1. Button switch principle - Introduction
Button switch, abbreviated as button, is usually used to connect and disconnect control circuits. It is a low-voltage electrical device that sends commands in electric drive, and is widely used as a main command device. In electrical automatic control circuits, it is used to manually send control signals to control contactors, relays, electromagnetic starters, etc. Its characteristic is that it is installed in machines and instruments that are in operation, and most of the time it is in the initial free state position. It only switches to the second state (position) under external force when required. Once the external force is removed, the switch returns to the initial position due to the action of the spring.
The button switch can complete basic controls such as start, stop, forward and reverse rotation, speed change, and interlock. Usually, each button switch has two pairs of contacts. Each pair of contacts consists of one normally open contact and one normally closed contact. When the button is pressed, both pairs of contacts act simultaneously, with the normally closed contact opening and the normally open contact closing.
In order to indicate the function of each button and avoid misoperation, the button caps are usually made in different colors to distinguish them, as shown in the following figure. Its colors include red, green, black, yellow, blue, white, etc. For example, red represents the stop button, green represents the start button, etc. The main parameters, types, installation hole sizes, number of contacts, and current capacity of the contacts of the button switch are all detailed in the product manual.
2. Button switch principle - structure
A button generally consists of a button cap, a reset spring, a bridge type moving contact, a stationary contact, a support rod, and a housing.
The opening and closing states of the contact when the button is not subjected to external force (i.e. static) are divided into start button (i.e. normally open button), stop button (i.e. normally closed button), and composite button (i.e. button that combines normally open and normally closed contacts into one). For the start button, when the button cap is pressed, the contact closes, and when released, the contact automatically disconnects and resets; The stop button is the opposite. When the button cap is pressed, the contacts separate, and when released, the contacts automatically close and reset. When the button cap is pressed, the bridge type moving contact moves downward, causing the normally closed contact to first disconnect before the normally open contact closes; When the button cap is released, the normally open contact will first disconnect and reset, and then close and reset.
3. Button switch principle - working principle
The working principle of the button switch is easy to understand, as shown in the following figure. To put it bluntly, there is an electromagnetic suction device inside. When you press the button, the electromagnetic coil inside generates magnetism instead of electricity, and then the circuit is connected or disconnected through this suction device. Thus achieving remote control and other functions of the line.
The opening and closing states of the contacts when the button is not subjected to external force (i.e. static) are divided into start button (i.e. normally open button), stop button (i.e. normally closed button), and composite button (i.e. button that combines normally open and normally closed contacts into one). For the start button, when the button cap is pressed, the contact closes, and when released, the contact automatically disconnects and resets; The stop button is the opposite. When the button cap is pressed, the contacts separate, and when released, the contacts automatically close and reset. When the button cap is pressed, the bridge type moving contact moves downward, causing the normally closed contact to first disconnect before the normally open contact closes; When the button cap is released, the normally open contact will first disconnect and reset, and then close and reset.