What type of tape is best for attaching thermocouples to a light?

[vandrop]

Hello all,

Sorry if this is under the wrong section. I need to attach some thermocouples to a light to test how it heats up over time, and I was wondering what type of tape I should use to attach them. I was thinking some kind of conductive tape. Has anyone done this before/have a suggestion for a specific tape that I can use?

 

[MATLABdude]

Welcome to Physics Forums!

That's a pretty broad question. Can you post a picture / diagram of what your light source looks like, and where you want to attach it? You can probably use something as simple as a zip-tie, or as elaborate as a tapped and threaded socket. If you're just worried about getting good contact between the thermocouple and the heat source, you can try a little thermal grease or silicone oil (or a temperature conductive potting compound or epoxy for more permanent applications):
http://www.mgchemicals.com/products/thermal.html

 

[vandrop]

I can't post a picture of what the light source looks like, but imagine a high powered pool light (about 500W). The surface I'm going to be attaching it to is plastic. This is also going to be temporary... I want to be able to remove it. I basically want to ensure that I'm getting an accurate reading to the plastic surface (which is directly on the back cone of the light).

 

[MATLABdude]

I'd probably go with a little bit of a high-quality thermal grease along with some way to secure it (if the grease isn't enough). If you have a ballpark for how hot the lamp is getting, then you can find an appropriate tape. If it's warm: scotch tape will probably work. Since it's probably hot, you probably want something like silicone-adhesive kapton tape (it comes off clean, even when used to mask contacts that undergo wave soldering at 200-250 C) For less extreme applications, the metal foil tape they use for ducting (NOT duct tape!) may also work, depending on the adhesive.

 

[vandrop]

Thanks very much. I'll try out that silicone-adhesive tape.

 

[vandrop]

Isn't the kapton tape insulating though? Won't this screw up my measurements?

 

[MATLABdude]

It's ELECTRICALLY insulating, yes. It's not a great thermal conductor, but, since you're taping the thermocouple so that it's in contact with the surface (and not with a tape loop) and you're not using very much of an already thin material (NOTE: don't use very much), it should be fine.

EDIT: if you're really, really concerned, you could use an IR (non-contact) thermometer.

 

[vandrop]

Oh ok, I thought it was thermally insulating. Should be fine.

 

[vandrop]

Also, what did you mean by high-quality thermal grease? The only stuff I could find online is thermal grease which cools down computers. I'm guessing that would be bad for me, because I want to just measure the temperature.

 

[Jiggy-Ninja]

Also, what did you mean by high-quality thermal grease? The only stuff I could find online is thermal grease which cools down computers. I'm guessing that would be bad for me, because I want to just measure the temperature.

The grease doesn't cool it down, it is a thermal conductor that connects the CPU package to the heat sink and let's the heat flow quicker.

It's exactly the sort of thing you want.

 

[Carl Pugh]

Plain old silicon rubber like you get in a tube at the hardware store might also work.

There are temperature sensitive paints that change color at different temperatures that might work.

 

[MATLABdude]

Also, what did you mean by high-quality thermal grease? The only stuff I could find online is thermal grease which cools down computers. I'm guessing that would be bad for me, because I want to just measure the temperature.

As Jiggy-Ninja says, that's the point! To smooth out gaps in the contact between the CPU and the heatsink, and ensure effective heat transfer between the two.

The thermal grease will ensure that your thermocouple is at (or very near) the temperature of the casing. You just have to find thermal grease that's effective (and won't melt / run) at the temperatures you're using it at (do you have a ballpark?) and which has good thermal conductivity.

Even good CPU thermal grease (like the stuff made by Arctic Silver) is only good up to 125 C long-term:
http://www.arcticsilver.com/as5.htm

If that's enough for your purposes, that's great! If not, you'll have to keep looking (for instance, this product which isn't as good of a conductor, but which will last long-term at 200C):
http://www.mgchemicals.com/products/860.html