Timer

A timer or clock is a clock that an electrical contact on or off at specified times. Switching times are individually adjustable in the rule.

For example, if the domestic water daily 6-22 clock should be warm, but to save energy in the rest of the time, not to be heated, so can be set to a timer that the heater is turned on at 6:00 clock and around 22 00 clock is switched off again.

• 3.1 Digital time switches
• 3.2 Mechanical time switches

Embodiments

In a normal switch, the cycle repeated every 24 hours, at a weekly different switching times can be set individually for each day of the week. The hot water heater could be set with a weekly timer so that is to be heated 8-23 clock on Saturdays and Sundays.

With a Yearly different switching times can be set for each calendar day. So even holidays or special events in the settings can be considered.

There are two types of switches, mechanical and electronic. For mechanical switches, a motor turns a screen into the pins or pinned like. These pins then press directly the contact. Electronic timers are programmed via a display and buttons on the unit.

To control short switching signals, such as a bell in a school, signal watches are used.

Types and time base

Absolute time - timers

Originally Clocks were performed with pendulum or balance - time basis as timers. The best known timers from that period should probably be the alarm clock or the church clock, which triggered the set time a bell or chime mechanism.

The spread in the first half of the 20th century synchronous clocks often had 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 controlled as a synchronization clock of the line frequency. About Codierschieber can be set, at which time and off. However, synchronous clocks have the disadvantage that they remain in power failure.

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

Switches in substations or controllers are also supplied from the mains. They worked earlier mechanical ( gear train with balance, electric lift ) and had a power reserve of a few days. Later, using a quartz timepiece with a stepping motor driving a gear train. These watches need a buffer accumulator in order to continue running during a power outage can. Today, electronic watches are used ( quartz or radio controlled ), which usually have a relay as a switch.

Some digital timers can be on and off, not only by selected time points, but turn pseudo- random ( eg in the evening turn on the light to simulate presence ), determine summer and winter time by sync to the time signal transmitter DCF77, or they determine the switching times after years of time-dependent sunrises and sunsets ( so-called astro function ).

Short- Timers

Short timers do not work after the absolute time, but switch loads for a preset period of time or to this delayed on or off. Discrete modules in controls are referred to as time relay. This includes exposure watches and automatic stairway lighting.

Short time switches are mechanical, electro- mechanically connected to a synchronous motor, or electronically by a clock generator and a frequency divider.

Previously they were often operated with a pneumatic delay, a mechanical inhibition or an aerodynamic brake.

In purely mechanical working short-time timers a spring mechanism is wound up by the operation of time delay. This design does not require an operating current.

Signal Watches

A Signaluhr is a timer that makes electrical contact at specified time points for a certain short period. Example: a day at 12 clock is raised for three seconds a break signal such as the gong in a school and the signal for a shift change in a production operation.

A Signaluhr which produces pulses for slave clocks, called master clock. A Funksignaluhr uses a clock for timing.

Comparison of mechanical / digital

Digital time switches

Provided with keys and a display, let digital timers accurate and - to any degree of complexity on / off times - depending on the equipment. You need a battery to store the settings. As electronic switches have a relay, they also consume when the load current (comparable with Synchronous clock - timers ). By using a bistable relay (impulse switch ) can reduce the energy demand even in the on state. The advantage of digital timers is that the switching accuracy is very high. Digital time switches can be exact to the second switch. Furthermore, can be programmed with some digital time random functions, so that a presence can be simulated on vacation.

Mechanical time switches

Also, the energy requirement of mechanical switches is low ( less than 1 watt ). You need no battery and are easy to use. The switching intervals are at least 15 minutes. On / off intervals can be set intuitively. In case of power interruptions they stand and must be set again. They constantly use electricity.

Previously, there were also mechanical switches with a movement and an engine lift or electronic / mechanical quartz movement. These had the lowest energy consumption of all the switches.

With an inhibition and a spring mechanism working short- timers do not have a power consumption.

Applications

Examples ( absolute time):

• Controlling of heating systems ( switching off a circulation pump and lowering the temperature at night)
• Reduce street lighting in the second half of the night
• Switchgear (feeding machines, arming of alarm systems, storage heaters, switching the mode of traffic light systems, Automatic control of electric roller shutter )