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. 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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