The optical raindrop measuring device OMD 470 has been used on different types of ships since 1992. They are used to calibrate ship rain gauges and to determine the raindrop spectrum of tropical precipitation on R/Vs POLARSTER N and RON BROWN.

Instrument principle:

The working principle is to measure the extinction when raindrops or hail pass through a cylindrical sensitive area with a length of 120 mm and a diameter of 22 mm. The strength of optical signals is directly proportional to the cross-sectional area of the target object. The light source of the raindrop measuring device is 150 mW, emitting an infrared light-emitting diode (IR-LED) with a wavelength of 800 nm. In order to obtain a homogeneous illumination sensitive area, a condenser lens and an optical blend were used, so only a portion of the light parallel to the optical axis can reach the diode. These optical signals are converted into electronic pulses. The depth and duration of the pulse are directly proportional to the size of the cross-sectional area and the residence time of raindrops in the sensitive chamber. Therefore, this raindrop measuring device can simultaneously measure the size and velocity of water droplets. The minimum detectable diameter of water droplets is 0.5 mm. Sensitive areas are kept perpendicular to the prevailing wind direction with the help of a wind vane. The cylindrical shape of the sensitive area ensures that the measurement results are independent of the angle at which raindrops fall.

Instrument composition:

Instrument body

LED (continuous working time 5000~7000 hours), operating temperature -25~+60 ℃

Measuring electronic components

Data interface unit

Power and data cables

Optional configuration:

Precipitation sensor IRSS 88: can be used to extend the service life of IR-LED.

Wind vane can keep the cylindrical sensitive scanning sensing area perpendicular to the real-time wind direction at all times.

project	parameter
measuring range	Raindrop diameter of 0.5~6 mm or 0.8~20 mm
accuracy	The diameter of raindrops is 0.5 mm
Voltage	24 VCD
output power	0.3 A
Input power	230 VCD, 20W
height	60 cm
width	60 cm
Including the length of the wind vane	60 cm
weight	9.5 Kg

From the known information, the distribution of raindrop spectra with a resolution of 0.05 mm in diameter can be calculated based on the residence time of water droplets or the number of raindrops under known local wind speeds. Practical experience has shown that the spectral distribution data calculated by the residence time of water droplets is relatively accurate. The rainfall rate can be obtained from the raindrop spectrum by assuming the ultimate velocity of raindrops (based on their size).

The optical raindrop measuring device can be regarded as an absolute instrument. However, because raindrops fall in a random pattern, sometimes 2 or more raindrops pass through the sensitive area at the same time, and sometimes only a portion of the raindrops pass through the sensitive area. The simultaneous passage of two or more droplets (known as simultaneous occurrence) and grazing incidence will inevitably affect all types of raindrop measuring devices. The simultaneous occurrence is manifested in an almost exponential distribution on the droplet spectrum: the image shows many small raindrops, but few large raindrops. Therefore, we need some compromises to ensure a sufficient probability of collecting large raindrops, in order to avoid them being recorded as small raindrops occurring simultaneously. The impact of simultaneous events on the outcome is estimated through a reverse engineering technique.

advantage:

The new optical raindrop spectrum measuring device can simultaneously measure the size and velocity of water droplets, and calculate rainfall rate and raindrop spectrum through software

Can provide particle size measurement ranges of 0.5~6 mm, 0.5~12 mm, or 0.8~20 mm

Specially designed for platforms with strong relative wind speeds, such as mobile ships and high-speed vessels with relative wind speeds exceeding 20 m/s. It is also particularly suitable for strong winds on land

The minimum detectable raindrop size is 0.5 mm (range 0.5~6 mm)

The calculation accuracy of raindrop spectrum distribution reaches 0.05 mm (range 0.5~6 mm)

One significant advantage is the optional wind vane, which keeps the cylindrical sensitive scanning sensing area perpendicular to the real-time wind direction at all times

The cylindrical shape of sensitive areas can effectively reduce measurement errors caused by the angle of raindrops falling

The LED can work continuously for up to 5000~7000 hours, with an operating temperature range of -25~+60 degrees Celsius, and can be used normally in high cold environments of 4000~5000 meters

Anti seawater shell