The Key Steps To Choose A Micro Switch

Since the introduction of the micro switch in the 1930s, this small electromechanical switch has been continuously developed to meet various application requirements, including aerospace, household appliances, boiler control, medical equipment, sprinkler systems, and testing. Equipment, timers and vending machines, etc. Micro switches are usually used to detect temperature, position and liquid level.

Precision micro switches usually have three specifications: basic type, type with operating handle, type with operating handle and shell type. The micro switch adopts a press and spring design.

Whether engineers are looking for thermostats used in residential heating or industrial boiler control, or liquid level switches in large fuel tanks, they need to consider the following five key features: external dimensions, electrical requirements (voltage/current) ), reliability (mechanical/electrical life), environmental factors (hazardous environment, temperature range) and agency certification. The following 5 key steps can help you choose the micro switch suitable for your specific application.

Step 1: Understand how the size of the switch affects other characteristics

Size is important when choosing a micro switch. The size of the switch is directly related to its characteristics, including current range, travel, and operating force. For example, the smallest micro switch currently on the market measures 0.50 inches x 0.236 inches x 0.197 inches (LxWxH). Although this tiny switch is suitable for detecting the state of a circuit in a compact circuit breaker, it usually only breaks 0.1 to 3 amperes (A) of current and has a short stroke.

Applications that require more current usually require larger switches. For example, in fuel tank applications, the micro switch used to detect the liquid level needs to be able to provide a large stroke and withstand large currents. Usually in liquid level switch applications, the switch must directly drive the water pump and carry a large current. This requires a large micro switch with a rated current of 20A or 25A at a voltage of 125VAC or 250VAC.

Tip: The smaller the size of the switch, the smaller the stroke and the current that can be broken.

In addition, the size of the switch also affects the operating force. In an ideal situation, what engineers need is a switch with low operating force and high current capacity. But in fact there is a compromise between these two parameters. To maintain good contact while providing a large current withstand range, the micro switch needs a stronger spring, which will increase the operating force and size of the switch. The operating force can range from 2 grams in pressurized pneumatic applications to 8 ounces in solenoid valve applications (requiring greater operating force). The largest switch size on the market is 1.94 inches x 0.69 inches x 1.3 inches (LxWxH).

Engineers should also pay attention to the differential travel of the switch—the distance between the switch's trip position and the reset position. The threshold will vary according to different applications. For example, in temperature switch applications, the on/off operating points should be as close as possible, and the differential stroke should be as low as 0.0001 inches. However, in the application of liquid level pumps, if the differential stroke is too short, it may cause the makeup pump to start and stop too frequently, shortening the service life of the pump.

Step 2: Know your electrical requirements

Micro switches are usually able to break currents from 5mA/5VDC to 25A/250VAC. The micro switch product line provides a series of products from low energy consumption to power load electrical type, suitable for various applications.

Engineers must know the rated current and voltage (AC or DC) required for a specific application in order to select the appropriate switch. Since various devices in all industries are committed to low energy consumption, the micro switch must be able to work under low current (logic level load) and DC voltage.

However, there are also some applications that require switches capable of breaking large currents and high voltages, such as industrial pump applications.

In addition to the load requirements, engineers must also select the appropriate circuit. The switch contact must be one of normally open (NO) and normally closed (NC). For NO-type contacts, there is usually no current flowing between the contacts. When the switch is activated, the contact is closed and the circuit is connected. For NC-type contacts, there is usually current flowing between the contacts. When the switch is actuated, the contact opens and the circuit is disconnected.

Step 3: Consider environmental conditions

Environmental requirements have a great influence on the selection of micro-switches, especially in applications requiring high reliability and criticality such as industrial control and medical equipment. Understand the environmental conditions of the application, including pollutants in the air that may enter the switch, the liquid in which the switch is located, and operating temperature requirements.

For applications under harsh environmental conditions, you need to choose a sealed switch with a wide operating temperature range. The highly reliable micro switch can work in the temperature range of -65 degrees Fahrenheit (-54 degrees Celsius) to 350 degrees Fahrenheit (177 degrees Celsius), which can easily cope with various applications. At the same time, it should be noted that the protection level of the switch should be at least IP67 to prevent liquid intrusion. This eliminates the need to spend a lot of time designing a housing that can achieve the same protection level.

Step 4: Clarify working life requirements

The reliability of the switch is critical. You need to clarify how many electrical and mechanical operating life is required for an application? Different switches have different contact materials, housings and terminals, which can meet the electrical and mechanical life requirements of different applications.

A highly reliable micro switch can be operated 10 to 20 million times before mechanical failure, and can be operated 50,000 to 100,000 times under maximum load before electrical failure.

As for the slight price difference between different quality switches, you need to consider the total cost of use. Because you not only have to pay for the switch, but also to ensure that the switch runs for a long time without failure. In many cases, the additional cost of using a more reliable switch will be offset by its lower warranty cost during use.

Step 5: Check agency certification requirements

Choosing a switch that meets various international electrical requirements can help you simplify product design for different regions. Some major standard certifications include UL certification in the United States, cUL certification or CSA certification in Canada, ENEC certification in Europe and CQC certification in China, and KC certification in South Korea.

When choosing a micro switch, you need to consider many factors, such as dimensions, load requirements, working environment and reliability. Therefore, you must understand the actual application requirements: What size switch is required? What is the rated power required? Is it a low-voltage application? Does the switch need to be sealed? Does the switch need to withstand extreme temperatures? Does it require international organization certification? Is it a critical application? Once these issues are clarified, it is easier to choose a switch suitable for the application.