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Frequently Asked Questions

What is the Thermochron iButton?
The Thermochron is a single-chip digital thermometer, thermostat, clock, calendar and data logging memory housed in the stainless steel iButton. Battery-powered and physically able to endure the most challenging environments, the Thermochron is ideal for data logging missions in the -40°C to 85°C temperature range.
Where would I use a Thermochron iButton?
You can use the Thermochron anywhere you want to monitor temperatures from -40°C to 85°C. Extremely durable and only 16mm in diameter, the Thermochron is ideally suited for remote and/or mobile thermal tracking in refrigeration units, trucks, crates, and incubators for purposes of chemical, food or other organic material storage, maintenance and transportation. It can stick to bottles, such as thermally sensitive chemicals, or mount on walls. Water, dirt and rough handling do not interfere with an iButton's functioning.
What's the life span of the Thermochron?
Either 10 years or 1 million temperature measurements (at 50 °C or less), whichever comes first.
How do you know when the lithium is low or nearly exhausted?
You can check the register that records the total number of conversions over the lifetime of the Thermochron. This register serves as a "gas gauge" because the primary consumer of lithium power is the conversion circuitry. By the way, the conversion process uses lithium even if the chip's other "front end" functions are externally powered.

See the lifetime graphs at the end of the DS1921G datasheet.
DS1921G-F5 Datasheet
What does 'water-resistant' mean for the Thermochron?
The DS1921 Thermochron iButton has a grommet that creates a seal that is water-resistant but not waterproof (hermetic). If you are using the iButton in an environment that exposes the iButton to high moisture content or is simply splashed with fresh or salt water, there should be no problem. Just wipe it off before touching it to the Blue Dot. If you have the need to submerge the iButton then we suggest that you place them in a plastic bag or coat them with latex to keep them dry while logging temperatures.

The DS1922 Thermochron iButtons have a new "can" design that allows them to be used in water up to 1m deep for up to 30 days. Therefore, we would recommend the DS1922 Thermochron versions for all submerged applications.

Some of our partners have encased the Thermochron in waterproof cases. Click on the link below to see their products.
Can I take the Thermochron deep sea diving, or submerge it in a conducting fluid?
Several years ago Dallas did a salt atmosphere exposure test for applications like access control systems in seaside towns, etc. We subjected a group of 10 iButtons to a salt spray for 96 hours and had no failures. The test was done according to Mil-Std-883C, Method 1009, Condition C with no electrical bias.

Note, however, that a salt-water film across the device may make it very difficult to read as the salt water creates a relatively low impedance shunt across the iButton. You might need to wipe it first before reading. In pure water, you can actually read the iButton when submerged since there are no ionic contaminants in the water to form the shunt
Of the different high temperature specifications documented for the Thermochron, how high can it really go?
There are two specifications: one for storing the DS1921 and another for using it. Because the DS1921 uses lithium backup to enable standalone operation, the data sheet states -40°C to 70°C as the range that yields maximum lithium life during storage.

Howeverand more importantlythe Thermochron's operational range is -40°C to 85°C (-40°C to 185°C). Of course, the higher temperature reduces the expected life of the lithium. See the last pages of the DS1921L datasheet for expected life span at different temperatures.
DS1921G-F5 Datasheet
How do I turn off the Thermochron?
You can stop the current mission from taking samples with a command under "Options" in the iButton Viewer (1-Wire for Windows TMEX). Also, the 1-Wire API for Java supports turning off the clock oscillator but no demos currently expose this feature.
Can I print the graphs generated by the iButton Viewer?
No, the data must be exported to some other program like Excel in order to create printable graphs.
Is there a Starter Kit for the DS1923 Humidity iButton?
There is not a starter kit just for the DS1923. While the Thermochron Starter Kit, DS1921K, does not contain a DS1923, the kit can be used with any iButton. The kit does have a USB Port adapter, a receptor cable, and a DS1921G Thermochron. The kit also contains the instructions as to where to download the free software from.
How long is the Thermochron good for (battery life)?
There are charts in the data sheets that show battery life. Battery life is effected by temperature and the rate of sampling. The higher the temperature or the quicker the sample rate, the shorter the battery life.
I've been using the DS1921. Now I want to use the new DS1922, can I use the same hardware?
Yes, the hardware used with the DS1921 can be used with all types of the DS1922 and DS1923.
The iButton Viewer won't recognize the DS1922 or DS1923. What is the problem?
To use the newer Thermochrons like the DS1922 and DS1923,an updated version of the software was created called the OneWireViewer. This new software will operate all the old iButton and 1-Wire parts and any new parts. It is still free for the download.
The new OneWireViewer won't start any Thermocron missions like the old iButton Viewer?
This is a common problem with people moving to the new OneWireViewer. The answer is to fill in the Temperature Alarm points. Even if the alarm is not turned on, the alarm points must have a value filled in.
The Temperature tab at the top of the OneWireViewer doesn't show the temperature like before?
The Temperature tab is used in the Forced Conversion mode. This can not be done when there is a mission in progress. Go to the Mission tab and use the lower Temperature tab to see the data from the Thermochron.
Is it possible to use the Thermocrons to measure the internal temperature of large mammals?
Dallas/Maxim does not recommend using the Thermochrons inside any living creature.

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