Next-gen temperature measurement: Two examples from Melexis
Combining high resolution and the ability to operate reliably in harsh environments, the MLX90640 infrared (IR) sensor array offers a cost-effective alternative to more expensive high-end thermal cameras. This 32 x 24 pixel device is suited to safety and convenience applications including vehicle seat occupancy detection in cars, fire prevention systems, smart buildings, intelligent lighting, IP/surveillance cameras and HVAC equipment. It works under environmental temperatures between -40°C and 85°C and measures object temperatures between -40°C and 300°C. Maintaining high levels of precision across its full measurement scale, the device delivers a typical target object temperature accuracy of ±1°C. It also exhibits superior noise performance, with a noise equivalent temperature difference (NETD) of just 0.1K RMS at a 1Hz refresh rate. Unlike the conventional microbolometer alternatives, the sensor does not need frequent re-calibration, thus ensuring continuous monitoring and lowering system cost. Field-of-view (FoV) options comprise the standard 55° x 35° version and a 110° x 75° wide-angle version. The MLX90640 is supplied in a compact, 4-pin TO39 package incorporating the requisite optics. An I2C-compatible digital interface simplifies integration.
The other product also related to temperature measurement and announced simultaneously by the chipmaker, bears the type number MLX90342 and is a quadruple thermocouple interface that provides rapid response and very high levels of accuracy when measuring extreme temperatures. It has been specifically designed to allow automotive designers to address the need for more stringent engine and exhaust thermal management and control. This need is being driven by the higher temperatures associated with new, smaller, more efficient engine designs.
Target applications include turbo charger temperature control, exhaust gas recirculation (EGR), selective catalytic reduction (SCR), diesel oxidation catalyst (DOC) and diesel/gasoline particle filtering systems. Drawing on nearly three decades of automotive engineering experience, the MLX90342 supports a -40°C to 1300°C thermocouple temperature range and has an operating temperature specification spanning -40°C to 155°C. Sophisticated on-board cold junction compensation and linearization, plus factory calibration, guarantee an intrinsic accuracy of ±5°C (at 1100°C). This effectively means the sensor is twice as accurate as other currently available devices. The sensor interface is housed in a miniature, 26-pin 6mm x 4mm QFN package and has a refresh rate of 50Hz, meeting the demand from OEMs for for high-speed response. Temperature data can be transmitted via a SENT Revision 3 digital interface, while extensive diagnostic capabilities monitor the health of the sensor and interface, identifying operational problems without the need for additional components. As a result, signal path integrity of data between the sensor and the engine management software is completely assured. Comprehensive integrated fault detection mechanisms also help sensor designs to conform to the latest vehicle exhaust regulations.