Jul 4, 2008
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    I am stuck on doing the math. But while I was trying to figure out the math I did take the liberty to look up those positive displacement pumps. This is what I finally found.

    http://www.welco.net/wp10a_e.html

    Then I did the ebay trick and came up with this.

    http://cgi.ebay.com/Welco-F1-8M2-G-...-Pump-/130415991425?pt=BI_Pumps#ht_4743wt_911

    I read from another website that this guy tried to order one straight from Welco and they said they don't just sell one. But they cost $25 for 100 of them.
    But the one on ebay doesn't tell if it is DC or AC.
    I emailed them on ebay about the specs about it. I hope they send some good news.
     
  9. marshallf3

    Well-Known Member

    Jul 26, 2010
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    I've got a bunch of those at work, they're used to inject the treatment chemicals into the chilled and tower water of the HVAC system.

    They work well but aren't capable of any sort of high volume flow rate. You might be able to find a used or resonably prced one at a large HVAC supplier or a firm that repairs chilled water HVAC systems and, in actuality, you could just as easily build one since the principle is so simple. In doing so you could use larger tubing and increase the capabilities. Hospitals use them all the time too as infusion pumps and there might be a surplus place somewhere around you that has a pile of them.

    Ages, and I mean ages ago we had what we simply called "the dump" out in Wheatland, a one street town not far from here. This guy would go to FAA and other government auctions and bring back trailers full of the most interesting and unique items you ever saw. You could spend all day out there, cut precision parts out of old equipment, gather up new in box mil-spec tubes and all sorts of new parts then take a couple of grocery sacks full up to him. Sitting on his porch in a rocking chair he'd gaze into the bags and say $5.

    What often amazed me was the way the military packages things. I ws digging through a huge bin of stuff and pulled out a metal can about the size frozen OJ comes in. It had a really long part # onit but nothing else and not having a way to open the can I just tossed it into one of my bags. When I got home a can opener revealed a foil lined padded bag. Opening that found the next layer to be heavil waxed paper and inside that yet another sealed foil bag. When I finally got to the core there was a small plastic tube with a screw on lid, inside that more wxed paper and another foil bag which contained - get this - one single screw and the final wrapping was lableled with a ton of numbers and the words screw, eyeglass, stainless steel 304. Not only was the packaging more extreme than you could imagine but for a common screw?
     
  10. Bigcountry

    Thread Starter Active Member

    Jul 4, 2008
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    Thanks I am going to look for one off a HVAC site now.

    I was in the military for 7 and half years. Marines and Army. When you told that story that reminded me of one myself.

    I was over at the dental clinc about to get my some work done and this trucking carry a huge crate pulled up and they had to off load it with a fork lift ( those huge fork lifts) then four or five Marines came and begin opening this big wooden crate. inside it was filled up with foam popcorn. I waited around to see what was going to come out of it. I thought it was some super secret device Out came another crate and inside that crate was well if you said a crate you right. Then inside that crate was a box. They opened the box and pulled out this monitor and a women came out and picked it up and carried it inside.
    I think sometimes they take the military grade and specs to some extremes. Is all that necessary for screw ? maybe one that went on Tomahawk missile or ICBM.
    I will have to start looking for a pump now.
     
  11. Bigcountry

    Thread Starter Active Member

    Jul 4, 2008
    71
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