The Type T measures the profile of an object passing transversely through the field of view. This model acquires object pro les at every 0.250 in. (6.25 mm). For a better efficiency, the distance between transmitter and receiver should not exceed 4 ft (120 cm). The Type L measures the length of an object with an accuracy of 0.125 in. (3 mm), scanning frequency is 4,000 times per second. This circuit is designed to operate under various temperature conditions from -14°F to 122°F (-10°C to 50°C) without the need of heating or cooling.