A device that uses electronic and mechanical elements and which is triggered after a certain period of time is a time relay. These mechanisms are widely used in many fields such as electronics, electrical and electrical engineering. To make a timer, you will have to use various schemes, differing in varying degrees of complexity.
Content
- Principle of operation
- Pneumatics and watch type
- Electronic relays
- Weekly timer
- Instruments with mechanical scale
- Mechanism activation
- Scheme for beginners
Principle of operation
The presence of a relay in a certain circuit allows you to assemble more flexible devices in terms of controllability. Moreover, a large number of solutions can be implemented. Therefore, it is necessary to consider each design proposal separately. According to the type of activity performed, electromagnetic, electronic and pneumatic systems are used in practice, as well as solutions for watch movements.
Electromagnetic devices, as a rule, can only be used in constant current source circuits. The duration of the action is usually 0.06-0.1 seconds. for turning on and 0.6-1.4 for turning off. Such relays contain two working layers of the winding, one of them is a short-circuited ring-shaped circuit.
When an electric current is applied to the first winding, the magnetic flux rises. It forms the current of the second winding, as a result of which the growth of the main flow stops. As a result, a time characteristic of the displacement of the armature of the mechanism appears, and a time delay is formed.
If you stop the supply of electric current to the circuit of the first winding, then the magnetic field of the second winding will remain active for some time. All of this is due to the inductance effect. It follows from this that the relay does not turn off at this time.
Pneumatics and watch type
Pneumatic systems are unique. These devices contain a special deceleration system - a pneumatic-type damper device. The holding time of "pneumatics" can be adjusted by expanding or narrowing the section of the pipe from which the air is supplied. For such an operation, a special adjusting screw is provided in the design.
The time delay here fluctuates in the region of 1-60 sec. However, there are instances that fire twice as fast. In reality, there are small errors in the indicated time.
Devices called clock relays are widely used in electrical engineering. This type is actively used for the construction of automatic switches that protect circuits with a voltage of 500-10,000 volts. Response time - 0.1-20 sec.
The clock relays are based on a spring that is charged by an electromagnetic mechanical drive. The contact groups of the clockwork switch after the elapsed time interval, set in advance on a special scale of the device.
The speed of the device directly depends on the strength of the current passing in the winding. This helps to configure the device for security functions. The main feature of such protection is complete independence from the influence of external factors.
Electronic relays
Electronic relays have replaced the aging electromechanical devices. Such devices have many advantages:
- Small size.
- Accuracy of action.
- Flexible customization module.
- Reproduction of information.
The operation of electronic relays is based on the principle of digital pulse counters. A large number of today's devices are based on high-performance microprocessors.
To set up the electronic mechanism, you only need to set certain parameters using the special function keys, which are located on the front of the device. Moreover, the setting is flexible, that is, you can set not only seconds, minutes, hours, but also days of the week.
Weekly timer
The electronic on-off timer in automatic mode is used in various fields. The "weekly" relay switches within a predetermined weekly cycle. The device allows:
- Provide switching functions in lighting systems.
- Turn on / off technological equipment.
- Start / disable security systems.
The dimensions of the device are small, function keys are provided in the design. Using them, you can easily program the device. In addition, there is a liquid crystal display on which information is displayed.
The control mode can be activated by pressing and holding the "P" button. The settings are reset with the "Reset" button. During programming, you can set the date, the limit is a weekly period. The time relay can operate in manual or automatic mode. Modern industrial automation, as well as various household modules, are most often equipped with devices that can be adjusted using potentiometers.
The front of the panel assumes the presence of one or more potentiometer rods. They can be adjusted with a screwdriver blade and set to the desired position. There is a marked scale around the stem. Such devices are widely used in the construction of control of ventilation and heating systems.
Instruments with mechanical scale
One of the devices that has a mechanical scale is a household timer. It works from a regular outlet. Such a device allows you to control home appliances in a certain time range. It has a "socket" relay, which is limited to a daily operation cycle.
To use the daily timer it needs to be configured:
- Raise all elements that are located along the disc circle.
- Omit all elements that are responsible for setting the time.
- Scrolling the disc, set it to the current period of time.
For example, if the elements are omitted on the scale marked with numbers 9 and 14, then the load will be activated at 9 o'clock in the morning and will be turned off at 14:00. You can create up to 48 device switch-ons per day.
In addition, the device has functionality that allows you to activate the timer in an out-of-program mode.
To do this, you need to activate the button, which is located on the side of the case. If you start it, the timer will turn on in urgent mode, even if it was turned on.
Mechanism activation
The device is connected in a strict position, prescribed by the data sheet. The instrument is usually installed in an upright position if it does not deviate from the vertical by more than 10 degrees. It is also necessary to adhere to the temperature regime: from -20 to +50 degrees Celsius.
The third parameter that is taken into account when installing the device is air humidity. The permissible level should not be more than 80%. When connecting, it is necessary to disconnect the electrical circuit from the power supply. Diagram of how to make a 220V time relay with your own hands:
Additionally, on the body itself there are designations indicating in what sequence to connect the elements. It usually looks like this:
- The first step is to connect the voltage line to the power terminals.
- Next, there is a connection of the phase line with a switch and an input contact.
- The last step is to connect the output contact to the phase line.
In fact, the time relay is connected along the classic path of many devices, that is, it goes connecting the power supply and activating the load through the corresponding contacts, which form groups, they can be several. It all depends on the relay, which can be single-phase or three-phase.
Scheme for beginners
As a novice radio amateur, you can make a 12V time relay with your own hands. Such a mechanism will work according to the simplest principle.
Time relay connection diagram:
However, even with such a device, it will be possible to turn on the load for a certain time. But there is a small feature - the load time will always be the same.
The button under the designation SB1 closes, C1 is fully charged. When the button is released, part of C1 will be discharged through R1 and the base of the transistor, which is indicated in the circuit under the pointer VT1.
While the capacitor is discharging, there is enough current to maintain the open state of the transistor VT1, which means the relay will work, then it will turn off. Of course, you can do it yourself with a time relay for 2 hours - it all depends on the capacity of the capacitor C1.
