MBW373 Cold Mirror Dew Point Meter

MBW373 Cold Mirror Dew Point Meter, Cold Mirror Humidity Measurement Method is a method used to measure gas dew point or frost point. Its working principle is as follows: light is irradiated onto a polished mirror surface, and the temperature of the mirror surface is controlled by a thermoelectric heat pump, namely a Peltier element. And the photosensitive receiver measures the intensity of direct reflection. When the mirror surface is clean and dry, the intensity of reflected light reaches a high value. On the contrary, a cold mirror with condensed water vapor on its surface will scatter light, resulting in a decrease in directly reflected light and a decrease in signal intensity.

High precision cold mirror dew point meter

The cold mirror humidity measurement method is a method used to measure the dew point or frost point of gases, and its working principle is as follows:

The light shines onto the polished mirror surface, and the temperature of the mirror surface is controlled by a thermoelectric heat pump, namely a Peltier element. And the photosensitive receiver measures the intensity of direct reflection. When the mirror surface is clean and dry, the intensity of reflected light reaches a high value. On the contrary, a cold mirror with condensed water vapor on its surface will scatter light, resulting in a decrease in directly reflected light and a decrease in signal intensity.

By using the received light signal as feedback for the closed-loop control system, the mirror surface can be cooled to a certain temperature, and the temperature detected by the intensity of the received light keeps the thickness of the mirror condensation layer constant.

A constant thickness condensed water layer, with no further net increase or decrease in condensed water, is in dynamic equilibrium with the gas around the mirror. Under this equilibrium condition, the dew point or frost point temperature of the gas is determined by measuring the temperature of the mirror surface.

If it is known that the condensate is in liquid form, even at temperatures below the frost point, the measured mirror temperature should be used as the dew point. If it is known that condensed water exists in solid form as ice or frost, the measured mirror temperature will be used as the frost point.

Is it dew or frost?

When the temperature of the mirror is above 0 ℃, water vapor condenses into liquid water (dew) on the mirror. The liquid condensation layer is considered the dew point. For mirror temperatures far below 0 ℃, water vapor condenses into solid ice (frost) on the mirror. The solid condensation layer is considered a frost point.

However, for mirror temperatures between 0 and -20 ℃, the state of the condensation layer is uncertain and can be water or ice, or some combination of the two as shown in the figure on the right.

Within this temperature range, it is difficult to determine whether the system is controlling at the dew point, frost point, or somewhere in between without visual observation. Since these states occur at different mirror temperatures of gases with the same water vapor content, it is important to determine which state it belongs to. The resulting error can reach 3 ℃.