DS18B20 - surface temperature?

Hi all

Returning to this forum after a break.

I have a project which requires me to (accurately) measure the temperature of water (around 30 - 40 degrees centigrade) within a sealed system i.e. I cannot drill the system and place a probe within the water. I have tried the trusty DS18B20 (both chip & waterproof variants) and though I get temperature readings, these are generally 1 - 1.5 degrees low as as I am only able to place the sensor on the outside of the (roughly 2") pipe.
Granted there will be some temperature difference between the pipe and the flowing water, (simply adding 1 or 1.5 to the measured temperature is also not a workable).

Anyone know of a suitable probe that I can try ?


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Using two DS18B20 waterproof sensors to read in/out water temperatures of my hydronic house heat.

Things I’ve tried:
Silicon heat paste and lots of tape to wrap it to the pipe. works ok, but messy and temperatures still off a bit. wrapping with insulation helps.

Better idea, that in use now. Is to use ceramic heat transfer epoxy and epoxy the sensor on the pipe and insulation wrapped around it. I put the sensor for water “out” as close as possible the boiler and “in” water sensor about 3-4 meters away.

It works but still not 100% perfect. The “in” water temp always has a big swing for temperatures when the circulator pump is off and bleeds heat off to the room.

That’s my best idea so far. Hope its of help.
Still looking to fashion a in water sensor or find a pre made fitting that’s usable as well.

Why is adding to the read temperature “not workable”. If it is not accurate enough, fair dues. But if you think it is not doable, it certainly is.

I don’t believe the discrepancy between actual and measured temperature is linear

Is it possible to create a table of offsets, ie

measured corrected
10 10.5
10.5 10.75

etc, then you could use a lookup table.