Contactless IR Thermometer

March 11, 2013 // By Steve Taranovich - EDN
The Melexis infrared (IR) thermometer makes it safe to measure the surface temperatures of hot, hazardous, or hard-to-reach objects without having to physically touch them.

 (Omega Engineering's website provides an introduction to IR thermometers .) Simply aim and push the front-panel button to display the remote temperature (in your choice of °C or °F) in less than a second. Pressing the button a second time will freeze the measured value on the display. The value will continue to flash until the button is again depressed, making the device ready for another temperature measurement. Aside from a few minor issues with the front-panel button, I found the device fairly easy to use.

1. The MLX90614 IR sensor is built from two chips developed and manufactured by Melexis: the MLX81101 IR thermopile detector and the MLX90302 signal-conditioning ASSP, which is specially designed to process the output of the IR sensor. The sensor is housed in a TO-39 can, which also comprises an integrated low-noise amplifier, 17-bit ADC, and DSP. The IC's digital 10-bit PWM is configured with a digital SMBus output to continuously transmit the measured temperature. The sensor is precalibrated for an object emissivity of 0.95.

2. The MSP430F413 16-bit ultralow-power microcontroller has 8 kbytes of flash, 256 bytes of RAM, a comparator, and a 96-segment LCD driver to drive the display. The microcontroller takes the IR sensor's DSP PWM signal and converts it to degrees Celsius or degrees Fahrenheit when the front-panel switch signal is sensed.