Understanding the IP (Ingress Protection) Ratings of iButton Data Loggers and Capsule
What Are IP Ratings?IP is an acronym for "Ingress Protection" against objects that intrude into the enclosure of any type of equipment. The IP ratings are defined in the IEC standard 60529, which was developed by the lnternational Electrotechnical Commission. Specifically, IEC 60529 defines an enclosure as, "a part providing protection of equipment against certain external influences and in any direction protection against direct contact."¹
The scope of IEC 60529 does not include corrosion resistance, construction requirements, and the effects of icing and coolants. These and additional aspects are addressed in the NEMA 250 product standard, developed by the National Electrical Manufacturers Association. With its more limited scope, an IP rating can be regarded as a supplement to a NEMA rating, but not as its equivalent. Consequently, caution is advised when using any IP/NEMA rating cross-reference tables published on the Internet. For more details refer to the NEMA publication, A Brief Comparison of NEMA 250—Enclosures for Electrical Equipment (1000 Volts Maximum) and IEC 60529—Degrees of Protection Provided by Enclosures (IP Code).²
The IP rating is formatted as "IP" followed by two digits. The first digit indicates a protection level against solids such as dust, and the second digit indicates a protection level against liquids. Figure 1 illustrates the IP formats and uses IP56 as an example.
Figure 1. IP rating format.
iButton Data Logger EnclosureThe iButton data loggers, which include the Thermochron temperature loggers and the Hygrochron temperature and relative humidity loggers, represent a significant advancement in miniaturization and reliability. The single-contact 1-Wire® communication protocol that each data logger employs is robust and simple. The iButton stainless-steel package is durable and resistant to intrusions from both solids and liquids. For the iButton to function reliably in an application, however, it is important that the limitations of this enclosure be understood.
DS1921G, DS1922L, DS1922T, DS1923 Are Certified IP56For a general introduction to iButton data loggers, their features, and how they are used see application note 3892, "Overview of iButton® Sensors and Temperature/Humidity Dataloggers." While iButton data loggers are water-resistant, they are not waterproof. An independent testing lab³ has certified several data loggers to be IP56 compliant: DS1921G (2kB memory, ±1°C accuracy, -40°C to 85°C); DS1922L (8kB memory, ±0.5°C accuracy, -40°C to 85°C); DS1922T (8kB memory, ±0.5°C accuracy, 0°C to 125°C); and the DS1923 (8kB memory, ±0.5°C/5%RH accuracy, -20°C to 85°C).
The initial sealing level of the DS1921G, DS1922L, and DS1922T Thermochrons at time of manufacture achieves IP56. From Figure 1 above, IP56 translates to "Protection against dust" and "Protection against strong jets of water." Aging and use conditions can, however, degrade the integrity of the seal over time. Therefore, for applications with significant exposure to liquids, sprays, or similar environments, it is recommended that the Thermochron devices be placed in the DS9107 iButton capsule.
The DS1923 Hygrochron logs humidity, so it should not be placed inside a waterproof container that will prevent it from functioning as intended. Therefore, consider mounting the Hygrochron where it is exposed to the air, but not to direct water. A shield housing is recommended.
While the DS1921H and DS1921Z did not formally go through the IP56 testing, they are constructed identical to the DS1921G and should perform similarly.
The DS9107 Is Self-Certified to IP68It is important to note that the data loggers are not recommended for any type of fluid immersion. If the application requires submersion in a liquid, then the device should first be placed in a waterproof container. An example of a suitable waterproof container is the DS9107 (iButton Capsule) (Figure 2) that is certified to IP68. IP68 indicates an extended immersion under pressure. The DS9107's IP68 rating has been defined as 100ft (30.5m) equivalent pressure for 24 hours (Table 1).
Figure 2. DS9107 iButton Capsule.
IP68 classifies any enclosure that can withstand liquid under pressure for "long periods." Additional specific parameters are then defined by, and for the device's individual enclosure characteristics. Maxim has performed a self-certification of IP68 for the DS9107, defined with the following specifics:
Table 1. DS9107 IP68 Self-Certification Results
¹ IEC 60529 standard quoted in, A Brief Comparison of NEMA 250—Enclosures for Electrical Equipment (1000 Volts Maximum) and IEC 60529—Degrees of Protection Provided by Enclosures (IP Code), published by NEMA in 2002. To download this document, see note 2. The IEC60529 standard is available for sale at: www.techstreet.com/cgi-bin/detail?product_id=861222.
² This comparison of NEMA 250 and IEC 60529 can be found at: https://www.nema.org/Standards/Pages/A-Brief-Comparison-of-NEMA-250-and-IEC-60529.aspx
³ IP56 certification for iButton data loggers can be found at: www.maximintegrated.com/products/ibutton/images/ip56_loggers_cert.pdf
All iButton and iButton accessories' certifications can be found here.
4 For more information on pressure measurements, measurement units, and the phase diagram of water, see Stephen R. Turns, Thermal-Fluid Sciences, An Integrated Approach, Chapter 2, "Thermodynamic Properties, Property Relationships, and Processes." Go to: www.cambridge.org/us/engineering/turns/assets/0521850436c02_p046-171.pdf