How does vacuum affect the DS1921G & DS1922L iButtons

The iButton devices are sealed in atmospheric pressure and we have not performed studies on how our iButtons will operate under vacuum conditions. We recommend that customers characterize or certify our iButtons in their systems prior to usage in those environmental conditions. The iButtons are not airtight/hermetic and the battery inside could leak lithium as a result of the vacuum forces. For more information on the batteries and their behavior in a vacuum, please contact the battery manufacturers. We use the BR-1225/DBN type from Panasonic in the iButtons that have a battery, like the Thermochrons mentioned here.

How to measure skin temperature with iButtons?

The iButtons can be placed touching human skin on the bottom side, provided no sweat or body liquids cover them or are too aggressive on its surface. The rubber grommet separating both poles (top lid and rest of iButton) is particularly delicate and should not be exposed to liquids at all. The customer must devise some sort of thin film liquid insulator that is not a heat insulator. In the case of the Thermochrons only (not a DS1923), a DS9107 capsule could be used if the application is given enough time to reach thermal equilibrium.

What is the range or reach of the Thermochrons?

The concept of reach is not exactly aplicable. The iButtons measure their own temperature. That means they are measuring the temperature of the area they are in, after thermal equilibrium is reached. It usually takes some time for this equilibrium to complete, this is mentioned in the data-sheet as time constant, which is around 150s.

Can you retrieve data from an iButton that is no longer being recognized or is dead?

Maxim makes quite a few iButton devices. Some of these don't require batteries, but several do. Unfortunately when an iButton battery dies, the data stored in the memory is lost. The only exception to this is the DS1925. Although it has a battery, data gets stored in non-volatile memory. The power to read the DS1925's memory does not come through the parasite-powered circuitry of the 1-Wire front end but through the strong pullup delivering power from the PC adapter.

Does the iButton temperature sensor measure surface temperature or air temperature?

In the iButton temperature sensor, the physical location of the temperature sensor is in the middle of the iButton. The circuit board and battery are closer to the side of the iButton with a flange and have a certain effect on the rate of heat conduction. The side of the iButton without the flange has a relatively higher heat conduction efficiency. Of course, both sides of the iButton can be used to measure temperature. However, if the iButton is to be placed between two media, for example, half in soil and half exposed in air, and there is a large temperature difference between the soil and water, then we recommend placing the side of the iButton without the flange in the medium to be measured.

Is the DS9093A Fob hard to snap an iButton in?

The mating of this two parts has to be done with considerable force. There is even a service that does it for you: https://www.ibuttonlink.com/products/insert-an-ibutton-into-fob In the past there was a machine that helped doing it but the company in South Africa (MBL Technologies) is apparently not selling it anymore.

Does the RTC on the DS1921G account for daylight savings?

While the RTC on the DS1921G does automatically compensate for leap year, it does not account for daylight savings. You can get around this by selecting the "Synchronize Real-time Clock" in the Start New Mission Window. This will synchronize the device's real-time clock to the PC that you are using. As long as your PC accounts to daylight savings, and you select "Synchronize Real-time Clock," the device will adjust with daylight savings.

Do you have any document that certify that the DS1921G is safe to send via mail carriers such as FedEx?

For iButton products that contain batteries, Maxim can provide the battery type and battery documentation necessary for air transit. The iButtons that contain batteries are classified as equipment containing batteries, and will need to follow specific IATA and carrier requirements. Once the customer has the information on the battery, they will need to determine how they will transport it via the carriers that they choose to use and what country regulations they need to abide by. If you provide the Maxim full part number of the ibutton in question, we can provide the battery documentation. However, it will be the customer’s responsibility to determine the shipping requirements based on what they ship, where and how much.