Reed switch also known as 'Reed sensor' & 'Magnetic sensor'. This sensor contains contact made with metallic ferromagnetic material which act as a magnetic switch. This contact changes its state in the presence of magnetic field. While moving away from magnetic field, the contact of this sensor get back to its normal state As shown in an image below.
The above explained reed switch contains mechanical phenomenon in its working. There are modern reed switches which contains electronic circuit at the place of mechanical contact but operates exactly similar to the mechanical contact reed switch.
For sake of simplicity; we are referring, The reed switch containing metallic contact as 'Normal Reed Switch' While the reed switch which contains electronic circuit as 'Solid State Reed Switch'.
IMPORTANT SPECIFICATIONS FOR REED SWITCH
1. Sensor Type
As we 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.
- While Solid State Reed Switches are available in 3 wires. Which are further classified according to the type of PNP or NPN. PNP or NPN are further classified whether they are NO type or NC type.
2. Operating Voltage
Normal Reed Switches are available for both AC & DC Supplies.(5-220VAC/VDC )
Solid State Reed Switches work only on DC supply.(10-30VDC)
3. Switching Current
Reed switch is made for low current upto 100mA(max.). 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 others 3 wires reed switches which has LED indication consumes current which can be upto 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, Next we will discuss the specification of reed switch made for pneumatic cylinders by JANATIC PNEUMATICS Model NO: AM40-1-FL-04.
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| Reed Switch/ Magnetic Sensor by JANATIC PNEUMATICS |
- Sensor Type : 3 Wires normal reed switch, NO Type
- Operating Voltage : 10-30VDC
- Switching Current : 100mAmps (max.)
- Current consumption : 25mAmps @24VDC
- 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 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.
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| Indication LED & Tightening screw on Reed sensor by JANATIC PNEUMATICS |
WIRING OF REED SWITCH
Wiring for normal reed Switch
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| Wiring of 2 wires Normal Reed Switch Marked in rectangle is complete portion of normal reed switch; Only two wires are brought out for the connections. |
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Wiring for solid state reed switch
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| Wiring- Solid state reed switch PNP type Marked portion represents complete reed switch while 3 wires are brought out for the connections. PNP type reed switch produces positive supply when contacts get changed. |
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Wiring- solid state reed switch NPN type
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INSTRUCTIONS FOR REED SWITCHES
1. For proper functioning of reed switches, connection polarity is very important. Positive should be connected to Brown wire, Negative should be connected to Blue wire While load output should be connected to Black wire.
2. In Normal reed switches, if supply polarity get reversed than reed switch will work but indication LED remains in OFF condition.
3. 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.
4. Before connecting load to the Reed switch, current rating of load & current capacity of reed switch is very important to consider.
5. 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 surge; Snubber circuit is must across the load.
6. If load's current rating is more than the current capacity of reed switch; than load should be connected indirectly through relay.
7. Keep sensor away from stray magnetic field to prevent malfunctions.
If you have any doubt, suggestion or query please do comments!