Visibility Sensor

SVS1 Sentry™

Measures atmospheric visibility, also known as meteorological optical range (MOR) by determining the amount of light scattered by particles (smoke, dust, haze, fog, rain, & snow) in the air that passes through the optical sample volume. A 42-degree forward scatter angle is used to ensure performance over a wide range of particle sizes. MOR is calculated by the user by converting the received signal strength (extinction coefficient, σ ) using Koschmeider's formula, where MOR (Km) = 3/ σ .

Performance in all weather conditions was a design prerequisite for the Sentry™. An integrated, one-piece housing design keeps all cabling internal to the sensor for the ultimate protection against the elements. The sensor housing is made from anodized aluminum and the enclosures are rugged, UV-resistant fiberglass rated to IP66. Based on the proven experience of the NWS and FAA, the sensor uses a "look down" geometry to reduce window contamination and clogging from blowing snow. The windows use continuous duty anti-dew heaters and thermostatically controlled external hood heaters are offered for protection in extreme environments. All power and signal lines to the Sentry™ are protected with surge and EMI filtering to help guarantee uninterrupted service for the life of the sensor.

Installation and maintenance effort is minimal for the Sentry™. An 1-1/2 inch IPS pipe or optional 1 inch IPS pipe flange located on the bottom of the Main Electronics Box mates with a user supplied pipe. Power and signal connections are made through waterproof cable glands to terminal boards in the Box.

Calibration of the Sentry™ in the field is as simple as connecting a factory supplied calibration fixture and following a simple procedure that takes less than 30 minutes. Annual calibration is recommended.

A special version of the Sentry is available for road & rail tunnel applications. It has a range of 15/km EXCO that is ideal for the typical visibilities found in tunnels. See SVS1-T Sentry brochure.

Performance

Visibility Range: 30m..16Km standard, 10m..16Km optional
Extinction Range: 100..0.1863 Km -1 , 300..0.300 Km -1 optional

Accuracy: +/- 10%
Time Constant: 60 sec
Scatter Angle: 42 deg nominal
Source: 880 nm LED

Power
AC Version: 100-240 VAC, 24 VA; 75 VA w/ Hood Heaters
DC Version: 10-36 VDC, 6 VA; 18 VA w/ Hood Heaters

Environmental
Temperature: -40 to 60 C
Humidity: 0-100%
Protection: IP66 (NEMA-4X)

Physical
Dimensions: 889 mm W x 292 mm H x 305 mm D (35" x 11.5" x 12")
Weight: 8 kg (18 lb)
Mounting: Nominal 40 mm pipe, 48.3 mm OD max(1-1/2" IPS, 1.9" OD max)

Optional 25 mm pipe, 33 mm OX max (1" IPS, 1.3" OD max)

Construction

Frame: Aluminum with exterior grade powder-coat paint and/or anodize

Housings: Molded fiberglass polyester

Hardware: 18-8 grade stainless steel

Data Outputs

Analog Voltage: 0-10 VDC standard, 0-5 VDC optional
4-20 ma Current Loop: Single ended and isolated optionally available
Relays: Control, control latching, & diagnostic optionally available
ASCII Coded Serial: RS-232, RS-422, RS-485 optional