skibum
Posts: 16
Joined: Fri Jan 27, 2017 1:45 pm

Temperature Sensors headache!

Sun Dec 22, 2019 5:34 pm

I'm wanting to use a temperature sensor attached to a stepper motor. It's going to be pretty well enclosed to want to monitor how hot it gets. My testing is currently with a higher voltage than its actually going to be as this is just a test of the different temp sensors. So things won't be this hot!!

So, I thought I'd try a simple 1-wire DS18S20. But noticed it wasn't reporting anywhere near the temperature either my fingers reported or my thermal camera.

So, for some fun, I decided to attach 3 different sensors to 3 different sides of the same stepper motor. A DS18S20, BME280 and BME680. They are only attached by electrical tape, but I would have thought at least for now that they would report similar temps. Wow was I wrong. Below is the output for 20 seconds after it had been on a little while. Oh my thermal camera says it was over 110c. Although the electrical tape is possibly causing it to read a little high (image attached) :-

Code: Select all

--------------------------------
|  bme280 |  bme680 |  onewire |
--------------------------------
|  93.865 | 110.710 |   75.687 |
|  93.926 | 110.720 |   75.687 |
|  93.946 | 110.750 |   75.750 |
|  94.007 | 110.780 |   75.812 |
|  94.068 | 110.810 |   75.812 |
|  94.129 | 110.850 |   75.875 |
|  94.154 | 110.890 |   75.875 |
|  94.180 | 110.930 |   75.937 |
|  94.251 | 110.960 |   76.000 |
|  94.291 | 110.990 |   76.062 |
|  94.322 | 111.020 |   76.062 |
|  94.327 | 111.040 |   76.125 |
|  94.337 | 111.070 |   76.187 |
|  94.352 | 111.110 |   76.187 |
|  94.368 | 111.150 |   76.250 |
|  94.378 | 111.190 |   76.312 |
|  94.368 | 111.240 |   76.375 |
|  94.307 | 111.280 |   76.437 |
|  94.266 | 111.310 |   76.500 |
|  94.251 | 111.340 |   76.562 |
|  94.251 | 111.360 |   76.625 |

Any one else have these sorts of ranges between different sensors? Basically 35c difference to me seems pretty awful. Even between the two different bosch sensors I'm getting a 17c difference.

Before I started, when the motor was at room temp they reported :-

Code: Select all

-----------------------------
| bme280 | bme680 | onewire |
-----------------------------
| 22.257 | 23.230 |  22.562 |
| 22.242 | 23.230 |  22.562 |
| 22.237 | 23.220 |  22.562 |
| 22.232 | 23.220 |  22.562 |
| 22.232 | 23.220 |  22.562 |
| 22.237 | 23.220 |  22.562 |
| 22.232 | 23.220 |  22.562 |
| 22.227 | 23.210 |  22.562 |
| 22.222 | 23.210 |  22.562 |
| 22.217 | 23.210 |  22.562 |
| 22.222 | 23.210 |  22.562 |
| 22.212 | 23.200 |  22.562 |
| 22.206 | 23.200 |  22.562 |
| 22.212 | 23.200 |  22.562 |
| 22.212 | 23.200 |  22.562 |
| 22.196 | 23.200 |  22.562 |
| 22.206 | 23.200 |  22.562 |
| 22.201 | 23.190 |  22.562 |
| 22.191 | 23.190 |  22.562 |
| 22.196 | 23.190 |  22.562 |
| 22.196 | 23.190 |  22.562 |
So about a 1c difference (which is fine). I'd say at this point the bme680 was the closest to room temp. But not going to worry about that.
Attachments
20191222-172713.jpg
20191222-172713.jpg (113.91 KiB) Viewed 327 times

pcmanbob
Posts: 10157
Joined: Fri May 31, 2013 9:28 pm
Location: Mansfield UK

Re: Temperature Sensors headache!

Sun Dec 22, 2019 8:43 pm

Assuming all your sensors are actually in thermal contact with the motor in question , have you actually tried using a digital thermometer to test the temperature at the same point as the sensors ?

Its possible that different parts of the case are at different temperatures.
We want information… information… information........................no information no help
The use of crystal balls & mind reading are not supported

Paul Hutch
Posts: 562
Joined: Fri Aug 25, 2017 2:58 pm
Location: Blackstone River Valley, MA, USA
Contact: Website

Re: Temperature Sensors headache!

Sun Dec 22, 2019 9:00 pm

None of those three sensors are designed to measure the surface temperature of objects, so they will never be able to read the motor's surface temperature very accurately.

There are many variations of surface temperature sensors on the market with various mounting systems. Using one of those will give you vastly better results, many far more accurate than thermal imaging can provide.

Here's a Google search that shows many options to explore.
https://www.google.com/search?q=surface ... re+sensors
(ignore any sponsored results because they often include sensors that are not suitable for surface temperature measurement)

skibum
Posts: 16
Joined: Fri Jan 27, 2017 1:45 pm

Re: Temperature Sensors headache!

Sun Dec 22, 2019 9:03 pm

Thanks, user error. I can live with that.

pcmanbob
Posts: 10157
Joined: Fri May 31, 2013 9:28 pm
Location: Mansfield UK

Re: Temperature Sensors headache!

Sun Dec 22, 2019 9:25 pm

You should be able to use the humble DS18B20 , if you mount it flat side to the motor using a thermal compound you should get a reasonably accurate result , after all that's how the water proof version of the sensor works, is just a standard DS18B20 in a tube with thermal compound.

The motor will have much more thermal mass than the sensor so fast temperature changes are unlikely.

if you already have the DS18B20 sensors you can all ways try it and see how well it works , before spending more on other sensors.
We want information… information… information........................no information no help
The use of crystal balls & mind reading are not supported

Return to “General discussion”