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  1. #1
    Moderator ShipWreck's Avatar
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    4-20ma Temperature Sensor

    Okay, so I have built my new heat exchanger, I have a PLC running my system but I don't have a temperature probe and electronic design is not my area.

    So if someone could help me design a circuit I would be very happy. Basically I need a circuit that I can provide 24vDC to and have it return a 4-20ma signal that would ideally represent 60-90 deg F. I can design the circuit board layout and have it built just need to know what to put on and what components to use.

    I am not concerned with the type of sensor used but would like something fairly accurate. My plan was to either epoxy coat the sensor and mount the board in a box or if the sensor is board mount then to epoxy coat the entire board and just have a set of leads from it.

    Thanks for any help.
    Rob
    -----
    Upgrade in the works! Keep looking for an update.


  2. #2
    ijo
    ijo is offline
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    Sounds like a cool project!!!

  3. #3
    Senior Member solowma's Avatar
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    I can get sensors that run both in dc and ac. I think your best bet would be a wrap around RTD style sensor. I prefer thermistor style myself because they tend to be more accurate and less chance of failure. These sensors could wrap around your pipe to the sump or back from it so you can see what your supply and return to the sump is. Now, I have access to a several types of control boards that could be programmed. It needs 24vac, can provide 0-5, 0-10vdc, 4-20ma. The 24ac is just a plug in transformer. 15 to 30 va. I can get you triac contacts or 24vac outputs. You name, I can probably do it for you.
    We could even program it to modulate an analog valve to maintain the temp in your sump. Average the sump temp and display tank temp together.
    Let me know if you would like some help. We can come up with something wild or mild. Oh and reliable too.
    Oh, what kind of PLC did you use?
    150 (reef) 56 (FOWLR)
    75 gal sump 25 gal refuge
    300lbs CaribSea Aragonite Reef Sand
    280 lbs of Assorted rock
    Tunze 9010 skimmer, Current USA 48" Fixture
    1 cleaner shrimp, pistol shrimp
    50 blue legged hermit, 15 nausaurus/astrea snails
    Yellow tang, 2 clowns, 1 blue chromis, 1 yellow watchman 1 corral beauty
    Colt coral, Frogspawn, Bubble, Donut coral, Mushrooms,Starburst green, Green and orange polyps an Umbrella coral, Purple Long Tentacle Anemone.

  4. #4
    Moderator ShipWreck's Avatar
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    Those sensors and boards sound very interesting. Do you have any links with more details on them?

    I don't think I need the valve to modulate as I plan on doing that within the PLC. I plan on controlling the hot water pump on/off while leaving the tank water pump running continuous but can turn it off in case of emergency.

    I am using a Siemens 227XM PLC and a TP270 HMI, that I got free from work :b6:. I program PLC's for a living so that side is no problem, it is just the electronics side.
    Rob
    -----
    Upgrade in the works! Keep looking for an update.


  5. #5
    Senior Member solowma's Avatar
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    I usually use alerton controllers. Just look up alerton. But I can get invensys, andover, novar etc etc etc. The list is almost endless. The controller you are using will do the same job as the alerton.
    As for the sensor, a greystone or general eastern pipe wrap sensor would be the best for your application. Don't need to build a circuit board, comes premade and can even get submersible.
    PM me if you are interested. Look up general eastern or greystone sensor, pick one out and I will get it at my price.
    150 (reef) 56 (FOWLR)
    75 gal sump 25 gal refuge
    300lbs CaribSea Aragonite Reef Sand
    280 lbs of Assorted rock
    Tunze 9010 skimmer, Current USA 48" Fixture
    1 cleaner shrimp, pistol shrimp
    50 blue legged hermit, 15 nausaurus/astrea snails
    Yellow tang, 2 clowns, 1 blue chromis, 1 yellow watchman 1 corral beauty
    Colt coral, Frogspawn, Bubble, Donut coral, Mushrooms,Starburst green, Green and orange polyps an Umbrella coral, Purple Long Tentacle Anemone.

  6. #6
    Moderator ShipWreck's Avatar
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    Oct 2004
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    I think I have a solution. This part was recommended to use and a friend here at work has already integrated one into a small circuit board. He has to make some changes to a resistor he chose but then I should have one.

    Now the next thing to do is post pictures (I will) but then I have to cover it in a 2 part epoxy to make it water tight and submersible.

    Is anyone aware of any issues with using the 2 part liquid epoxies in the tank? After it's cured of course.
    Rob
    -----
    Upgrade in the works! Keep looking for an update.


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