5 Things You Need To Know About Inductive And Hall Effect Sensor Proximity Switches

Sensors are devices that detect the presence or change of physical input from the surrounding environment. Most people nowadays will have some type of sensor installed on their house to detect the presence of a person for security and safety. But there are a lot more things these devices can detect such as heat, light, moisture, pressure and even metallic and magnetic items. In this post, share with you 5 things you need to know about inductive and hall effect sensor proximity switches.

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1: What Do The Inductive Sensor And Hall Effect Sensor Detect

Since both types of sensor work on magnetic principles, it might be easy to get these two sensors mixed up. Let me clarify the differences.
An “inductive” sensor uses the principle of “induction” to detect metallic objects, whereas
a hall effect sensor uses the principle of “the hall effect” to detect a magnetic field.

But what is the difference between the induction and hall effect?

2: Induction vs Hall Effect

Induction

The theory behind electromagnetic induction is that if you pass alternating current (AC) through a coil of wire, you will produce an alternating magnetic field around it.

If we move a conductive material into this changing magnetic field, a current will be induced. These currents circulate the conductor in closed loops and are called Eddy currents.

Any conductor that has current produces its own magnetic field, and that’s what happens with these Eddy currents, they create a magnetic field which then opposes the magnetic field of the coil of wire.

Hall effect

What about the hall effect? Well, this principle also uses magnetic fields but in a different way. Put simply, if we have a conductor supplied by a constant flow of current and we move a magnetic object over it a voltage will be produced across the material.

3: How Do Inductive And Hall Effect Sensor Proximity Switches Work?

Inside an inductive sensor is a coil of wire with alternating current running through it. This produces an alternating magnetic field which reacts to a conductive material. When this magnetic field is disturbed by a conductor such as a metal ruler, for example, a detection circuit inside the sensor picks it up and triggers the switch output.

Essentially, if a disturbance in the magnetic field is sensed then the switch turns “ON”, and if a disturbance in the magnetic field is not sensed, then the switch turns “OFF”.

A hall effect sensor has a thin conductive metal strip commonly referred to as the “hall element”. This conductor has a current applied through it, and when you pass a magnetic object over the top, a voltage is produced across the edges of the strip which then triggers the switch output.

So, if a voltage is sensed across the strip, the switch turns “ON”, and if no voltage is sensed across the strip, the switch turns “OFF”.

4: How To Wire Inductive And Hall Effect Sensor Proximity Switches

1. Identify the type of switch.
It is crucial to recognise which type it is before making any connections, NPN or PNP, because both connections are different. This also ensures you don’t damage anything in the process.

So here I have two sensors: A PNP type inductive proximity switch and an NPN types hall effect proximity switch.

2. Turn off the supply.
Always disconnect the power supply before making any connections. This allows you to double-check your wiring before turning anything on and prevent possible damaging of the sensor.

3. Identify the wires.
Notice that both switches are 3 wire switches: a brown, black and blue wire. This is one of the industry standard connections.

Brown wire connects to the positive terminal of the supply
Blue wire connects to the negative terminal and
Black is the output

Some switches can even have an additional white wire, making it a 4-wire sensor. This extra wire allows you to control an additional load.

4. Make the connections.
The inductive sensor proximity switch here is a PNP type, so the load will connect between Black and Blue wires. And because the hall effect sensor proximity switch here is an NPN type, the load will connect between Red and Black wires

If the switches were to connect to a PLC or a programmable relay, you would need to know if the PLC input in sinking or sourcing. We will discuss this in another post.

5. Check the rating and turn on supply.
The inductive sensor proxy here is rated between 6-36 VDC and our hall effect sensor proxy is rated between 5-30 VDC.

6. Test the sensor to verify its operation.
To do this hover a metallic object over the inductive sensor and a magnetic object if it’s a hall effect sensor. Please note: the hall effect proximity switch used here is unipolar, which turns “ON” for only one magnetic pole. You can check how your hall effect responds by referring to its datasheet.

5: How To Test The Inductive And Hall Effect Proximity Switches

Before we use the multimeter to test the proximity switches, let’s test out different types of material in our Electromag Pracbox. Here are the responses from each switch for each material

Material	Inductive Sensor	Hall Effect Sensor
Metal Ruler	Yes	No
Piece of Foam	No	No
Neodymium magnet	Yes	Yes (Only one side)
Pencil	No	No
Spanner	Yes	No
Motor magnet	No	Yes (Only one side)

Almost, all proximity switches have a built-in pilot lamp, which will react when there is a detection. But what if the sensor was mounted in a way that you couldn’t see it?

You can always wire an external LED pilot lamp to see if the sensors detected the material. But what if we didn’t have that indication light?

Last option is to measure the voltage across the load. For example, if we energise the sensor with 24VDC we should get approximately 24VDC across the load as well.

I have shown examples all three methods in the video below on our Electromag Pracbox.

NOTE: These sensors are rated to provide a maximum output current of approximately 100 – 300 mA so do not expect it to be able to drive a large load such as a motor or heated lamp or you will damage them.

Conclusion

As you can see, inductive sensors detect metallic objects and hall effect sensors detect the presence of a magnetic field. So, depending on the application, you could use one over the other. In any case, these devices are quite easy to set up and can be an important tool in your projects.

Thanks for reading the post. I hope I helped you understand how these sensors work and what they can do. If you’re interested in finding out more explanations and guides like this one, then feel free to subscribe to our emails and YouTube channel.

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About the Author

Anthony Nguyen

Anthony is a passionate electrical engineer with an affinity for problem solving. He's always eager to tackle a mathematical challenge or wherever he can apply logical reasoning. His aspirations are to continually develop technical knowledge and apply it to innovate product systems and design.