Although flying balloons has been my great passion, creating stuff to improve that activity has also attracted my attention. This is one example.
In the 1990s, not long after I had moved on from balloon manufacturing, I had the idea to create a temperature logger that could be permanently installed at the top of a balloon envelope to document its entire lifetime temperature history. I suppose this came out of my years manufacturing balloons and seeing a few balloons along the way that had not held up as long as they should have. In these cases one question hanging in the air was whether the envelope had been subjected to unusually high temperatures in flight. Thinking of balloons stored in a dark colored van or trailer, a secondary question was how hot had these envelopes been while they were packed between flights.
So I imagined an electronic device that would periodically measure the temperature at its probe and determine whether it was in a dark or light place. If the device saw light when taking a temperature reading that would mean the envelope was unpacked, presumably for use. If the device saw dark, presumably the envelope was packed. The device would increment by one the appropriate cell in one of two tables in its memory – one table for “light” temperatures and one for “dark” temperatures. Each table would be a set of cells of four-Fahrenheit-degree range each that together covered the entire range of possible envelope temperatures.
Large-capacity lithium batteries with a specified life of ten years would power the unit for a time approaching that. This would be possible because the microcomputer central to the unit could be programmed to “sleep” for most of the time while using virtually no power, waking itself only every 26 seconds for a split second to observe and store a reading.
The data in the table would be able to be downloaded with a special cable and software, but there would be no way to alter the data in the table. The electronics in the device would fully imbedded in silicone material that protected it from damage or tampering.
To be sure the batteries powering the unit were not getting too hot in use, I installed a set of temperature telltales inside the device to track its maximum internal temperature. Installing the unit on the outside of the envelope, with the temperature probe on the inside, did keep the internal temperature well below the batteries’ maximum allowable temperature.
I built four of these units and installed them in balloons I had access to. The device was attached to the outside of the envelope with two machine screws through a vertical load tape a short distance from the parachute valve hole, with the temperature on the inside of the envelope against the vertical load tape.
The unit worked as planned, but with one critical exception. It turned out that the batteries failed to meet their published capacity specifications, failing after several years. I assumed that the occasional higher temperatures to which they were exposed caused this, despite the adequate temperature limits contained in the specs.
Frustrating though this was, at least I did end up with quite an elegant paperweight.