Insulation and adhesive

[Dave11420]

Is there a liquid coating, that I could brush onto  thermocouple wires to provide electrical insulation.

Also, what kind of adhesive woul be good to attatch them to a surface. Wires are as small as .071 mm in diameter

Regards,

Dave

[RavensFan]

How about the adhesives that are used to mount strain gages?  Vishay makes them.  When you say thermocouples, I think Omega, so I looked there and that is what gave me the idea  http://www.omega.com/pptst/STRAIN_ACC.html.

I'm pretty sure these adhesives are electrically insulating.  I'm not sure how thermally conductive they are.  But since they are pretty thin, I don't think they would have much of an effect on the accuracy of the temperature reading.

[Dave11420]

Thanks for the info. I ordered the adhesives. We'll see how it goes.

Regards,

Dave

[nitad54448]

Hi,
For low temperature applications (down to few K) you may wish to look for Lakeshore products. Anyway, in my experience superglue is excellent bellow RT. From -80 deg to 200 degrees C, there are silicone adhesives, excellent thermal conductors and good insulators (they even resist 19 KV/mm)... Give details for your applications if you need more info
regards
N

[RTSLVU]

We use Loctite 384 in our R/D lab for attaching thermal couples to electronic components.


Message Edited by RTSLVU on 12-02-2007 01:06 PM

[Dave11420]

I have four thermocouples which are not insulated.  I need to measure temperatures within a -4 deg C to 4 deg C(approx).

I thought it might be a problem that since the wires are bare, if they touch I would not get accurate readings, which is why I asked about insulation.

The combined wire and insulation itself has to be thin. Also, the thermocouple end is immersed in a cold fluid of which the temperature range is given above. The rest of the thermocouple passes through another fluid at room temperature. The thermocouples need to be attached along the length of the tube with the tip inside the specified tube.

The dashed line is the second tube with the fluid from -4 to 4 degC. The line right above it is the thermocouple wire which has to be attached to the tube length. The two faded lines, is the second tube at room temp. I only care to measure the cold fluid.

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[nitad54448]

hi
I did't understood the wires and all the stuff; if you need to insulate the TC wires a thin teflon tube is OK, you need a good thermal contact on the TC tip only. Also, you need to be sure to have both TC legs connecting at the same temperature.
for that temperature range you can use any kind of adhesive (loctite mentioned above should be a good solution). Lakeshore product I mentioned is good for few K !!!
however,  if you need accurate mesurements for only a decade around 0° it is best to use a thermistor (typically you have 0.1 to 0.2 mV per degree with one, but with a thermocouple you get much less signal, thus smaller sensitivity).
regards

[Tohatsu]

As suggested, maybe thermocouples is not the thing for you, they are mainly used when you want to influence your object very little, and the objects are small in mass..but since you are working with fluids, maybe another sensor is what you want. Secondly, why do you need to insulate the wires? Most sampling units have differential input channels, and I assume you do not run a high(>250V) voltage in your fluid...so there should not really me an issue with that. We use regular scotch brand tape (looks like metal) to attatch our type K thermocouples, and unless there is a possible >250V difference, and you have diffirentiated inputs, you really dont need to care about insulation.

[johnsold]

Dave,

Krylon sold a spray-on acrylic coating years ago. If something like that is still available, it might work well for you. Cover the junction with tape while spraying. Check for compatibility with the fluids.

Lynn