A quartz crystal microbalance (QCM) sensor is a type of sensor that uses the principle of a quartz crystal oscillator to measure the humidity in compressed air. The QCM sensor consists of a quartz crystal oscillator, which is a thin slice of quartz crystal that vibrates at a precise frequency when an electrical current is applied to it. When the humidity in the compressed air changes, the weight of the crystal changes due to the adsorption or desorption of water molecules on the surface of the crystal. This causes a change in the frequency of the crystal’s oscillation, which can be measured and used to calculate the humidity.
The QCM sensor is typically coated with a hygroscopic material, such as aluminum oxide, which attracts and adsorbs water molecules. As the humidity in the compressed air increases, more water molecules are adsorbed on the surface of the crystal, increasing its weight and causing a decrease in the frequency of the crystal’s oscillation. Conversely, as the humidity in the compressed air decreases, fewer water molecules are adsorbed on the surface of the crystal, decreasing its weight and causing an increase in the frequency of the crystal’s oscillation.
By using the changes in frequency in the quartz crystal the sensor can measure the humidity in the compressed air. QCM sensors are known for their high accuracy, fast response time, and excellent long-term stability. They are also relatively low-cost and have a small footprint, making them suitable for use in compressed air systems.
