The DUT series of relays provide over-current protection. The action of these relays is much like a circuit breaker. If the current in the circuit exceeds the design limits, the relay will trip, shutting off the circuit. According to Fuji, these relays are computer controlled. The computer senses the incoming current and trips the relay. When the current returns to normal levels, the computer resets the relay. The relay is programmable by faceplate controls, allowing the user to program at what voltage and current levels the relay should trip.
A contactor is part circuit breaker and part motor controller. When a voltage is sensed by the contactor, it turns on the motor. Internally, it has over-current protection. If too much electricity is drawn, it shuts off. The motor on and off times are also controlled, depending on whether the voltage is present or turned off. For the DUO series of contactors, the voltage is anywhere from 220 to 440 volts AC for the SC-M series. The SC-M can handle a wattage rating anywhere from 2.2 to 4 kilowatts. A kilowatt is 1,000 watts For the SC-E series; the high-voltage side is also 220 to 440 volts. The wattage rating, however, is anywhere from 4 to 75 kilowatts.
A photoelectric switch turns on and off depending on whether or not a beam of light is shining. PH8AU photoelectric switches are widely used in automation, sending signals to a programmable controller to turn various devices on and off. The PH8AU has a "U" shape. One leg of the "U" contains a small light source. The other leg of the "U" contains the sensor. When an object is placed in between the legs, it breaks the light beam, turning the switch off. The input voltage to drive the light source can be anywhere from 10 to 30 volts DC. The time it takes for the switch to turn off is 1 millisecond, or 1/1,000 of a second.