Timer
A timer or timer is a clock that switches an electrical contact on or off at set times. The switching times can usually be set individually.
For example, if the domestic water should be warm from 6 a.m. to 10 p.m. every day, but not to be heated during the rest of the time in order to save energy, a timer can be set so that the heating is switched on at 6 a.m. and at 10 p.m. : 00 clock is switched off again.
Embodiments
With a normal time switch , the cycle repeats every 24 hours, with a week time switch, different switching times can be set individually for each day of the week. The domestic water heating could be set with a weekly timer so that it should be heated on Saturdays and Sundays from 8 a.m. to 11 p.m.
With a yearly time switch, different switching times can be set for each calendar day. Holidays or special events can also be taken into account in the settings.
There are two types of time switches, mechanical and electronic. In mechanical time switches, a motor turns a disc into which pins or the like are inserted. These pins then directly actuate the contact. Electronic time switches are programmed using a display and buttons on the device.
To control short switching signals, e.g. B. a bell in a school, signal clocks are used.
Types and time base
Absolute time switches
Originally wheels watches were pendulum or - Unruh - time base designed as timers. The best-known time switches from this era are probably the alarm clock or the church tower clock , which triggered a bell mechanism or a bell at the set time.
The synchronous clocks that were widespread in the first half of the 20th century also often had switching contacts.
Electromechanical time switches for household use are often designed as an adapter plug and have a switched socket. They are driven by a synchronous motor and controlled by the mains frequency like a synchronous clock. The coding slider can be used to define the point in time when switching on and off.
However, synchronous clocks have the disadvantage that they stop in the event of a power failure.
Today there are electronic, battery-operated quartz or radio-controlled versions with a relay output. Almost all of these time switches are either so-called weekly time switches , which allow switching times to be programmed on a specific day of the week, or annual time switches , which switch on a specific date. Yearly time switches also always have the functionality of a week time switch, so they also allow a switching process on a specific weekday regardless of the current date.
Time switches in switchgear or control systems are also fed from the mains . They used to work mechanically (gear train with balance wheel, electric winding) and had a power reserve of a few days.
Later, a quartz clockwork with a stepper motor that drove a gear train was used. These clocks require a buffer accumulator in order to be able to continue running in the event of a power failure. Today electronic clocks (quartz or radio controlled) are used, which usually have a relay as a switch.
Some digital time switches can not only switch on and off according to preselected times, but also switch pseudo-randomly (e.g. switch on the light in the evening to simulate presence), determine summer and winter time by synchronizing themselves via the DCF77 time signal transmitter , or they determine switching times according to the time of year sunrises and sunsets (so-called astro function).
Short-term time switches
Short-time switches do not work according to the absolute time, but switch consumers on or off for a preset period of time or with a delay. Discrete assemblies in controls are called timing relays . This also includes exposure clocks and automatic staircase lighting .
Short-time switches work mechanically, electromechanically with a synchronous motor, or electronically with a clock generator and a frequency divider.
In the past, they were often operated with a pneumatic delay, a mechanical escapement or an aerodynamic brake.
In the case of purely mechanical short-time time switches, a spring mechanism is pulled up by actuating the time preselection. This design therefore does not require any operating current.
Signal clocks
A signal clock is a time switch that establishes electrical contact at set times for a specific, short period of time. Example: Every day at 12 o'clock a pause signal is triggered for three seconds, such as the gong in a school or the signal to change shifts in a production facility.
Additional devices determine the duration of the signaling. You can also control a sequence of signals.
A mechanical clockwork , a quartz clock or a radio clock can be used as a timer . If the signal clock does not have its own timer, but is controlled by a master clock , it is called a signal slave clock .
If a signal clock also generates the pulses for slave clocks , it is also a master clock .
Mechanical / digital comparison
Digital time switches
Equipped with buttons and a display, digital time switches allow precise and - depending on the equipment - any complicated on / off times. Their advantage lies in their ability to switch gear changes to the second. Furthermore, with some models, random functions can be programmed so that a person can be faked on vacation.
You need a battery or a buffer accumulator to save the settings. The digital clockwork can be powered by this battery or an internal power supply unit . Different models have very different self-consumption in the range of 0.5–6 watts. Since electronic time switches have a relay, they also consume electricity when the consumer is switched on (comparable to synchronous time switches). By using bistable relays ( impulse switches ), the energy requirement can also be reduced when the device is switched on. Digital time switches have recently been equipped with so-called astro functions, which, after user input of the respective latitude, process internal astro programs that take into account the seasonal day / night lengths for the daily switching times. Furthermore, with digital time switches, a pulse signal of the usual 2s is possible for other control devices, as is the gentle switching of loads when they cross zero.
Mechanical timers
The energy requirement of mechanical time switches is also low (less than 1 watt). They do not require a battery and are easy to use. The switching intervals are at least 15 minutes long. On / off intervals can be set intuitively. In the event of a power failure, they stop and have to be reset. They use electricity all the time.
In the past there were also mechanical time switches with a clockwork and a motor winding or an electronic / mechanical quartz clockwork. These had the lowest energy consumption of all time switches.
Short-time switches working with an escapement and a spring mechanism have no power consumption of their own.
Applications
Examples (absolute time):
- Control 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 systems ( automatic feeders , arming alarm systems , night storage heaters , switching the mode of light signal systems , automatic control of electric roller shutters)
