Introduction of capillary sensor

Like the MEMS sensor, the capillary sensor also uses laminar flow components to generate pressure difference, so that a small part of the flow into the bypass pipeline. The main difference is that the capillary sensor is not in direct contact with the medium. Two temperature-dependent resistors are wound around stainless steel capillaries to form a half Whiston bridge. When the gas flow through the capillary, it will take away part of the heat and flow from R1 to R2. At this time, the resistance of R1 decreases, while the resistance of R2 increases. If a constant current is supplied to the bridge, its output voltage is proportional to the difference between the two resistors. Therefore, the output voltage has a linear relationship with the mass flow rate of the gas flowing through it. The linearity of the sensor even makes it possible for the sensor to be used in uncalibrated gases; the measurement of the current medium is modified by using a current factor of the conversion factor. This simplifies the calibration and ensures that the capillary sensor is suitable for corrosive gases by correctly selecting the material of the sensor. The dynamic characteristics of the sensor depend on the characteristics of the stainless steel capillary wall, which acts as a thermal barrier. The response time is usually several seconds, which is suitable for most corrosive or toxic gases.