Appeared in recent years, electronic technology has led to the creation of a large number of previously inaccessible to ordinary citizens of devices that facilitate many types of work and create additional amenities and comfort in human life. Among such devices there is also a photo relay, sometimes called a twilight switch, which today is represented on the market in a variety of modifications, which differ in the set of functions that they have, and in the amount of switching power, and in price.
In fact, such a device is a normal relay, but "turned on" by the sun. It can be successfully used not only at production sites, for example, to automatically turn on the lighting of workshops and the territory of an enterprise in the evening. In many cities, the installation of a photorelay for street lighting made it possible to ensure the inclusion of lamps precisely at nightfall, and not according to time or at the command of the dispatcher.
What does the photocell design include?
First of all, it is:
- PCB with microelectronic elements;
- plastic case;
- external contacts (or wires) for connecting the load.
All such relays equipped with photocells, depending on the design features and their inherent functionality, can be broken down into the types below.
Relays with photocell inside their case
Such devices are most often used as automatic lighting switches in rooms or on the streets. They look like a small plastic box (completely transparent or having a transparent window), providing both protection of the internal elements of the electrical circuit from rain and access of light rays to the photocell.
Photocell equipped with a remote photocell
The device differs from the previously described in that the photocell is not located inside this device, but can be placed at a considerable distance from it (up to 150 meters). In this case, the unit in which the electronics and working mechanism are located can be installed in any weatherproof place, for example, in a special electrical cabinet.
This device can be used:
- to control street lighting;
- for the inclusion of outdoor lighting in private households;
- to turn on room lighting in apartments;
- to turn on the lighting of aquariums and greenhouses;
- for lighting the interior of apartments and houses;
- for night illumination of decorative items, wall clocks, figurines, paintings, awards;
- for illuminating small architectural forms, flower beds, arbors, alpine slides, miniature bridges and other landscape design elements;
- for lighting of buildings and monuments, and in general any architectural structures of historical and aesthetic value;
- to set the turn-on time of any devices and units, for example, watering, etc.
When purchasing a twilight switch, especially if you want to install it yourself, carefully study its passport data. Each such device has special characteristics, which are the main argument for its acquisition.
The choice of photorelay should be based on the knowledge of the values of the following parameters. Since they are the most important indicators, taking into account of which and their correct selection, the reliability and durability of the device you have acquired will be ensured.
Degree of protection
As you know, all electrical appliances are divided according to the degree of protection of their IP shells, and for sensors installed outside the premises, this indicator is particularly important. For example, photocell mounted on poles with streetlights requires a degree of protection of at least IP44. Sometimes it is possible to use in such cases a relay with a lower IP value, if any additional measures are used to protect them (for example, in the form of a separate sealed box).
Photocell with remote photocells can also have a low IP degree, but only if these photocells are reliably protected at the installation site and the relays themselves are in a room protected from adverse climatic influences.
In this case, for photorelays with remote photosensitive elements, the degree of protection is indicated in the form of two parameters: the IP value for the photocell separately and the IP value for the unit.
Today photorelays are in great demand in many countries. The main producers of this type of products are such companies:
The cost of the devices they manufacture is determined, first of all, by the price of the photosensitive element included in their composition, which is their most expensive part. It also depends on other parameters of these products related to their quality, size and other indicators.
Usually it is easy to do, as there is always a set of instructions, as well as either in it or on the box in which the product is located, shows the wiring diagram.
The relay outputs are always made with wires having multi-colored insulation. In this case, the red wire should be attached to the load, black (or brown) to the phase, and blue (or green) should be zero. To connect the wires you must use a junction box with terminals. The switching of the load is carried out by interrupting and applying current through the phase conductor.