Small but perfectly formed

Apart from being secure, dataloggers must be rugged, reliable and cost efficient. The thermochron and hygrochron iButtons from Dallas Semiconductor/Maxim are such devices.

What is an iButton?

An iButton is a computer chip with a globally unique address, factory-lasered at the time of manufacture (think of it as a URL for each iButton), enclosed in a 16mm stainless-steel case. They can include read/write memory, clocks, thermometers and dataloggers. They deliver or record data wherever needed. All this power and capability make iButtons ideal for a wide range of applications including environmental datalogging, access control, e-cash transactions and asset tracking.

The globally unique tag – 281,000,000,000,000 different addresses!

An iButton’s 64-bit address provides a simple, secure way of identifying a location or an item. It can serve as an electronic serial number that is never duplicated. With onboard memory, iButtons can also store critical information about an item or location, such as container contents, shipping destination or owner information.

Rugged durability that lasts and lasts

iButtons bring unparalleled durability to datalogger applications. Expose one to high or low temperature extremes. Step on it. Drop it in water. There is no need to worry about destroying this datalogger because iButtons can withstand harsh indoor or outdoor environments. The durable iButton can be remissioned and reused for many years, significantly reducing operating costs.

Simple, low-power interface

iButtons require a physical/electrical connection to whatever is reading or writing data. However, a novel digital communication scheme called a 1-Wire interface reduces the number of electrical contact points to just one, plus a ground reference. A single conductor for both power and data communications is all that is needed. Devices that read and write to iButtons have all their electrical components inside, with only the two electrical contact points exposed, separated by a wide gap. With the connection so simplified, you get very durable, dust and moisture immune probes that interface to most surfaces. An iButton reader draws virtually no power in standby mode and less than 2mA during communication – making it ideal for battery-powered devices such as handheld computers and PDAs. Reading an iButton’s unique address takes no more than 5ms. Now users can finish their data collection tasks without having to worry about constantly changing batteries in their handheld device every few hours.

Temperature and humidity data loggers – the products

The iButton Thermochron (temperature data loggers) and Hygrochron (temperature and humidity data loggers) family of iButtons (DS1921/DS1922/DS1923) are temperature and or temperature and humidity data loggers that track the temperature of specific assets or locations. Now you can easily log the thermal exposure of an asset during shipment to see if it stays within specified temperature ranges. With a Thermochron or Hygrochron it is simple and inexpensive to monitor all types of products that are temperature or humidity sensitive, including pharmaceuticals (vaccines, drugs, reagents), fresh or frozen foods (fruits, vegetables, dairy/dessert items), biological items (animals, blood products, soil), or heating/refrigeration/freezer systems. The Thermochron and Hygochron could also be used for warranty tracking purposes on equipment that must be kept within a certain temperature range or to log the results of a process that must be monitored for compliance to a temperature or humidity profile. Like all iButtons, the stainless steel casing of a Thermochron or Hygrochron makes it rugged, reusable and portable. It is so small that it fits anywhere and can deliver years of reliable, highly accurate temperature and or humidity readings.

Thermochrons and Hygrochrons support two temperature logging styles: time/temperature mode

Each Thermochron will log up to 2K (DS1921) or 8K (DS1922) temperature readings (-40°C to +125°C. Operating temperatures vary dependent on Thermchron type) before the logger memory is full. At that point, the user can configure the device to terminate logging or roll over and begin writing over the oldest data points. If the logger is set to record a temperature every five minutes, the DS1921 memory will be full after approximately seven days and the DS1922 after approximately 28 days.

Time/temperature/humidity mode

The DS1923 Hygochron temperature/humidity logger iButton is a rugged, self-sufficient system that measures temperature and/or humidity and records the result in a protected memory section. The recording is done at a user-defined rate. A total of 8192 8-bit readings or 4096 16-bit readings taken at equidistant intervals ranging from one second to 273 hours can be stored. In addition to this, there are 512 bytes of SRAM for storing application specific information and 64 bytes for calibration data. A mission to collect data can be programmed to begin immediately, or after a user-defined delay or after a temperature alarm. Access to the memory and control functions can be password-protected.

The DS1923 measures temperatures in the range of -20°C to +85°C, 0-100 percent RH. Temperature values are represented as an 8- or 16-bit unsigned binary number with a resolution of 0.5°C in the 8-bit mode and 0.0625°C in the 16-bit mode.

Histogram mode (DS1921 only)

A temperature histogram runs concurrently with the time/temperature logging for each DS1921 Thermochron. The histogram logs temperature occurrences into one of 64 different temperature ranges. A counter is incremented for the corresponding range each time a measured temperature falls within that range. The counter for each range can count up to 65536. If the logger is set to record a temperature every five minutes, the histogram counter would reach 65536 after approximately 227 days (even longer if the measured temperatures fell into multiple ranges). Therefore, the histogram can be used in applications where total thermal exposure is important but the exact times particular temperatures occurred is not. For example, it may be important to monitor a process and record the total number of minutes of exposure at various temperatures.

Turnkey systems available

Dallas Semiconductor/Maxim has teamed with a number of third-party systems integration experts around the world to combine the power of its iButton products with the market knowledge, systems expertise and local support of these independent companies to create a powerful suite of ready-to-use products. Its authorised solutions developers (ASDs) have already developed turnkey iButton systems to address typical datalogging applications such as cold chain shipping, process monitoring/quality control, and refrigerator/freezer system tracking. In addition, these developers can also design custom iButton software and/or hardware solutions.