The acronym NAMUR identifies a family of proximity sensors having a completely different type of output from that of the common NPN and PNP sensors.
The abbreviation NAMUR draws its origins from the German language and literally means “normenarbeitsgemeinschaft für Mess- und Regeltechnik in der Chemischen Industrie”, in other words “association for the standardization of measurement and control in the chemical industries”.
The standard symbol of NAMUR sensors is shown in the picture below:
As can be seen, the connection has two wires only since these sensors have current and not voltage outputs. The power supply necessary for the functioning of the electronics inside the sensor is also conveyed through these two wires.
The typical output characteristic of a NAMUR can be represented as follows:
In this case, as the distance S between the sensor and the object to be detected increases, there is an increase in the current in the sensor itself. The behavior can also be reversed, to provide the possibility of choosing between “normally open” and “normally closed” sensors. Although the graph may suggest analogue behavior, the NAMUR must be considered a digital sensor, with well established thresholds: the object is considered not detected for currents ≥2.1mA and detected for currents <1.2mA. The nominal no-load voltage at the ends of an interface for NAMUR sensor is 8.2V with an output impedance of 1kΩ. Such a low output impedance is intended and aimed at avoiding, in the event of a fault, the creation of possible ignition sources in the event of a fault. In addition to proximity sensors, there are also encoders with NAMUR output. Of course, for the correct use of devices with NAMUR output, it is necessary to use appropriately designed hardware. There are also conversion interfaces between NAMUR and NPN or PNP signals to allow the connection of NAMUR sensors to normal PLCs, as well as PLCs which natively have inputs suitable for the direct connection of NAMUR sensors.
The normative reference regarding the electrical output parameters of a NAMUR sensor is the EN 60947-5-6:2020 Low-voltage switchgear and controlgear – part 5-6: control circuit devices and switching elements – DC interface for proximity sensors and switching amplifiers (NAMUR).
NAMUR sensors are typically used in potentially explosive environments, as intrinsically safe devices: the energy that passes through them does not constitute an ignition hazard. If it is also necessary to have a certain degree of functional safety, if the sensor provides protection in this sense, safety hardware with NAMUR inputs is also available.