AN3892| Application Note
Maxim/Dallas > App Notes > 1-WIRE DEVICES AND TEMPERATURE RECORDERS
TEMPERATURE SENSORS and THERMAL MANAGEMENT
TIME
Keywords: ibutton, data, logger, datalogger, dataloggers, thermochron, hygrochron, hygrometer, temperature, recorder, sensor, sensors, overview
Aug 14, 2006
APPLICATION NOTE 3892
Overview of iButton Sensors and Temperature/Humidity Dataloggers
This application note defines a basic iButton datalogger and shows how these products can vary to track temperature and/or humidity data. Typical applications are presented. The article explains how the datalogger is constructed, tested, and certified to pass various safety and EMI standards. Flexible and programmable, each iButton datalogger is designed to be setup (a step called 'missioning') by the user to collect data for an application. The software for missioning is discussed and made available to the reader. The formats for data presentation are shown.
Introduction
Businesses need to guarantee customers the best quality and freshness in their products or services. For many businesses, this means that tracking temperature and humidity throughout a product's lifetime, through the duration of a service, or through various stages of manufacturing and delivery, are critical. To support this business need, Dallas Semiconductor designed several digital thermometers and temperature/humidity data loggers.
Digital Thermometer
The DS1920 iButton is a digital thermometer that reads the temperature of the environment or of the object to which it is attached. Simply touching a 1-Wire probe to the DS1920 reveals the surrounding temperature, measured from -55 C to +100 C.
Temperature Dataloggers
The Thermochron family of iButtons are globally addressable, dedicated 'trackers' that accompany products vulnerable to temperature fluctuations, wherever they go. The tiny, durable Thermochron monitors time and temperature, and then stores the data. The data can easily be uploaded and analyzed to detect possible thermal damage to the product. There are several iButtons from which to choose. The DS1921G, DS1921H, and the DS1921Z are standard Thermochrons. The DS1922L, DS1922T, and the 1-Wire chip DS2422 are high-capacity Thermochrons with more logging memory, increased accuracy, and increased resolution. The computer chip embedded in the Thermochron integrates a 1-Wire transmitter/receiver, a globally unique address, a thermometer, a clock/calendar, a thermal history log, and 512 bytes of additional memory to store user data (such as a shipping manifest). The recyclable Thermochron logs data for more than 10 years.
Digital Hygrometer
Our HygrochronTM iButton (DS1923) adds an embedded humidity sensor to the temperature-logging capability of the Thermochron. The tiny opening in the Hygrochron's lid uses a special filter that allows water vapor to pass through and reach the internal humidity sensor, but repels liquid-phase water (Figure 1). Gathering both temperature and humidity data, the Hygrochron logs relative humidity as a function of time.
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