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2 questions:

  1. How would you connect a temperature sensor to an aluminum block? Could I use a thermal adhesive, basically just gluing the sensor to the block?

  2. Which sensor would you buy? I like the nice cables of the waterproofed versions, but I'm thinking the plain sensor is maybe better suited to gluing to the aluminum block?

Background:

For our DIY PCR project we need to continuously measure the temperature of an aluminum block. The temp. range will be from room temperature to around 100 °C. From what I have read I understand that we need a digital temp. sensor, because the Pi does not have analog inputs (not without additional extensions anyway).

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    \$\begingroup\$ The Pi does not have any analogue inputs so you will need to either buy digital sensors (serial/SPI/I2C etc.) or use an ADC. The rest of the question appears to be off topic for this site. \$\endgroup\$
    – joan
    Apr 3, 2015 at 17:07
  • \$\begingroup\$ @joan yes, I basically noticed the analog/digital issue just in time before ordering an analog sensor ;-). re off topic: since one of the pi's main strengths seems to be its ability to connect to the physical world, I would hope that it should be possible to ask questions about how to make these connections in the best way... \$\endgroup\$ Apr 3, 2015 at 17:19
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    \$\begingroup\$ You can ask any question you want. Some questions are better asked on other sites where they are more likely to be seen by people with expertise in the subject. \$\endgroup\$
    – joan
    Apr 3, 2015 at 17:24
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    \$\begingroup\$ For a similar project, I used a thermistor attached to some aluminium block with silver paste. The advantage of (small size) thermistor is their fast response time, and lot easier to attach closely to what you are trying to measure. Raspberry Pi does lack ADC, but to measure the resistance of a thermistor, a simple R-C charge/discharge circuit is good enough. Raspberry Pi runs GPIO and measures pulse width. \$\endgroup\$
    – Zhe Hu
    Apr 3, 2015 at 18:20
  • \$\begingroup\$ Questions "Which [fill the blank] would you buy?" are off-topic on EE.SE. Please edit that part away, or I'll do that. \$\endgroup\$ Apr 3, 2015 at 19:07

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A lot will depend on the size of your aluminum block. The bare sensor takes more work to connect reliably, but for blocks less than (say) 2" x 2" x 2", it will give significantly faster response times than the encapsulated versions. For the prepackaged units, you're best off drilling a hole in the block and inserting the tube, or you can make a clamp for it. Be careful, whichever technique you use, to get good thermal contact - this generally means a lot of surface area in contact with the block.

If you go with the bare sensor, almost any expoxy will do. Just make sure you apply pressure to the sensor and squeeze out as much epoxy as possible. There's no need to worry about silver paste or anything like that, since there is almost no heat flow through the sensor. But make sure you also make a cable clamp to securely hold your wires to the block, so you don't accidentally rip them off. That means drilling (and tapping if necessary) holes to provide a strong attachment.

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    \$\begingroup\$ Also insulate the device's leads (thermally) from the ambient temperature and keep their temperatures as close as possible to that of the surface you are measuring. The copper leads are much more thermally conductive than the plastic case and will bias your measurement toward the ambient temperature if they are exposed. \$\endgroup\$
    – JRobert
    Apr 6, 2015 at 21:01
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I currently have the waterproof sensor. Keep in mind it has a plastic cylinder at the end, which would be hard to hot glue/epoxy, though it would still be possible. I just use mine to sit outside and monitor that temperature. Also, The first one HAS NO CORD. you would need a little more work connecting it. Unless you're playing with high voltage, you won't need the third one. That's for industrial purposes.

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  • \$\begingroup\$ Oh, on the picture it looks like some kind of metal. Do you think it would be possible to remove the cap without destroying everything? \$\endgroup\$ Apr 4, 2015 at 12:23
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If it absolutely must not move, then the best is to tap a hole in the aluminum block and either use a sensor with a screw thread in it or use a bolt/washer to secure the sensor. Be sure of course to use some thermal grease.

enter image description here

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  • \$\begingroup\$ Thanks for the image, I didn't know about these kinds of sensor heads. \$\endgroup\$ Apr 4, 2015 at 12:26
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I recently used a thermal epoxy for a heat sinking application to connect an aluminum plate to a larger aluminum body for good heat transfer and heat dissipation. It should work nicely for a sensor application as well.

enter image description here

Buy on Amazon

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  • \$\begingroup\$ Thanks for the info, I was looking at these adhesives online and was wondering if they were any good... \$\endgroup\$ Apr 6, 2015 at 16:52
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I use a temp sensor in a TO220 package because it has low thermal impedence junction to case .Also it is easy to install with a M3 bolt.This gives good response and makes closed loop temp control easy to stabilise.

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