Electrical wiring in the broadest sense of the term is the same essential component of a modern home as water supply, sewerage and ventilation. It is quite natural that as the wiring becomes more complex, the question arises of managing this system, which can be carried out by means of computer technology, organizationally part of the home automation.
The essence of such control is extremely simple: a computer in one form or another of its execution implements a given program taking into account additional information generated by various sensors, after which it forms the corresponding control impact. The latter is a low-current signal.
An intermediate link is required to control power electrical circuits. Currently, there are two varieties of functionally similar elements available that take on this function: classic relays, known as contactors, and solid state relays. Accordingly, in the process of creating a wiring control system, the question arises of choosing one or another type of actuator.
Contactor and solid state relay design features
The contactor is a conventional electromagnetic type relay, designed in a standard housing for mounting on a DIN rail, Figure 1. When a signal is applied to the control input, the contacts move with opening and / or closing of the power circuits.
Solid state relays or electronic contactors, Figure 2, are controlled in the same way by applying a signal to the auxiliary input. The functions of the key element are performed by a transistor.
The independence of the operating and control circuits is ensured by optocoupler isolation. Figure 3 shows a simplified diagram of such an element using a phototransistor in the power circuit.
Advantages and disadvantages
The advantages of the contactor are determined by the fact that for one and a half hundred years of its existence its design has been worked out to perfection, and mechanical contact provides a unique combination of excellent load capacity and very high open-circuit resistance condition. There are also a lot of disadvantages: low speed due to the inertia of the mechanical system, large control currents, audible clicks when triggered.
Solid-state relays in the sense of the list of advantages and disadvantages are almost the complete opposite of an electromechanical relay. They combine quietness, low control current and high performance. All this was bought at the cost of the need for heat dissipation due to significant resistance under load, increased sensitivity to impulse noise and a tendency to fail in case of short circuit on going out. In addition, elements of this type are often not designed for DIN rail mounting.
Applications of technology
From the list of advantages and disadvantages, the main areas of application of the considered technique immediately follow.
Solid state relays are advisable:
- in advanced home automation systems with a large number of computer-controlled loads;
- to ensure the efficiency, first of all, of low-power consumers;
- in the presence of a high-quality 220 V.
In all other situations, it seems preferable to use a traditional contactor.