Relative humidity measurement

An evaluation of the HVAC system may include limited measurements of temperature, humidity, air flow, as well as smoke tube observations. Complex investigations may require more extensive or sophisticated measurements of the same variables (e.g., repeated COj measurements taken at the same location under different operating conditions, continuous temperature and relative humidity measurements recorded with a data logger). 

Tan, K. M. Tay, C. M. Tjin, S. C. Chan, C. C. Rahardjo H., High relative humidity measurements using gelatin coated long period grating sensors, Sens. Actuators B 2005, 110, 335 341... 

Sherer Environmental Chambers models CEL-512-37 and CEL-34-14 were freshly outfitted with incandescent (93W) and cool white VHO fluorescent bulbs. Eleven plants from each of the three sources were divided between the two chambers. Plant-top light-intensity varied from 2,800-3,300 ft-c, depending on plant height and the chamber involved. Controls were set for maximum relative humidity (measurements varied between 50 and 100%). Temperature was set at 22°C day (16H) and 17°C night (8 H). Plants were grown under these conditions for 12 wk. Beginning 24 Jan 1980, daylength was decreased from 16 to 11 h over a 4 wk period. 

Snavely, M.J., Price, J.C., and Jun, H.W. 1990. A comparison of three equilibrium relative humidity measuring devices. Drug Dev. Industrial Pharm. 16 1399-1409. 

Relative humidity measures the saturation of water in air. One way to calculate relative humidity is to divide the amount of water in the air by the solubility of water in the air. 

Dew point is detected by either lithium chloride or, if high precision is required, by the cooled mirror-type sensors, discussed in Section 3.2.13. For relative humidity measurements, the elongation and contraction of hygroscopic elements are used. 

Figure 8.12 Spectral percent transmission of an atmosphere at several relative humidities. Measurements were taken over a path length of 1.83 m at a temperature of 26.67°C [19].

Figure 12.4. Hardening of dry beans stored at 32°C and at different relative humidity measured as the penetration force after standard cooking. Curves show relative hardness (i.e., force at time 0 divided by force at any time after storage) as a function of storage time. Inset Light micrographs of cotyledons of hard (upper) and soft beans (lower). Notice separation of cells in...

Method (iv) is used to find the humidity and (Jew point from a relative humidity measurement at a given temperature. 

Miloshevich, L., H. Voemel, A. Paukkunen, A. Heymsfleld, and S. Oltmann, 2001 Characterization and correction of relative humidity measurements from Vaisala RS80-A radiosondes at cold temperatures. JAOT, 18, 135-156. 

Measurements in a vacuum were performed with an STA 429 thermal analyser, and those in air, with STA 429 and 449 thermal analysers. The partial water-vapour pressure in air was estimated from the relative humidity (measured with a hygrometer) and tabulated pressures of saturated water vapour at the temperatures in the room (see Appendix, Table A6). 

Special note must be made of the presence of water vapor, as it presents an often-overlooked factor. The amount of water a gas mixture is capable of containing is limited by the availability of water and the temperature of the mixture. The relative humidity measures the percentage of this upper limit actually achieved. The relationship between temperature and the maximum possible partial pressure of water has been determined empirically one suitable equation over common temperature ranges is... 

Relative humidity measurements underneath elothing of both low and high air resistance as a function of the angle aronnd the cyhnder, together with the calcnlated results, are shown in Fig. 11.16. 

Relative humidity measurements underneath clothing of high air resistance. 

FIGURE 1.49 Conductivity in dependence on relative humidity measured by FT EIS. ITO structured glass was spin coated with PAni and PEDT and dried at 180°C leading to coating thicknesses of 80-100 nm. (Reprinted from Werner, B., Posdorfer, J., Wessling, B., Becker, H., Heun, S., Vestweber, H., and Hassenkam, T., Proc SPIE 4800, 115,... 

Standard Test Method for Water Vapor Transmission Rate of Sheet Materials Using Dynamic Relative Humidity Measurement... 

Moisture properties n. All fibers when exposed to the atmosphere pick up some moisture the quantity varies with the fiber type, temperature, and relative humidity. Measurements are generally made at standard conditions, which are fixed at 65% RH and 70°F. Moisture content of a fiber or yarn is usually expressed in terms of percentage regain after partial drying. 

Fig. 18.9 (a) Dynamic response of the capacitance of a TC-PSi humidity sensor. Electrical parameters were measured using 85 Hz frequency, (b) Dependence of the capacitance on relative humidity measured using 85 Hz frequency, (c) Repeatability of a TC-PSi humidity sensor. Relative humidity is changed between 6 and 58 %. Capacitance was measured using 120 Hz frequency (Reprinted with permission from Bjorkqvist et al. (2004). Copyright 2004 Elsevier)... 

FIG U RE 2.26 Relation between pull-off forces and relative humidity measured on asperity arrays. Each plot shows the average of pull-off forces from 256 measurements on (a) CH-LB film and on (b) CFCH-LB film. Two asperity arrays were selected from each plate, and their curvature radii are shown in the inset boxes. 

Figure 21 is two sets of measured results on relative humidity measurements with the polyimide-coated FBG humidity sensor. In this experiment, the sensor was placed inside the environmental chamber, and the relative humidity level in the chamber was changed from 25 %RH to 85 %RH in a step of 5 %RH at two chamber temperatures, 25 °C and 35 °C,... 

Randin, J.P. and Ziilig, F. (1987). Relative humidity measurements using a coated piezoelectric quartz crystal sensor. Sensors Actuators 11 319. 

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