MLX90617 Infrared Thermometer Revolutionizes Induction Hob Design

­Melexis unveils 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 through the ceramic hob surface, improving 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 MLX90617, Melexis has developed an advanced but cost-effective solution capable of ‘looking through the glass’ to provide the real-time temperature at the base of a cooking vessel.

The principle

Through precise optical filtering techniques tuned specifically to the ceramic glass used in induction hobs, the MLX90617 is able to capture the radiation emitted by the lower part of the cooking pot that is transmitted through the ceramic glass plate. The energy originating from the ceramic glass plate itself is taken into account by using an advanced algorithm.

In Operation

The MLX90617 is designed to be used alongside another non-contacting temperature sensor, (such as the MLX90614 or MLX90632), which is also mounted below the ceramic surface of the hob. Optionally an in situ emissivity measurement using an LED and a light sensor can be considered for best-in-class accuracy.

In order to ascertain the temperature of the cooking vessel, the emitted radiation from the pot or pan’s base is measured by the MLX90617, with the second sensor measuring the radiation emitted by the ceramic glass plate and the sensor. The accompanying LED and light sensor are used 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.

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

Enhancing Induction Hob Design

By integrating the Melexis MLX90617, it is possible for induction hob manufacturers to create a solution that elevates the precision of its product to the benefit of 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 especially advantageous for cooking operations, which require precise thermal regulation across small temperature ranges. It can also contribute to an increase in the system’s safety by detecting out-of-range temperatures, as well as enabling the development of more advanced automated cooking systems.

The MLX90617 features a factory-calibrated wide temperature range of -0°C to 125°C for the sensor operating temperature and is designed to measure cookware temperatures ranging from 70°C to 250°C. It is available in industry-standard TO39 packaging with a 5V supply voltage. The SMBus digital interface can be easily integrated into induction hob designs.

The T039 packaging encompasses the integration of both 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.

Extensive Development

“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.

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