What is a NAMUR Sensor?

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In this video, we’re going to introduce you to a sensor called a NAMUR proximity sensor. We’re going to discuss how this NAMUR sensor differs from other proximity sensors, and we’ll show you where and why these sensors are used in the field.

NAMUR proximity sensors can be capacitive, inductive, magnetic, or can be photoelectric sensors.

One could be easily fooled by assuming that a NAMUR sensor is a typical proximity sensor because they look very much alike. But physical shape and appearance are the only characteristics they have in common.

Let’s begin by reviewing the electrical characteristics of a typical proximity sensor.
The proximity sensor acts just like a simple switch. When the target is away from the sensor, the switch is open. When the target is close to the sensor, the switch is closed.

In most industrial applications today, a proximity sensor is not connected to an actual load resistance but is connected to an input on a Digital Input Module on a PLC or DCS.

The PLC input will have +24 volts or 0 volts applied depending upon the operational condition of the 3-wire proximity sensor internal switch.

The term “NAMUR” is an acronym for a very long German description.

The NAMUR proximity sensor has been in use for many years but like any electronic device, there are many different symbols in use.

In a nutshell, NAMUR proximity sensors were developed to ensure safety in hazardous locations.
NAMUR proximity sensors are used in classified hazardous location areas that have explosive gas, dust, or fibers present.

NAMUR proximity sensors are considered Intrinsically Safe.

The NAMUR proximity sensor operates much like a typical proximity sensor but does not have an open or closed output condition. Instead, a NAMUR proximity sensor will produce two different and distinct current output levels corresponding to the target position.

NAMUR proximity sensors limit current so that the current is not capable of causing ignition in hazardous atmospheres.

Typical proximity sensors that continually make and break an output circuit could create sparks that could cause an explosion.

Let’s have a closer look… A NAMUR proximity sensor has a switching circuit similar to a typical proximity sensor, but instead of making and breaking an external circuit, the switching circuit is used to change the output current flow by altering an internal resistor network.

Let’s take a look at a real-world example.

There are 4 NAMUR proximity sensors used to measure the shaft speed on four separate chemical pumps.

The pumps are located in a hazardous area, therefore typical proximity/speed sensors are not suitable.

The current output of each NAMUR proximity sensor is detected by an Intrinsically Safe Barrier Converter that provides a square wave pulse train to a Siemens PLC counter module.

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You might want to review one of our other articles:

How to Wire Discrete DC Sensors to PLC - Part 2 https://realpars.com/discrete-sensors...

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