Small economical and accurate MEMS sensor

Würth Elektronik has developed a MEMS sensor measuring just 2mm x 2mm x 0.9mm in size. Due to its low energy need and its calibrated and temperature-compensated digital output, the sensor calculates humidity and temperature with long-term stability. The WSEN-HIDS humidity sensor is based on advanced MEMS technology: A dielectric polymer absorbs or releases water molecules in ratio to the relative humidity in the surroundings, thereby altering the permeability of a capacitor structure. The humidity sensor with integrated ADC and temperature sensor can be connected to commonly employed microcontrollers via an I2C or SPI interface. With the help of the software development kit, which is also offered, it offers a faster and easier way to individually set data rates and utilise the interrupt pin.

Alongside classical applications, such as heating, ventilation, building automation, air conditioning, and cooling systems, due to its small size and minimised energy requirement, the humidity sensor is also ideal for dataloggers, as well as stationary and portable IoT applications. For modern applications, the company offers developers an evaluation board. The MEMS sensor provides calibrated measurement results with excellent accuracy of ±3.5% RH in the 20% to 80% RH humidity range. The sensor outputs at a data rate in the millisecond range. Condensate forming on the surface of the polymer structure can be removed by activating a built-in heater so that the sensor can generate measured data again within an extremely short time. The operating temperature range of the robust sensor is -40C to +120C.

"With WSEN-HIDS, we are pleased to be able to offer one of the most innovative humidity and temperature sensors. The sensor promotes rapid terminal device development because developers can use a digital output directly via I2C or SPI and do not have to worry about calibration or temperature compensation," explains Vinod Kumar Ramu, product manager at Würth Elektronik eiSos. "Very practical: The sensor’s interrupt pin can also be used to wake up the microcontroller if the humidity changes. This is ideal for economical and low-maintenance monitoring functions." The current consumption of the humidity sensor is 8.9 µA in continuous operation with measurement data available every second. Using a CR2032 button cell with 230 mAh capacity, this corresponds to a battery life of about three years. If the sampling rate is reduced, applications stay maintenance-free even longer.

"It is the ideal solution for every manufacturer of terminal devices to integrate this miniaturised WSEN-HIDS sensor into their application. The possibility of data evaluation for humidity and temperature in case of a complaint concerning the terminal device and the knowledge of what was "going on" with it, means the investment pays off very quickly," says Dr Michael Brauer, head of product management of the Wireless Connectivity and Sensors Division at Würth Elektronik eiSos.