Cold mirror dew point meter is a high-precision humidity measurement instrument designed based on the principle of cold mirror. By cooling the mirror surface and detecting the temperature of gas condensation (or frost) on the mirror surface, the dew point temperature of the gas is directly determined, and the humidity parameters (such as relative humidity and absolute humidity) are calculated. Its core advantages lie in high measurement accuracy, strong stability, and no need for sensor drift compensation, making it suitable for industrial and laboratory scenarios with strict humidity control requirements.
The cold mirror dew point meter has a miniature polished metal mirror surface that is cooled using a solid-state Peltier electric heating pump. When the temperature of the mirror surface drops to the dew point temperature of the measured gas, the water vapor in the gas will condense into dew or frost on the mirror surface, causing diffuse reflection of the light shining on the mirror surface. A electro-optical circuit composed of light-emitting diodes and high gain photodetectors detects the formation of condensation. The reduction in the intensity of the reflected light from the mirror is used as a feedback input to adjust the cooling power applied to the Peltier device in the instrument control circuit, so that the mirror is controlled in equilibrium. At this point, the mirror temperature measured by the platinum resistance thermometer is equal to the dew point temperature of the measured gas.
working principle
Mirror cooling: The built-in refrigeration system (such as semiconductor refrigerators or Peltier refrigeration modules) actively reduces the temperature of the mirror, gradually bringing the water vapor in the gas closer to saturation.
Condensation layer formation: When the mirror surface temperature drops to the gas dew point, water vapor condenses into liquid dew or solid frost on the mirror surface, forming a visible condensation layer.
Optical detection: The optical system composed of LED light source and photodiode monitors the intensity of specular reflection in real time. After the formation of the condensation layer, the specular reflection light undergoes diffuse reflection, and the light intensity received by the photoelectric sensor decreases.
Dynamic balance control: The control system adjusts the cooling power to dynamically balance the mirror temperature at the dew point state (with equal evaporation rate and condensation rate).
Temperature measurement: High precision platinum resistance thermometer embedded in the mirror surface directly measures the mirror surface temperature at condensation equilibrium, which is the dew point temperature of the gas.
The maintenance of the cold mirror dew point meter should focus on cleaning, calibration, environmental control, and component inspection to ensure measurement accuracy and equipment lifespan. The following are specific maintenance points:
Daily cleaning and inspection
Mirror cleaning: Use a dust-free cloth dipped in isopropanol to gently wipe the surface of the cold mirror to avoid scratches or residual contaminants. It is recommended to install a pre filter in high dust environments.
Sensor maintenance: Regularly check for sensor contamination and clean with anhydrous ethanol if necessary to avoid oil or dust affecting response speed.
Pipeline sealing: Check for leaks in the sampling pipeline and valve joints, and promptly repair or replace aging components.