PLC-Multipoint Photo Diode sensor provide a linear analog input signal to controllers proportional to the light measured. Sensors shall be enclosed in heated weatherproof housings to prevent icing and condensation. Sensors signal the controller via 4-20mA current loops.
Luminance Measurement
TLUM Tunnel luminance sensors provide analog measurement in Candelas per square meter (cd/m²) that target refl ected light at each traffic direction’s entrance portal. Long distance signal transmission, up to 4,000 feet is accomplished through a 4-20mA current loop. TLUM Tunnel luminance sensors see a restricted field of view, e.g. 20° and are aimed at the tunnel portals composing the fi eld of vision that a driver at a safe stopping distance before entering the portal. The TLUM sensor is capable of measuring outdoor ranges of 0 to 10,000 Candelas per square meter (cd/m²). An amplifi er in the sensor enclosure provides sensitivity adjustment for the sensor. Sensors located in severe weather environment are protected from accumulated snow and ice through the use of thermostatically heated housings. Sensors subject to corrosive gases are housed in a gasket enclosures.
Illuminance Measurement
TMAS Tunnel illuminance sensors provide analog measurement in Foot-candles. TMAS sensors may be mounted to monitor ambient light near each entrance tunnel portal in unidirectional traffic bores or be located in a compromise location when both traffic directions share the same bore. The TMAS sensor mounting location is selected from several factors; unidirectional or bidirectional traffic flow, dominant traffic direction, time of year requiring most contrast lighting and maintainability.
