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Data Logger, Temperature/Humidity Loggers, and Sensors
Businesses desire to give customers a guarantee of quality and freshness in regards to the products they make or the services they provide. For many businesses, tracking temperature and humidity throughout the lifetime of a product or service, or throughout various stages of manufacturing and delivery, are integral to achieving this goal. With this in mind, Dallas Semiconductor Maxim designed several digital thermometers and temperature/humidity data loggers.
Digital Thermometer
The first product in the iButton® line of Temperature Sensors is the DS1920. The DS1920 is a digital thermometer that reads the current temperature of the environment or object to which it is attached. Using a 1-Wire® probe, a simple touch of the DS1920 reveals the current temperature of its surroundings from -55°C to 100°C.
Temperature Data Loggers
The Thermochron® family of iButtons are globally addressable, dedicated trackers that can go wherever thermally vulnerable products go, monitoring time and temperature and storing the data. The data can then be easily uploaded and analyzed to detect possible thermal damage.
There are several Thermochrons from which to choose. The DS1921G, DS1921H, and the DS1921Z represent our standard Thermochrons, and the DS1922L, DS1922T, and the 1-Wire chip DS2422 represent our high-capacity Thermochrons with more logging memory, increased accuracy, and increased resolution.
The iButton's embedded computer chip 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 iButton logs data for more than 10 years.
Digital Hygrometer
Our Hygrochron™ family of iButtons (DS1923) adds an embedded humidity sensor to the temperature-logging capability of the high-capacity Thermochron family to create a data logger that records both temperature and humidity. With these two pieces of data, relative humidity can be logged as a function of time. The tiny opening in the lid of the Hygrochron iButton employs a special filter that allows water vapor to pass through and reach the internal humidity sensor, but repels liquid-phase water (see picture).
For applications where both temperature and humidity are important (foods, chemicals, powders, HVAC systems), the Hygrochrons deliver unprecedented performance in an unbelievably compact size.
Rugged iButtons Attach to Almost Anything
The 16mm iButtons (about the size of 5 stacked dimes) attach unobtrusively to almost any container surface or wall-on bottles, totes, boxes, crates, pallets, air cargo containers, refrigerators, semi trailers, railroad freight cars, etc. The iButton's stainless steel armor withstands dirt, moisture and rough treatment.
Versatile Data Storage: Log and Histogram Formats
Thermochron and Hygrochron iButtons can wake up to take time-stamped temperature and/or humidity readings at equal time intervals, then store them in a log format in on-board "datalog" memory. The standard Thermochrons (DS1921G/H/Z) allow 2048 readings with time intervals of 1 to 255 minutes, while the high-capacity Thermochrons/Hygrochrons allow 8192 readings with time intervals from 1 second to 273 hours. Additionally, the Hygrochron allows for simultaneous temperature and humidity logging and offers selectable resolution settings.
Log Graph
The way in which the iButtons log data can be setup by the user prior to use. This is called "missioning". Typically, during missioning the user chooses the time to begin temperature/humidity readings, sets a sampling rate, sets high and low alarm thresholds, and determines whether to rollover when the readings fill up the datalog memory or to simply stop logging. This method of data storage records when a critical thermal/humidity exposure occurs and helps to assign accountability for any resulting loss of product quality.
Standard Thermochrons, the DS1921G, H, and Z also simultaneously store each temperature sample in a histogram. The histogram memory consists of 63 bins in 2-degree increments for the DS1921G or 64 bins in 0.5-degree increments for the DS1921H or Z. Each bin holds 65,500 temperature readings for up to 10 years. The histogram method of data storage is perfect for applications with a need for long-term monitoring but with less-strict accuracy requirements. The higher capacity Thermochron and Hygrochron lines do not have the histogram function, but they have nearly 4 times the data logging memory.
Thermochron Family of Products
Our standard Thermochron, the DS1921G, logs temperatures over a wide temperature range of -40C to 85C. The H and Z Thermochrons are our high-resolution versions. The DS1921H is designed for the human temperature range while the DS1921Z is designed for applications that need high resolution around 0°C.
The high capacity Thermochrons are the DS1922L, DS1922T, and the DS2422. The DS1922L is the standard high capacity Thermochron iButton that logs temperatures over the range of -40°C to 85°C. It has an 8192 byte temperature log with accuracy correctible (by software) to ±0.5°C from -10°C to +65°C. It has selectable 8-bit (0.5°C) or 11-bit (0.0625°C) resolution. The temperature log values are also selectable (between 8-bit or 16-bit ). The DS1922T Thermochron iButton is similar to the DS1922L only with a higher temperature logging range (that can be used in manufacturing processes involving sterilization techniques). The main differences between the two is that its temperature range is 0°C to 125°C, and it's accuracy is software-correctible to ±0.5°C from 20°C to +75°C.
Finally, the DS2422 operates the same way (through a 1-Wire interface), and with the same functionality as the DS1922L. However, it is a packaged ic (24-lead, 300-mil SO) that when connected to an optional analog-to-digital converter (ADC) and a charge pump, application-specific dataloggers can be built (i.e., humidity, pressure, light sensor, material stress, etc).
| Product |
Temperature Range |
Humidity Range |
Temperature Accuracy* |
Temperature Resolution |
Humidity Resolution |
Data Log
Memory |
| DS1921G |
-40°C to 85°C |
N/A |
±1°C |
0.5°C |
N/A |
2048
bytes |
| DS1921H-F5 |
15°C to 46°C |
N/A |
±1°C |
0.125°C |
N/A |
2048
bytes |
| DS1921Z-F5 |
-5°C to 26°C |
N/A |
±1°C |
0.125°C |
N/A |
2048
bytes |
| DS1922L |
-40°C to 85°C |
N/A |
±0.5°C
Software Correction
(SC) |
0.5°C
or
0.0625°C |
N/A |
8192
bytes |
| DS1922T |
0°C to 125°C |
N/A |
±0.5°C (SC) |
0.5°C
or
0.0625°C |
N/A |
8192
bytes |
| DS2422 |
-40°C to 85°C |
N/A |
±0.5°C (SC) |
0.5°C
or
0.0625°C |
N/A |
8192
bytes |
| DS1923 |
-20°C to 85°C |
0 to 100%
RH |
±0.5°C (SC) |
0.5°C
or
0.0625°C |
8-Bit
(0.6%RH)
or
12-Bit
(0.04%RH)
RH |
8192
bytes |
*Temperature accuracy denoted in this table is effective over most of the temperature range of the part. For full-range accuracy, please refer to the part's datasheet.
Looking for the DS1921L?
Missioning the Thermochron
Missioning the Thermochron or Hygrochron iButton is done with a PC or handheld. The iButton connects to a Blue Dot receptor (a low cost reader interface) which in turn is connected to a 1-Wire Adapter attached to a computer. This site provides free evaluation software to set start time, sampling rate, and alarm thresholds.
The low cost reader interface includes:
DS1402D-DR8 - Blue Dot Receptor
DS9097U-S09 - 1-Wire to RS-232 Adapter
Or
DS9490R - 1-Wire to USB Adapter
How to Download Free Evaluation Software
Two different evaluation software programs are available to be downloaded. They can be downloaded here. Both programs depend upon the 1-Wire Drivers installation package. Version 3.21 of the 1-Wire Drivers (also known as the TMEX Runtime Environment—RTE) includes the iButton Viewer. It supports the DS1921G, H, and Z. Version 4.00 of the 1-Wire drivers includes a link to download and install the OneWireViewer. It is a Java program that contains support for both Thermochrons and Hygrochrons. The software, of course, depends upon the correct hardware being installed on a PC. To do this, plug the 1-Wire adapter into the PC, connect the Blue Dot Receptor to the adapter, and plug in a Thermochron or Hygrochron in the Blue Dot. Then, run one of the above-mentioned programs to locate and click on the iButton's serial number. This starts the program/mission wizard. It is a guide that provides the steps to set up a temperature/humidity logging mission. Briefly, the steps include:
- Set the clock.
- Set the time alarm.
- Set the sample rate.
- Set the temperature/humidity alarm.
- Set the mission start delay.
- Check when mission will end; select data rollover or not.
- Finish.
Programmers: The following kits contain example applications to mission and download Thermochrons/Hygrochrons.
Starter Kit Available
If you want to get up and running quickly, the DS1921K Thermochron iButton Starter Kit contains all of the hardware necessary to configure a Thermochron iButton and review the resulting data. The data can also be saved or imported into other applications.
The kit includes:
- DS1921L-F51 Thermochron iButton
- DS9093F iButton Keyring Fob Attachment
- DS9490R 1-Wire to USB Adapter
- DS1402D-DR8 Blue Dot Receptor with RJ-11 Connector
- Instruction Sheet
The DS1921K Starter Kit can be ordered from our on-line store.
Thermochron FAQ
Visit the Thermochron FAQ section.
Thermochron/Hygrochron Solutions
We have several partners that have developed hardware and software solutions around our Thermochron products. Software products that run on both the PC and PDA give you the ability to mission, upload, and manage the data from thousands of Thermochrons. Hardware products range from small devices to mission Thermochrons and read their alarm status to data collection devices for HACCP applications. Check out our online Solutions Search for all of our partner's products.
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