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Reed switch in industrial applications

- May 22, 2018 -

Reed pipes have been widely used in the industrial field. For example, hydraulic cylinders or pneumatic actuators require a reed sensor for end position sensing. Unlike inductive sensors and Hall-effect sensors, the reed sensor does not use a power supply and has good isolation. The reed sensor is compatible with a programmable logic controller (PLC) and a microcontroller with a wide range of operating voltages and has a high operating speed. When using weak magnets, the reed sensor can also detect any ferrous metal part. Reed switch manufacturers Reed and reed switch sensors are used in the following areas:

Safety-oriented application

Pneumatic and hydraulic cylinder position sensing

Rotary actuator end position sensing

Linear and rotary encoders

Iron detection

Gear speed and direction sensing

Bridge at airport control

Transformer tap changer converter

Gasoline and diesel pumps

High-voltage reed relay


Reed switch safety guide application

Optical fiber sensor lenses require exceptionally clean, guided sensing applications. A reed switch and a magnet are combined into a unit with a specific distance, and a (NC) normally closed reed sensor is formed between them. When the permanent magnets come in between them, the magnetic field begins to shunt and the reed switch opens. (NO) The normally open reed sensor can be designed to use a normally closed reed switch on one side and a magnet on the other side, enough to ensure that the normally closed reed switch opens. The reed switch sensor can work in a very dirty industrial environment. Grease and dust do not affect its operation. Common applications include conveyor belt sensing and industrial agitator speed sensing.

Sensing at the end of the cylinder and piston

        Most cylinders, pistons, linear slide and rotary actuators and built-in magnets produce tip position sensing. Reed sensor sensors are used to sense the position and middle position of the tip and signals can be processed to further indicate the application of the PLC. The reed sensor's very high detection speed works in conjunction with the higher scanning speed PLC program. Reed sensors can also be fitted with indicators (light emitting diodes) to help locate easily adjusted piston and cylinder stroke or rotary actuator angles.

Iron detection

        The iron containing part detection sensor is built-in to locate the two weak magnets close to the sealed reed switch. The two magnets themselves are not strong enough to transfer the magnetic lines between them and close the reed switch. If this system is close to the nearby iron-containing part, the magnetic flux passes through part of the iron, close to the two smaller areas of the reed switch, and expands into a large area.

Gear speed and direction sensing

        The miniature ferrous part detection sensor can be positioned near the gear to sense the rotational speed. Based on the high sensing speed of the reed switch sensor, it can feel up to 30,000 RPM. A special sensor for the orientation of the gears with iron-based induction gears can be constructed with two reed switches and a bias magnet, and combined with a D flip-flop (D-Flip-flop) quadrature sensor. One of the reed switches is connected to the D input and the other clock is input. In this way, one direction is different from the other by monitoring the output Q at the D-FF.

Boarding bridge control

        The operator needs to guide the docking of the boarding bridge and the aircraft. The boarding bridge is a door about a meter away, and the height of the bridge needs to be adjusted. It is necessary to position the bridge mechanism in the reed sensor and magnet. The feedback operator through the bridge reed sensor can obtain whether the boarding bridge needs to move upwards or downwards. After a successful height adjustment, the boarding bridge is docked with the aircraft door and parked.

Transformer tap changer converter

        The transformer tap changer in the transformer involves the protection and control scheme if the joint assembly is in an odd or even position. A set of magnets or magnets mounted on the moving assembly arm triggers a reed sensor mounted on the transformer. Since this component will be located in the transformer tank, special reed sensor can withstand high temperatures.

Gasoline and diesel pumps

        Gasoline and diesel pumps use a reed switch to detect if the nozzle has been placed in the correct holster so that the final volume fill display can be reset to zero. A tiny magnet on the nozzle handle activates a reed sensor mounted on the holster. Based on reed switch flow sensors, a very low level of inductive load, such as 10V/10mA, can operate up to 1 billion operations. In these encoder type flow sensors are used to calculate the actual petrol pump and can display data on the digital board.

High voltage relay

        The power industry uses multiple types of relays for signal switching and high voltage and high current switching. Special reed switches with high breakdown voltage can be used to make high-power switch relays and can carry relays up to 5 amps. Multiple reed switches can be used for reed relays to make different contact forms. For example, two normally open contacts and normally closed contacts can be driven at voltages as low as 5 volts. These relays not only save power but also simplify the circuit-switching logic.

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