Micro-action switches are key components in various electronic devices, and can be said to be the basic guarantee for the operation of many devices. For example, the rice cooker buttons used at home, the window control buttons on the car, and the automatic control devices on the factory assembly line will all use this switch. Its principle is actually not difficult to understand. It is to change the internal metal contacts in contact or disconnection through the slight displacement of physical buttons, thereby controlling the current on and off. To give a specific example, such as the locking device of elevator doors and the emergency stop buttons on factory machines, the reliability of switches in these important safety devices directly determines whether the equipment can operate normally, and even affects the personal safety of the operator.
The necessity of detecting the quality of such switches is mainly reflected in two aspects: one is that when there is a problem with the equipment, the other is to prevent possible safety hazards in advance. For example, if the switch contact is poor, it may cause the equipment to stop operating suddenly, or the contact oxidation is severe, and electric sparks may occur and cause accidents.
During the specific inspection process, three aspects of the state need to be confirmed: first, whether the contact point can be switched normally (that is, the normally open and closed state often referred to as the normal opening and closing state), second, test how much force it needs to be applied to trigger (this is related to the service life), and finally, check whether the insulating material is aging (preventing the risk of leakage).
What are the basic test parameters of micro switches?
Contact on-off performance verification
· For normally open contacts (NO), that is, when the switch is not triggered, the current flow should theoretically not be detected (the resistance is infinitely large). After triggering, this value will drop to nearly zero ohms. Conversely, the normal closed contact (NC) is just the opposite. The resistance is very small in normal state, and after triggering, it will be disconnected to form a break. In actual operation, the resistance gear of the multimeter can be used to measure and compare before and after the switch operation.
Action Strength Parameter Test
· This test mainly confirms how much force is required to press the switch. For example, the product specifications usually include numerical ranges such as 1 to 5 N. Through a dynamometer or a special equipment with a pressure sensor, the minimum force that changes the switch state can be recorded. This is very important for actual use. For example, if the buttons of the on-board equipment are too strong, it may be inconvenient for the driver to operate during driving.
Insulation performance detection
· According to conventional standards, the insulation performance between each conductive component must be good enough. Simply put, the resistance value between the contact point and the metal shell and between different pins must reach at least 100 megohms. At this time, the high resistance gear of the megohmmeter needs to be tested. Especially for switches installed in humid environments, if this indicator fails, leakage or even short circuit may occur.
Service life evaluation experiment
· Simulate long-term use scenarios through automated equipment, such as allowing the switch to work continuously for 100,000 times. During the process, changes in several key indicators need to be observed: such as the problem of increased resistance caused by contact surface oxidation, the attenuation of pressing pressure caused by spring structure fatigue, and abnormal noise caused by wear of plastic parts. This type of test is particularly important for product quality control. For example, high-frequency switches such as elevator buttons must pass strict testing.
How to preliminarily judge whether the micro switch is damaged through appearance inspection?
. Shell inspection
· If there are cracks or deformations, it may affect the sealing effect, such as the waterproof and dustproof performance. In particular, the protection level requirements such as IP67 may not be met.
· Pay attention to whether the metal parts have rust or corrosion marks, especially for switches used in relatively humid environments such as kitchens and bathrooms. This oxidation phenomenon will directly affect the conductive effect.
Pin inspection
· If the pin is oxidized and blackened or loose, it is easy to cause poor contact problems, such as occasional signal or direct disconnection. At this time, you can find the problem by measuring it with a multimeter.
· If the pin is found to be broken, basically you can only replace the switch with a new one. In this case, it is safer to scrap it directly.
Contact inspection
· If the contact surface is burnt and blackened or carbonized, it feels rough and uneven to the touch. At this time, the resistance value will increase abnormally, which may cause poor power supply. For example, sometimes there is no response when pressing it, which may be this problem.
· Wear caused by long-term use will make the contacts thinner. At this time, the contact area is not enough, which may cause poor contact. For example, the flickering of the light may be caused by this reason.
Check the drive rod
· If the drive rod is stuck or deformed, there will be a sense of blockage or extra force when pressing, and the switch may not be triggered. For example, some buttons need to be pressed hard to respond, which may be a problem with the drive rod.
· A completely broken drive rod will cause the switch to fail completely. This situation is more common on devices that often need to be pressed repeatedly, such as game controller buttons.
What are the detailed steps for using a multimeter to test the continuity of a micro switch?
1. Preparation
· Be sure to disconnect the power supply first, such as unplugging the device or turning off the main switch, which is safe and will not damage the instrument. If you operate with power on, the multimeter may burn out.
· Select the measurement gear, such as using the buzzer gear to measure continuity, and using the 200 ohm gear to measure resistance. The operation of different models of multimeters may be slightly different.
2. Measure the normally open contact
· When the switch is not pressed, the two contacts should be disconnected, and the multimeter display should be infinite at this time. For example, the digital display 1 or OL indicates normal.
· After pressing the switch, the value should be close to zero and the buzzer will sound. If there is no response or the value is high, it means that the contact may be oxidized or the contact is poor.
3. Measure the normally closed contact
· When it is not pressed, the resistance value should be very small and the buzzer will continue to sound. For example, a display of about 0.5 ohms is considered normal.
· When the switch is pressed, it should be disconnected, and the displayed value will suddenly increase. If the value does not change, it may be that the contacts are sticking or the spring is invalid.
4. Insulation test
· It needs to be adjusted to a high resistance position, such as a 100MΩ range. When measuring, the red test lead should touch the point and the black test lead should touch the shell. The larger the displayed value, the better.
· For example, if the measured value is less than 50 megohms, it means that the insulation layer may be aged or damaged. If this switch is used continuously, there will be a risk of leakage.
How to simulate actual working conditions to test the reliability of micro switches?
1. Mechanical life verification
For example, equipped with automated life test equipment, this equipment can generally simulate more than 100,000 repeated pressing actions. The following aspects need to be focused on:
· Will the resistance value of the contact point become larger and larger when in contact, like the poor contact of the old switch
· Whether the attenuation of the pressing force exceeds the allowable range of the product manual
· The wear of mechanical parts, especially whether there are cracks in the shell or deformation of the drive rod. These structural damages will directly affect the normal use of the switch
2. Environmental adaptability detection
The test can be divided into two dimensions: temperature and humidity. For example, under extreme temperature conditions from -40 degrees to 85 degrees, the actual test of the change in the pressing force of the switch and whether the insulation resistance meets the standard. The humidity test mainly depends on whether there will be leakage risks in high humidity environments, such as the performance in the rainy season in the south or in the bathroom environment.
3. Load capacity assessment
For example, if you perform routine tests according to the standard current value marked on the product manual, you need to record the temperature rise of the contact points and the oxidation of the metal surface. Overload testing needs to simulate emergencies, such as too many high-power electrical appliances at home causing a trip. The current is adjusted to 1.2 times the standard value and continuously energized to see how long the switch can last without damage. This is a key step in verifying product quality.
What safety precautions should be taken when testing micro switches?
1. Power-off detection
· For example, before starting the test, the power supply line must be disconnected first. This step can be confirmed by using a tester or a multimeter to confirm that there is no current in the line, just like the routine operation we do when changing fuses or adjusting lines
2. Leakage protection
· When operating, you need to choose tools with an insulating layer, such as a screwdriver with a rubber sleeve or insulated pliers
· It is recommended to wear an anti-static device on the wrist, such as a wristband with a metal clip, to prevent the static electricity generated during the test from causing accidental damage to the sensitive components of the micro switch
3. Parameter control
· Never exceed the numerical parameters written on the equipment label, such as the current size or voltage range. This overload test can easily cause the contacts to burn, and in severe cases, it may also cause a fire in the line
4. Site requirements
· Try to arrange the operation in a dry space with air circulation, such as a place with an exhaust fan in the workshop, and avoid testing in places with high humidity or volatile gases
· Special attention should be paid to the absence of ignition sources in the work area. For example, when conducting inspections, welding operations or the use of open flame devices such as lighters should not be carried out at the same time.
