delta-T meter?

Plumbob

Thermocouples are fundamentally temperature difference measuring devices: they measure the difference in temperature between 2 junctions, each of which can be attached to the outside of the relevant pipe. This is actually better than two separate thermometers, not just for cost but because the two may be inaccurate and/or calibrated differently. In general, a thermometer that has a large range cannot also be very accurate, and when taking the difference between two separate thermometer readings, the errors are magnified. A direct deltaT measurement is much better.

But...I can't find a device that is set up to measure deltaT using a thermocouple (or any other technique). Any suggestions appreciated.

hr

A couple favorites

My Fieldpiece stick meter has a delta T head for it. One position actually measure and displays the delta T.

These Azel are real handy. Battery or 24V power, captures high reading, faily cheap, great for leaving on a job.

Use em for balance, injection mixing setup or troubleshooting. www.azel.com

hot rod

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Plumbob

correct URL

many thanks for the lead! The correct url is www.azeltec.com .

Christian Egli

Voltage polarity magic

Play around with two thermocouples. All that thermocouples do is produce a voltage (DC) The readout apparatus is nothing more than a voltmeter with the correct scale.

When you connect a thermocouple to a readout unit you can get a positive temperature or a negative temperature just by reversing the polarity (of course the negative number should not be taken for the temperature of the fire; the scale is the same but the direction is opposite)

Voltages being additive (and deductive) when thermocouples are connected in series, connect the supply thermocouple according to the correct polarity for a correct reading, then add the return thermocouple into the loop following a reverse polarity.

Your ordinary readout unit will give a temperature difference. It should be that simple.

Pay attention to the junctions you make and the extension wire you use, if any.

Have fun

Brad White_3

I agree with Hot Rod

on the Azels. Nice folks to deal with but the shipping time was a bit long, about 3 weeks in my case. I use mine for S/R temperatures on my secondary loop and same for the primary, also next to direct indicating flow meters. This way I can tune the flow rates to keep below the condensing line. Pretty handy.

The site lists them for $75 each but I saw them on special for enough less that I bought three.
I asked Tommy at Azel if they could develop a unit with an output (0-10 VDC or 4-20 mA) for driving a VSD. As they are, they are just temperature indicators. Nice touch though.