The dry and wet ball method adopts the indirect measurement method. The humidity value is calculated by measuring the temperature of the dry bulb and the wet bulb. The accuracy depends on the accuracy of the two thermometers of the dry bulb and the wet bulb. The traditional dry and wet bulb method and the Nano wave electronic resistance-capacitance humidity sensor method for comparison:
The dry and wet ball method adopts an indirect measurement method. The humidity value is calculated by measuring the temperature of the dry bulb and the wet bulb, and the accuracy depends on the accuracy of the two thermometers of the dry bulb and the wet bulb. The wet bulb temperature meter must be in a ventilated state. Only when the gauze water jacket, water quality, and wind speed meet certain requirements can the specified accuracy be achieved. The dry and wet bulb method measures humidity with an accuracy of 5% RH~7% RH.
The wet and dry ball method measures the humidity. The advantage is that the maintenance is quite simple. In actual use, it is only necessary to regularly add water to the wet ball and replace the wet ball gauze. As the service life increases, the dry and wet balls will not age and the accuracy will decrease. And other issues. But there are also obvious deficiencies. Getting accurate measurements requires some skill and requires manual calculations to get the final result. A large amount of gas sample is required, and the gas sample may be humidified by the wet gauze. When the relative humidity of the gas to be measured is lower than 15% RH, it is difficult to sufficiently reduce the wet bulb temperature. When the wet bulb temperature is below 0 °C, it is difficult to obtain reliable results. Since the wet bulb thermometer is constantly replenished with water, the volume cannot be too small. As dust, oily substances or other contaminants can contaminate the gauze, or the water flow is insufficient, the wet bulb temperature will be high, and the resulting relative humidity will be high. In addition, factors affecting the results include temperature measurement error, wind speed, and radiation error.
The RC sensor uses a polyamine salt or a cellulose acetate polymer film deposited on two conductive electrodes. When the film absorbs water or loses water, it changes the dielectric constant between the two electrodes. The method has a wide range of humidity measurement, and the dew point temperature can be measured from -50 ° C to 100 ° C. The advantage is that there is basically no hysteresis and aging, the temperature coefficient is low, the cost is low, and the energy consumption is small. It can also be used in a wide temperature range, and the temperature coefficient is small in the temperature range of -50 ° C to 180 ° C, so it can be easily measured in a wide range. The repeatability of the measurement results is better than 1% RH, and the accuracy is high, generally ±2% RH, and can reach ±1% RH in a narrow range. The disadvantage of this method is that it is an indirect measuring instrument that requires periodic calibration, is sensitive to certain contaminants, and cannot operate in corrosive environments; although it is low, it is temperature dependent.
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