Time relay: operating principle, wiring diagram and tuning recommendations
A device that is triggered upon the expiration of the designated time interval is called a time relay - the device has found wide application in electrical engineering, electrics, and electronics. Thanks to its use in circuit solutions, it is possible to implement more flexible control functions for various equipment and devices.
Depending on the design and the principle of operation of the device, it is possible to organize electrical circuits of varying complexity.
We offer to understand what types of time relays exist, what are their specifics of operation and application. The theoretical material is supplemented by practical recommendations for connecting and configuring a temporary control device.
The content of the article:
- The principle of operation of the timer
- Setting up electronic mechanical analog relays
- Instrument adjustment with digital scale
- Time relay connection in the control circuit
- Conclusions and useful video on the topic
The principle of operation of the timer
Electronic devices are represented by a constructive variety, therefore, the principle of a timer should be considered taking into account each design variation individually.
From the point of view of the actions performed, in practice, electromagnetic, pneumatic, electronic structures and clockwork devices are used.
Option # 1: electromagnetic devices
Devices that support the electromagnetic principle of operation, as a rule, are designed to work exclusively in DC-powered circuits.
The response time range is usually 0.07 - 0.11 sec. For switching on and 0.5 - 1.4 sec. For switching off. The design of such timers contains two working windings, one of which is a short-circuited loop in the form of a copper ring.
When an electric current passes through the main winding, an increase in magnetic flux is noted. This current forms a short-circuited current, due to which the growth of the magnetic flux of the main winding is limited.
As a result, a temporary characteristic of the movement of the armature of the actuator is formed or, in other words, a time delay for switching on is created.
If the current supply to the main winding circuit is interrupted due to the inductance effect, the magnetic field of the short-circuited winding remains active for some time. Accordingly, during this time the relay does not turn off.
Option # 2: pneumatic devices
Structures based on pneumatic systems are a kind of exclusive device. Such devices are equipped with special deceleration mechanics - a pneumatic damper mechanism.
You can adjust the exposure time of pneumatic relays by reducing or increasing the bore of the tube through which air is supplied. For these purposes, pneumatic relay designs are provided with an adjusting screw.
The setting range for the time delay of pneumatic relays is on average 1-60 sec. However, there are instances that almost double this range. True, in practice, small errors were noted (about 10%) in terms of accuracy of operation according to the established values.
Option # 3: watch type modifications
The so-called clock timers are widely used in electrics. This type of device is often used in constructions. circuit breakersdesigned to protect circuits with a voltage of 500 - 10,000 volts. The exposure range is 0.1 - 20 seconds.
The principle of operation of watch models is based on the work of a spring charged by a mechanical drive (anchor) of an electromagnet. The contact groups of the time clock are switched by the fact of elapsed time, the value of which was previously set on the scale of the device.
The speed of the mechanism of the device is directly related to the current flowing in the winding of the electromagnet. This factor allows you to configure the device to fulfill the protection functions. The peculiarity of such protection is expressed by complete independence from the influence of ambient temperature.
Option # 4: electronic relays
The last few years, almost everywhere where time relays can be used, electronic versions replaced the outdated electromechanical models.
This type of device has a number of advantages:
- small dimensions of the case;
- high accuracy of operation;
- convenient setting mechanism;
- visual display of information.
Electronic versions operate, as a rule, on the basis of digital pulse counters. Many modern devices are built on high-performance microprocessors. Digital relays are usually designed for switching low-inductive or non-inductive loads.
To configure a digital timer, it is enough to set the necessary time parameters using the function keys located directly on the front panel of the case.
The setting is usually available over a wide range of time; it covers not only seconds, minutes, hours, but also days of the week. For example, we can consider the model of a weekly electronic relay - timer.
An electronic timer with automatic on-off functions can be successfully used in control schemes for different types of devices. The so-called “weekly” time relay provides switching functions in accordance with the set period of time within a weekly cycle. Such devices are used in systems "smart House".
For example, thanks to the device, there are opportunities:
- switch lighting systems at a given time;
- start or stop technological equipment;
- activate / deactivate security systems.
The device is small in size, has several function keys. Using the system keyboard, the user can easily configure it (program).
The programming mode is activated by pressing and holding the button indicated by the symbol “P”. To perform a system reset, the Reset key helps. Changing the relay time settings is carried out with the keys for setting the minutes, hours, days of the week with the programming mode active.
The standard time relay connection scheme provides for the installation of one of two action control modes - manual or automatic. The convenience of setting up a digital type relay is provided by an informational liquid crystal display.
Setting up electronic mechanical analog relays
Industrial automation systems, as well as various household modules are often equipped with electromechanical devices, the design of which involves tuning using potentiometers.
On the front panel of the case of such devices is a potentiometer rod (or several rods) designed for rotation with a screwdriver blade. On the circumference of the rod (s), a marked scale of installation values is applied.
The slot on the rod under the blade of the screwdriver is a kind of pointer that changes its position when the rod rotates. By setting this pointer opposite to certain values of the marked scale, the desired parameter is set.
Appliances of this type (e.g. NTE8) are widely used in control schemes for ventilation systems, heating modules, artificial lighting devices.
Instrument adjustment with digital scale
The use of devices with mechanical adjustment functions can be demonstrated by the example of a household brand timer REV Ritterdesigned to be plugged into a home electrical outlet.
With help timer outlets can be controlled in a given time range by almost any household appliance. To use this daily timer, just plug in the device and configure.
The setup is accompanied by the following steps:
- Raise all segments located around the circumference of the setting dial.
- Omit only those segments that correspond to the setup time.
- Turn the dial to set the disk pointer for the current time.
For example, if segments between the digits of the scale 18 and 20 were omitted, after the relay starts the countdown, the load will be turned on at 18 hours and off at 20 hours.
In general, the design of the mechanical REV Ritter relay allows you to organize up to 48 starts in a full 24 hours.
At the same time, the device supports the function of off-program load switching. To do this, there is a separate button located on the side of the case. If the user activates this button, the load is connected to the network directly, regardless of the state of the relay contacts.
Time relay connection in the control circuit
The device must be connected taking into account the conformity of the installation site with the conditions stated in the technical data sheet of the device. As a rule, installation involves vertical installation of the device with tolerances of deviation from the vertical of no more than 10º.
The temperature limits of the room where the installation and operation of the time relay is supposed to usually do not exceed the range of -20 ° C + 50 ° C.
The air humidity level in the installation zone of the device must not exceed the value of 80%. The electrical circuit where the timer is installed should be disconnected from the mains supply during installation.
A device of any design traditionally has a technical passport, where the connection diagram is indicated. Many electronic-mechanical and digital timers are supplemented by a circuit printed directly on the case and showing how and in what sequence to connect the time relay.
The classic connection option looks like this:
- Connect the voltage line to the power supply terminals of the device.
- The phase line through the circuit breaker is connected to the input contact of the relay load.
- The relay load output contact is connected directly to the load phase line.
In fact, the connection diagram for the bulk of the devices is built on an identical principle: connecting power to the device itself and turning on the load through a group of switched contacts.
Depending on the type of relay (single-phase, three-phase), as well as on the design features, there can be several of these contact groups.
A simple version of the timer can be done with your own hands. Schemes of various homemade products are described in this article.
Conclusions and useful video on the topic
The video considers the possibility of using a modular device, where there are two independent time-commuting devices. The scheme provides for the inclusion of two appliances of household appliances, the adjustment of their work in time intervals and other functions.
Of course, all existing modifications of the time relay can not be covered by one modest review. To consider the entire range of devices you will need to write a whole book. Actually, reference books on timers of various types are available, and you can always find the necessary information if you wish.
Is there anything to supplement, or have questions about the operation, selection, connection and configuration of the time relay? You can leave comments on the publication and participate in discussions. The contact form is located in the lower block.