Measuring line temperatures Methods

I wonder if people could give me there opinions on best methods of measuring line temperatures ( ie suction line for superheat )
I have been trying different methods and temperatures can vary quite a bit , i would like to think a Velcro strap thermocouple would be the best , but i just can't seem to get accurate readings with them, maybe it's the contact that's the problem .
I find a touch probe works well but not ideal trying to hold it there ,infrared is just too hit and miss, and the pipe clamps don't seem very accurate.
Infact a basic thermocouple with a cable tie seems to work best for me

Hi kfjoe
Best method is direct measurement - measure the refrigerant temperature not the pipe. You can do this with a yellow jacket superheat calculation kit tool. The temperature will be constantly changing with the load & valve position. in my mind measurement of the pipe is only a rough guide. Others will no doubt have different opinions. You could search this site as it has been discussed many times. Also if measureing the outside of pipe it helps to tape some insulation around the pipe ehre you are measureing.

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If you are doing a quick test to see if the system seems to be doing what
it should, then I use the touch probe. Like you though they are somtimes
tempramental and are affected by drafts from fans and such.

If I'm doining a proper investigating I use thermocouples that I make up
and then tape them tight to a bit of pipe I have cleaned. If I'm leaving them
I put some armaflex tape over also.

I have just recently been given a couple of Testo gauge manifolds so I will
be experimenting with those thermacoulpes in the crocodile clip thingies..........

Regards

Rob

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is that where the probe actually goes in the refrigerant through a schrader connection ?

i have actually just been looking at ordering a Testo digital manifold
and was wondering exactly that , and if i can maybe make up my own thermocouple / probe for it
Be interested how you get on with them?

Yes it goes through the 1/4" schrouder valve hole and directly measures the refrigerant temp.

Sounds good
Only problem is a lot of the systems I work on don't have an available Schafer port, at least not until at the compressor

Personally?
I either use a surface probe or a bead probe with some heat transfer paste on it secured with with electrical tape around the pipe.
Accurate? Probably not...

Agreed, the best reading would be direct in the refrigerant.

But why would it matter if we are slightly out with our readings, why are we chasing accuracy?


Before we start looking at the best probes and practices, what thermometer are you using?
Most thermometers I see engineers using is electronic ones in the £50-£150 price range.
I just did a quick web search and compared the accuracy of different thermometers (not necessary scientific but it does give an idea).
>£100 there seem to be a "standard" accuracy of +/- 1.5 to 2ºK
£100 to £400 seem to be +/- 1ºK
£400 to £800 seem to be +/- 0.5ºK
Found one thermometer priced £1295 which claimed an accuracy of 0.2ºK providing the unit itself were at 19-24ºC and 40-60% rel hum.

Further more, the above values are true for when the thermometer leaves the production line or just after it been calibrated. Not after it spent a freezing cold night at the bottom of a toolbox in the back of a van...

So I know, whatever reading I look at on my thermometer the true temperature is within a degree of that reading.
Maybe...

:cool:

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