How do pnp proximity sensors work

The drawing below shows 2 wires for sensor power and 2 for the switch. Most sensors use only 3 wires by having one wire do double duty, carrying both power and output signals. This is similar to a bathroom with only one line carrying water to both the sink and toilet as opposed to individual lines for each.

Solid-state discrete sensors functions similar to a switch, but current only flows in one direction. Solid-state devices are reliable, economical, small and fast. The only drawback is, that you have to know the direction of current flow.

The type of transistor determines the direction of current flow. Add explanation of push-pull output would be a bonus to the reader. Thanks for the positive feedback, tlane. Thank you for the explanation, I was thinking the NPN sensors were normally used when the sensor and the PLC do not work on the same voltage.

Also, in dangerous environments is it probably better to have a 0VDC to activate something in case of a short circuit? The switching logic PNP or NPN are not related to the supply voltage of the sensor or the operating voltage of the input. Referring to the NPN wiring diagram above, note that the sensor supply voltage and the high side of the load are connected to the same point and are therefore at the same voltage.

In hazardous or explosive atmospheres, special care must be exercised to determine the classification of the hazard and to employ components with an approved protection method certified for the classification at hand.

Refer to this previous post for more information. Informative better exploration on diagrams. Nice explanation, however could someone explain the pros and cons of using one over the other? I typically see Japanese controls that require NPN sensors.

Industrial automation is a field that, for all its sophistication, is sometimes slow to change and legacy methods sometimes die hard. So early solid-state sensors were more likely to use NPN transistors in their switched outputs, so they were load-sinking. When used in a traditional relay type control circuit, it is normally possible to use either the PNP or the NPN type of sensor as shown below.

PNP sensors tend to be more commonly used. Traditional relay type control circuit; Use with a programmable logic controller PLC. When selecting a sensor to be used with a PLC, it is very important that the sensor matches the type of PLC input card to be used.

Two types of input cards exist, those that 'sink' current also known as positive logic and those that 'source' current also known as negative logic. Most common in Europe is the 'sinking' type of input, these will be used with the PNP sensor as shown below.

To connect to a sensor you will need to be able to match the type of signal the device uses. In a NPN transistor, current flows from the emitter to the collector. The transmitter is powered on when sufficient current is supplied to the base of the transistor. The higher the current the more an NPN transistor will be powered on. A PNP transistor is the opposite, current flows from the collector to the emitter.

The transmitter is powered on when there is no current at the base of the transistor. To set these inputs there are a series of jumpers on the board. These are also shown in the ED manual. How to open the case and how to locate the jumpers Yellow case: Open the ED case using a small flat head screw driver pushed into the sides of the product which connect the yellow lid to the lower case. Grey case: Open the ED case using a small flat head screw driver pushed into the sides of the case which connects the lid to the case base and find the jumper with PNP and NPN next to it.

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