Pepperl+Fuchs NAMUR Output Solutions
In a hazardous environment it is extremely important to limit all factors that could potentially cause an explosion or ignite flammable materials. Proximity sensors have multiple output types, which is why it is essential to note the difference between a 2-wire DC and a 2-wire DC NAMUR sensor. Two-wire DC NAMUR output sensors are used in hazardous environments due to their low operating current and voltage. An intrinsically safe sensor configuration consists of a NAMUR output sensor, an intrinsically safe barrier, a power supply, and a connector. The normally-closed NAMUR sensor and blue connector can be placed directly in the hazardous area, while the current-limiting intrinsic safety barrier and power supply are located in the safe area.
- Why Would I Use a NAMUR Output Sensor?
- Don't Treat a NAMUR Sensor like a Standard Sensor
- Does My Application Require a NAMUR Output Sensor?
- How to Connect a NAMUR Sensor to a Switch Amplifier
- The Other NAMUR for Valve Position Sensors
Why Would I Use A NAMUR Output Sensor?
NAMUR is a type of sensor output that gives an on or off indication. There are different reasons why you may need a NAMUR sensor. I will go through some of them here.
First, some information about NAMUR. NAMUR is a German acronym for (normenarbeitsgemeinschaft für Mess- und Regeltechnik in der Chemischen Industrie). This translates to: Standardization Association for Measurement and Control in Chemical Industries.A NAMUR sensor is a non-amplified sensor that supplies two different signal levels depending upon switch state. These signal levels are low-level current. A logic interface circuit, controller, PLC, DCS, or intrinsically safe (IS) barrier is needed to read these current levels. A NAMUR output sensor is required in installations where special safety measures are necessary (locations with explosion hazard, or personal safety). The standards for NAMUR output sensors are EN 60947-5-6:2000 and IEC 60947-5-6:1999.
A NAMUR output sensor can be normally open or normally closed, but usually, it's normally closed. This output is solid state, so there will be some current level on the output whether it’s on or off. When you look at a NAMUR output sensor data sheet, it will list nominal voltage (8.2 V), load (1 k ohm), and current for measuring plate detected (<1 mA) and not detected (>2.2 mA) (for normally closed output). Because of the low-current switching level, you'll need an amplifier or an input that is designed specifically for NAMUR. Although the sensor may be able to handle a range of voltages (7 VDC to 12 VDC or 5 VDC to 25 VDC), the voltage level should be at 8.2 VDC with 1k ohm resistance as the load.
Proximity sensors and encoders can have NAMUR output. Some of the specific types of proximity sensors that have NAMUR output are capacitive, inductive, magnetic, and photoelectric sensors. Depending on the application, you could need any one of these products to detect your target, but if they meet the NAMUR standards, the output would be the same.
Don't Treat a NAMUR Sensor like a Standard Sensor
On quick visual inspection, a 2-wire NAMUR sensor looks the same as a standard 2-wire DC sensor. But do not confuse the wiring connections between these two types of sensors. On the inside, NAMUR sensors have different circuitry than standard 2-wire DC sensors and need special treatment.
Due to approvals required for hazardous environments, intrinsically safe sensor configurations require a NAMUR output sensor and an intrinsic safety barrier. These configurations operate at a lower current and lower voltage to prevent the electrical equipment from causing an explosion.
Does My Application Require a NAMUR Output Sensor?
NAMUR sensors solve the same applications that standard inductive and capacitive sensors or rotary encoders would—but they are safe to use in hazardous areas. NAMUR output sensors are ideal for applications where the presence of a volatile gas, vapor, dust, or fiber creates a possible hazard.
To prevent an explosion in hazardous areas, these sensors protect the circuit by operating at 8.2 V and less than 5 mA. These levels prevent the device from storing sufficient energy to initiate an explosion. NAMUR sensors are connected to an isolating amplifier, which limits the current and voltage to the sensor and amplifies the signal upon return.
For more information about how these sensors work, read our blog post Why Would I Use a NAMUR Output Sensor?
Does your application require a NAMUR sensor? To help you decide, here are some applications that the sensors commonly solve:
How to Connect a NAMUR Sensor to a Switch Amplifier
NAMUR sensors are used in hazardous locations, and can provide both explosion hazard and personal safety protection. NAMUR sensors and switch isolators are highly reliable and have proven-in-use characteristics, making them a perfect choice for safety-related applications when connected to suitable control circuits.
Most devices are independently rated with Probability of Failure on Demand (PFD) and Safe Failure Fractions (SFF) that enable them to be used in functional safety areas up to SIL2 or SIL3. In this blog, Product Manager Robert Schosker talks about how to connect a NAMUR sensor to switch amplifier KFA5-SR2-Ex2.W, and then tests to ensure proper operation.
The Other NAMUR for Valve Position Sensors
Mention the word NAMUR to a valve specialist and the first thing this person will think about are the interfaces used to connect solenoids to actuators and switch boxes or positioners to rotary pneumatic actuators.Mention NAMUR to a controls person and the first thing that will come to mind are intrinsic safety techniques.
Both are correct. A typical automated valve assembly for on/off service consists of a valve (rotary or linear travel), an actuator, position sensors, and a solenoid. An automated valve for control service adds a valve positioner but subtracts the solenoid.
The selection of the components needed in the assembly is dependent upon the service application and the area (environment) where the assembly will be installed.