GM550 Non-Contact Infrared Digital Thermometer calibration - Page 1
Forum section: electronics / general

author: rtek1000
author_rank: Contributor
timestamp: February 24, 2020, 04:32:01 am
content: Hello,I would like to know if anyone knows how to calibrate the GM-550 thermometer, I noticed that there is a connection called CAL on the printed circuit board.It seems that it is necessary to have a reference of 300 °C.Warning: do not perform the steps below on your device, it will be permanently uncalibrated, until it is correctly re-calibratedI noticed some procedures:1- Press the trigger.2- Jump the 'CAL' contact points (PCB)3- Press the 'C/F' button (Red button), the display shows the word 'CAL'4- Direct the sensor to the 300°C reference5- Press and hold the trigger until the display shows 'C-F'6- Remove the jumperI still haven't been able to observe how to read the low temperature reference, it seems that only the reference of 300 ° C is necessary.Can anyone confirm these procedures?Note: the sensor and display fairings are fitted, no screw. There is asecondscrew under the support point of the battery cover, need to completely separate the battery cover to be able to remove the screw.The sensor wires are connected in order, from top to bottom, (the red wire is closest to the EEPROM 24C02 memory):- Green TR+- Black TR-- Red TP+The TR+, TR-, and TP+ are marks that are on the sensor PCB.P.S.: User Manual:http://zotektools.com/wp-content/uploads/2017/06/GM32026GM550-Eng.pdfQuoteNote - This low cost model with only 3 buttons has an emissivity value fixed at 0.95, the manual describes the following:QuoteThank you.

author: beanflying
author_rank: Super Contributor
timestamp: February 24, 2020, 04:43:42 am
content: Without a calibrated most likely black body source why would you want to play with the calibration? These cheap IR Guns are what they are an 'ok' measuring tool providing you point them at non reflective darker coloured items.Mine was initially for food use as a quick non contact check but they don't work well on Milk as an example and pointing them at heated Chrome or Stainless is a more miss than hit affair and the results are questionable at best. Worked great for soups, curries, jams/coloured syrups but on oil, water uncaramelized sugar more or less useless.

author: rtek1000
author_rank: Contributor
timestamp: February 24, 2020, 04:51:07 am
content: Quote from: beanflying on February 24, 2020, 04:43:42 amIt may be necessary for the user to read and understand what is written in the manual, with regard to the issue of emissivity. Without setting this parameter, it is not possible to achieve the correct reading.QuoteManual link added in the first post,Good luck.

author: beanflying
author_rank: Super Contributor
timestamp: February 24, 2020, 05:02:59 am
content: I am aware of the emissivity issue and I had an 'animated' discussion with our local health inspector who tried to lecture me on thermometers when he was suggesting I reduce the use of contact thermometersThe simple facts are IR has shortcomings.The question I posed to you is why would you want to play with the Calibration if you don't have an appropriate source?Something like this would be about minimum and the brass inserts would be ok as they are fairly matt and dark on the inside borehttps://www.eevblog.com/forum/testgear/sika-18600e-dryblock-temperature-calibrator-teardown-pictures-testing/msg2249781/#msg2249781even with this I wouldn't be mucking around with a sub $20 IR Gun trying to 'improve' it's calibration.

author: rtek1000
author_rank: Contributor
timestamp: February 24, 2020, 05:17:15 am
content: Yes, the cost is low for some places, but in other places, the value can be much higher, due to import taxes etc., which can end up making it interesting to "play with cheap things"

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: February 24, 2020, 04:30:34 pm
content: Armchair speculation, but I'd think you could take a block of aluminum, paint a face flat black, drill a hole and stick in a known accurate thermometer or thermocouple, heat it up and read the black painted face. Just be sure it's big enough as the IR gun has to see its full coverage. IR isn't terribly accurate unless calibrated for a specific situation, but sometimes you don't need terribly accurate. The emissivity thing is what trips everybody up. When in doubt, paint it flat black!