3 ms·

I don't know if such things are used on passenger aircraft, but I've heard that fighter jets use time domain reflectometry to detect potential faults in wires,

I don't know if such things are used on passenger aircraft, but I've heard that fighter jets use time domain reflectometry to detect potential faults in wires, and how far along the wire the fault lies. Even a small nick in the insulation is supposed to change the impedance enough to create a detectable reflection. At least some gigabit ethernet interfaces have built in weaker TDR that measures the length of each twisted pair, but I've only ever had one computer that showed that info in the BIOS/UEFI. So, maybe if TDR is used for inspection, we can rest assured.

toast0 6y ago
> At least some gigabit ethernet interfaces have built in weaker TDR that measures the length of each twisted pair, but I've only ever had one computer that showed that info in the BIOS/UEFI. I've seen this info in the Realtek NIC diagnostic tool for windows (on one machine, anyway), and I've got a couple of semi-managed switches that show a line length estimate which I assume is based on similar measurements.
wiremaus 6y ago
Unfortunately I don't think TDR would help here: the issue isn't gross damage to the metal of the wires, it's subtle damage to the insulation.
- nitrogen 6y ago
  From my prior comment: "Even a small nick in the insulation is supposed to change the impedance enough to create a detectable reflection." This is what I was told by the person who saw the demo. I believe them, because it'd just be a matter of sending an impulse (or sweeping a tone) and looking at all of the spikes in the impulse response.
jcrawfordor 6y ago
Sort of unrelated, but a very interesting application of TDR on cables: in military, infrastructure, and certain other installations, a common security measure is a fiber optic cable woven into the chain-link fence or shallowly buried. Any deflection of the cable (e.g. due to a person climbing the fence) results in a subtle reflection in the cable. By knowing the layout of the embedded cable, not only can the event be detected, but it can be localized and used to e.g. trigger automatic pan of PTZ cameras. A major brand-name for this system is FiberPatrol but there are several vendors. Unfortunately it is rather false-positive prone when applied to fences, significant wind loading can cause the chain-link to lash back and forth and repeatedly deflect the cable. The resulting alarm fatigue was implicated in the somewhat (in)famous case of the nuns as site Y-12. Nonetheless this application is very common at federal installations and also certain non-federal infrastructure installations, e.g. the legacy iron fences around Portland, Oregon's surface water reservoirs (where remote-controlled PTZ cameras appear to be used for rapid remote confirmation of FiberPatrol detections... you can give the fence a shake and watch a camera pan to you almost immediately).

toast0 6y ago

> At least some gigabit ethernet interfaces have built in weaker TDR that measures the length of each twisted pair, but I've only ever had one computer that showed that info in the BIOS/UEFI. I've seen this info in the Realtek NIC diagnostic tool for windows (on one machine, anyway), and I've got a couple of semi-managed switches that show a line length estimate which I assume is based on similar measurements.

wiremaus 6y ago

Unfortunately I don't think TDR would help here: the issue isn't gross damage to the metal of the wires, it's subtle damage to the insulation.

nitrogen 6y ago
From my prior comment: "Even a small nick in the insulation is supposed to change the impedance enough to create a detectable reflection." This is what I was told by the person who saw the demo. I believe them, because it'd just be a matter of sending an impulse (or sweeping a tone) and looking at all of the spikes in the impulse response.

jcrawfordor 6y ago

Sort of unrelated, but a very interesting application of TDR on cables: in military, infrastructure, and certain other installations, a common security measure is a fiber optic cable woven into the chain-link fence or shallowly buried. Any deflection of the cable (e.g. due to a person climbing the fence) results in a subtle reflection in the cable. By knowing the layout of the embedded cable, not only can the event be detected, but it can be localized and used to e.g. trigger automatic pan of PTZ cameras. A major brand-name for this system is FiberPatrol but there are several vendors. Unfortunately it is rather false-positive prone when applied to fences, significant wind loading can cause the chain-link to lash back and forth and repeatedly deflect the cable. The resulting alarm fatigue was implicated in the somewhat (in)famous case of the nuns as site Y-12. Nonetheless this application is very common at federal installations and also certain non-federal infrastructure installations, e.g. the legacy iron fences around Portland, Oregon's surface water reservoirs (where remote-controlled PTZ cameras appear to be used for rapid remote confirmation of FiberPatrol detections... you can give the fence a shake and watch a camera pan to you almost immediately).