Fog Sentry - Visibility Sensor

The Fog Sentry measures atmospheric visibility (meteorological optical range) by determining the amount of light scattered by particles (smoke, dust, haze, fog, rain, & snow) in the air that passes through the 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, sigma) using Koschmeider’s formula, MOR (Km) = 3/sigma. Performance in all weather conditions was a design prerequisite for the Fog 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 antidew heaters and thermostatically controlled external hood heaters are offered for protection in extreme environments. All power and signal lines to the Fog 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 Fog Sentry. A flange located on the bottom of the sensor signal processing box mates with a user supplied 1-1/2 inch IPS pipe. Power and signal connections are made through waterproof cable glands to terminal boards in the Signal Processing Box.

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

• 16 km (10 mile) range
• Flexible Power and Output Options
• Field Repairable with Test Points and Indicators
• EMI and Surge Protection on Power and Signal Lines
• Easy Installation and Field Calibration

Performance

• Range : 30 m to 16 km (other ranges available)
• Accuracy : ±10%
• Time Constant : 60 sec
• Scatter Angle : 42° nominal
• Source : 880 nm LED
• Outputs :
• 0-10 VDC standard
• 0-5 VDC optional
• Optional: 4-20 ma, 4-20 ma isolated, control relay, diagnostic relay,
• RS-232C, RS-422, RS-485

Electrical Specifications
Power Requirements:

• AC Version: 100-240 VAC, 24 VA; 75 VA w/ Hood Heaters
• DC Version: 9-18 VDC, 6 VA; 18 VA w/ Hood Heaters

Physical Specifications

• Weight 8 kg (18 lb)
• Dimensions 889 mm W x 292 mm H x 305 mm D (35 in x 11.5 in x 12 in)
• Mounting See Table Below

Environmental Specifications

• Temperature -40° to +60°C (-40°F to +140°F)
• Humidity 0 – 100%
• Physical Protection IP66 (NEMA-4X)