Abstract
A novel way to measure humidity through testing the emissivity of an area radiant source is presented in this paper. The method can be applied in the environment at near room temperature (5~95 °C) across the relative humidity (RH) range of 20~90% RH. The source, with a grooved radiant surface, works in the far infrared wavelength band of 8~12 μm. The Monte-Carlo model for thermal radiation was set up to analyze the V-grooved radiant surface. Heat pipe technology is used to maintain an isothermal radiant surface. The fuzzy-PID control method was adopted to solve the problems of intense heat inertia and being easily interfered by the environment. This enabled the system to be used robustly across a large temperature range with high precision. The experimental results tested with a scanning radiant thermometer showed that the radiant source can provide a uniform thermal radiation capable of satisfying the requirements of humidity testing. The calibration method for the radiant source for humidity was explored, which is available for testing humidity.
Highlights
Compared to traditional humidity measurement methods, innovative electronic testing methods involving humidity sensors such as hygristors and humicaps are the current research direction.Even though electric methods have fast responses, they often lack stability and their accuracy is improved little
Available commercial humidity sensors composed of humicaps use embedded microprocessors, such as the DHT11 with ±5% relative humidity (RH) precision, and 1% RH resolution which are convenient to use
The radiant source is composed of the V-grooved radiant surface, plus a cylinder to shield the circumference of the surface
Summary
Compared to traditional humidity measurement methods, innovative electronic testing methods involving humidity sensors such as hygristors and humicaps are the current research direction. Because humidity is often mingled together with temperature, the precision and the humidity measurement range are affected by the temperature. As to environmental humidity measurement, according to MRTD, an area radiant source ranging from 5~95 ◦ C in the wavelength bands of 8~12 μm, is required. The radiant surface of the source possesses concentric V-grooves which can increase the effective emissivity. Capacitor sensors which possess fast response advantages are employed to test humidity, but their measuring precision is affected by electromagnetic interference. Humidity testing is often affected by the environmental temperature, which is a factor that makes humidity sensors’ precision not be high. Humidity testing through radiation possesses advantages of fast response and robustness with high precision. Our research on an infrared source which has highly sensitivity for humidity may provide an improved way to measure humidity
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