A timer clock

A timer or clock is a clock that is at fixed times an electrical contact on or off. The switching times are typically adjustable.

For example, if the water daily 6 to 22 clock should be warm, at other times, however, to save energy, not to be heated, so a switch will be set so that the heating is switched on at 6:00 clock and by 22 : 00 clock goes off.

With normal switch the cycle repeats itself every 24 hours, at a weekly countdown timer can vary switching times are set individually for each weekday. The hot water heater could be set at a weekly time so that on Saturdays and Sundays from 8 to 23 clock should be heated.
With a yearly for each calendar, different switching times are set. Thus, even holidays or special events are included in the settings.

There are two types of switches, mechanical and electronic. In mechanical switches, a motor rotates a disk, are inserted into the pins or the like. These pins then press the contact directly. Electronic timers can be programmed using a display and buttons on the device.
To control short switching signals, such as a bell in a school, signal watches are used.Types and time baseAbsolute time-timers

Mechanical clocks were originally designed with swing or balance-time basis as timers. The famous timers from that period is, perhaps, the alarm clock, or even the church bell, the bell at the set time prompted an internal mechanism or stroke.

Even in the first half of the 20 Century popular synchronous clocks had often switch contacts.
Electromechanical switches for home use are often implemented as an adapter plug and have a switched outlet. They are driven by a synchronous motor, and is controlled as a Synchronous of the mains frequency. About coding slider can be set, at which time and off.

Today there are electronic, battery-quartz or radio controlled models with one relay output. Almost all of these switches are either so-called seven-day clocks, which allow switching time programming on a certain day, or year time switches, which turn to a certain date. Yearly timers have also always the functionality of a day time, thus also allowing a switching operation on a particular day of the week regardless of the current date.

Timers in switchgear and controls are also fed from the mains. She formerly worked mechanically (train with balance, electric lift) and had a power reserve of a few days.Later was used a quartz movement with a stepper motor, one of the drive wheel train. These watches need a buffer battery to keep running during a power failure can. Today electronic watches are used (quartz or radio-controlled), which usually have a relay as a switch.

Some digital timers can not only preselected times on and off, but pseudo-random switching (eg evenings turn on the light, to the presence of fake) to determine summer and winter time, by synchronizing over the DCF77, or they determine shift points After years time dependent sunrises and sunsets (called Astro function).