Even the first GEM could detect an open probe and blank its indication. Over the years by helping owners and their mechanics trouble shoot instrument problems I developed a new understanding and sympathy for the challenge they faced.
Troubleshooting avionics is an expensive and time-consuming process. Often times the procedure requires access to the instrument connector for continuity measurements. This might take hours of instrument panel disassembly just to touch the connector. We needed something better, easier to use, less time consuming and therefore less expensive.
Why not have the instrument diagnose itself? Then you don’t have to disassemble the airplane or even touch the wiring. This is not as easy as it might seem. Adding resistance measurement hardware for each and every probe wire would more than double the complexity of the measurement system. I considered this carefully during the development of the GEM-610 second generation instrument. It would at least add a second PC board to the instrument and have even greater adverse impact on the GEMINI twin version. Even if we endured these problems to get the information we had no practical way to display it on an orange bar display.
So I abandoned it then, but revisited again this time. The new color display was certainly adept at displaying the information, eliminating that problem, but the resistance data was still hard to get.
The reasons for not doing it were every bit as strong as before. It’s probably a character flaw that attracts me to insurmountable problems or maybe a form of hypoxia induced insanity from too many hours in the air but that’s the way I am. So this time I was able to invent a new way of measuring resistance. The simple idea worked beautifully without adverse impact on the design. It was so simple in fact even I was skeptical at first.
My patent attorney laughs, claiming we’ll have the first patent on resistance measurement in 200 years. Without this simple breakthrough we’d still be diagnosing things the hard way.
So what does the diagnostic system do?
It measures the resistance of the temperature probe junction and each of its lead wires. You can tell if any wires are broken, chafing, or shorting and whether the probe is degrading or near failure.
You can replace probes at your convince instead of waiting for them to fail. This will totally eliminate intermittent behavior caused by probe problems.
No more unplanned maintenance or out of town repairs. I think everyone will benefit from this feature.
