Why NAMUR Sensors are Essential in Explosive and Hazardous Areas ?

What is a NAMUR Sensor?

The NAMUR sensor serves the dual function of being a specialized proximity device with hazardous application capabilities mainly present in chemical operations along with oil & gas facilities together with pharmaceutical facilities and wastewater treatment systems.

The guidelines for NAMUR sensors exist through protocols established by Germany-based NAMUR organization. Instead of outputting a traditional on/off signal like most sensors, a NAMUR sensor outputs two different levels of current. This method allows them to:

• Work reliably in dangerous areas.
• Avoid electrical sparks, which could ignite flammable gases.
• Maintain safe operations even if a wire breaks or the sensor fails (especially in fail-safe versions).

Detection of metal and motion requires more than basic functionality since NAMUR sensors operate securely and dependably in explosive environments.

How does a NAMUR Sensor Work?

NAMUR sensors function using 2-wire connections to receive constant 8.2 VDC from external amplifiers and intrinsic safety barriers.

The sensor’s key principle is based on impedance variation, not mechanical switching.

Here’s how it functions:

Condition	Impedance Change	Current Output	Interpretation
Target Present (metal nearby)	↑ Impedance	↓ < 1.2 mA	“Object detected”
Target Absent	↓ Impedance	↑ > 2.1 mA	“No object detected”

These small changes in current are interpreted by a switching amplifier, which converts the analog signal into a clean digital output that can be read by a PLC, DCS, or controller.

Since there’s no mechanical or transistor switching, the risk of sparking is eliminated a must-have in explosive areas.

When Target Object is Not Detected

This above image shows the NAMUR proximity sensor in its idle state  no target object is present. In this condition:

• The sensor outputs a higher current, typically more than 3 mA.
• The sensor receives approximately 8.2V across its terminals during this operation.
• When the switching amplifier functions as an isolator it identifies higher current flows as a signal indicating “no target detected.”
• After sensing the signal the control system receives it for processing.

This mode represents the sensor’s default behavior when no metallic or detectable object is in its sensing range.

Understand the critical distinctions that affect your safety and compliance decisions.: Difference Between Intrinsically Safe and Explosion-Proof

When Target Object is Detected

This above image illustrates the sensor when a target object is present:

• The NAMUR sensor detects the target and its internal circuitry causes the output current to drop to 1 mA or less.
• The output voltage stays stable at 8.2V while the changing current values serve as the essential detection signal.
• A low current signal activates the switching amplifier which functionally identifies target detection.
• This detection signal functions to activate system alerts together with actuator elements and logic inputs inside the control system.

The ability of NAMUR sensors to vary their current output makes them both reliable and safe when used in intrinsically safe environments such as oil, gas and chemical plants.

Get a clear grasp of intrinsically safe systems and why they matter in industrial setups: What is intrinsically safe system and what is its importance?

The selection of NAMUR sensors goes beyond detection capabilities because they feature safety features alongside compliance with regulations and inter-operability benefits:

Why use NAMUR Output Sensors?

Key Benefits:

• Limited energy through Intrinsic Safety (Ex ia) operations helps to prevent ignition.
• Simple Wiring – Only two wires needed.
• The operational strategy of SIL-rated systems has built-in safeguards to ensure safe system failure.
• The output generates no sparks because it does not perform physical switching.
• Universal Compatibility provides a standardized output which functions with all types of system platforms.
• Long-Term Reliability – Suitable for high-temperature, corrosive, or dusty environments

Follow this must-have checklist for flawless and compliant IS installation: Installation Checklist for Intrinsically Safe Instrument (Apparatus)

Where are NAMUR Sensors Used?

These sensors shine in mission-critical environments where failure could mean explosions, downtime, or unsafe conditions:

Factory Automation

• Detect if a part is present in assembly.
• Monitor conveyor belt positions.
• Control robotic arm positions accurately.

Oil and Gas

• Installed in Zone 0 or Class I Div 1 areas with gas or vapors.
• Used to monitor: Valve positions, Pump speeds, Turbine RPMs

Wastewater Treatment

• The system operates in safe conditions when installed within chemical or humid areas.
• Monitor:Agitator movement, Pump operation cycles, Overflow detection

Pharmaceutical Production

• The system enables precise measurements for machinery operation.
• Process automation for clean areas becomes possible while ensuring no ignition risks occur.

Sensor Types with NAMUR Output

NAMUR isn’t a sensor technology, it’s a standard for output signal. That means different sensor types can use NAMUR output, including:

• Inductive Sensors: Detect metal objects.
• Capacitive Sensors: Detect non-metal objects or level detection.
• Magnetic Sensors: Detect magnets (used in valves, actuators).
• Photoelectric Sensors identify objects through illumination methods.
• Rotary Encoders function as speed and position measuring devices in systems which rotate.

Different NAMUR-compliant sensors enable the detection of metal parts and fluid level measurement and motion tracking all while maintaining safety protocols.

Intrinsic Safety & Certification

NAMUR sensors operate effectively in explosive environments that contain gases or dust throughout all 24-hour periods at Zone 0 / Class I Div 1 locations.

They carry certifications such as:

• ATEX (Europe)
• UL/FM (USA)
• CSA (Canada)
• IECEx, TÜV, PTB (International)

And they can be used with IS barriers (intrinsically safe devices) that control voltage and current going to the sensor, making sure no spark or heat can trigger an explosion.

What Makes a NAMUR Sensor “Fail-Safe”?

Some NAMUR sensors are fail-safe, meaning:

• If the sensor wire is cut or damaged → the current drops below the threshold.
• The system recognizes it as a fault (e.g., object detected when none is present).
• The system automatically switches to a protected state while performing tasks that mirror valve shutoffs or machine stops or alarm activation.

Such safety systems generally receive an SIL 3 rating in accordance with IEC 61508 making them highly robust safety devices. The sensors demonstrate their compatibility with systems that protect human safety through their design requirements.

How the Whole System Comes Together

This above diagram shows the connection of a NAMUR sensor from the field (hazardous area) to the control system (safe area). The NAMUR sensor is installed in Zone 0 or 1, where explosive gases may be present. The signal from this device travels from the junction box located in Zone 2 toward an intrinsically safe barrier installed in the interface cabinet. The barrier implements measures to restrict energy levels which protect areas in explosive environments. The process completes as the signal moves to the control system rack located inside the safe area for automated signal processing. The implemented arrangement allows for secure data transfer from danger zones to control areas in accordance with intrinsic safety requirements.

A typical NAMUR system includes:

1. NAMUR Proximity Sensor
2. Switching Amplifier / IS Barrier
3. PLC / DCS Input
4. The cable connecting field components utilizes regular unarmored wire networks.
5. Explosion-rated housing (if required)

This system delivers:

• Accurate detection
• Safety compliance
• Reliable automation even in volatile environments

The NAMUR output sensor provides more than detection capabilities as it ensures safe and reliable information transmission across the most demanding operating conditions. The implementation of NAMUR sensors makes performance possible while ensuring safety criteria in all types of monitoring applications ranging from refinery valves to cleanroom object counting systems.

Master the essential calculations every instrumentation engineer should know: Intrinsic Safe Calculation for Instrumentation Design Engineers

Intrinsic Safe Calculation for Instrumentation Design Engineers

FAQ on NAMUR

What is the difference between PNP and NAMUR?

Aspect	PNP Sensor	NAMUR Sensor
Type	Standard 3-wire DC proximity sensor	Specialized 2-wire intrinsically safe sensor
Wiring	3 wires: Power (V+), Ground (0V), Signal	2 wires: Power + Signal combined
Output Signal	Digital voltage output (High/Low, typically 24V)	Analog current levels (typically <1.2 mA / >2.1 mA)
Voltage Supply	Usually 10–30 VDC	Typically 8.2 VDC via isolator/amplifier
Suitable for Hazardous Areas?	No (unless specially certified)	Yes, intrinsically safe (Ex ia rated)
Failsafe Operation	No built-in fail detection	Yes, current drop can indicate failure or broken wire
Spark-Free Operation	No,  switches internally using transistors	Yes, no switching elements, only impedance variation
Typical Use	General industrial automation	Hazardous/explosive environments (oil, gas, chemical)

Note:

• PNP sensors are general-purpose and switch a voltage output.
• NAMUR sensors are designed for intrinsically safe environments and transmit a current-based signal, ideal for applications where ignition prevention and reliability are critical.

Discover why intrinsic safety is the go-to protection method in hazardous environments.: Why Choose Intrinsic Safety (IS) for Hazardous Area Instrumentation?

What does NAMUR stand for?

NAMUR: Normenarbeitsgemeinschaft für Mess- und Regeltechnik in der chemischen Industrie
Translation: User Association of Automation Technology in Process Industries (Germany-based).

What is the NAMUR Interface?

A 2-wire current loop interface used with sensors in hazardous areas.

• Works at ~  8.2 VDC
• Sends low current when detecting a target (<1.2 mA)
• Sends high current when no target is present (>2.1 mA)
• Requires a switching amplifier to convert signal
• Intrinsically safe, spark-free, fail-safe

What is the NAMUR Interface?

A 2-wire current loop interface used with sensors in hazardous areas.

• Works at ~8.2 VDC
• Sends low current when detecting a target (<1.2 mA)
• Sends high current when no target is present (>2.1 mA)
• Requires a switching amplifier to convert signal
• Intrinsically safe, spark-free, fail-safe