Daily Archives: July 12, 2022

MEMS Technology for CO2 Sensing

Most technologies for detecting CO2 are based on photo-detection, where smoke particles reflect light that photo-sensors can detect. However, MEMS technology now offers a more sensitive technology for detecting CO2. Using their knowledge in sensors and MEMS technology, Infineon has now introduced a disruptive gas sensor for sensing CO2 gas.

Coming in a minuscule form factor, the XENSIV PAS CO2 from Infineon is a real CO2 sensor. Infineon has based it on the principle of photoacoustic spectroscopy or PAS. Infineon uses a MEMS microphone, which they have optimized for low-frequency operation. The sensor has a cavity that can detect pressure changes generated by CO2. An integrated microcontroller in the sensor then delivers the CO2 concentration in the form of a direct ppm readout. As the absorption chamber of the sensor is acoustically isolated from external noise, the sensor guarantees highly accurate readings of CO2.

XENSIV PAS CO2 has impressive features. Its operating range extends from 0 ppm to 10,000 ppm, with a linear response giving an accuracy of 30 ppm +3% of reading between 400 ppm and 5,000 ppm. The operating temperature range of the sensor is 0-50 °C at a relative humidity (non-condensing) of 0-85%.

The sensor requires two supply voltages, 12VDC for the emitter and 3.3VDC for its other components, and its average power consumption is typically 30 mW when operating at 1 measurement per minute. With a package dimension of 13.8 x 14 x 7.5 mm, the sensor offers three interface standards—I2C, UART, and PWM.

XENSIV PAS CO2 has several potential applications. On account of its high accuracy, SMD capabilities, and compact size, the sensor is ideally suitable for indoor air quality monitoring with numerous potential applications. For instance, the sensor is highly suitable for home appliances for air conditioners and air purifiers. It is also suitable for smart home IoT devices like smart lighting, indoor air quality monitors, personal assistants, baby monitors, speakers, and thermostats. Apart from use in in-cabin air quality monitoring in aircraft, the sensor is eminently suitable for city management and CO2 emission control in advertising billboards, bus stations, and outdoor lighting.

While measuring the CO2 concentration, the sensor operates in one of two modes—active state and inactive state. In the active state, the integrated CPU is in an operating state and performs tasks like running a measurement sequence or serving an interrupt. However, when the sensor has no specific task to perform, the CPU enters an inactive state. The device may enter an inactive state from an active state at the end of a measuring sequence.

During an inactive state, the CPU controlling the device can enter a sleep mode to optimize the consumption of power. Several events can wake up the CPU from its inactive state—a falling edge on the PWM pin, reception of a message on the serial communication interface, or the internal generation of a measurement request when the device is in continuous measurement mode.

It is possible to program the sensor module via its serial communication interface to operate in one of three modes—idle mode, Continuous mode, and Single-Shot mode.