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Space Forum / Shuttle / December 2007ECO sensor operation theory
Hi, I searched around without success for a description of how the ECO sensor works. Does it detect a change in capacitance in the platinum wire grid when immersed in cryogenic fuel? Thanks, Patrick >Hi, I searched around without success for a description of how the ECO >sensor works. Does it detect a change in capacitance in the platinum [quoted text clipped - 3 lines] > >Patrick My guess is that it is a delta resistance sensor. With either E(measures) = I(fixed) x R(temperature) or I(measured) = E(fixed) / R(temperature). Any flaws in the sensor wire, connecting wires, connectors, or joints (solder or wield) can cause instability and error. And that over the extreme temperatures involved. The measured resistance delta is probably quite small. Self heating must be considered. Self heating may be part of the actual usage process as the thing is immersed in liquid H2 or not. A problem is that the very surrounding air(N2?) is going to liquefy and freeze. The various joint mechanical stresses must be quite large. The physics doesn't care about the politics of the issues. >>Hi, I searched around without success for a description of how the ECO >>sensor works. Does it detect a change in capacitance in the platinum [quoted text clipped - 16 lines] > >The physics doesn't care about the politics of the issues. Some potentially useful background info : http://en.wikipedia.org/wiki/Resistance_thermometer While temperature is not the primary interest, thermal properties of the surrounding medium is probably the prime indicator, those properties can be inferred from the self heating of the transducer. From the article the temperature coefficient of resistance is about .00385 ohms per degree centigrade per ohm of nominal resistance. From the article : "Commercial platinum grades are produced which exhibit a change of resistance of 0.385 ohms/°C (European Fundamental Interval) The sensor is usually made to have a resistance of 100O at 0 °C. This is defined in BS EN 60751:1996. The American Fundamental Interval is 0.392 O/°C. Resistance thermometers require a small current to be passed through in order to determine the resistance. This can cause resistive heating, and manufacturers' limits should always be followed along with heat path considerations in design. Care should also be taken to avoid any strains on the resistance thermometer in its application. Lead wire resistance should be considered, and adopting three and four wire connections can eliminate connection lead resistance effects from measurements." I compiled an article with an in-depth view at the ECO sensor system. It's at http://spacelaunch.gerhards.net/2007/12/space-shuttle-eco-sonsors-in-depth-view.html There are also a number of pictures, schematics and a few interesting quotes from the STS-114 ECO sensor incident. Comments and additions are most welcome. Rainer > I compiled an article with an in-depth view at the ECO sensor system. > It's at [quoted text clipped - 4 lines] > quotes from the STS-114 ECO sensor incident. Comments and additions > are most welcome. Good stuff. I saw the pics on the NASA shuttle site last week, but you put a good context around them, and then also mine the earlier report. Count me among those who are interested in how the tests during the countdown are done. /dps > Count me among those who are interested in how the tests during the > countdown are done. It looks like they have at least one serious suspect: http://www.nasaspaceflight.com/content/?cid=5309 It will be a very interesting day tomorrow :) Rainer |
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