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I'd like to measure the surface temperature of of a metal surface, to see how much that metal surface is heating up. I'm trying to recreate The EngineGuard.

The EngineGuard uses a 10mm washer, that is somehow capable of reading temperature. I've done a bit of reading, and there are things like the LM35, but they seem to measure ambient temperature. Could you attach an LM35 to a metal washer somehow to measure the temperature of the metal washer? Is it as simple as putting some thermal paste between the washer and the LM35? If I used thermal paste to mount an LM35, how would I know which "side" if the LM35 is doing the measurement?

I've seen these washer type devices referred to as "Ring lug thermistor" so maybe the question is, "How do I make a ring lug thermistor"?

If we abstract the problem a little bit, is there a way to mount a temperature sensor to a surface to measure the temperature of that surface?

In the use case I am looking at, we only care if the temperature changes more than 5°C, so super high resolution is not that important. The temperature range is 20°C to 130°C. The ambient temperature will be 10 - 30°C, so hopefully insulation from the ambient temperature could be controlled by some shrink wrap?

I mention the LM35 because it seems popular, but if a thermocouple or other thermistor is more appropriate, please let me know.

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    \$\begingroup\$ Arduinos can't measure temperature, only a temperature sensor can. Glue or mechanically attach the sensor to the point at which you want to measure the temperature. \$\endgroup\$
    – Bimpelrekkie
    Jul 20, 2021 at 7:23
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    \$\begingroup\$ @Bimpelrekkie - Do you have a recommendation for glueing or mechanically attaching the sensor? \$\endgroup\$
    – Tyler DeWitt
    Jul 20, 2021 at 7:48
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    \$\begingroup\$ @TylerDeWitt Go to COTRONICS and look over their products. They are a unique company providing unique products that can provide the kind of bonding and thermal conduction you may need (my opinion, only.) They are ceramic products, generally speaking, and can withstand very high temperatures. I cannot speak to their ability to handle vibration, though. So I'd recommend you give them a call with your application ideas and see what they can offer in terms of recommendations or ideas. \$\endgroup\$
    – jonk
    Jul 20, 2021 at 7:59
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    \$\begingroup\$ What kind of temperature do you expect to measure, and what will be the expected ambient temperature range? Also, what accuracy do you need? Those are key information to help you make the best choice. \$\endgroup\$
    – Vladimir Cravero
    Jul 20, 2021 at 9:15
  • \$\begingroup\$ @Bimpelrekkie Technically an Arduino Due (Cortex M3 core) can measure its own die temperature with the on-chip sensor but that's irrelevant to the OP's situation, of course. \$\endgroup\$
    – Spehro Pefhany
    Jul 20, 2021 at 14:05

3 Answers 3

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Ring lug thermistors start from about $4. e.g., https://www.digikey.com.au/product-detail/en/vishay-beyschlag-draloric-bc-components/NTCALUG01A103FL/BC2892-ND/4896929

Not sure DIY would be a good option as bonding the thermistor to the lug while maintaining a thermal connection that could be reliably calibrated would be a challenge.

If you are keen on the DIY maybe you could mount a 3D printer thermistor into a suitable lug with thermal paste and careful crimping.

As you say, covering with Kapton tape or other insulation might be sufficient to reduce the ambient temperature impacting your reading.

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  • \$\begingroup\$ @RowanP- Thanks for the link. I have no experience in this field, so just trying to learn. Is the thought that any irregularities in the bonding material could produce wildly different temperature readings? Also, my google foo wasn't that great - are you able to find an example of a lug that is capable of going over an 8 mm nut? The lug thermistors I can find all seem to be in the M3/4 range. \$\endgroup\$
    – Tyler DeWitt
    Jul 20, 2021 at 7:57
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    \$\begingroup\$ @TylerDeWitt, I was thinking about vibration rather than irregularities in the bonding material. The comment from Joni above about Cotronics thermal materials looks very informative. Digikey (just one example of an aggregating supplier) list 200+ different types of thermistor lugs. I suggest you have a browse. digikey.com.au/products/en/sensors-transducers/… (Edit - I just noticed the search link in this comment doesn’t seem to include that I refined the linked search with the search word “lug” to get the 200+ refined search results.) \$\endgroup\$
    – RowanP
    Jul 20, 2021 at 13:46
  • \$\begingroup\$ thanks for the advice! I agree with you, for the price, digikey is the way to go. For DIY, there's a couple things to consider. Should give me something fun to play with the next few weeks \$\endgroup\$
    – Tyler DeWitt
    Jul 21, 2021 at 6:27
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There's a TO220 version of the LM35 that you can bolt to a device to measure its temperature. LM35DT

TC74 is also avaialble in TO220, this part uses an I2C interface, and seems to be cheaper than the TO220 version of the LM35

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you can use a NTC thermister. Calibrate it with Arduino using a digital or analogue thermometer. 10 kOhm NTC is good. it is cheap. From Aliexpress it may be around 0.2$.See for yourself. use a potential devider. can be glued to the metal.just type as NTC in search box.

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    \$\begingroup\$ I don't see why even a transistor/amplifier would be needed. With the 10 k thermistor and a 10 k resistor a voltage divider can be made to divide the supply voltage. Feed the divided voltage into an ADC input of the Arduino and you're done. Supply voltage variations are irrelevant if you set the ADC to use the supply voltage as the reference voltage. See: electronics.stackexchange.com/questions/465548/… \$\endgroup\$
    – Bimpelrekkie
    Jul 20, 2021 at 7:58
  • \$\begingroup\$ 10 k ressistor means the ressistance of the NTC. \$\endgroup\$
    – upali
    Jul 21, 2021 at 11:33

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