A cam timer is a mechanical device powered by electricity that controls a series of switches by the movement of a rotating wheel or cam. These timers were extensively used before the invention of digital programmable timers. Cam timers are useful when a machine or process needs to be controlled in a series of steps that occur one after another.
Production control in industrial systems was a common use of a cam timer well into the 20th century. The timer was connected to mechanical switches that sent control signals to valves or pumps. Complex systems were difficult to control with cam timers, due to issues with inaccuracy. In addition, changing any operating parameter required taking apart the timer and changing cams.
Consumer products, such as home washing machines, commonly used cam timers. Moving the wash cycle knob turned a cam behind it, and the desired wash setting was aligned with the cam switch. Early machines had no flexibility for different wash loads or water pressure, so actual wash time was affected. Later machines added a water load switch that turned off the cam timer motor until the washer was filled, resulting in more accurate wash times.
Cam timers have been used regularly in vending machines. Inserting money into a machine activates a timer that controls the vending functions. Vending cam timers may not operate as a standard clock timer, but rather were used to provide sequential or series operations in a set amount of time.
Cam timers can operate as clock timers, with a series of cams installed to provide functions at regular times. Water treatment systems also use these in some designs to activate backwash or water softening functions. The cam timer may operate like a clock for a regular control operation such as backwashing a filter every day. Activating the timer with a separate control is also possible, such as using a total water flow meter to trigger water softener regeneration.
Digital process or digital logic controllers have replaced cam timers for many applications since the 1980s. Electronic controllers are more accurate for timing functions. Programming a change in a controller can be as simple as accessing a computer screen, rather than having to disassemble a timer to change cams. Logic controllers can be programmed with a variety of control functions, rather than a single timer function. This can result in lower costs by requiring fewer controllers.