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Digital temp display #183675 01/19/09 12:45 AM
Joined: Jan 2004
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Merlin Offline OP
Member
I am looking for a way to install a temperature probe in a low pressure water line to measure the temperature and display it digitally in another room. Now this can be as simple as a sensor connected to a display via thermostat wire. I need to be able to read the water temperature of an outdoor wood boiler from inside the house.

Does anybody know where I can find such an apparatus at a reasonable expense?

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Re: Digital temp display [Re: Merlin] #183676 01/19/09 01:29 AM
Joined: Dec 2001
Posts: 300
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maintenanceguy Offline
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I'm not sure how far you need the signal to travel.

I use Mcmaster-Carr for a lot of stuff. Their website is http://www.mcmaster.com

When there, search for Panel mount thermocouple thermometers. They'll be in the catalog on page 579. With one of these, you still need a thermocouple sensor. For anything more than a few feet away, I'd buy thermocouple wire by the foot. You just twist the ends of the pair of wires together where you want to sense temperature and hook the other end of the thermocouple wire to the thermometer.

Thermocouples produce a tiny voltage, millivolts. So any electrical interference or excessive resistance will affect the reading. For this reason, wire lengths are limited to about 100'. Shielded thermocouple wire can work a little longer than that.

If you go this route, McMaster is great about answering questions.

Re: Digital temp display [Re: maintenanceguy] #183677 01/19/09 01:40 AM
Joined: Jul 2004
Posts: 9,569
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gfretwell Offline
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The simplest method would be an "indoor/outdoor" thermometer and extend the "outdoor" lead. These are usually thermistors that have an operational swing in the 100-300 ohm range so a little extra wire will not change the reading that much.
Put the probe on the pipe with a little thermal grease, a piece of aluminum foil and cover it it with insulation.


Greg Fretwell
Re: Digital temp display [Re: gfretwell] #183681 01/19/09 08:53 AM
Joined: Jul 2002
Posts: 8,379
Trumpy Offline
Member
How big is the pipe that you are looking to monitor?

What I am thinking is a probe set into a sleeve-mount around the pipe, sealed with RTV 732 sealant, allowed to cure before being fitted to the pipe.

Bear in mind you will need to drill into the pipe to give true temperature reading.

Re: Digital temp display [Re: Trumpy] #183691 01/19/09 01:26 PM
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Merlin Offline OP
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I would rather have a sensor that I can thread into a tee or something rather than drilling or attaching to outside of pipe. This is going to be on 1" PEX water line. Keep in mind it has no pressure just a steady circulation of water. I am thinking of something similiar to a normal temp gauge that threads into a pipe but would like it to be with a digital display at a remote location about 20 feet away.

Re: Digital temp display [Re: Merlin] #183694 01/19/09 04:25 PM
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Posts: 783
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LarryC Offline
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Try E-Bay.

Re: Digital temp display [Re: LarryC] #183698 01/19/09 05:32 PM
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Posts: 9,569
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gfretwell Offline
Member
How hot is the water?
Another off the shelf item might be the temp gauge and sender they use in a boat. That will be 1/4" or 1/8" NPT


Greg Fretwell
Re: Digital temp display [Re: gfretwell] #183699 01/19/09 06:21 PM
Joined: Sep 2001
Posts: 806
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NJwirenut Offline
Member
Have used products from Omega Engineering for projects like this many times. I usually prefer RTD probes to thermocouples, to eliminate the special cabling and cold junctions needed with TCs Here's a good probe that will screw into a 1/2" pipe port:

http://www.omega.com/ppt/pptsc.asp?ref=PR-19&Nav=temc05

And here's a basic readout unit:

http://www.omega.com/ppt/pptsc.asp?ref=DP25B_TC&Nav=temm03

Re: Digital temp display [Re: NJwirenut] #183706 01/20/09 12:00 AM
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Merlin Offline OP
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The water temp ranges between 170-200 F degrees.

Re: Digital temp display [Re: Merlin] #183713 01/20/09 04:20 AM
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gfretwell Offline
Member
That sounds like some kind of automotive/boat solution if you want to be cheap.
Omega is the gold standard on these things but spendy.


Greg Fretwell
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