Sensor Sense: IP ratings for sensors

Aug. 4, 2005
A classification system established by the International Electrotechnical Commission (IEC) rates how well enclosures and packages for electrical components seal against intrusion by foreign materials such as dust and moisture.

Sensor ingress protection, a.k.a. IP, ratings detail how well sensors resist infiltration by foreign materials such as dust and water. These IP67-rated sensors should be able to withstand a water bath without leaking.

The system entails various levels of ingress protection identified by the letters "IP" followed by three numerals. The first numeral represents the degree of protection afforded against solid objects, while the second numeral signifies the degree of protection against the ingress of water. The third numeral is seldom specified in the ratings of an object. It represents the degree of impact an object may sustain and still function normally.

In general, higher numbers identify more stringent protection from a particular environment. Additional suffix letters attached to the rating specify variations from the standard, again typically to a higher level. However, these ratings tell nothing about how well devices react to the introduction of outside variables such as temperature fluctuations.

Proximity sensors and other electronic sensing devices are typically rated between IP65 and IP69K. In this case, the first numeral "6" indicates that the equipment is dusttight. The second numeral rates the amount of water ingress allowed:

IP65 signifies protection against low-pressure water jets from all directions for 1 min with limited ingress permitted. IP66 signifies protection against strong jets from all directions for 1 min with limited ingress permitted. IP67 signifies protection against the effects of immersion from 15 cm to 1 m for 30 min without water ingress. IP68 signifies protection against complete continuous submersion in water without water ingress under conditions specified by the manufacturer. IP69K is a special designation for devices subjected to high-pressure and temperature wash-downs, such as those found in food processing. Its use identifies protection against hot-steam-jet cleaning per EN 60529 and DIN 40050-9. The rating's K suffix means the sensor must withstand direct application of extremely high-pressure water jets. Water at a pressure of 100 bar (1,450 psi) blasts the sensor at angles of 0, 30, 60 and 90° for 30 sec at each point (120 sec total time) at a temperature of 80°C. Absolutely no water ingress is permitted in devices that obtain this rating.

Ratings are often misunderstood and misapplied. For example, many assume that a rating of IP67 or IP68 means the device functions under water for the time specified by the IP rating. This is not the case. The rating only means the device functions properly after removal from water.

Another misconception is that an ingress protection rating of IP69K automatically complies with IP67 and IP68. While IP69K-rated parts can withstand pressure and jet spray, the sensor is still unsuitable for use under water. Thus IP69K sensors typically serve in wash-down environments such as breweries, car washes, and food and beverage applications, not where the sensor spends any time underwater.

To be rated IP68 a sensor must also meet the requirements of IP67. But its manufacturer determines what additional ingress protection the device must meet for the IP68 rating. The component maker additionally determines any temperature constraints that, if exceeded, might affect proper operation.

Some manufacturers produce components that meet only minimal requirements above IP67 for their IP68 rating while others far exceed IP67. Turck Inc., for instance, requires its IP68-rated proximity sensors meet the following specifications: full IP67 protection; 7 days submerged 1 min in water at a constant temperature; 24 hr at 70°C; 24 hr at 25°C; and 10 cycles of temperature fluctuation between 70 and 25°C with a minimum of 1 hr at each temperature.

Specifications for other IP68-rated sensors may not match those of Turck or of any other manufacturer. Yet manufacturers can use the IP68 rating as long as their product exceeds the IP67 rating. The differences between IP68 sensor ratings may lead to sensor comparisons that are not apples-to-apples.

Turck Inc. ( information for this article.

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