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A cam timer or drum sequencer is an electromechanical system for controlling a sequence of events automatically. It resembles a music box with movable pins, controlling electrical switches instead of musical notes.
A programmer may change or rearrange (reprogram) peg or cam positions. Much like the pegs in a music box cylinder activate the notes, in a drum sequencer, as the drum of the sequencer spins, the pegs run across switches, activating machine processes. The placement of the pegs along the length of the cylinder determines which switch will activate along the length of the drum. Where the peg lies along the circular circumference of the drum determines at what point the peg will activate the switch in the drum's spin. The drum performs repetitive switching operations by controlling the timing and sequence of switches.
Most cam timers use a miniature mains synchronous motor to rotate the mechanism at an accurate constant speed. Occasionally, more complex timers with two motors are seen.
A drum sequencer is a reprogrammable electromechanical timing device that activates electric switches in repetitive sequences. These sequencers were primarily used in industrial applications to enable automated manufacturing processes.
The most common use for cam timers is in automatic , which drive the washing sequence according to a pre-programmed pattern. They are gradually being superseded by microprocessor-controlled systems, which have greater versatility and thus can more efficiently respond to various feedback.
Another example is the usage in electromechanical pinball machines, where the Cam timer is also known as a 'Score Motor.'
With washing machine cam timers, it is necessary to wait a variable amount of time (for example, waiting for a tank of water to heat up to a preset temperature). To achieve this, the cam electric motor is subjected to control by one of its . The timer sequence switches the cam motor off, and the motor is started again by the signal from the thermostat when the required temperature is reached.
Usually, washing machine thermostats have fewer fixed temperature detection points than the number of wash temperatures used. For intermediate temperatures, the cam mechanism uses the stop and wait for the method to heat to the nearest temperature below the one desired, then uses only the fixed timing of the heating element to increase the water to the desired temperature.
Some cam timers also have a fast forward mode, where applying power to a point on the controller causes rapid advance of the mechanism. This is often seen on washing machine controllers. Rapid advance can be achieved by moving of Gear train, which may be triggered by various means.
Using feedback, external time delay, and other sensory circuits, it is possible to build an electromechanical state machine using a cam timer. These are common in , where the cam timer runs in phases, but also stops and waits for external signals such as a fill level sensor, or a water heating temperature sensor.
Electronic controllers have largely replaced cam timers in most applications, primarily to reduce costs and also to maximize product features.
Cam timers don't offer the greater flexibility that CPU-based controllers provide. In addition to offering more wash program variations, a CPU-based washing machine controller can respond to malfunctions, automatically initiate test cycles, reducing manufacturing costs, and provide fault codes in the field, again reducing repair costs. It also provides feedback on real-world failure rates and causes. All of these reduce manufacturing and business costs.
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