The push button switch may be the simplest component in the electrical circuit, but it does control the lifeblood of the entire control circuit, so it is also called the "master switch".
As a novice, a comprehensive understanding of various button switches and clever and flexible use can help us get twice the result with half the effort. Push button switches are used to turn on or off small current circuits in a short time, and are mainly used in electrical control circuits.
The current allowed to flow through the push button switch is small, generally not exceeding 5A.
- Type, structure and appearance Buttons generally consist of button caps, return springs, bridge-type moving contacts, static contacts, pillar connecting rods and shells. The opening and closing state of the contacts when the button is not affected by external force (i.e. static) is divided into stop button (i.e. moving-off button), start button (i.e. moving-closing button) and reset button (i.e. moving-on and moving-off contact combination). integrated button). When the button is subjected to external force, the opening and closing status of the contacts changes: the normally open contact in static state is closed, and the normally closed contact in static state is opened.
Push button switches are represented by the symbol "SB" and can be divided into three types: normally closed push button switches, normally open push button switches and composite push button switches. The internal structure diagram and circuit graphic symbols of these three switches are shown in Figure 1.
Figure 1(a) shows a normally closed push button switch. When the button is not pressed, the internal metal moving contact relies on the force of the return spring to connect the normally closed static contacts a and b; when the button is pressed, the moving contact separates from the normally closed static contact, a , b is disconnected; when the button is released, the contact automatically resets (closed state).
Figure 1(b) shows a normally open push button switch. When the button is not pressed, the metal movable contact is disconnected from the normally open static contacts a and b; when the button is pressed, the movable contact is connected to the normally closed static contact; when the button is released, the contacts automatically Reset (disconnected state).
Figure 1(c) shows the composite button switch. When the button is not pressed, the metal moving contact is connected to the normally closed static contacts a and b, and disconnected from the normally open static contact; when the button is pressed, the moving contact is disconnected from the normally closed static contact , and connected with the normally open static contact; when the button is released, the contact automatically resets (normally open opens, normally closed closes).
Some push button switches have multiple pairs of normally open and normally closed contacts inside, which can connect multiple circuits and cut off multiple circuits at the same time. The physical appearance of a common push button switch is shown in Figure 2.