Timer and Time Clock Tech
Early timers were simple, electro-mechanical devices. Interval timers
used a set time-period for load control. For instance, I used interval
timers to control fans in cooling sheds. Using a 10-minute interval
timer, the fans were set to come on two minutes out of every 10.
Other timers have up to a 24-hour interval with as many as 12 on/off operation settings. They are often used to control lighting, signs, fans and conveyors. Pool heaters, blowers and pumps can be connected to them as well.