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?

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.

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.

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.

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.

Try E-Bay.

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

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

The water temp ranges between 170-200 F degrees.

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.

I don't think this is necessary unless the temperatures change very quickly. Temperature gradients are linear; if you lag around the probe with enough insulation, it will accurately read the internal water temp even if the probe is outside the pipe.

I'm using a [wired version] barbeque thermometer to measure oil temperatures on my vegetable-oil heating burner; goes up to around 200C / 400F.

Remote wireless versions of these devices are inexpensive, [aimed at a mass market]. Oregon Scientific's AW129, for instance, reads up to 392F at 100 feet range, about $28, on Amazon.

http://www.amazon.com/Oregon-Scientific-AW129-Wireless-Thermometer/dp/B0006G2WYK


I just lightly fix the 'meat' probe to the relevant pipe with a worm-drive stainless hose clip and cover it with a bit of regular split-foam pipe insulation.

The hot water from a wood-fired boiler will fluctuate during the stages of a burn far more than the accuracy of the thermometer. I guess you want this device as a refueliing indicator?

Alan

I just read some of the reviews of the above product. Not looking too good! Ah well, it's the thought that counts!

Alan

I personally would use an LM34CZ from Digi-Key (<$6.00) soldered and shrunk onto a 3 or more conductor cable. DPMs from MPJA range from about $8 to $15. The power supply would depend on the DPM, probably 5 or 9 volts, derived from a used wall wart. Output is 10mV per degree F from -40 to +230 degrees. Set the meter for a 2 volt range and one decimal place and you will read the temperature within a couple of degrees.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LM34CZ-ND
http://www.mpja.com/products.asp?dept=52

Joe

RTD's and thermocouples come with NPT pipe thread. Male and female. Check http://www.pyromation.com/

All you need is an RTD (so you can extend the conductors) and a temperature controller. Since you only need the display, you will not need to concern yourself with the outputs. But you will have to set/program the sensor type.
The controller will calculate distance and resistance, so you can be accurate with extending the conductors. Use THWN or similar. You also will need a small enclosure for the controller.

Ps.....They can make the RTD cable any length you need. "Special Order"

OK,
Reason I suggested what I did (even though Merlin had the better idea of using a tee), is during my training, I was always told to get the sensor probe as close as possible to the sensed medium,as it makes the readings that more accurate.
Actually in it, is about as close as you can get, however that should not be beyond the expertise of most electricians as far as keeping things from leaking goes.