Can you measure the temp of a pipe, because i can not!

[mad fridgie]

I produce a high temp heat pump now called "super heat pumps" bla bla bla. Producing hot water 85C+
So last week I was out training/commissioning a system, with a contractor, his foreman and boy.
So well over 100 years experience.
We were trying to measure the temp of the water leaving the machine. The pipe was 1/2" (or the size of magoo,s old fellow when he working in a blast tunnel). We had 7 different instruments 20 different probes, (surface, clamp, and so on) Do you think we could get any form of reasonable and/or repeatable reading. Not a cat in shows chance! We taped, insulated, wiggled, when for a cuppa. Readings all over the place, all we new was that when we used our finger, it was F***ing hot, as I would expect.
To fix the problem, we just disconnected the pipe and inserted the probes directly into the flow, all came right all reading with 1C "good enough for me anyway"
So the question should we just trust what our instruments are saying, are we loosing the feel for our job! Or am I and my mates bloody useless?;)

[Magoo]

Cheers MF, I would be proud of 1/2 an inch at minus 40 C, usually counter sunk, with string attached incase it forgets to come out again. And thats with all the freezer gear on, looking a bit like the Michelin man.

Did you try an IR thermo right up close to pipe.?
Were any of the instruments test certified as tset cert would give deviation across a scale of min/max, techrentals do certs for a largish fee.

[Tesla]

Mad I have a simillar experience with measuring refrigerant temperature - directly is the best as measureing the outside of a pipe leads to too much increased error. Also different types of sensors have a range of repsonse times.

[MikeHolm]

Mad, what was the overall range. If you can determine it for each measurment type, you may be able to compensate in the controller programming, unless you like immersion probes for everything. You were using klixons for some stuff....how accurate is that LOL

[aramis]

You have to use the correct probe. If the probe does not make perfect contact with the pipe you should use heat paste. Never leave an air gap.

If the temperature differential with ambient is high you need to insulate the tube+probe at least 10 diameters up and downstream.

If the sun or any other source of distortion (usually by radiation but could be convective/conductive) disturbs the pipe, you need to isulate 20 diameters up and downstream, if possible. So as to make sure the pipe takes the temperature of the media inside it.

No air currents on the probe allowed.

The stronger the disturbances (air draft, radiation) OR the longer it takes to measure, the thicker the insulation.

The thinner the pipe lets you relax this rule (a little).

Under no circumstances would I use an infrared thermometer on a small pipe!

[chemi-cool]

the only accurate way is thermography camera with the right range. it would cost more then the heat pump itself but it will give you good results.

http://www.flir.com/cs/emea/en/

[aramis]

http://www.flir.com/cs/emea/en/

Nice! But you also need someone trained to distinguish between the 180 million different pantone colours!

[mad fridgie]

I do not like IR for pipework, so I do not use!
The actual issue was contact point and influence of the ambient.
This was made worse by it being such a small pipe. The worst results actually came from the clamp type of temp sensor (2 different makes), the ones that are now very commonly used in our industry (spring loaded). Sort of standard with electronic gauges.
The issue I was trying to indicate is that with all the fancy tools that are around, are we forgetting to use our best tools "our senses and knowledge"
On aside note, on my production machines, I install a long 1/4" pocket which runs inside the pipe. Also at these high temps if you just place the probe in the water leaving the pipe, you get a much lower temp, the water starts vaporize instantly. The probe has to be push up the flowing pipe.
PS not a domestic heat pump, so a little more expensive, it has four zeros in the installed price.

[chemi-cool]

Nice! But you also need someone trained to distinguish between the 180 million different pantone colours!

Wrong. you only have to know how to use it.

[mad fridgie]

the only accurate way is thermography camera with the right range. it would cost more then the heat pump itself but it will give you good results.

http://www.flir.com/cs/emea/en/

What do these beasties cost!

[install monkey]

cheapest way is to stick a binder point on the pipe and use a air sensor thermocouple-and insert it into the liquid medium, otherwise did u try heatsink paste on the pipeand insulate the exterior of the probe?