8/6/2019 NpN and PnP Sensor Outputs Finally Explained

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NpN and PnP Sensor Outputs Finally Explained.

Most engineers will have suffered at the hands of NpN/PnP at one point in their

career.

If the incorrect type is wired into your machine, the downstream device (relay, PLC

etc) will not function correctly.

Once the differences between PnP and NpN are fully understood you can identify the

type of sensor currently installed and find a suitable replacement.

It is also surprisingly easy to convert an output to the desired type. This could half the

amount of spare sensors you have to keep and save valuable production time spentwaiting for the correct output type.

It is important to realise that NpN and PnP are completely different to normally open

and normally closed. You can have an NpN n/o or an NpN n/c, and a PnP n/o or PnPn/c sensor.

NPN (sinking)

This is a switched Negative output. A permanent +vdc supply will be connected to

the device that is to be activated (relay coil, PLC common terminal etc)

When the sensor turns on, it switches the 0vdc used to power the sensor, through the

transistor in the sensor body (fig 1).

This 0vdc is now present on the sensor output wire (normally the black wire) and will

be wired to the device that is to be turned on (eg ve input on relay coil).

If +vdc is connected to the other side of the relay coil, then a circuit is completed and

the relay or PLC input will turn on.

It is effectively just a switch that connects the 0vdc side of a supply to another device.

Fig 1.

8/6/2019 NpN and PnP Sensor Outputs Finally Explained

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PNP (sourcing)

This is a switched Positive output. A permanent -vdc supply will be connected to thedevice that is to be activated (relay coil, PLC common terminal etc)

When the sensor turns on, it switches the +vdc used to power the sensor, through the

transistor in the sensor body (fig 2).This +vdc is now present on the sensor output wire (normally the black wire) and will

be wired to the device that is to be turned on (eg +ve input on relay coil).

If -vdc is connected to the other side of the relay coil, then a circuit is completed and

the relay or PLC input will turn on.

It is effectively just a switch that connects the +vdc side of a supply to another device.

Fig 2.

If you do have the incorrect sensor type More Control has the solution in the form of

two types 5mm din rail mount converters in a standard terminal style body. They arecompact and cost effective devices that will easily convert from NpN to Pnp or PnP to

Npn. (please see attached specification sheet).

With one of each device kept in your stores you will never again be left waiting for a

particular sensor type but can use any sensor you have available at the time.

To order the converters please fill in the attached order form or contact our office on

01908 364555