REED SWITCH

A Reed Switch is similar to a standard switch in that it makes/breaks an electrical connection. Unlike a push button switch though, a reed switch works via magnetic field. This reed switch is normally open (N.O.), which means when no magnetic field is present the contacts/circuit are open.
Working Principle:
A reed switch is an electromagnetic switch used to control the flow of electricity in a circuit. They are made from two or more ferrous reeds encased within a small glass tube-like envelope, which become magnetised and move together or separate when amagnetic field is moved towards the switch

Types of Reed Switch:

1. DRS-DTH Series – 39.7mm High Power DRS-DTH Switch

http://www.littelfuse.com/products/magnetic-sensors-and-reed-switches/reed-switches/drs-dth.aspx

2. Standard Heavy Duty Reed Switch Sensors

http://www.arun-electronics.co.uk/sensor_reed.htm

Additional info about types:

1. The DRS-DTH Reed Switch is a large changeover switch with a 39.70mm long x 5.33mm diameter (1.562″ x 0.210″) glass envelope, capable of high voltage and power switching up to 500Vdc at 2mA or 0.5A at 30W/VA. The DRS-DTH has an insulation resistance of 10^9 ohms minimum and contact resistance less than 125 milli-ohms.
2. A miniature, PCB mount reed switch 17.78mm x 4.32mm x 3.30mm (0.700″ x 0.170″ x 0.130″) with a normally open contact. Contains molded stand-offs to allow board washing. Available with customer-defined sensitivity. Capable of switching up to 200Vdc at 10W. Available with a range of sensitivity options. Well suited for position and limit sensing, security, door and window alarm systems. Functions best with the 57045 actuator.

3. The standard heavy duty range are housed in robust zinc die castings and as standard have a 0.7 metre heavy duty cable.

The N/O3 is a normally open switch, the contacts close in the presence of the actuator magnet.

Features:

(1) Reed contacts are hermetically sealed within a glass tube with inert gas and do not receive any influence from the external atmospheric environment.
(2) Quick response
(3) The structure comprises the operating parts and electrical circuits arranged co-axially. Reed switches are suited to applications in radio frequency operation.
(4) Reed switches are compact and light weight.
(5) Superior corrosion resistance and wear resistance of the contacts assures stable switching operation and long life.
(6) With a permanent magnet installed, reed switches economically and easily become proximity switches.

Specifications

Maximum Switching Power: 15W
Maximum Switching Current: 1A
Maximum Carrying Current: 2.5A
Maximum Switching Voltage: 200VDC
Breakdown Voltage: 300VDC
Initial Contact Resistance: 0.1Ω

Link to Data sheet :

1.http://www.littelfuse.com/~/media/electronics/application_guides/littelfuse_hamlin_reed_switch_selection_guide.pdf.pdf
2.https://standexelectronics.com/wp-content/uploads/OKI_Reed_Switch_ORD213.pdf
3. https://www.parallax.com/sites/default/files/downloads/910-27225-Reed-Switch-Datasheet-v1.0.pdf

Do’s and dont’s:

Do use a strong magnet.
Do prevent the switch from getting high vibration and shock, the reed switch may be damaged or exhibit contact bounce.
Do keep the area dry.
Do Not use where high switching application is required.
Do Not apply high current.

Storing Instructions:

1. Store in a closed rigid container.
2. Don’t put any other heavy components with reed switch as they can break the covering.

 

Advantages:

Simple and reliable reed switch sensing and actuation capabilities
•Low-profile designs offer ease of integration
•Requires zero power for operation
•Durability and performance over extended service life
•Low weight prevents mass loading of sensitive electronics
•Low price point per unit
•High performance with low overall cost of ownership
•Relative ease of customization

Disadvantages

1. Remember that earlier I mentioned it was mechanical… well with mechanical devices and moving components the results are a finite life.

2. Oh did I mention it was mechanical…well mechanical devices are typically slow; I mean we are talking several milliseconds. Reed switches may not respond fast enough in high-speed applications.

3. Reed switches can also demonstrate double switch points. What’s this? As the magnet, passes underneath the sensor mounted on a pneumatic cylinder, the twin lobes of certain magnets may cause the reeds to open and close.
4.Reed switches will not work with a radially magnetized magnet because only one pole of the magnetic field is presented to the reeds and both poles are required to magnetize the reeds

 

Schematics:

Connections with Arduino

Arduino Code:

int pinSwitch = 2; //Pin Reed
int pinLed = 13; //Pin LED
int StatoSwitch = 0;
void setup()
{
pinMode(pinLed, OUTPUT); //Imposto i PIN
pinMode(pinSwitch, INPUT);
}
void loop()
{
StatoSwitch = digitalRead(pinSwitch); //Leggo il valore del Reed
if (StatoSwitch == HIGH)
{
digitalWrite(pinLed, HIGH);
}
else
{
digitalWrite(pinLed, LOW);
}
}

Applications:

1. Automotive electronic devices
2. Control equipment
3. Communication equipment
4. Measurement equipment
5. Household appliances

FAQ’s:

Q1. What is the max. operating time limit? The circuit will remain closed as long the magnet is next to the switch or only for 0.45ms(max. Operating time)?
Ans. Yes, the circuit will remain closed as long as the magnet is next to the switch.
Q2. Will it work with a 12 volt car battery?
Ans. Not without a lot of circuitry.

Q3. Does each one of the reed relay come with the magnet? or I have to buy the magnet separately.
Ans. No magnets come with these.

 

Referral Links:

1. https://learn.sparkfun.com/tutorials/reed-switch-hookup-guide
2. https://www.explainthatstuff.com/howreedswitcheswork.html
3. http://www.littelfuse.com/products/magnetic-sensors-and-reed-switches/reed-switches.aspx

Documentation links :

 

1.http://www.instructables.com/id/Arduino-Reed-Switch/
2. https://en.wikipedia.org/wiki/Reed_switch

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