What Is a Door Lock Switch?
A door lock switch is a device that produces a contact output when a door is opened or closed.
Widely used contact-type door lock switches are similar in construction to limit switches and microswitches, and are characterized by the fact that they are fixed to the door or doors.
Uses of Door Lock Switch Applications
Door lock switches are one of the most widely used devices in industry and household appliances.
Door lock switches are used in the following applications:
- Detecting the opening and closing of refrigerator and microwave oven doors
- Automatic lighting of barns
- Interlocking large presses and transport equipment
- Automatic lighting of control panels
- Detecting the opening and closing of trays in printers and multifunctional machines
- Automobile door open/close detection
The most common application is in refrigerators. Many refrigerators sound a buzzer if the door is kept open for a long period, or turn on internal lighting when the door is opened. In this case, door lock switches are used to detect the opening and closing of the door.
Door lock switches are also used as safety interlock devices in some industries. They are mainly used in large manufacturing equipment and are often installed to prevent personal injury.
Accidents involving large equipment and high-torque power equipment have been occurring more frequently than in the past. To prevent such accidents, we take measures such as covering the entire equipment with a safety fence. Since it is difficult for people to approach the equipment if only covered with a fence, a door is installed, and an interlock is often installed so that the equipment stops when the door is opened.
Door lock switches used for interlocks are sometimes called safety door switches. If the door lock switch alone is judged to be inadequate for interlocking, a door switch with an electromagnetic lock, etc., may be employed.
Principle of Door Lock Switch
A door lock switch consists of a contact, a mechanism, and mounting hardware.
1. Contact Point
The contact is a component that transmits a digital contact signal. Mainly materials such as silver and gold are used. The allowable current value of contacts is generally around several amperes, and they are often incorporated into control circuits.
2. Mechanism Part
The mechanical part is a component that detects the opening and closing of doors. Depending on the application, there are contact-type products and non-contact-type products. Contact-type products mainly incorporate microswitches, while non-contact-type products incorporate reed switches.
3. Mounting Brackets
Mounting hardware is used to attach the product to the door. Products with a structure such as screw fastening are common. Products using one-touch plugs are also available.
Types of Door Lock Switch
Door lock switches come in a variety of types, depending on the application.
Typical types are as follows:
1. Non-contact Door Lock Switch
Non-contact door lock switches are door switches with an internal reed switch. It comes with a dedicated actuator and uses a built-in magnet to detect the opening and closing of the door. Since it does not make contact with the door, it is characterized by the fact that it has a few parts that are subject to mechanical wear.
General reed switches can open and close contacts by using a magnet, but for safety applications, the structure requires the use of a dedicated actuator. This is to prevent malfunction of the reed switch.
2. Contact-Type Door Lock Switch
The contact type is a door lock switch with an internal microswitch. The door closing is detected when the actuator at the tip of the switch contacts the door. Various actuator types are available.
Because they are robust and inexpensive, contact-type door lock switches are used for refrigerator doors and printers. However, there is a risk of malfunction if the internal spring weakens with use over time.
Door Lock Switch With Electromagnetic Lock
Door lock switches with electromagnetic lock are a door switch that has the function of locking the door with an electromagnetic lock. If a door lock switch is used for safety purposes, a malfunction of the door lock switch may cause personal injury.
By selecting a door lock switch with an electromagnetic lock, it is possible to prevent accidental entry by locking the door. Generally, an interlock is provided so that the equipment will stop if the door is forced to be pried open when locked.