Concord, N.H. Melexis Inc. claims that its infrared thermometer module is capable of measuring to better than 0.1 degrees C.
The MLX90601 "IR thermometer-chip" module is made possible by the company's new MLX90313 programmable signal-conditioning sensor interface IC, which is used in combination with Melexis' MLX90247 micromachined IR thermopile. The module can be configured for many IR-related applications with particular adaptability to unique lenses, apertures and scaling situations.
The MLX90313 is a dedicated DSP chip that possesses full digital sensor calibration, scaling and linearization of dual nonlinear input signals from any voltage source over a desired temperature range within unusually tight parameters. Its dual amplifiers are chopper-stabilized types that are said to provide excellent noise performance and low offset. The I/O configuration, as well as the analog settings, are in-circuit programmable by means of the SPI serial interface. This serial link, operating at 125 kbits/second with a four-wire protocol, can also be used to read out the signals digitally.
In addition to target temperature, the DSP packs several combinations of analog and digital comparator-driven outputs. Two on-chip comparators, controlled by either of the two linearized signals, can be used with different settings for threshold level, polarity and switching hysteresis.
The MLX90313 has its own voltage regulator and thus provides everything necessary for an IR thermometer-only a display and a power source are required. Its on-chip supply regulator can be powered by an automotive ignition supply line (8 to 80 volts) and can withstand SAE standard ignition transients. The power-on reset circuitry is completely internal. The chip is operational in 16 ms, and it can also be supplied directly with a 5-V regulated supply on pin Vdd.
Packed into the MLX90313 chip along with the dual chopper-stabilized amplifiers are a 12-bit A/D converter, a signal-conditioning linearization unit, an 8-bit D/A for analog linear signal output with an input for an external level reference and a 10-bit digital output for linear signal data. Supply voltage range is 5 to 80 V.
For portable infrared thermometers, the designer need only add battery and display circuitry, Melexis said. The device suits IR ear thermometers, industrial IR thermometers, consumer IR thermometers, microwave ovens, dryers and numerous other applications. It is available in automotive quality grade with QS9000 manufacturing and -40 degrees C to 125 degrees C ambient operating temperature range.
A development kit for MLX90313-based modules is available containing the PTC-01 Melexis ASIC programmer and PC software. Communication between PC and programmer is provided through standard RS-232.
All versions of the MLX90601 module, meanwhile, come fully loaded with thermopile and internal temperature reference algorithms as well as full calibration. Melexis can also customize the module for unique requirements.
Depending upon the configuration, the MLX90601 IR module containing the MLX90313 IC, MLX90247 micromachined membrane IC thermopile and a very small printed-circuit board (10 x 23 mm) is priced at approximately $5 in quantities of 100,000.
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EETInfo No. 603