Product Introduction

High performance and high-precision carbon dioxide temperature and humidity sensor module

Module model: GY-SCD40-SCD41

Supply voltage: 2.4-5.5v

Interface: Standard IIC interface

Measurement range:

SCD40 CO2 measurement accuracy2 400 ppm – 2’000 ppm ± (50 ppm + 5% of reading)

SCD41 CO2 measurement accuracy2 400 ppm – 5’000 ppm ± (40 ppm + 5% of reading)

New SCD40 sensor and photoacoustic technology

The SCD40 miniaturized CO2 sensor provides a new approach for product design and will lay the foundation for various new sensing applications. Sensirion's experience has enabled it to innovate its CO2 sensor technology, providing a new device that is one seventh smaller in volume than its predecessor SCD30. The photoacoustic principle can reduce the size of the cavity used in SCD30 without affecting performance.

Advanced CO2 sensors, such as Sensirion's SCD30, are based on non dispersive (NDIR) optical detection principles. Due to their size and cost, the use of these NDIR sensors is limited to a few applications.

NDIR type sensors are optical sensors commonly used for gas analysis. The main components are an infrared light source with a wavelength filter, a sample chamber, and an infrared detector (Figure 2 and 3). The NDIR detector can measure the volumetric concentration of CO2 in the sample by irradiating an infrared beam passing through the sample cell (containing CO2) and measuring the amount of infrared light absorbed by the sample at the desired wavelength.

The sensitivity of sensors based on the NDIR principle is proportional to the beam path. The significant reduction in paths can lead to performance degradation, thereby limiting the miniaturization potential of this technology. In addition, sensors based on the NDIR principle do not have an economical BOM structure due to their size, structure, and large number of discrete components.

Gysel said, "In terms of miniaturization, NDIR technology seems to have reached the limit of CO2 sensors because the sensitivity of the sensor is proportional to the length of the beam path, and therefore proportional to the size of the sensor Sensirion has always aimed to disrupt the sensor market by making components smaller and more cost-effective without compromising performance. For CO2 sensing, we believe that photoacoustic technology is the most promising method: in addition to reducing the size and cost of CO2 sensors, this technology also allows SMT assembly to replace laborious through-hole soldering. Combining these three factors may open up new markets for CO2 sensing. I personally believe that photoacoustic technology has the potential to replace NDIR as the standard CO2 in the next five to ten years

The new SCD40 is based on Sensirion's photoacoustic PASens technology. The principle of photoacoustic detection can miniaturize sensors without affecting performance. This is because the sensitivity of the sensor is independent of the size of the optical cavity. By simultaneously using Sensirion's CMOSens technology for miniaturization, these two technologies can be combined to create a new type of sensor (Figure 4).

Figure 4: Size comparison between NDIR (SCD30) and PASenstechnology (SCD40) (Image: Sensirion）

The principle of photoacoustic is relatively simple: 4.26 µ m modulated narrowband light corresponding to the absorption band of CO2 molecules

Launch in a small enclosed space. Measure the absorption of CO2 molecules in the pool by partially illuminating the light. The absorption energy of CO2 molecules mainly excites molecular vibration, which leads to an increase in translational energy, resulting in periodic changes in pressure in the measurement unit, which can be measured using a microphone.

Giselle said, "After absorption, the energy of photons is first transferred to CO2 molecules, and then to surrounding molecules." "The absorbed energy leads to an increase in microscopic pressure. Due to millions of absorption events occurring inside the optical cavity, pressure increase becomes a macroscopic phenomenon. By tuning the IR emitter, we sense the increase and decrease in pressure at a clearly defined frequency - just sound waves. The frequency of sound is determined by the modulation frequency of the infrared emitter, but the amplitude of sound is proportional to the concentration of CO2

The microphone signal is then used to measure the number of CO2 molecules in the measurement unit and can be used to calculate CO2 concentration.

Serial TTL output GY-MCUSCD40 41, providing upper computer display software:

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