Monday, July 30, 2012

The TENMA 72-8730 IR Thermometer

Some time ago the folks at Farnell UK wrote to me offering to send me any piece of equipment they sell (up to a certain £ amount) on the condition that I review it. I racked my brains for something I'd want (excluding a free Raspberry Pi which was an impossible ask) and settled upon an infrared thermometer.

They sent me a TENMA 72-8730.



It's a very simple to use device: point at it the thing you want measured and get a temperature reading. The display shows the current temperature and the maximum temperature read so far (this can be changed to show minimum).



The thermometer does C and F measurements and has a backlight for the screen and a laser for aiming.

The thermometer has a 10:1 spot ratio which means that the spot being measured will have a diameter of 1/10 of the distance away from the thermometer. Thus when measuring at a distance of 1m the spot has a diameter of 10cm. You need to get close to get a precise measurement. It's accuracy is given as 2% with a range of -18C to 280C according to the data sheet.

The other important factor with IR thermometers is that they are measuring the thermal radiation from the thing being measured and the thermal radiation will differ for different types of materials. A black piece of paper and a white piece of metal at the same temperature will have different radiation characteristics and give different measurements.

Some, more expensive thermometers allow the surface type to be set so that an automatic adjustment is made. This model does not. According to the data sheet the emissivity is assumed to be 0.95. Looking at a table of emissivity you'll see that this is good for many dark things, but poor for shiny metal (for example).

Pointing the thermometer in my mouth (laser off!) I get a measured temperature of 36.2C (so, looks like I'm pretty healthy). That's because human skin has very good emissivity close to the 0.95 this thermometer assumes.

Here's a long blog post that goes into more detail on emissivity and this type of thermometer. You can hack around the emissivity by applying black tape to the thing you are measuring and measuring that. (Or you can buy fancy tape )

Inside the battery compartment there's a 14 pin connector that connects directly to the microcontroller inside the thermometer and looks like it can be used for communication with it. Putting a logic analyzer on it I was unable to get any interesting signals from it (I'd hoped to be able to remotely control it) so I wrote to TENMA who responded: "This is used only at the factory for initial setup." If I get time I'd still love to play with that interface.



The only problem I experienced with it was that it would occasionally lock up requiring the battery to be removed and reinserted.

If you enjoyed this blog post, you might enjoy my travel book for people interested in science and technology: The Geek Atlas. Signed copies of The Geek Atlas are available.

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