Some answers to questions on the Thermocron Temperature Datalogger...
Of the different high temperature specifications documented for the Thermochron Button, 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.
However—and more importantly—the Thermochron's operational range is -40°C to +85°C (+185°F). Of course, the higher temperature reduces the expected life of the lithium. We will be providing some derating curves as soon as possible, and update the data sheet.
What's the life span of the Thermochron?
Either 10 years or 1M 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.
A study is in process of a full-temperature characterization of the battery's power consumption. When we have the data we will provide charts with which you can calculate the anticipate lifetime, given the temperature sampling frequency and average operating temperatures.
What does "water-resistant" mean for the Thermochron?
The Thermochron's grommet creates a seal that is water-resistant but not waterproof (hermetic). Under conditions where the Thermochron is submerged to a depth greater than 10 feet for an extended period of time, the pressure may force water into the Thermocron buttons . If you are simply swimming in the ocean with an Thermocron button or the Thermocron button is on equipment that gets exposed or splashed with fresh or salt water, there should be no problem. Just wipe it off before touching it to the Blue Dot.
Can I use the Thermochron in conducting fluids? Can I take the Thermochron deep sea diving?
Several years ago a study was done of salt atmosphere exposure test for applications like access control systems in seaside towns, etc. We subjected a group of 10 Thermocron buttons 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 Thermocron buttons. You might need to wipe it first before reading. In pure water, you can actually read the Thermocron buttons when submerged since there are no ionic contaminants in the water to form the shunt.