Push buttons, switches, commutators. Without this simple device a lot of machines would not operate. In the field of technical solutions there is a great variety of buttons, switches, rotary switches, toggle switches, slide switches, rocker type switches, etc.
Some of them emit light after they have been turned on, others have only one stable state ор pass into an active state through a switch. Others are quite small and are mounted on printed-circuit boards (micro switches).
Push-button switches control executive mechanisms, such as contactors and relays through commutation.
They are mounted on the control panel, most often in a hole and are secured by a nut on the rear side of the panel. Their electrical connection is via soldering. Switches, depending on the number of contacts and the way they switch, have different ways of marking. The simplest one is by a toggle switch (ON-OFF). Its symbol is SPST. The main symbols and indications are shown in the diagram below.
There are, of course, a lot of other options and variations of the contact configuration.
Another important feature of any device equipped with a contact system is the system’s resistance. You should always remember that contacts are the weakest part of the circuit. The contact resistance is affected by dirt, air humidity, pressure force applied on the contacts, material of the contacts, roughnesses on contact areas (the areas where the contacts get in touch), etc.
In the course of time and switching contacts get oxidized. Every time we open or close the contact this leads to the occurrence of a micro electric arc. The arc facilitates oxidation processes which increase the contacts’ resistance and help for the formation of a stronger and earlier occurring arc. The arc also generates high-frequency electronic interference and changes in the sinusoid of current and voltage.
Increased resistance leads to contact heating and energy losses in the system. Gradually soot appears between the switching areas and if nothing is done, it can lead to welding of the contact system and failure. In order to prevent these undesirable processes, we need to undertake a number of special measures while designing the contact bodies: in order to reduce the resistance – the contacting surface is greater than the cross section of the conductive cable core, in order to prevent oxidation, the contacts are covered with a layer of nickel or silver, which are difficult to oxidize and have high conductivity, thus reducing the inevitable voltage drop. The clamping force is large enough to increase the effective cross-section of the conductive surface. Push-buttons with silver contacts like this one have low contact resistance and long electrical durability.
