On Delay Timer and off Delay Timer:
Generally, timers are used to control the circuit for certain amount of time. Using timers we can delay the circuit operation. Three type of timers are most commonly used in electric circuit. One is On-delay timer, second one is off relay timer and third one is star delta timer. All are functionally same but the delaying operation will be varied. Let see in this article, the main difference between on-delay and off delay timers.
In the word itself you may come to know, that is “off-delay = delayed off”. It means that, even if you cut the input power to the timer, the timer still provides the contacts to the exiting circuit. Simply to say, we take an example…Now consider you have an off delay timer and you set the delayed operation of 25 sec in the time dial. Now you give the input voltage to the timer, then the timer immediately picks the voltage and the makes contact change over which means NO to NC vice versa.
If you have NO contact means, the contact will be NC until the timer receives the power supply. Now you switch of the power to the timer. Here, you can see the magic is that, the timer will not reset the contact until the time delay which you set in time dial, in our case 25 sec. They have capacitors to keep contacts closed even if the timer loses power.
Refer the picture is that, the input signal is stopped but the contact remaining in closed. Such timers are called off delay timer. Such off delay timers are used in motor cooling system, cooling systems are generally designed with the cooling motors and they run with the main motor, to cool the motor after the main motor is stopped, the cooling motor will be made to run for some time with the help these off delay timers.
Some time off delay timers are used in auto transformers starter circuit. Off delay timers are costlier than on delay timers.
On Delay Timer:
On delay timers is the most used timer in electric circuit. The word itself you may come to know, that “on delay = delayed on”. It means the timer does not give the contact changeover until the preset time reached. See the picture that, the input supply is given to the timer coil, but the there is no output until the preset time. After reaching the preset time the timer makes the contact changeover. Such Timers are called On delay timers.
On delay timers are used in Star-delta starter, capacitive load starter etc.