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#183675 - 01/18/09 09:45 PM Digital temp display
Merlin Offline
Member

Registered: 01/27/04
Posts: 170
Loc: NW Indiana
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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#183676 - 01/18/09 10:29 PM Re: Digital temp display [Re: Merlin]
maintenanceguy Offline
Member

Registered: 12/02/01
Posts: 303
Loc: Southern NJ, USA
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.

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#183677 - 01/18/09 10:40 PM Re: Digital temp display [Re: maintenanceguy]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
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.
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#183681 - 01/19/09 05:53 AM Re: Digital temp display [Re: gfretwell]
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
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.
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#183691 - 01/19/09 10:26 AM Re: Digital temp display [Re: Trumpy]
Merlin Offline
Member

Registered: 01/27/04
Posts: 170
Loc: NW Indiana
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.

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#183694 - 01/19/09 01:25 PM Re: Digital temp display [Re: Merlin]
LarryC Offline
Member

Registered: 07/05/04
Posts: 776
Loc: Winchester, NH, US
Try E-Bay.

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#183698 - 01/19/09 02:32 PM Re: Digital temp display [Re: LarryC]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
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
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#183699 - 01/19/09 03:21 PM Re: Digital temp display [Re: gfretwell]
NJwirenut Offline
Member

Registered: 09/15/01
Posts: 816
Loc: Bergen County, NJ
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

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#183706 - 01/19/09 09:00 PM Re: Digital temp display [Re: NJwirenut]
Merlin Offline
Member

Registered: 01/27/04
Posts: 170
Loc: NW Indiana
The water temp ranges between 170-200 F degrees.

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#183713 - 01/20/09 01:20 AM Re: Digital temp display [Re: Merlin]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
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.
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Greg Fretwell

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