Micro switches types are essential components in sensing and control instruments. These instruments are vital in various machinery, be it industrial, agricultural, transportation, construction, etc.
Unlike devices like proximity switches, this component is quite simple. But its uniqueness lies in the ability to perform snap-action switching with precision. Because it is critical in multiple applications, here is a close-up look at the micro-switch types and other details about the device.
What is a Micro-Switch?
A micro switch is a precise snap-action change-over switch containing a tiny contact gap. Also known as a snap-action miniature switch, the snap action refers to a change-over where the breaking speed and contact-making are independent of the actuator's operating speed.
How a Micro-Switch Works
After making physical contact with an object, a micro switch's contacts change state. When the mount pin plunger switch is in the rest/released position, the NO (Normally Open) circuit opens. On the other hand, the NC circuit (Normally Closed) closes and can carry current.
However, when the plunger depresses or switches, current flows in the NO circuit, and the NC circuit opens.
Features of Micro Switches
A micro switch has the following features.
- Suitable for logic-level loads and power-duty switching
- Gold-plated silver alloy contacts to provide logic-level control
- Silver alloy contacts for power duty switching
- SPNO, SPDT, or SPNC switch options
- Mount pin plunger switch
- Several stainless steel lever options (including external and internal mount levers)
- Multiple electrical terminations
- UL, cUL to UL 61058-1, CQC to GB 15092.1, and ENEC to IEC 61058-1 certified
Construction of a Micro Switch
Building a micro switch is simple. It requires only the following parts.
- NO, and NC terminals
- Actuator (plunger)
- Moving arm
- Moving piece
Micro Switch Types
These switches come in various types, including the following.
Flexible rod micro-switches can operate in any 360° direction, except the one running along the rod's center. It detects shape/direction inconsistencies effectively and has a small operating force. Additionally, the actuator absorbs the overtravel, creating a substantial leeway in object play operation.
This device features a rotating low-torque actuator. It is perfect for detecting lightweight objects such as paper currency.
Reverse Operation Hinge Lever
With its changeable lever shape to match the operating body, this switch is suitable for low-speed, low-torque cam operation. The lever material is usually steel.
Reverse Operation Hinge Roller Lever
This switch is similar to a reverse operation hinged lever but with a roller attached. It is also suitable for cam operation.
This switch features a bend in the lever to create a large stroke. It is ideal for detecting moving objects, such as dogs and cams.
A powerful leaf spring gives this device a large stroke, making the actuator ideal for cylinder drives or low-speed cams. Also, it features a fixed bearing point, so the overtravel must be within the application's specifications to avoid damage.
Roller Leaf Spring
This device is similar to a leaf spring but with a roller attached. It is ideal for dog or cam operations.
Simulated Roller Lever
A micro switch with a hinged lever bent at the end to a curve for use as a simple roller type.
Simulated Roller Leaf Lever
While the simulated roller lever contains a hinged lever, this one features a leaf lever. This lever has its end bent to a curve for use as a simple roller type.
Pin plungers are ideal for short & direct strokes (perfect for high-precision position detection). However, the downside is having the shortest overtravel of any actuator. Therefore, it requires a reliable stopper.
Spring Pin Plunger
Although it has the same applications as the pin plunger, the spring pin type has a longer overtravel. Also, the plunger diameter is a bit larger, but avoid the off-center loads when using the device.
Spring Short Pin Plunger
Contrary to the "short" word in its name, this switch has a long overtravel, like with the spring pin plunger. But it has a short plunger with a large diameter for easier alignment.
A hinge-lever is ideal for a low-speed, low-torque cam. Usually, the lever is steel-made, and you can alter its shape to match the operating body.
Hinge Roller Lever
This device is a hinge lever with a roller attached and is suitable for high-speed cam operation.
Panel Mount Pin Plunger
Mounted to a panel by a hexagonal nut and lock nut for positional adjustment, panel mount pin plungers offer the largest overtravel of all the plunger types. You can operate the device manually or mechanically and use it with a low-speed cam.
Panel/Cross Mounted Roller Pin Plunger
This plunger is similar to the panel mount pin type but with a roller attached. However, it has a shorter overtravel, and you can operate it using a dog or cam. Also, you can get cross-rollers running parallel to the switch.
How to Select the Micro Switch?
Consider the following factors when selecting a micro switch.
There are various actuator types. They include a push-button, roller, pin, or lever. When considering this factor, think about how long or short (big or small) you want the actuator. You have the option of picking one of the following:
- Pin plunger
- Standard straight lever
- Long lever arm
- A short roller lever arm
- Long lever arm (ultra micro)
- Roller arm (ultra micro or heavy-duty)
- Roller plunger (heavy-duty)
- L-shaped lever
Will you be using AC or DC power supply, and at what voltage? Also, what is the largest current the contacts will have to handle? Each micro switch type has current and voltage specifications, and you should ensure these match your application requirements.
Number of NC and NO Contacts
Usually, micro switches contain one NC and one NO contact, but you can get more.
Pole and Throw Count
It is vital to note that the number of movable contacts in the switch determines how many poles you need. Similarly, the number of fixed contacts determines the required throws.
The switch's outer cover should withstand the environmental factors in its operational area. Ensure it has the necessary IP or NEMA rating to withstand explosions, water, etc.
Micro Switch Advantages
A micro switch has the following advantages.
The contact and actuator's movement and speed are independent. Therefore, you can rely on the terminals changing state predictably unless the switch is almost at the end of its lifespan.
In other switches, the actuator's movement causes the contacts to move. However, contacts in a micro switch do not change state until the actuator gets to a specific reset/trip point.
Reduced Arcing Damage
A micro switch has high switching speeds that extinguish arcs quickly. This fast movement minimizes arcing damage to the contact surfaces.
An electrical arc
How to Use a Micro Switch?
There are two ways to use a micro switch.
- With a pressed lever
- With an unpressed lever
The switch is in NC (Normally Closed) mode with an unpressed lever. Therefore, the movable contact (lever terminal C) connects with the NC terminal, allowing the current to flow in this circuit. However, there is no contact between C and NO.
But when you press the lever, terminals C and NO connect because the lever pushes the movable contact down to touch NO. Therefore, the current will flow in this circuit, but NC will be open.
You can use the SPDT micro switch separately or simultaneously (in NC or NO mode) as per the application.
Maintenance of Micro Switches
Although micro switches do not require user maintenance, you should keep them clean and paint-free, especially in the actuator area. Besides that, regularly check how secure the mounting is and monitor the switch actuator-to-actuating medium relationship.
Remember, the switching action causes arcing, so avoid installing the switch in areas with explosive gasses. Also, do not lubricate or use chemical/aqueous cleaning fluids on the device. Lastly, avoid dropping or disassembling the unit because this can cause damage, shock, or burning.
Mounting of Micro Switches
If soldering the switch, avoid overheating the insulation part. It is advisable to use a heat shunt to prevent this issue. The insulation is vital between the micro-switch and metallic plates because it increases the clearance on open terminals. But for optimum mechanical strength, wrap the conductor around the terminal's tip to avoid the occurrence of loose wire strands.
With side mounting, place the switch on a smooth, flat, firm surface and fasten it using the recommended screw size. Do not enlarge the mounting holes, and you can use epoxy resin for additional security.
Micro Switch Applications
- Copy machines and cash registers
- Dental/medical and office equipment
- HVAC wall controls
- Instrumentation and aerospace equipment
The overhead panel in the airplane simulator
- Refrigerators, microwave ovens, and water heaters
- Tailgate lock modules
- Timing devices
- Convertible roof sub-assemblies
In short, micro switches are simple devices with numerous applications in several industries. However, they come in various types, and you should pick the one with the right features for the job. We hope this article will make it easier to choose the most suitable device, and if you have any questions or comments, leave a message in the chat/contacts section.