Infra Red temperature sensors

Preamble

I was looking for an Infra Red thermometer to measure the heat on my solar PV panels and for checking my 3D printer. These sensors sense electromagnetic waves in the 700 nm to 14,000 nm range. Whilst tempted by thermal imaging cameras, I was somewhat put off by the £2000-3800 price tag. So, I opted for the cheaper gun like tools. However, there are some DIY options that I will briefly look at first.

Arduino DIY video

Arduino DIY ebay

An eBay search: Infrared Temperature Sensor Arduino

The cheapest module for the Arduino seems to be the Digital Infrared Temperature Sensor For Arduino MLX90615 GY-90615 Module, for £3.81

Modules

There seem to be two modules available:

  • MLX90615 GY-90615, and;
  • MLX90614 GY-90614

Handheld

Laser Thermometers on AliExpress

Parameters

The key parameters to look for in a handheld IR thermometer are:

  • Distance-to-Spot (D/S) ratio:
    • 8:1 and 12:1 average
    • 16:1 good (Etekcity Lasergrip 800)
    • 30:1 very good (Maxsio MS803)
  • Temperature range
  • Response time (generally less than 500ms)
  • Emissivity (typically 0.95/0.96, variable is good for shiny/reflective surfaces)

Links

Here are some interesting reviews: http://thermometerguru.com/
This is a great buying guide: Ultimate Infrared Thermometer Guide

Examples

Etekcity Lasergrip 800 – -50 – 750°C
Maxsio MS803 – 30:1, -50 – 1050°C
Fluke 561 HVAC Pro – has thermocouple , 12:1, -40 – 550°C

Uni-Trend:

Model, B$, ebay, D/S, Temp, Emissivity, response time
300A ???, (£20 on ebay), 10:1, -18 – 280, 0.95, 500ms
300B 1500, (£27.50 ebay)
300C ???, (£16.80 ebay) 12:1, -20 – 400, 0.10 – 1, 500ms
300S ???, (£11.98 on ebay), ???, -32 – 400, 0.10 – 1, 500ms
301A 2500 (£42.18), 12:1, -18 – 350, 0.10 – 1, 250ms
301C ???, (£44 on ebay), 12:1, -18 – 550, 0.10 – 1
302A ???, (£67 on ebay), 20:1, -32 – 450, 0.10 – 1, 250ms
302B ???, (£72 on ebay), 20:1, -32 – 550
302C ???, (£45 on ebay), 20:1, -32 – 650
302D ???, (£47 on ebay), 20:1, -32 – 1050, 0.10 – 1
303A ???, (£84 on ebay), 30:1, -32 – 650, 0.10 – 1, 250ms
303B ???, (£124 on ebay), 30:1, -32 – 850
303C 4500. (£70 on ebay), 30:1, -32 – 1050, 0.10 – 1, 250ms
303D ???, (£119 on ebay), 30:1, -32 – 1250, 0.10 – 1, 250ms
305A ???, (£197 on ebay), 50:1, -50 – 1050, 0.10 – 1, 250ms
305B ???, (£308!!! on ebay), 50:1, -50 – 1250, 250ms
305C ???, (£243 on ebay), 50:1, -50 – 1550, 0.10 – 1, 250ms

Thoughts

Looking into it a bit more, the “Distance to spot” ratio comes into play, especially for solar panels high up on the roof, and a long way from ground level. Typical D/S ratio is 12:1, so if the panel is 1 meter squared, then you can be 12 meters away to get a reading, only of that one square meter. For locating hotspots (of say 5 cm square) on a particular panel, you’ll need a much higher D/S ratio. The highest I’ve found is 50:1.

Also, if the panels are at an angle, measuring it from the ground will make accuracy a lot worse, as the “angular area” will be greater, than just head on (if you see what I mean).

So, the cheap thermometers on AliExpress probably wouldn’t cut it…

In short, the IR thermometer wouldn’t be much good for solar panel analysis, of any great depth, from a distance – you would have to get up close and on a level with the installation.

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