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3 key steps for selecting a micro switch Jun 28, 2018

Micro switch This small electromechanical switch has been developed since the 1930s to meet a variety of different application requirements, including aerospace, home appliances, boiler control, medical equipment, sprinkler systems, testing Equipment, timers, vending machines, etc. Micro switches are commonly used to detect temperature, position and level.

Precision micro switches usually come in three sizes: basic, with operating handle, with operating handle and housing type. Micro switches are designed with and springs.

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

 

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

 

The size is important when selecting a micro switch. The size of the switch is directly related to its characteristics, including current range, stroke, and operating force. For example, the smallest micro switch size on the market today is 0.50 inch x 0.236 inch x 0.197 inch. Although this tiny switch is suitable for detecting circuit conditions in a compact circuit breaker, it is usually only capable of breaking currents of 0.1 to 3 amps (A) with a short stroke.

Applications that require more current typically require larger switches. For example, in a tank application, a micro switch for detecting the liquid level needs to be able to provide a large stroke and withstand large currents. Usually in liquid level switch applications, the switch drives the pump directly and carries a large current. This requires a large micro switch rated at 20A or 25A at 125VAC or 250VAC.

Tip: The smaller the switch size, the smaller the stroke and 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 trade-off between these two parameters. In order to maintain a good contact while providing a large current withstand range, the micro switch needs a stronger spring, and this will make the switch's operating force and form factor larger. Operating forces range from 2 grams in pressurized pneumatic applications to 8 ounces in solenoid applications requiring greater operating forces. The largest switch size on the market is 1.94 inches x 0.69 inches x 1.3 inches.

Engineers should also note the differential travel of the switch—the distance between the switch trip position and the reset position. The threshold will vary depending on the application. For example in temperature switch applications, the on/off operating points should be as close as possible and the differential travel should be as low as 0.0001 inches. However, in liquid level pump applications, a differential stroke that is too close may result in frequent startup and shutdown of the makeup pump and shorten the service life of the pump.

 

 

Step 2: Understand your electrical requirements

 

The micro switch can usually break the current from 5mA/5VDC to 25A/250VAC. The micro switch product line offers a range of products from low-power consumption to power-loaded electrical applications for a variety of applications.

Engineers must know the rated current and voltage (AC or DC) required for a particular application to select the appropriate switch. Since all kinds of equipment in all industries are dedicated to low power consumption, the micro switch must be able to operate at low current (logic level load) and DC voltage.

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

In addition to 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 contacts, there is usually no current through the contacts. When the switch is actuated, the contact is closed and the circuit is connected. For NC type contacts, current is usually passed between the contacts. When the switch is actuated, the contact opens and the circuit opens.

 

Step 3: Define the working life requirements

 

The reliability of the switch is critical. You need to determine how many electrical and mechanical operating lives an application requires. Different switches have different contact materials, housings and terminals to meet the electrical and mechanical life requirements in different applications.

A highly reliable micro switch can operate 10 to 20 million times before mechanical failure, and can operate 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 are not only paying for the switch, you have to make sure that the switch pays for trouble-free operation for a long time. In many cases, the additional cost of using a more reliable switch will be offset by its lower warranty costs during use the application.