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Space Forum / Shuttle / December 2007ECO sensor flakey failures
Finally found some info on the ECO sensors. Bottom line is that it is an interface problem due to an inherent sensitivity to impendance mismatch, stray capacitance, signal condtioning problems, etc, IMO. NASA is trying to take a tank out of inventory, hook it to the vehicle, and expect it to work. What needs to be done is to attach the sensors to the interface card that is going to fly with the tank, do an hydrogen immersion test, and adjust the impedance of the sensor and cable to the hybrid ICs on the card. And then install the sensors on the tank.  SignaturePosted via a free Usenet account from http://www.teranews.com > Finally found some info on the ECO sensors. �Bottom line is that it is an > interface problem due to an inherent sensitivity to impendance mismatch, [quoted text clipped - 10 lines] > -- > Posted via a free Usenet account fromhttp://www.teranews.com why wasnt it a problem till the last few years? degradation of old parts? additions of tank cameras or other poorly shielded electronics. rally must find the root cause I think this is what was assumed, but its only part of the story, which is why they now measure the voltages. Of course, the mere fact of adding extra wiring to achieve this, is probably a problem too. Brian SignatureBrian Gaff....Note, this account does not accept Bcc: email. graphics are great, but the blind can't hear them Email: briang1@blueyonder.co.uk ______________________________________________________________________________________________________________ On Dec 9, 6:42?pm, "Revision" <ttsREM...@NOJUNKcharter.net> wrote: > Finally found some info on the ECO sensors. ?Bottom line is that it is an > interface problem due to an inherent sensitivity to impendance mismatch, [quoted text clipped - 12 lines] > -- > Posted via a free Usenet account fromhttp://www.teranews.com why wasnt it a problem till the last few years? degradation of old parts? additions of tank cameras or other poorly shielded electronics. rally must find the root cause > I think this is what was assumed, but its only part of the story, which is > why they now measure the voltages. Of course, the mere fact of adding extra [quoted text clipped - 35 lines] > > rally must find the root cause People may have already seen this, but check out Wayne Hale's comments at: http://www.spaceref.com/news/viewnews.html?id=1255 His conclusion: The system is inherently unreliable, and they may have to simply ignore the H2 ECO sensors from now on. He goes as far as suggesting the system has been unreliable from the start, and proposes a review of other safety systems that have never been needed before, to check if they are reliable. Jeroen The problem is not likely an impedance mis-match but probably a connector contact problem that occurs when it gets cold. The line was measuring 13V instead of 3 to 8 V. This is a steady state voltage (essentially as I understand it) and impedance matching should not play a part with the problem seen. Jeroen Bouwens wrote: > http://www.spaceref.com/news/viewnews.html?id=1255 If Hale says that the H2 ECO has always been unreliable, how come launch scrubs because of them are relatively recent ? Has NASA changed launch procedures since Columbia to check those sensors whereas in the past, they were not checked prior to launch and just assumed to work (since they weren't needed). Right. The additional circuitry to force wet/dry states has only flown twice. I think Hale is referring to the possibility that the system, if indicating wet and the engines shut down with some margins remaining, could have been defective all along and just never come into play. Current plan is to 1) use a time domain reflectometer to inspect the connections for an opens circuit in the approx 30m of wiring, basically a radar that measures the length of a wire. and 2) set up a lab test with a cryo tank and test equipment to get a better idea of how the sensors behave from "the tank feed through connector to the sensor." This to me is not a good test because it would not include the chips on the point sensor interface board, which is where I think the problem is, wild guess. Good audio here re: status of Atlantis featuring Wayne Hale from Dec 11 I think. http://www.space-multimedia.nl.eu.org/index.php?option=com_content&task=view&id= 3191&Itemid=1 > If Hale says that the H2 ECO has always been unreliable, how come launch > scrubs because of them are relatively recent ? > > Has NASA changed launch procedures since Columbia to check those sensors > whereas in the past, they were not checked prior to launch and just > assumed to work (since they weren't needed). SignaturePosted via a free Usenet account from http://www.teranews.com If that were all it was though, surely the comments about some area going open circuit which is seen as a result, when the OC condition should not be possible with working sensors. I built a burglar alarm like this once. The circuit was called a window comparator, in that your sensors when looked at were never anything but resistive. The window of impedance was calculated to show if, say, a switch was open or closed, but resistors were wired across switches to keep the impedance within a certain limit. Thus, shorting or open circuiting the loop would trigger an alarm, and the only way a burglar could disable a sensor was if they knew about the resistors dn could substitute the right one instantly. Trouble was, due to the high impedance of a working system, any interference picked up by the wiring was also seen as an alert! Brian SignatureBrian Gaff....Note, this account does not accept Bcc: email. graphics are great, but the blind can't hear them Email: briang1@blueyonder.co.uk ______________________________________________________________________________________________________________ > Finally found some info on the ECO sensors. Bottom line is that it is an > interface problem due to an inherent sensitivity to impendance mismatch, [quoted text clipped - 7 lines] > the impedance of the sensor and cable to the hybrid ICs on the card. And > then install the sensors on the tank. Brian Gaff wrote: >If that were all it was though, surely the comments about some area going >open circuit which is seen as a result, when the OC condition should not be [quoted text clipped - 13 lines] > >Brian Brilliant! While we're on the subject, the resistance chosen should be a moderately low value, say 100 ohms. A low impedance circuit would be immune to RFI interference, natural or man-made. The only cost is higher current draw, but still negligible in the scheme of things. Il mittente di questo messaggio|The sender address of this non corrisponde ad un utente |message is not related to a real reale ma all'indirizzo fittizio|person but to a fake address of an di un sistema anonimizzatore |anonymous system Per maggiori informazioni |For more info https://www.mixmaster.it |
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