Selecting A Micro Switch Needs Five Key Steps
Since its advent in the thirties, micro switches have been continuously developed to meet various application requirements, including aerospace, household appliances, boiler control, medical equipment, spray systems, test equipment, timers and vending machines. Micros witches are typically used to detect temperature, position and liquid level.
Precision micro switches are usually available in three sizes: basic, with the operating lever, operating lever and housing. The micro switch adopts a plunger and spring design.
Whether engineers are looking for thermostats for residential heating or industrial boiler control, or level switches for large oil tanks, they need to consider five key characteristics: switch form factor, electrical requirements (voltage/current), reliability (mechanical/electrical life), environmental factors (hazardous environments, temperature ranges), and agency approvals. Here are 5 key steps to help you choose the right micro switch for your application.
Step 1: Understand how the form factor 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, operating travel, and operating force. For example, one of the smallest micro switches on the market measures 0.50″ x 0.236″ x 0.197″ (LxWxH). Although this tiny switch is suitable for detecting circuit status in compact circuit breakers, it typically only breaks currents of 0.1 to 3 amperes (A) and has a short travel.
Most Applications that require higher currents require larger switches. For example, micro switches for level detection in-tank applications must provide a long travel and withstand large currents. Typically in level switch applications, the switch drives the pump directly and carries a large current. It requires a large micro switch rated at 20A or 25A at 125VAC or 250VAC.
Tip: The smaller the switch size, the smaller the travel and the current that can be broken.
In addition, the size of the switch also affects the operating force. Engineers need a switch with low operating forces and high current capability. But in fact, there is a compromise between these two parameters. Micro switches require stronger springs to maintain good contact while providing a large current withstand range, which will increase the switch’s operating force and shape size. Operating forces can range from 2 grams in pressurized pneumatic applications to 8 ounces in solenoid applications where a greater operating force is required. The largest switch on the market measures 1.94″ x 0.69″ x 1.3″ (LxWxH).
Engineers should also note the differential travel of the switch—the distance between the travel position of the switch and the reset position. The threshold varies 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 level pump applications, the differential travel is too close to cause the make-up pump to start and stop too frequently, shortening the pump’s service life.
Unionwell’s micro switches are available in various configurations to meet engineers’ specific needs.
Step 2: Know your electrical requirements
Micro switches typically break currents from 5mA/5VDC to 25A/250VAC. The micro switch product line offers a range of products from low energy consumption to power load electrical versions for various applications.
Engineers must know the rated current and voltage (AC or DC) required for a specific application to select the appropriate switch. Since a wide range of equipment in all industries strives for low energy consumption, micro switches must be able to operate at low currents (logic level loads) and DC voltages.
However, some applications require switches that can break high currents and voltages, such as industrial pump applications.
In addition to load requirements, engineers must select the right circuit. The switching contact must be one of the normally open (NO) and normally closed (NC) types. For NO-type contacts, there is usually no current passing between the contacts. When the switch is actuated, the contacts close and the circuit is connected. For NC-type contacts, there is usually a current flowing between the contacts. The contact opens, and the circuit is disconnected when the switch is actuated.
Step 3: Consider environmental conditions
Environmental requirements greatly influence the choice of microswitches, especially in applications that require high reliability and criticality, such as industrial control and medical equipment. Understand your application’s environmental conditions, including contaminants that may enter the switch in the air, the liquid in which the switch is located, and operating temperature requirements.
It would help if you sealed switches with a wide operating temperature range for applications under harsh environmental conditions. Highly reliable micro switches operate from -65 degrees Fahrenheit (-54 degrees Celsius) to 350 degrees Fahrenheit (177 degrees Celsius), making it easy to handle a wide range of applications. At the same time, it should also be noted that the protection level of the switch should be at least IP67 to prevent liquid ingress. It eliminates the need for a lot of time to design an enclosure that achieves the same degree of protection.
Step 4: Clarify the working service life requirements
The reliability of the switch is critical. How many electrical and mechanical operating cycles do you need for an application? Different switches have different contact materials, housings and terminals to meet different applications’ electrical and mechanical life requirements.
A highly reliable micro switch can operate 10 million to 20 million times before mechanical failure and 50,000 to 100,000 times at maximum load before electrical failure.
As for the slight price difference between different quality switches, you need to consider the total use cost. Because you not only pay for the switch but also for ensuring that the switch runs trouble-free for a long time, in many cases, a lower warranty cost offsets the additional cost of using a more reliable switch during use.
Step 5: Check the agency certification requirements
Choosing switches that meet international electrical requirements can help simplify your product design for different areas. Some main standard certifications include UL certification in the United States, cUL certification or CSA certification in Canada, ENEC certification in Europe, CQC certification in China, and KC certification in South Korea.
When choosing a micro switch, you need to consider many factors, such as form factor, load requirements, operating environment and reliability, so it is important to understand the actual application requirements: What size switch do you need? What is the power rating required? Is it a low-voltage application? Does the switch need to be sealed? Does the switch need to withstand extreme temperatures? Is certification from an international organization required? Is it a critical application? Once these issues are figured out, choosing the right switch for the application becomes easier.
Unionwell Micro Switch Manufacturer From China
Huizhou Unionwell Sensing & Control Electronics Co., Ltd specializes in quality micro switches for the automotive industry and white goods of home appliances.
Main products include basic micro switches, waterproof switches, air pressure switches, mechanical keyboard switches, and door switches.
A one-stop system will be built, covering product development, precision molding, injection molding, precision stamping, automated equipment R&D, assembling, and testing.
The professional sales team is on hand to provide assistance and quick response to 3D drawing requests, price quotes, and access to an adequate sample program that allows engineers to test and qualify switches for their end product applications.