Shigeaki Matsumoto

Laser Dew-Point Hygrometer

A rough-surface-type automatic dew-point hygrometer was developed using a laser diode and an optical fiber cable. A gold plate with 0.8 µ m average surface roughness was used as a surface for deposition of dew to facilitate dew deposition and prevent supersaturation of water vapor at the dew point. It was shown experimentally that the quantity of dew deposited can be controlled to be constant at any predetermined level, and is independent of the dew point to be measured. The dew points were measured in the range from -15° C to 54° C in which the temperature ranged from 0° C to 60° C. The measurement error of the dew point was ±0.5° C which was equal to below ±2% in relative humidity in the above dew-point range.

Determination of the dew point using laser light and a rough surface

Abstract The dew point is determined using a rough surface of copper plate and laser light. A HeNe laser of 1 mW is used as a light source. The apparatus for determining the dew point consists simply of a laser, a small copper plate of 3 mm in diameter with a thermoelectronic cooler, and a phototransistor. A small quantity of the dew deposited on the surface of 0.8 μm rms roughness is detected easily with scattered laser light. The dew point is determined with an accuracy of ±0.4°C, that is ±3% in relative humidity in room temperature.

A new type hygrometer using a double ionization chamber with α-rays

Abstract Humidity measurements using a double ionization chamber with α-rays are developed in the present paper. The double cylindrical ionization chamber consists of two chambers for humid air and for dry air. Both positive and negative potentials were applied to the walls of both chambers independently so that the output current of the double ionization chamber became zero when the air in both chambers was kept dry. A variable gain amplifier using a thermistor was used to remove the effect of the temperature. The output currents of the double ionization chamber amplified by the variable gain amplifier were measured in dry air and for relative humidities of 20, 50 and 80% for temperatures ranging from 10 to 35°C. As a result, the effect of the temperature was removed in the temperature range mentioned above and the amplified output current proves to be directly proportional to the relative humidity. Therefore, the humidity can be measured with an accuracy of ± 5% in the relative humidity.

Measurement of dew droplets in initial deposition at dew point by using a phase-shift interference microscope

In order to measure the total mass per unit area of dew droplets deposited on a metal plate in the dew-point hygrometer, the shape of a dew droplet deposited on a copper plate was measured accurately by using an interference microscope that employed a phase-shift technique. The microscope was constructed by adding a piezoelectric transducer to an usual interference microscope. A simple method that uses a conventional speaker horn and an optical fiber cable was introduced to depress speckle noise. The shape of a dew droplet deposited on the copper plate surface with 0.1 μm in average roughness was measured with an accuracy of ±3nm. The mass of a dew droplet could be calculated numerically from the volume of its shape and was of the order of 10-9 g. The total mass of dew droplets deposited per unit area and the deposition velocity were obtained under a gentle wind. The total mass was the order of 10-5 g/cm2 at the beginning of deposition and the deposition velocity was ranged from 2x10-6 to 6x10-5 g/cm2.min.

Measurements of dew droplets deposited on a metal plate by using an interference microscope with laser light

Small dew droplets, which deposited on the mirror surface of a copper plate, were measured by using an interference microscope to evaluate the quality of dew deposited on the mirror surface of the dew-point hygrometer. A He-Ne laser of 10 mW and an optical fiber cable of 3 mm in diameter and 120 cm in length were used as a light source and an optical guide to the microscope. The fiber cable was shaken slightly with an acoustic speaker to reduce speckle noise in the interference images. A shape of dew droplet deposited on the mirror surface of the copper plate was obtained from the interference fringes, and the mass thickness of dew droplets was also obtained by numerical calculation of the volumes of each dew droplet deposited and was of the order of 10-5 g/cm2. The deposition velocities of dew on the surface under slow wind velocity were also measured.

A Simple Detector for Measuring the Density of Air Using an α-Ray Source

A simple detector, which consists of a radioactive α-ray source and a ZnS(Ag) scintillator connected with an optical fiber cable, was devised for measuring the density of air under atmospheric pressure. It was shown that the density of air could be measured with the rms error of ±4×10-6 g/cm3 in the range from 1.074×10-3 to 1.309×10-3 g/cm3.

An automatic dew-point hygrometer making use of .BETA.-ray backscattering and controlled at the constant amount of dew.

A control system which consists of proportional and integral control to maintain the constant amount of dew was developed in this hygrometer. The dew points were measured within an accuracy of±1 °C in the ranging from -4 to 32°C. The response time for suddenly changing humidity was about 8 min.

Determination of the dew point and the frost point below 0 degrees C making use of the beta-ray backscattering and the electric conductivity on the narrow surface of insulated layer.

It is necessary to distinguish between the dew point and the frost point below 0 degrees C. The freezing of the dew and the melting of the frost are respectively detected by the rapid decrease and the increase of the conduction current on the narrow surface of insulated layer made of epoxy, 0.5 mm in width and 10 mm in length, on which the dew deposits. The dew point -9 degrees C and the frost point -8 degrees C in the humidity 21% at the temperature 13 degrees C are clearly distinguished in this method.