L&T Timers Price List w.e.f 2nd May 2013 (VIEW) L&T Customer Care No:18002094545
Introduction of Timers
A timer is a specialized type of clock for measuring time intervals.A timer which counts upwards from zero for measuring elapsed time is often called a stopwatch; a device which counts down from a specified time interval is more usually called a timer. A simple example is an hourglass. Some timers sound an audible indication that the time interval has expired. Time switches, timing mechanisms which activate a switch, are sometimes called "timers". Short-period bimetallic electromechanical timers use a thermal mechanism, with a metal finger made of strips of two metals with different rates of thermal expansion sandwiched together; steel and bronze are common. An electric current flowing through this finger causes heating of the metals, one side expands less than the other, and an electrical contact on the end of the finger moves away from or towards an electrical switch contact. The most common use of this type is in the "flasher" units that flash turn signals in automobiles, and sometimes in Christmas lights. This is a non-electronic type of multi vibrator.
An electromechanical cam timer uses a small synchronous AC motor turning a cam against a comb of switch contacts. The AC motor is turned at an accurate rate by the alternating current, which power companies carefully regulate. Gears drive a shaft at the desired rate, and turn the cam. The most common application of this timer now is in washers, driers and dishwashers. This type of timer often has a friction clutch between the gear train and the cam, so that the cam can be turned to reset the time.
Electromechanical timers survive in these applications because mechanical switch contacts may still be less expensive than the semiconductor devices needed to control powerful lights, motors and heaters.
In the past these electromechanical timers were often combined with electrical relays to create electro-mechanical controllers. Electromechanical timers reached a high state of development in the 1950s and 1960s because of their extensive use in aerospace and weapons systems. Programmable electromechanical timers controlled launch sequence events in early rockets and ballistic missiles. As digital electronics has progressed and dropped in price, electronic timers have become more advantageous.
APPLICATION OF ON-DELAY TIMER & OFF-DELAY TIMER
An off-delay timer is used when the circuit needs to be energized for a specific amount of time after the off-delay's timers coil becomes de-energized. An example of this is when a cutoff saw becomes de-energized but the conveyor, to move the wood along, needs to be operational until the wood clears the saw head.
An on-delay timer is used when you don't want all of the equipment to come an at once. After a power failure, in motor circuit starters you don't want to create a high inrush to the MCC (Motor Control Center) when all of the motors try and start at once. This high inrush could trip the MCC breaker an then none of the motors would start. Each motor module has its own on-delay timer so that the motor starts are staggered. The first motor will start, when the on-delay timer of the second motor times out, it will start, and so on until all of the motors are back on line and running again.
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