John, Richard, Nutsinee
Today's plan was to go out to TCSX table, take out the old IR sensor, and replace it with the new one (+VP inspection). John wanted to make sure that the sensor actually does what it was designed to do before we unwrap the light pipe and put it in so we did some tests. The comparator box was thought to be calibrated to trip at ~45 degree C. However, I forgot to write down how I did it so the number was very shady... We waved a small soldering iron in front of it, starting at low temperature (~150 deg F). The box would trip when the soldering iron was waved at half a centimeter away from the sensor. Keep in mind that the sensor is mounted at ~2.5 inches away from the center of the viewport with a small angle (the sensor is looking straight down while the optical window is about 0.6 cm deep under the viewport cover. So, the sensor must be able to trip when seeing a heat source at 2.5" away with ~22 deg viewing angle. We did a quick test by waving the soldering iron in front of the sensor with several temperature settings at several distances (At this point the potentiometer was about a quarter turn away from the room temperature tripping point. It's a 10-turn pot!). 800 deg F setting tripped the box at ~3" away, 600 deg F and 500 deg F tripped the box when waved at ~2" away. But these temperatures are impractical settings. At 800 deg F, 3" away we were able to make the box trip when placed the soldering iron rounghly 1cm above the sensor's viewing axis. This gives as a viewing angle of ~8deg, about a factor of 3 less than what's required. We did the same test with the sensor that was mounted on the TCSY viewport. The results were similar (400F, 500F soldering iron didn't trip the sensor when places at the center of the viewport but tripped the sensor when moved to the edge of the viewport. 600F at the center of the viewport did trip the sensor.)
To confirm the temperature of the soldering iron we used to do this test, we used Richard's FLIR camera and a thermocouple. Turns out the actual temperature of a certain spot on the soldering iron we pointed the IR sensor to was lower than the display. The thermocouple measured 304 F when display reads 350F, 630 F when reads 700F, and 750F when reads 850F.
Conclusion: The sensor unit isn't doing what's it supposed to do and we should rethink about installing them without an improvement to the comparator box circuit. Note that we were only using half a turn out of 10 turns available on the pot to set up this test. There's no way to fine tune this thing to where we want it to trip!
