thermometers

[Sledge]

I am in need of an accurate digital thermometer, but do not know which to buy.

I have spent about $1500.00 Canadian on digital thermometers so far, and they are all off. I dont want to waste money but spend what I have to for quality stuff.
I have tried the calibration test, by checking the temperature of water with crushed ice stirred constantly, and also checking boiling water stirred constantly.

I have tried the infra-red style, thermo-couples off my Fluke meter, multiple probe, and the pocket ones. They all read differently and none of them measure boiling water at 212F or freezing water at 32F. They were all off by 3-5 degrees, some lower, some higher.

I became aware of the problem while attempting to do a factory start-up on a PoolPak (unit for dehumidifying pool enclosures and reclaiming heat).
How can we possibly do precision work if the commercial test equipment is inaccurate.
A variance of 5 degrees on a tester can be a big impact for SH set-up.

Can anyone recommend an accurate digital thermometer.

[Brian_UK]

Do you get then calibrated before you buy them ?

[El Padre]

Try Testo, I am very impressed by the quality of their products.

Cheers

[mad fridgie]

I am not an electronics expert, but I think that good instruments work on 32000 bits, with an accuracy of .25%, so what actually determins this accurracy is the working range, so if you want a unit that is design for example to go from -100C to 500C then your actual accuracy per C will be poor, for high accuracy, you need to have a small(er) working range. A good quality instrument supplier should be able to give what you want for a price less than you have indicated.
Infra red instrument should be great, but you really have to know how to use and set them up (different materials absorb and refrect light dfferently, thus can give differing reading)

[Buckrider]

All my Testo equipment has been within 1 degree when checked against calibration.

Well, actually I had a new one that was off by more than 3 degrees (I always check calibration on new sensors) - I sent it back and they sent a new one thta calibrated fine.

I use 605 H2 for air temps, PT100's with the 556 for pipe temps, and sometimes Type K thermocouples with their 435 on misc pipe temps.

[shooter]

sledge how are you measuring the temps, with an infrared you will have to put a black label on the boiling water
with frozen you can not even see correct as infrared can only measure radiation and not the lack of it.
meaning the sensor should be colder then the object.
thermo couples are not very precise,
platinum is precise, 0.1 celsius is normal.
btw superheat should not be setup by temperature but by level in the evaporator.
i know normal is 7 celsius but i do put them much lower, depending on installation.
and yes testo is good.
however every meter is as good as the operator is.
buy some pt100 sensors and clamp them on the pipes needed.
a switch or a relay box can do the job.