Remote thermometer??

When I burried my hot water pipes from the boiler-outbuilding to the house, I added several wires in the trench.

I burried two lengths of 12-2 wg and a 'communications' cable.

The 'communications cable' has five pairs of wires, I think it was underground phone or DSL cable, I'm not sure. It has a metal shield around the wires and is packed with di-electric grease.

What I would like to do is to put a remote thermometer probe in the boiler and have the guage to read in the house. This is to reduce the number of trips outside just to satisfy my curriosity.

Can someone tell me if I'm going to get an accurate reading from the temperature probe that is 160' away, and will the 120v lines burried alongside the 'communications cable' cause some interferance or induce some error in the temp reading??? Or a 60-cycle pulsing error?

Here is a photo of the shielded cable, maybe it is shielded enough .

Any links to sources for the probe and gauge would be appreciated.

Thanks in advance, Greg L

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Congratulations on advance planning in adding the cable.

Electronic boiler temperature probes use 10,000 ohm NTC thermistors. Honeywell P/N 32002100-001. You will also need a "Immersion Well", available in 1/2 or 3/4 inch NPT. More that you will ever want to know about temperature sensors is here:

http://www.analog.com/UploadedFiles/Ass ... Fsect7.PDF

Scroll down the pdf file until you get to the section about thermistors.

Your 160 foot run of cable will be a small fraction of the 10,000 ohm thermistor resistance. So any readout meter will not be affected by the long cable run. Temperature thermistor meters are typically industrial devices and are too expensive for this application. However the inexpensive homeowner type electronic indoor/outdoor thermometer with the digital readouts use thermistors. I don't know the valve of the thermistors in these consumer products. Pickup a cheap unit, cut off the external thermistor and make some ohm meter measurements. Depending on your electronic skills you could likely get something to work.

Yanche
Electronics Design Engineer
(now retired having fun with coal heat)

Thanks Yanche, I'll have to put an indoor/outdoor thermometer on my 'christmas list'. Do you think the home versions will read up to 200* or so??

Greg L

Greg--

I would suggest a 4-20ma circuit using a temperature transducer. We use a similar system to read tank levels from a remote location thru analog phone lines. You would need a device to supply the 4-20ma circuit. The unit we use in the field can also be supplied with software so the customer can track the readings in the bulk tanks from there own office.

Obviously the unit I am referring would be more advanced than what you would require but the idea can work. I am not familar with a similar unit you can use but shouldn't be hard to locate. All plants use 4-20ma devices to read levels sent to the control room with a transducer connected at the tank or whatever equipment needing readings.

Yanche--

What could Greg use in the way of an electronic circuit power supply which could provide 24vdc for a 4-20ma loop? It would also need an led readout. Most industrial plants use remote sensors in the control rooms. Greg would need to find an Ashcroft or similar supplier of high temperaturs transducers or thermistors. The typical indoor/outdoor store bought unit unlikely would read high enough in temperature as I suspect he would want to read between 150F -210F or possibly greater.

Fenwall Controller in MA design thermistors with boards to operate control circuits for liquid co2 to vapor heaters. I am sure they carry a remote temp sensor and readout too.

Hey Greg, since you burried the power with the signal you might have a slight problem with stray EMF. A 0 to 5 volt signal will be a little more robust and possibly cheaper than 4 to 20 miliamps.

This site http://www.aprsworld.com/wind2/ has a 0 to 5 volt wind data logger (that will start your very own weather station for when you build the airstrip! LOL). It is powered by a DC adapter of 7 to 40 volts, you probably have a old phone charger or similar that you could adapt or buy their adapter (a whopping $4!). And now the bad news, the data logger sells for $225 , it uses an SD memory card (like in a camera) and can store tons of data (for looking at system performance while you were away) they offer a 0 to 5 volt sensor kit that goes up to 100 degrees C for $8 (it uses ethernet cable similar to what you buried), you could hook up to 3 temp sensors. They also have a 4 channel expansion card for $75 that could add 4 more sensors!

Their SW is totally documented and can be exported to excel, access or SW of your choosing. You can trend and review the data, plus keep it on your computer for future use.

The only thing I am not sure about is whether you can make the sensor cable longer than the 25 FT they show. That might be a deal breaker (aside from the price! hehe), but they state that the anemometer can be hundreds of feet away so there must be some wayto make it work.

Oh goody another science project!

Just one idea that might be of merit, or maybe way more involved than you wanted to get!

i like cap and matthaus comments. i use 4-20 and 1-5 vdc (same thing) signal from a 24vdc supply. either way it would work. the nice part is you can change dc to ma with a 250 ohm resistor. find a rtd or thermocouple and your in business.

it would sure beat having to go out in the garage to see the temp. get hooked up wth a dP transmitter and you could see your draft from the house and still use the same power supply for both.

After a memory-jogging PM from Barley Master, I remembered that I had this auto/truck digital thermometer.

I fear that it won't work over the 160 feet of cable. But maybe I can use the readout??

Greg L

No, the instrument has a "thermocouple" type sensor not a "thermistor". Only the thermistor type can be extended with ordinary wire. The display would not be helpful either. Sorry.

It would be a good instrument for measuring flue gas temperatures. The probes are a little large compared to the thermocouple probes I'm used to using. Normally you just drill a 3/16 inch hole in the stovepipe and insert the probe while making the measurement. It might be difficult to do with a large probe. Only the tip needs to be in the gas flow. All other things being equal lower flue temperatures indicate higher efficiency operation.

Yanche

Thanks Yanche, I may use the 'contact' probe and use it to measure the exhaust duct temps. I won't need to do it that often so the probe shouldn't get too dirty. The air temp probe has a very fine wire inside the 'flash suppresor' guard, and I think it would get sooted up pretty fast.

So I'm back to square one, I need to find a cheap outdoor thermometer to play with, I have an overnight tonight/tomorrow next to a Best Buy, I'll go looking.

Thanks for the info. Greg L

I've got a "Springfield" brand, model "precise temp". It has a three line LCD display; time, indoor temp & outdoor temp. The outdoor sensor is a 3/16 black plastic cylinder. I put it in hot boiling water. The display worked up to 154 deg F. Then it displayed all "H"s to indicate over range reading. I'll have to try some tricks to get it to read higher. Have a good safe flight. Check for a thermometer in one of those overpriced mall tool stores. It will give you an idea what to look for. Oregon Scientific sells them also.

http://www.oregonscientific.com

Yanche

Greg, check out item 140059656293 on ebay. Could use a pair of your buried wires to light an alert you when temp is below set point of your choosing. Unit goes up to 250* F and is an immersion typer sensor.

Just an idea

Ground one end of the shield (one end only). This should filter most of the noise out. We run thermocouples that far where I work and it works fairly well.

timberman wrote:Ground one end of the shield (one end only). This should filter most of the noise out. We run thermocouples that far where I work and it works fairly well.

Opps had a brain freeze. Although this will filter noise out of the wire, the thermocouple signal would either have to have thermocouple extension wire brought back to the read out device or in your case converted to another signal (4-20 0-5v 0-10v) as mentioned above. I don't know what I was thinking duh. Guess I should just keep quiet.

Greg--

See the link below. I know this is overkill but read the descriptions of the different instruments/controls to gather some information. If you can find a used Rosemount, you'd be on the right path.

http://www.emersonprocess.com/rosemount ... /m248.html