Time relay

Time Relay is a device that allows you to control equipment according to a schedule. The principle of operation varies. For example, in a microwave oven, this is usually a regular timer. In home appliances, time relays are mostly called programmers. More precisely, the combination of the object of review review and control devices of actuators( for a washing machine: engine, intake valves, pump, etc.).

Electromechanical Relay

History of the Time Relay

Surprisingly, already in 1958 the first book on electronic time relays was published. It said that it was extremely important during the production process to turn on or off the equipment according to the schedule. The first division into classes was proposed: Pneumatic

  1. .Often equipped with an attachment( working chamber, cataract, pneumatic damper) with intake opening. Adjusting the cross section changes the response time. The contact is usually held by an electromagnet with constant force. The rate of pressure change in the chamber becomes the determining factor.
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  3. Thermal. An example of such relays is well-known; they are automatic circuit breakers for electrical circuits. Present in distribution box. The basis is the use of bimetallic plates. As the current flows, they heat up and change the bend, which causes the relay to trip. Such a step protects the equipment from overheating. Similarly, these relays are used in the composition of household appliances, for example, refrigerators.
  4. Electromechanical. The ability of chokes to accumulate energy is used. Then, in the process of damping, the magnetic field of the coil weakens, causing the relay to trigger at the right time.
  5. Electronic. The basis is usually the time of discharge of the RC-chain. The capacitor is charged to the desired value, then slowly gives energy. At a specific point in time, the voltage level is compared with the threshold, the operation occurs. This principle is now used everywhere: from power supplies of electronic equipment to microwave ovens. The product of R and C is called the time constant, and for three intervals the system is fully discharged exponentially.

In 1958, semiconductor electronics was not developed; in the book on the element base, time relays are allocated to:

  • electronic tubes;
  • discharge devices.

Subject literatureconditions for the flow of electric current. As readers have guessed, it is logical to add semiconductor time relays to this tandem. Here, the RC chain controls the operation mode of a key element, for example, a transistor or thyristor.

Wrong people who consider written in 1958 the Stone Age. Already at that time, on the basis of basic knowledge, it was possible to assemble battery chargers, today, gas-discharge devices are widely used as part of a daylight starting relay. This differs from that described by the authors of books of the last century, where, due to an increase in voltage in the RC system, at some point a breakdown of the discharge gap occurs, causing contact switching. In digital technology, comparators are also used as analyzers. The knowledge provided promotes a better understanding of the topic.

We add that today the time relay has been replenished with programmable options. Everyone knows that Windows through the Task Scheduler reminds of events. View as a software time relay. Although in a broad sense, any electronic system cannot do without it. Even the threads in the personal computer processor are processed in their own time interval. System clocks are usually called hardware( hardware), and software as opposed to this - software. It is clear that the latter work on the basis of the first.

The counting unit in the latter case is the clock pulses. On the specified principle, timers are actively built in the circuitry of any series of microcircuits. Mechanical timers are used in washing machines and microwave ovens, representing ordinary watches. Thanks to special tricks, they tick only with the power on. A variant of this type are motor relays, where the speed of the counting mechanism is regulated by means of gearboxes.

Relays from Panasonic

Characteristics of the time relay

The logical classification of the properties of the devices goes in four directions:

  1. The range of exposure times. Today, the parameter varies in limitless limits: in the direction of increasing and decreasing time.
  2. Stability. The parameter concerns electronic relays more. It implies the ability of the device to perform functions when the supply voltage changes. It is clear that in circuit breakers at 240 V the operation will occur earlier than at 220 V at the same current. This follows directly from the Joule-Lenz law( thermal power is calculated as the product of current and voltage).
  3. Durability. Usually measured in on and off cycles.
  4. For electronic devices: power consumption.

Even a bimetallic plate, which is not an electrical device, dissipates power due to heat. The automatic switch will work for a long time in a given mode, and the energy will continue to flow into space. And the operation will not happen. With similar losses reconcile in view of the efficiency of the structure. If we take electric kettles, even a current does not flow through a bimetallic plate: the sensitive element stands under the button and flows around the vapor. As a result, at the right time the heating is turned off, and the water has time to boil. It turns out that the same physical principles are used in different ways:

  1. In the case of starting protection relays of refrigerators and automatic switches, current flows through the bimetallic plate, the Joule-Lenz law comes into effect.
  2. An electric kettle heats the sensor indirectly from steam rising above water.
  3. As part of the ballast of daylight lamps, the bimetallic plate is heated by thermal energy generated in a small gas-discharge flask.
  4. In the iron and oil heater, the bimetallic plate is mounted directly near the helix and serves to control the power supply.

Time delay circuit of the

relay. Say, examples of time relays have little relation, and we will answer that the mentioned things allow you to understand more deeply the principle of organization of the devices considered today. A person with much greater interest relates to the phenomena that he understands. The characteristics of the time relay are complemented by a list of parameters:

  1. The number of trip values. The parameter is not relevant for most household appliances.
  2. Number of switching contacts. It is agreed for simultaneous control of several devices, plus in the case of three-phase circuits, when it is required to remove the supply voltage from all lines simultaneously.
  3. When choosing timers in the switchboard, pay attention to the possibility of installation on a DIN rail.
  4. The normal position of the contacts: closed or open. Relays are able to turn on or off the power.
  5. Electrical relays are characterized by transmitting power. For automatic switches, this is the rated current and the maximum breaking current. The second parameter concerns the destructive mode in conditions of uncontrolled growth of power, when the relay is still able to function. For circuit breakers, the order of the digits sometimes amounts to thousands of amperes, and the occurrence of such a situation is characterized as abnormal and unlikely.
  6. Electrical relays are available for direct and alternating current. For high voltages, various methods are used to extinguish the spark. Described in the review about the circuit breakers.

Electrical Relay Where

Time Relays are Used The list of designs is truly extensive. It is appropriate to divide the time relays into the built-in technology and sold separately. It is clear that the microwave oven, the washing machine work according to the program, people have little influence on the process. It is logical to use separate timers that control the operation of lighting, heating, doors, and locks as your own ideas.

In advanced models, the possibility of changing the program by days of the week is built in, periodically there is a correction in latitude for adequate operation of lamps and lamps. For heating timers are not considered the best option, although they can be used to maintain the microclimate.

But the most common type of relay is considered the timers of digital technology, without which no electronic device can do today. The devices are based on a quartz resonator with a frequency of high stability. Temperature and temporal departures of the parameters from the nominal are so small that they are usually neglected. Quartz crystals made possible the existence of computer technology. Although initially oscillations were obtained on the basis of resonant circuits from capacitances and inductances, it turned out that the process needs external stabilization.

The quartz resonator is already considered an oscillatory system. When the applied frequency coincides with its own frequency( selected by the configuration of a SiO2 crystal), the electrical resistance of the structure decreases sharply. This fact is monitored by a pulse generator and is used to stabilize the frequency. People known quartz watches that use the effect and do not require adjustment. It has considerable importance in computer technology.

Each manufacturer is struggling to increase the frequency, which ensures the competitiveness of products. Any failure is fraught with system instability, which will naturally cause a drop in demand. By the clock of the generator, any action in the system unit is counted. Even the RAM works on the basis of latching triggers according to the indicated principle. Fluctuations are used to store system time in the CMOS memory. This is important, if this parameter fails, the Windows operating system gives significant errors, up to the loss of activation( hackers tried to trick the shareware software by changing the CMOS system time).

Time relays are used massively, in built-in and external versions. Especially great is their role in the composition of digital technology. In the conventional sense, these are timers that determine the logic of other systems. Alarm clock - a well-known time relay, at a certain moment waking the buzzer. Similar devices built into kitchen furniture made it possible for more than one hostess to recall the dishes cooked on the stove. And the burned pots are difficult to clean, the value of such time relays is difficult to overestimate.

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