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Inexpensive Dual Channel Digital Thermometer--HVAC monitoring...

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cliffyk:
We recently had some issues with our HVAC system underperforming--turned out electronically controlled blower motor in the evaporator/air handler was running slow. This was readily apparent when I monitored the temperature drop "across" the intake and outlet plenums (it was 25° F, should have been 15°-18°)

Looking for a permanent monitoring solution I ran across this $20 dual channel digital thermometer on Amazon--a great deal, with the instrument and two type K thermocouples.

So, using FreeCAD and my Elegoo Mars 3D printer I "printed" a couple of ferrules for mounting the thermocouples into the fiberglass board plenums:

FreeCAD screenshot (the flange is 17 mm dia x 1.5 mm, the tube is 5 mm dia x 75 mm w/a 3 mm bore):
   

Mounted in the inlet plenum:


I also, again using FreeCAD made a mounting cradle for the instrument.

With this installed I can easily monitor both the inlet (T2) and outlet (T1) temperatures:


And the delta (without all that nasty math, using the instrument's T1-T2 function):


Upon receipt I validated the meter and probes at room temperature and in ice and boiling water baths--they tracked perfectly.

Not bad for $20...

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