What is the principle of the push button switches?

We encounter various push button switches almost every day, such as medical equipment, automated production lines, and communication equipment. It is a very simple component, but because it controls the entire control circuit, it is called the "Control switch".

Introduction

The push button switch is usually used to turn on and off the control circuit, and it is a kind of control switch appliance that is widely used. It is used in electrical automatic control circuits to manually send control signals to control contactors, relays, electromagnetic starters, etc. Its characteristic is that it is installed in the machine and instrument in the process of work, most of the time is in the initial free state position, and only when needed, it is converted to the second state (position) under the action of external force. Once the external force is removed, due to With the action of the spring, the switch returns to the initial position.

The push button switch can complete basic controls such as start, stop, forward and reverse rotation, speed change and interlock. Usually each push button switch has two pairs of contacts. Each pair of contacts consists of a NO contact and a NC contact. When the button is pressed, the two pairs of contacts act simultaneously, the NC contact is disconnected, and the NO contact is closed.

In order to indicate the function of each button and avoid misoperation, the button caps are usually made into different colors to show the difference, as shown in the figure below. Its colors are red, green, black, yellow, blue, white, etc. For example, red means stop button, green means start button, etc. The main parameters, type, mounting hole size, number of contacts and current capacity of the button switch are described in detail in the product manual.

Siemens-APT Switches

Structure

The push button switch generally consists of a button cap, a return spring, a bridge-type moving contact, a static contact, a pillar connecting rod and a shell.

According to the opening and closing state of the contacts when the push button switch is not subjected to external force (ie static), it is divided into start push button switch (normally open button), stop push button switch (normally closed button) and composite push button switch (NO and NCd contact combination buttons). The contact of the start push button switch is closed when the button cap is pressed, and the contact is automatically disconnected and reset when released. When the stop push button switch is pressed down on the button cap, the contacts are separated, and the contacts are automatically closed and reset when released. When the composite push button switch presses the button cap, the bridge-type moving contact moves downwards, the NC contact is opened first, and then the NO contact is closed. When the button cap is released, the NO contact is first broken and reset, and then the NC contact is closed and reset. Extended learning: What is the internal structure diagram of the push button switch?

Working principle

The working principle of the push button switch is shown in the figure below: There is an electromagnet adsorption device inside the button. When the button is pressed down, the electromagnet is energized to generate magnetism, and the circuit is connected or disconnected by the adsorption device to realize functions such as remote control circuit.