Timers
(1 403)Time delay relay acts as an actuator and a control system for switching on or off the relay, according to a certain function dependent on the variable time. Despite the development of PLCs (Programmable Logic Controller), time delay relays are still widely used in automation systems, domestic, and industrial installations, e.g., to control lighting, ventilation, traffic lights, or heating systems.
Relay applications
Relays are used to switch electrical circuits. Using them, a fairly low-power electrical signal can be used to switch the contacts of a high-power circuit (high voltage and/or current power supply). A simple electromechanical relay is usually made of a magnetic coil on a ferromagnetic core. and a movable iron armature linked to the contacts and moving contacts. When an electric current is passed through the coil it generates a magnetic field that activates the armature, and the consequent movement of the movable contacts makes or breaks a connection to either open or close a circuit. There can be several actuating contacts within a single relay, so it is possible to control several electrical circuits simultaneously. There are also electronic relays, otherwise known as solid state relays or SSRs (Solid State Relay), which do not have mechanical contacts. For this reason, their durability is incomparably longer. However, they have some disadvantages, e.g., a significant amount of generated heat or a small current leakage.
Functions of timing relays
Time delay relays have an electronic circuit that controls the switching on of the moving contacts according to the selected operation mode and the value of the time variable, which is set by the user. These components can be in the form of single function relays, performing one specific function such as delayed activation, or multifunctional relays, where the user has the choice of which of the available relay functions they wish to use. You can also find two-time relays, where two-time variables are available.
Delayed switch-off and cyclic timer relays
The most common functions of time relays are on-delay (pre-set time switch-on), symmetrical cyclical operation, delayed switch-on and switch-off, star-delta starting pulse generation or cyclical operation with two independent times. These are just some of the functions that relays can perform, but their number is much greater, depending on the choice of a particular model. Time settings and selection of the function that the device will perform can be programmed using knobs, DIP switches (for analogue relays) or buttons (for digital relays with LED displays). Thanks to the development of technology, there are now also relays that can be programmed using NFC technology or a dedicated mobile application with a graphical interface, which makes the programming of the relay itself quite intuitive.
Detailed data on the functions, as well as diagrams of their sample time functions, can be found in the technical documentation of the relay, although usually the basic data can also be found on its housing. They sometimes have an additional control input, thanks to which it is possible to obtain more advanced time functions of switching on, switching off, or switching between electric circuits.
Selection of time delay relays
One of the most important parameters that can be set in time delay relays is the time variable. In the case of a component where this is done by knobs, you will usually find one knob called the time range and another called the time adjustment. The measured time, i.e., the value of the time variable, is the result of the multiplication of the time range and the time setting. When choosing the right relay for your application, pay attention to the maximum and minimum value of the time variable that can be set on it. It can vary from fractions of a second up to several dozen days or even a year.
12V and 230V time relays
When selecting a time relay, just like a regular relay, pay attention to the supply voltage. The correct voltage value is important, but also the type of current, which can be DC (Direct Current) or AC (Alternating Current). However, there are universal time relays that use witched-mode power supplies and thus can work in systems that require voltage of 12 V - 230 V AC/DC. Obviously, it is not allowed to exceed the maximum current specified by the manufacturer, which can flow through such a relay, as this may lead to its permanent damage and incorrect operation. In the case of relays, the most common fault is that the contacts weld together or burn out, which is particularly common for relays switching high-power and high-current circuits, as a result they can no longer be switched.
Time delay relays come in different housings. We can distinguish standard enclosures, which are most often used in household distribution boards (panelboards), and industrial enclosures, which are usually modular and thus can be expanded; the time module of such a device can be disconnected, which makes the time relay work as an ordinary relay, without the possibility of switching on or off electrical circuits according to a selected time-dependent function. The most popular mounting method, primarily in industrial automation, is DIN rail mounting. According to the mounting methods, the timing relays can be divided into flush mount, surface mount, panel mount, PCB mount (Printed Circuit Board) or screw mount relays.
Just like all other electronic components, time relays operate within specific operating temperature ranges. Some, if not most of these devices, will eventually be placed under constant, friendly temperature conditions close to room temperature. However, some applications may require operation in freezing temperatures or in an environment where the temperature will be significantly elevated. There are time delay relays that can operate even in temperatures as low as -40°C, but also in temperatures as extreme as 125°C.
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