Timers are quite common in our life. They are devices that send signals at a set time interval. Many household appliances (washing machines, ovens, microwaves) have counters on which you can set the response time in hours, minutes and seconds. A separate type is the weekly timer, which is also widely used in various techniques.
Content
- Application area
- Operating principle
- Varieties of timers
Application area
According to the principle of operation, the weekly timer (or time relay) is similar to all other similar devices with that the only difference is that the time interval programmed in it is not a few minutes or hours, but seven days.
An electronic time timer of this type is used in lighting structures:
- streets;
- administrative and industrial buildings;
- billboards and banners;
- shop windows.
Very often, a weekly time switch is built into the motors of pumps and ventilation systems.
Weighing a little more than 150 grams and a power consumption of about 5 W, it shows a fairly accurate operation with an error of only 2 seconds per day.
The ability of the device to turn on and off on its own within a few days greatly simplifies and makes electrical engineering more convenient in the apartment. For example, in the case of a long absence of residents in the house, such a relay will ensure the regular operation of the autonomous watering system of street plants, the supply water and food for pets, periodically turning on lights, TV, radio or music in order to prevent intruders from entering House.
Operating principle
The electronic timer is a new and more advanced version of an electromechanical device.
An electronic device has a number of advantages in the form of:
- compact size;
- high accuracy of operation;
- modern interface;
- convenient settings.
As for the disadvantages of such a device, they should include the limited service life of the battery installed inside it. If it fails, you will either have to look for the same battery to replace it, or change the entire timer.
In the event of a power outage, the electronic timer is not reprogrammed, but continues to count down the specified time after the appearance of voltage. This leads to the fact thatthe device may turn off and on at the wrong time.
Setting the weekly timer for a certain time period is quite simple. To start the setup, it is enough to activate the corresponding key on the case. After that, using additional buttons, you need to set the required interval within seven days and save it. If an error is made when specifying the parameters or they turn out to be irrelevant after the expiration of the time, then programmed readings can be easily resetby using the Reset key.
The principle of operation of an electronic relay is based on digital or analog circuits. They provide charging and discharging capacitor and counting a specific number of pulses.
In an analog circuit, closing the contacts causes the voltage across the capacitor to rise. A special threshold element monitors this voltage and compares it with the value indicated earlier. When these two indicators match, the element sends a signal to switch the timer. Time delay is adjustable changing the capacitance of the capacitor.
The digital circuit operates from the voltage applied to the power supply. This starts generatortransmitting pulses to the counter. They will continue to flow until they are equal to the value programmed in the timer control system. If they coincide, the output amplifier will receive a signal to stop the supply of pulses. After the voltage is removed from the power supply, the timer will return to its original position. Digital relays have a longer time delay. It can range from a split second to several hours.
Varieties of timers
Time relays with a programmed weekly cycle can be made in the form of various devices. The choice of a suitable model depends on what exactly the timer is needed for.
The device in the form of an outlet is the most convenient and simple to use, since it does not imply complex installation. Such a relay just needs to be plugged into a regular electrical outlet, and then make the necessary settings. However, its power has limited values. from 3000 to 3500 W. In this case, the maximum permissible load should not be more than 16 A.
In a time relay in the form of a socket with a seven-day duty cycle, it can be used 140 different programs. They successfully turn on and off. electric heaters, control heating garage, aquarium etc. Also, the socket timer can start watering plants, create the effect of the presence of residents, including various electronic devices (radio, TV).
Modular type device requires installation on a standard DIN rail electrical distribution board. The rated current of the power contacts of the modular device also does not exceed 16 A, however, the range of its functions is much larger than that of the socket model. Most often, this type of time relay is used to automate the operation of large equipment. Modular timers control lighting streets, shop windows, building facades, industrial premises, various pumps and fans.
The relay in the form of a module can function effectively in conjunction with magnetic starter - a combined device that starts and accelerates electric motors to the rated speed and ensures their continuous operation. The combination of a timer and a magnetic starter allows increase the switching capacity and manage single-phase and three-phase loads.
Another difference between a modular relay and a socket relay is the number of channels. The timer in the form of a module is able to control several independent circuits at the same time.
