Talk:Cam timer

Few points

"They are gradually being superseded by microprocessor-controlled systems, where greater versatility and feedback is much easier to obtain."

Obtaining feedback is a process independant of the controller, iow its equally easy to obtain with either type of controller. The controller responding to that feedback dynamically is where the difference lies.

"For example, a typical cam timer continues to rotate regardless,"

Not so. Washing machine cam controllers tend to stop and wait for the thermostat to trigger moving on again, and its common for cam controllers to have a fast forward mode as well, in which they progress at many times the speed.

"so if there is a situation that requires a variable amount of time (for example waiting for a tank of water to heat up to a preset temperature), the cam timer is less than ideal,"

popular WM cam controllers have handled this as standard for many decades.

"though it is possible to make the cam motor itself subject to control, as most washing machine designs do."

"While still fairly popular, cam timers are mechanical and hence subject to wear and reliability problems. Purely electronic systems have largely replaced them for most applications."

These weaknesses do exist (as there are weaknesses for electronic controllers too), but their reliability record remains very good, and this isnt why theyre being phased out in favour of electronic control.

Their weakpoint is more the greater degree of flexibility that cpu based controllers provide. As well as offering more wash program variations, a cpu based WM controller can automatically initiate test cycles, reducing mfr costs, and provide fault codes in the field, again reducing repair costs and providing feedback on real world failure rates and causes. All of these reduce manufacture and business costs. Tabby (talk) 01:17, 22 December 2007 (UTC)

A cam timer is an electromechanical system for controlling a sequence of events automatically. Contents [hide]

   * 1 Description
   * 2 Uses
   * 3 Methods used to increase control
   * 4 Replacement with electronic controllers
   * 5 See also

[edit] Description

An electric motor drives, through a reduction gearbox, a shaft on which is arranged a series of cams. Associated with each cam is one or more switches. The motor rotates at a fixed speed, and the camshaft follows, usually extremely slowly. Indentations or protrusions on the cams operate the switches at different times. By arrangement of the cams and switches, complex sequences of opening and closing switches can be made. The switches then operate different elements of the controlled system - for example motors, valves, etc.

Most cam timers use a miniature mains synchronous motor to rotate the mechanism at an accurate constant speed. Occasionally more complex timers with 2 motors are seen. [edit] Uses

The most common use for cam timers is in automatic washing machines, where they are used to 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 easily respond to various feedback.

Historically, cam timers were employed on industrial machines to control repetitive sequencing operations. In this case the cam followers often operated hydraulic valves. Cam timers in industry were superseded with the introduction of PLCs, which offer improved reliability and allow the operation to be optimised. [edit] Methods used to increase control

The most basic type of cam timer continues to rotate regardless, which is not suitable when needing to wait for events that occur at variable times.

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 motor itself subject to control by one of its switches. 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 machines thermostats have less fixed temperature detection points than the number of wash temperatures used. For intermediate temperatures, the cam mechanism uses the stop and wait method to heat to the nearest temp below the one desired, then uses only 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 gearing, which may be triggered by various means.

Using feedback and external time delay and other sensory circuits, it is possible to build an electromechanical state machine using a cam timer, which is what such a system within e.g. a washing machine amounts to. [edit] Replacement with electronic controllers

While still fairly popular, cam timers are mechanical and hence subject to wear and reliability problems. Their reliability record remains good, but there is always some failure rate with mechanical switch contacts.

Electronic controllers have largely replaced cam timers for most applications, primarily to reduce business costs, and also to maximise product features.

Cam timers don't have the greater degree of flexibility that cpu based controllers provide. As well as offering more wash program variations, a cpu based washing machine controller can automatically initiate test cycles, reducing manufacturing costs, and provide fault codes in the field, again reducing repair costs, and providing feedback on real world failure rates and causes. All of these reduce manufacture and business costs. —Preceding unsigned comment added by 115.118.89.214 (talk) 09:38, 7 March 2010 (UTC)