Category: Standards & Ratings

IP67 means dust-tight and survives 30 minutes under 1 metre of water. IP68 means dust-tight and survives continuous immersion on conditions the manufacturer states. IP69K means dust-tight and survives 80 bar water at 80 °C from a close-range nozzle. They are different tests, and a higher number is not automatically a superset of a lower one.

Reading an IP code

An IP rating is two digits, occasionally with a letter suffix. The first is protection against solid objects and dust; the second is protection against water. They are tested independently.

First digit	Protection against solids
4	Objects larger than 1 mm
5	Dust protected — ingress permitted but not enough to interfere with operation
6	Dust-tight — no ingress at all, tested with the enclosure held at reduced pressure

Second digit	Test	What it actually proves
4	Splashing from any direction	Survives incidental splash
5	6.3 mm nozzle, 12.5 l/min, 3 m distance	Survives a hose-down
6	12.5 mm nozzle, 100 l/min, 3 m distance	Survives heavy seas and powerful jets
7	Immersion, 1 m depth, 30 min	Survives being dropped in a puddle or briefly flooded
8	Continuous immersion, depth and duration per manufacturer	Whatever the manufacturer declares — always read the small print
9 / 9K	80 bar, 80 °C, 14–16 l/min, close range, four angles	Survives food-industry high-pressure washdown

The IP69K test in detail

IP69K is the one people most often quote and least often understand. The test is specific and severe:

• Water pressure 80–100 bar at the nozzle.
• Water temperature 80 °C.
• Flow rate 14–16 litres per minute.
• Nozzle held 100–150 mm from the specimen.
• Sprayed at 0°, 30°, 60° and 90° to the specimen, 30 seconds at each angle.
• Specimen on a turntable rotating at 5 ±1 rpm.

Note what this is testing: a hot, high-velocity, close-range jet. That combination attacks seals in a way immersion never does, because it drives water into any gap and the thermal shock cycles the seal material. It does not test whether the device survives sitting under water for an hour, which is why IP69K and IP68 are genuinely independent claims.

The “K” suffix is a legacy of the German DIN 40050-9 origin. IEC 60529 later added an IP69 designation of its own, and ISO 20653 covers it for road vehicles. In practice the industry still writes IP69K and means the DIN/ISO test above.

Choosing a rating by environment

Environment	Minimum sensible rating	Notes
Dry panel interior	IP54	Dust and incidental splash only
General machine shop	IP65	Swarf, coolant mist, occasional hose
Machine tool coolant zone	IP67 minimum	Check coolant chemical compatibility separately
Outdoor, exposed to monsoon	IP67	Add UV-stable cable and consider condensation
Food, dairy, beverage washdown	IP69K	Plus 316 stainless housing and FDA-compliant seals
Pharmaceutical clean area	IP69K	Cleanability and material certification matter as much as the rating
Car wash, vehicle underbody	IP69K	The application the standard was written for
Submerged, permanently	IP68	Confirm the declared depth and duration, and the cable entry
Cement, mining, quarry dust	IP67 or IP69K	First digit 6 is the critical one; abrasion resistance is separate

What an IP rating does not tell you

This is where specifications get expensive. The IP code covers dust and clean water at ambient-ish conditions. It says nothing about:

• Chemicals and detergents. Caustic CIP solutions attack seal elastomers and housing plastics in ways plain water does not. An IP69K sensor with the wrong O-ring material will still fail in a dairy.
• Steam. Steam penetrates by a different mechanism — pressure differential and condensation inside the housing as it cools. Steam sterilisation needs a specific declaration.
• Thermal cycling. Repeated heating and cooling pumps air, and eventually moisture, through any imperfect seal. A hot washdown followed by a cold rinse is a pump.
• Cable and connector. A sensor is only as sealed as its weakest entry. An IP69K head on an unmated M12 connector is an IP69K head with an open hole. Rate the connector, and fit caps on unused ports.
• Abrasion and impact. Cement dust and mill scale erode housings. An IP67 sensor that has been sandblasted for two years is no longer IP67. In hot-mill environments the housing specification matters at least as much as the IP code — see our guide to hot metal detectors for rolling mills.
• Long-term ageing. IP tests are performed on new samples. Seals harden, and the rating degrades over service life.

Practical specification advice

1. Specify the environment, then the rating — not the other way round. “IP69K” on a drawing without a housing material and seal specification is an incomplete requirement.
2. Ask for both ratings if you need both. If the device will be washed down and occasionally flooded, the datasheet must say IP67/IP69K or IP68/IP69K.
3. Check the connector rating separately and confirm it is achieved when mated with the cable you are actually using.
4. Match the housing material to the chemistry. In washdown environments, 316 stainless with the right seal compound matters more than the last digit of the IP code.
5. Mount to shed water. Cable entry downward, no horizontal ledges that pond, no upward-facing cable glands. Good mechanical practice buys more real-world life than one step of IP rating — see our guide to installing a proximity switch correctly.

Ingress protection is one of the quality characteristics we test to at our Mumbai plant, alongside 100% burn-in and in-process inspection — see our quality policy and certificates.

Frequently asked questions

Is IP69K better than IP68?

Neither is strictly better — they test different things. IP68 proves the device survives continuous immersion; IP69K proves it survives close-range hot high-pressure jets. A device can pass one and fail the other. If your application involves both, insist on a dual declaration.

Does IP67 mean waterproof?

It means the device withstood 30 minutes at 1 metre depth in clean water at test conditions. It does not mean it can live underwater, resist a pressure washer, or tolerate chemicals. “Waterproof” is a marketing word; the IP code is the engineering statement, and it is narrower than most people assume.

What does the K in IP69K stand for?

It is a legacy marker from the German standard DIN 40050-9 where the high-pressure, high-temperature test was first defined for road vehicles. That standard has been superseded by ISO 20653, and IEC 60529 now defines an IP69 of its own, but the industry has kept writing IP69K and everyone understands what is meant.

Can an IP rating degrade over time?

Yes. Seals harden and take a compression set, housings are abraded by dust and scale, cable glands loosen under vibration, and thermal cycling gradually pumps moisture past imperfect seals. The rating describes a new device under test conditions. Plan inspection intervals for sensors in wet or dusty duty rather than assuming the rating is permanent.

Do I need IP69K for a cement plant?

Usually not for the water rating — cement plants are dusty rather than washed down. What you need is the dust-tight first digit (6) plus abrasion resistance and, in many locations, high-temperature capability. IP67 with a robust housing is normally the right specification, with IP69K reserved for areas that genuinely get hosed at pressure.

A NAMUR proximity sensor is a two-wire inductive switch that does not switch a load at all. It varies the current it draws from an 8.2 V supply — below 1.2 mA when damped, above 2.1 mA when undamped. An isolating amplifier outside the hazardous area reads that current, and because the levels are unambiguous it also detects cable break and short circuit.

The problem NAMUR solves

An ordinary PNP proximity switch tells you one of two things: target present, or target absent. It has no way of telling you a third thing that matters far more in a refinery or a pharmaceutical plant — that the sensor itself, or its cable, has failed.

If a rodent chews through the cable of a standard NO sensor, the input reads “no target”. If the sensor’s output transistor fails open, the input reads “no target”. A valve that has not moved and a valve whose feedback cable is severed look identical to the control system.

NAMUR removes that ambiguity by encoding the sensor state as a current level rather than a switched voltage, and by leaving deliberate gaps between the levels. Any current outside the two valid bands is a fault, and the amplifier says so on a separate output.

The current bands in full

Sensor current	Meaning	Amplifier response
< 0.15 mA	Open circuit — cable break or disconnected sensor	Fault output operates; signal output goes to its defined safe state
0.15 – 1.2 mA	Damped — target present in the sensing field	Signal output switches
1.2 – 2.1 mA	Transition band — no defined state	Output holds its last valid state
2.1 – 6 mA	Undamped — no target present	Signal output in its rest state
> 6 mA	Short circuit in the field wiring or sensor	Fault output operates

Note that “damped” means the target has entered the field and damped the oscillator — which corresponds to the lower current. This trips people up, because intuition says more target should mean more current. It is the opposite.

Whether the amplifier’s output reads as “on” or “off” for a given sensor state is set on the amplifier, not the sensor, so the same NAMUR sensor can serve an NO or NC function depending on how the loop is configured.

Why this makes intrinsic safety straightforward

Intrinsic safety works by limiting the electrical energy available in the hazardous area to below the level that can ignite the gas or dust present. A NAMUR sensor operates on 8.2 V at a few milliamps — a few tens of milliwatts. There is simply not enough stored or available energy in the loop to produce an igniting spark or hot surface, even under fault conditions.

That makes NAMUR loops naturally suited to Ex ia certification, the highest intrinsic-safety protection level, which permits use in Zone 0 (gas present continuously) and Zone 20 (dust). The isolating amplifier sits in the safe area and acts as the barrier: it limits voltage and current into the field circuit and provides galvanic isolation between the hazardous-area loop and the control system.

The division of responsibility is worth being clear about. The sensor alone is not a safety device. Certification applies to the combination of the certified sensor, the certified amplifier or barrier, and field wiring that meets the stated cable parameters (capacitance and inductance limits). Substituting an uncertified amplifier voids the whole loop.

Where NAMUR sensors are used

• Oil, gas and petrochemical — valve position feedback on manifolds, pump and compressor monitoring, tank farm equipment.
• Pharmaceutical — solvent handling areas, reactor and centrifuge interlocks, where Zone 1 classification is routine.
• Chemical processing — anywhere flammable vapour is a normal part of operation.
• Grain, sugar, flour and pigment handling — dust atmospheres in Zone 20 and 21, where dust-cloud ignition is the hazard.
• Paint and coating plant — spray booths and solvent stores.
• Safety-related duties in non-hazardous areas, purely for the line-monitoring benefit.

That last case is often overlooked. Plenty of installations use NAMUR sensors with no explosion risk at all, simply because knowing the difference between “no target” and “broken cable” is worth having on a critical interlock.

Specifying a NAMUR loop

1. Establish the zone and gas or dust group. This determines the required equipment category and the certification the sensor and amplifier must carry. Get it from the site’s hazardous area classification drawing, not from assumption.
2. Choose the sensor. Thread size and rated operating distance are selected exactly as for a standard inductive sensor, including the reduction factor for the target material and the assured-distance rule. NAMUR changes the electrical interface, not the physics of detection.
3. Choose the amplifier. One channel per sensor. Confirm the entity parameters (U_o, I_o, P_o, C_o, L_o) are compatible with the sensor and the cable run.
4. Check the cable. Total capacitance and inductance of the field wiring must stay within the amplifier’s C_o and L_o limits — this is what caps the permitted cable length. Use the cable manufacturer’s per-metre figures.
5. Decide the fault action. What should the plant do when the amplifier reports a line fault? Alarm only, or trip? Design it deliberately rather than leaving the fault contact unwired, which is depressingly common.
6. Keep intrinsically safe wiring segregated and identified in light blue, in its own trunking, terminated on marked IS terminals.

NAMUR compared with a standard three-wire sensor

	NAMUR (2-wire)	Standard PNP/NPN (3-wire)
Supply	8.2 V from amplifier	10–30 V DC
Output	Current level, 0.15–6 mA	Switched voltage, up to ~200 mA
Drives a load directly	No — needs an amplifier	Yes
Detects cable break	Yes	No
Detects short circuit	Yes	Only via output protection, not reported
Suitable for Zone 0 / 20	Yes, with certified barrier	No
Cost per point	Higher — amplifier channel required	Lower
Wiring	Two cores, segregated IS routing	Three cores, standard routing

If your application needs neither hazardous-area approval nor line monitoring, a standard three-wire sensor is simpler and cheaper — see our comparison of PNP and NPN outputs and of two, three and four-wire wiring schemes.

Frequently asked questions

Can I connect a NAMUR sensor directly to a PLC input?

No. A NAMUR sensor has no output stage — it only modulates its own supply current, and at levels a standard 24 V digital input cannot interpret. It requires a NAMUR isolating amplifier or a dedicated NAMUR-capable input module. Connecting one to a normal 24 V input will not work and may damage the sensor.

Does a NAMUR sensor make my installation intrinsically safe on its own?

No. Intrinsic safety is a property of the complete loop: certified sensor, certified associated apparatus (the amplifier or barrier), and field wiring within the stated capacitance and inductance limits. All three must be right, and the documentation must show the entity parameters match.

What is the difference between damped and undamped?

Damped means a target is present in the sensing field and is damping the oscillator — the sensor then draws less than 1.2 mA. Undamped means no target is present and the sensor draws more than 2.1 mA. The lower current corresponds to target present, which is the reverse of most people’s intuition.

Why is the supply exactly 8.2 V?

It is the value fixed by the NAMUR recommendation and carried into IEC 60947-5-6, chosen to sit comfortably below the ignition-energy limits for intrinsically safe circuits while still giving the sensor enough headroom to run its oscillator reliably. The amplifier supplies it through a defined internal resistance, so the sensor and amplifier form a consistent, interchangeable pair across manufacturers.

Can NAMUR sensors be used outside hazardous areas?

Yes, and it is a sound choice for critical interlocks. You give up the ability to drive a load directly and pay for an amplifier channel, and in return the control system can distinguish a genuine “no target” from a broken cable or a shorted line. On a safety-related position feedback that distinction is often worth the extra cost on its own.