Reed Switch Sensor – Working, Types & Applications

Sensors play a very important role in this modern world. There are multiple types of sensors available with different functions & ranges.

” Sensors are like magic gadgets which monitors physical quantities like temperature, pressure, flow, light, motion, weight, vibration & then; produces an output in the form of an Electrical signal.“

Similarly, There are reed sensors Which detects the magnetic field & produces an electrical signal. In this post, We are going to discuss reed sensors, Its important specifications & explanation through wiring diagram.

REED SWITCH

Reed switch is also known as ‘Reed sensor’ OR ‘Magnetic sensor’. Normal reed switch contains a contact made with metallic ferromagnetic material which act as a magnetic switch. Sensor’s contact changes its state in the presence of magnetic field. While moving away from magnetic field, The contact of the sensor get back to its normal state.

In an image below, Reed switch normally open type is shown. In the absence of magnet, Contact remains open while contact get closed in the presence of magnet.

A schematic diagram of reed switch which shows the behavior of reed sweet around the magnet — Contact’s State of Reed Switch in the presence & absence of magnet !

The above explained reed switch contains mechanical phenomenon in its working. There are modern reed switches which contains electronic circuitry replacing the mechanical contact arrangement but its functions are exactly similar to the mechanical contact reed switch.

For the sake of simplicity; We are referring, The reed switch containing metallic contact as ‘Normal Reed Switch’ While the reed switch which contains electronic circuitry as ‘Solid State Reed Switch’.

IMPORTANT SPECIFICATIONS OF REED SWITCHES

1. Sensor Type

As discussed above, There are two types of reed switches ‘Normal’ & ‘Solid state‘.

Normal Reed Switches are available in 2Wires & 3Wires which are further classified whether they are NO type or NC type. ( Click here To know more about NO & NC contact ! )

2 wires sensors just act to divert the signal without a need of external power supply. In 3 wires sensors, 1 wire act as a common terminal while remaining 2 wires act as a NO & NC contact similar to changeover relay.

Solid State Reed Switches are also available in 2 & 3 wires. Similarly, 2 wires solid state reed switch do not requires an external supply. While in 3 wire sensors, 2 wires are power supply terminals while the 3rd wire act as an output terminal.

Due to third wire, Sensor is further classified according to the type PNP or NPN. Reed sensor whose 3rḍ wire produces positive supply is know as PNP type sensor. While sensor whose 3rd wire produces negative supply is known as NPN type sensor. PNP or NPN are further classified whether they are NO type or NC type.

2. Operating Voltage

DC operated reed sensors, Voltage ranges from 10-30V DC.
AC operated reed sensors, Voltage ranges up to 230V AC.
AC as well as DC operated reed switches ranges up to 230 V.

3. Switching Current

Reed switch is made for low current up to 100mA(max.).

Reed switches should be used as a signal in control wiring & Current flow through the reed switch should be lower than current capacity of reed switch.

4. Current consumption

2 wires normal reed switch which don’t have an LED indication don’t consume any type of current. While other 3 wires reed switches which has LED indication consumes current which can be up to 25mA @24VDC.

5. Temperature range

Reed switch has limit of ambient temperature under which it works precisely for long time. Normally, It has temperature range of -10°C to 70°C.

6. Type of protection

Ingress protection is also important to consider which explain the sealing effectiveness from solid & liquid particles.

IP should be choose according to the place of installation.

For better explanation about the specification, A reed switch is discussed next made for pneumatic cylinders by JANATIC PNEUMATICS Model NO: AM40-1-FL-04.

A Collage of Reed Switch/ Magnetic Sensor by JANATIC PNEUMATICS — Reed Switch/ Magnetic Sensor by JANATIC PNEUMATICS

SPECIFICATIONS OF REED SENSOR AM40-1-FL-04 BY JANATICS

Tightening screw & Indication LED of Reed sensor/Magnetic sensor by JANATIC PNEUMATICS — Indication LED & Tightening screw on Reed sensor by JANATIC

Sensor Type : 3 Wires reed switch, NO Type
Operating Voltage : 10-30V DC
Switching Current : 100mAmps (max.)
Current consumption : 25mAmps @24V DC
Temperature range : -10°C to 70°C
Type of protection : IP67

This reed switch is specially made for pneumatic air cylinder which actually tells about the position of piston moving inside the cylinder. This sensor contains a screw on to it so that it easily get tightened into the Groove of the cylinder.

The air cylinder contains a magnet on its piston head which moves inside the cylinder. When sensor come in the vicinity of the magnetic field than contact of the sensor changes its state which explains the position of the piston. This sensor also contains a small LED which get ON when contact changes its state.

GIF shows the working of REED switch — **Working** of Reed sensor fitted on pneumatic cylinder

” A GIF shown above, Shows the working of reed sensor fitted on pneumatic cylinder. (Reed sensor used in this GIF; is a type of NO contact)

Reed sensor is fitted at front side of pneumatic cylinder. While Piston inside the cylinder stationed at the back. When a pressured air is get applied at back air inlet, Piston starts moving forward due to air pressure. Piston remains moving until air remains present at the back.

On reach the piston’s front side under the reed sensor, Due to magnet present on piston shaft, reed sensor produces an electrical signal. & air supply get stop.

After some delay, Air is applied at cylinder’s front inlet Which results piston starts moving backward & senor’s signal get break. “

INSTRUCTIONS FOR REED SWITCHES

For proper functioning of solid state reed switches, connection polarity is very important. Positive should be connected to positive(Brown wire), Negative should be connected to negative (Blue wire) While load output should be connected to Black wire.
In Normal reed switches, If supply polarity get reversed than reed switch will work.
In Solid state reed switches, If supply polarity get reversed than reed switch will not work & remains in off position completely. Because it contains protection circuit for power source reverse polarity.
Before connecting load to the Reed switch, Current rating of both the load & reed switch should be considered.
If load’s current rating is lower than the current capacity of reed switch; than load can be connected in series with reed switch. But for the protection from spikes & voltage surges; Snubber circuit is must across the load.
If load’s current rating is more than the current capacity of reed switch; than load should be controlled indirectly through relay or contactor.
Keep sensor away from stray magnetic field to prevent malfunctions.

WIRING OF REED SWITCH

Next, some of the wiring connection of both the reed sensors, normal & solid state reed sensor is been discussed.

Wiring for normal reed Sensor

A wiring diagram of 2 wired normal reed sensor is shown below. In this diagram, Marked rectangle represent the complete reed sensor. A positive supply is connected across designates positive terminal While negative is connected across another second terminal through a connected load in between. When a reed switch get in the vicinity of magnetic field, Power supply get available across the load.

Marked in rectangle is complete portion of normal reed switch; Only two wires are brought out for the connections.

A wiring diagram of 3 wired normal reed sensor is shown below. 2 terminals are supply terminals positive & negative. While 3rd terminal is used as an output, Which is connected to a load. Negative is directly connected to load. In the periphery of magnetic field, Reed sensor produces an output.

Marked portion represents complete reed switch; 3 wires are brought out for the connections.

Wiring for solid state reed switch

In a 3 wired PNP type solid state reed sensor shown in a diagram below. 2 wires are supply terminals While the 3rd black wire is output terminal; where load is connected. Negative is directly connected to load. In the periphery of magnetic field, reed sensor produces a electrical signal.

Schematic diagram of Solid state reed switch PNP type — Wiring- Solid state reed switch PNP type

Marked portion represents complete reed switch where 3 wires are brought out for the connections.
PNP type reed switch produces positive supply when contacts get changed.

A 3 wired NPN type solid state reed sensor shown below. In this diagram, Supply is connected to positive & negative terminal. While 3rd terminal, a output terminal, Where load is connected. This output terminal produces a negative terminal in the vicinity of magnetic field. Positive terminal is directly connected to load.

Schematic diagram of Solid state reed switch NPN type — Wiring- solid state reed switch NPN type

Marked portion represents complete reed switch while 3 wires are brought out for the connections.
NPN type reed switch produces negative supply when contacts get changed.

CONCLUSION

The post focusing on reed sensors, which detect magnetic fields and produce electrical signals.
Reed switches exist in two main types: Normal and Solid State, each with specific wiring configurations and operating characteristics.
Normal reed switches can be either normally open (NO) or normally closed (NC).
Solid State variations contain electronic circuits.
Important specifications include operating voltage, switching current, temperature range, and ingress protection.

FAQ – Reed Switch / Reed Sensor

Q1. What is a Reed Switch or Reed Sensor?
A reed switch (or magnetic sensor) is a sensor that detects magnetic field presence and changes its contact state accordingly.

Q2. How does a Reed Switch work?
It works using magnetism. When a magnet comes close, its internal contacts either open or close depending on sensor type.

Q3. Does a Reed Sensor work with DC voltage?
Yes, reed sensors operate on DC voltage.

Q4. What is the meaning of NO and NC in reed switches?
NO means normally open (closes with magnet), and NC means normally closed (opens with magnet).

Q5. What is the difference between Mechanical Reed Switch and Solid-State Reed Sensor?
Mechanical reed switches are contact-based, while solid-state sensors are electronic and provide cleaner output.

Q6. What does PNP and NPN mean in Reed Sensors?
These terms define the output type used in automation and control applications.

Q7. Are Reed Sensors used for piston position sensing?
Yes, reed sensors are commonly installed in pneumatic cylinders to detect piston position.

Q8. Can Reed Switch drive load directly?
No, reed switches are meant for signal-level control. For load switching, an intermediary device such as a relay is used.

Q9. Does Reed Sensor have wires for output?
Yes, reed sensors include wires like +V, –V (GND), and OUT for signal.

Q10. Can a Reed Sensor be used indoors and outdoors?
Yes, based on type and housing, they can be used in multiple environments.

Q11. What voltage does a Reed Sensor need to work?
Reed sensors operate within specified DC voltage ranges (as mentioned in your post diagrams and notes).

Q12. What is the practical use of a Reed Sensor?
They are used in automation panels and pneumatic cylinders for detecting position.

Q13. Can Reed Sensors send signal to a PLC?
Yes, reed sensors output a DC logic signal suitable for PLC inputs.

Q14. Does the Reed Sensor require a magnet to operate?
Yes, initiation and switching require a nearby magnet.

Q15. Is Reed Sensor polarity sensitive?
Yes, solid-state reed sensors require correct polarity for +V and –V wiring.

If you have any doubt, suggestion or query please do comments!

Tagged Sensors, switches

Reed Switch/Sensor

REED SWITCH