Infrared thermometer revolutionises induction hob design

Melexis has unveiled the MLX90617, an infrared thermometer for non-contact temperature measurements in induction hob applications. This breakthrough sensor uses optical filtering to measure the temperature of the cooking vessel's base via the ceramic hob surface, enhancing cooking control, safety, and end-user experience.

Due to existing technology limitations, the temperature control in a typical induction hob is based on the backside temperature of the ceramic glass plate used in induction hobs. With the new device, the company has developed an advanced but cost-effective solution capable of 'looking through the glass' to deliver the real-time temperature at the base of a cooking vessel.

Through optical filtering techniques tuned precisely to the ceramic glass used in induction hobs, the device can capture the radiation emitted by the lower part of the cooking pot transmitted through the ceramic glass plate. The energy originating from the ceramic glass plate itself is considered by using an advanced algorithm.

The device is designed to be employed alongside another non-contacting temperature sensor (such as the MLX90614 or MLX90632), which is also mounted below the hob's ceramic surface. An in-situ emissivity measurement using an LED and a light sensor can be considered for best-in-class accuracy.

To ascertain the temperature of the cooking vessel, the emitted radiation from the pot or pan's base is measured by the device, with the second sensor measuring the radiation emitted by the ceramic glass plate and the sensor. The accompanying LED and light sensor are utilised to measure the reflectivity of the pot, and therefore calculate its emissivity. Through relatively simple real-time processing, it is then possible to determine just the temperature of the cooking vessel's base, ignoring the radiation from the ceramic surface and sensors.

Compared to a standard induction hob setup that measures the temperature of the ceramic glass (Tglass) through advanced optical filtering, the device peers through the glass to provide a real-time output of the base of the cooking vessel (Tpot measured). When the results are compared, the measurement provided by the MLX90617 is significantly closer to the actual temperature of the cooking pots and pans (Tpot measured).

By integrating the device, induction hob manufacturers can create a solution that elevates the precision of their product to benefit the end user's cooking experience.

As the temperature of the pot or pan's base is monitored by the sensor rather than the glass, the hob's control electronics have a closer insight into the temperature of food. This is particularly advantageous for cooking operations requiring precise thermal regulation across small temperature ranges. It can also increase the system's safety by detecting out-of-range temperatures and allowing the development of more advanced automated cooking systems.

The device features a factory-calibrated wide temperature range of -0C to 125C for the sensor operating temperature and is designed to measure cookware temperatures ranging from 70C to 250C. It is available in industry standard TO39 packaging with a 5V supply voltage. The SMBus digital interface can be readily integrated into induction hob designs.

The T039 packaging integrates the IR-sensitive thermopile detector chip and the signal conditioning ASSP, accompanied by a built-in low-noise amplifier, a 17-bit ADC, and a powerful DSP unit.

"Our customers' requests initially sparked the development of the MLX90617. However, the challenges of working with relatively small signals of infrared at short wavelengths made us question its feasibility," admits Joris Roels, marketing manager at Melexis. "Through extensive development and application testing, we've not only overcome these hurdles but also delivered a cost-effective, user-friendly solution that truly meets our customers' needs.