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The picture of the "Megger" and its caption promote a particular brand of test equipment. The photo is contributed by Megger Ltd. Furthermore, the photo is so small that it does not contribute any knowledge to the article. I have provided a diagram and a photo of a generic TDR composed of a pulse generator and an oscilloscope. The brand names of the scope and pulse generator are suppressed. I propose to delete the Megger photo and promote the generic TDR diagram to the lead off position. Constant314 (talk) 18:50, 23 January 2011 (UTC)[reply]
I have no objection to replacing the "Megger" photograph with something better. To me, better means illustrating something useful about a TDR.
The Megger photo is very poor resolution. It does not illustrate much.
I have some minor problems with the generic TDR. For example, the 6dB loss in the open and short examples (cable attenuation 3dB/100ft) and smearing (dispersion/group delay). I have no problems with the incidental display of a logo.
Just curious, what problem due you have with the loss and dispersion? Could you elaborate? Constant314 (talk) 16:05, 3 October 2011 (UTC)[reply]
"Simple TDR made from lab equipment" picture does not show ideal situation; pulse 1 and 2 should have similar shape. Ideal cable would not have any attenuation, so reflection would be same size.
"TDR trace of a transmission line with an open termination." There's an amplitude loss: 3.8 div initial pulse with 2.0 div reflection. No explanation for the attenuation (reflection from an open is unity); one explanation is cable attenuation. No explanation for extended tail on reflection; doubtful that the length of the open circuit is tens of nanoseconds (3 m); dispersion on cable; poor open circuit termination also possible but less likely. Dispersion (group-delay) causes a pulse to spread out because different frequency components have different delays.
Short circuit termination has similar issues.
The loss should be explained; only amplitude mechanism in current article is ρ. Reader may confuse ρ with cable loss.
Mixed feelings about the roughly 10 ns resolution of the pulse; 10 ns is a lot of cable. Fast rise square wave would give better resolution (unless 10 nS rise is the scope -- unlikely for 500MHz scope). My Tek TDR uses 25 ps or 1 ns risetimes.
I have an old Tektronix TDR, but it uses a 25ps risetime step rather than an ersatz impulse.
I have twice reverted the replacement of the Megger with pictures of a Livewire TDR. I removed the Livewire photographs because they just showed a box with logos; the Megger photograph at least included a display of a reflection.
I have received an email from User:Mhaugen99 that shows a WP:COI with Livewire. The email claimed advertising was not intended, acknowledged that other of his/her links had been removed, claimed the newer pictures were offered as updates, and inquired about having both the Megger an Livewire photos coexist. The offered Livewire photographs are not acceptable.
When I proposed changing the photo, its caption included the word "Megger". After my objection, someone removed that word and what is left is at such a low resolution that the name and brand cannot be made out anymore and so my objection to displaying some particular brand was moot. I do agree that the resolution is so small that it is almost useless. If you can see the trace and make sense of it, you probably already know what a TDR is. Of course, I prefer my own drawing because it shows the source, display and transmission line, whereas the megger photo only shows a box with a display. But I definitely support getting a higher resolution picture.Constant314 (talk) 18:29, 1 October 2011 (UTC)[reply]
The second paragraph of Explanation section states “...the voltage at the TDR abruptly jumps to twice the originally-applied voltage.”
From what I can tell, the original author means to the previous example of the shorted termination. I could be understanding that wrong, but the supplied image did NOT match up with the explanation. Instead the reflected pulse is about half the original pulse input into the oscilloscope.
If I am correct about the interpretation, the line should be rewritten so as not to be confusing. If I am wrong, can someone explain to me what I don't get and refer to the open circuit termination image?
--*elAndres (talk) 02:46, 15 August 2014 (UTC)[reply]
You are correct. The pulse at the far end doubles but not so at the near end. In the case where the input is a step, that is still present when the reflection returns, then what the TDR sees is the original step plus the reflection. If source impedance matches the transmission line impedance and the line is lossless then what the TDR sees is an initial step and then, after a delay, a second step of the same amplitude so that the final voltage is twice the voltage of the initial step.Constant314 (talk) 14:30, 15 August 2014 (UTC)[reply]
Upon more careful reading, I think the Explanation section is talking about a step input and not a pulse input. The step input is an interesting application, but it does not match any of the scope photos. Probably, the Explanation should be edited and moved down into the Usage section, since that mode of operation is used to send logic signals across a printed circuit board. Then a completely new Explanation could be written. Or some pictures of a step input could be added.Constant314 (talk) 14:43, 15 August 2014 (UTC)[reply]
TDR of step into disconnected SMA male connector. S-52 pulse rise time 25 ps; S-6 rise time 35 ps.TDR of step into disconnected APC-7mm connector. S-52 pulse rise time 25 ps; S-6 rise time 35 ps.TDR of step into APC-7mm precision open. S-52 pulse rise time 25 ps; S-6 rise time 35 ps.TDR of step into APC-7mm precision load. S-52 pulse rise time 25 ps; S-6 rise time 35 ps.TDR of step into APC-7mm precision short. S-52 pulse rise time 25 ps; S-6 rise time 35 ps.TDR of step into APC-7mm precision open at 20 ps per division. S-52 pulse rise time 25 ps; S-6 rise time 35 ps.TDR of step into mated BNC connector pair. S-52 pulse rise time 25 ps; S-6 rise time 35 ps.
I uploaded some TDR files using step inputs. The pulse is about 1 unit high. I give examples for an open made with a disconnected male SMA connector, a disconnected APC 7-mm connector, and a precision APC 7-mm open. There's a time expanded view of the precision 7-mm open. I also show reflections for a precision load and precision short. The precision terminations are from an HP 7-mm calibration kit (18 GHz). There's also the reflection from a mated BNC pair at expanded vertical and time scales.
The images were made using a Tektronix 7854 digital scope, a 7S12 TDR/Sampler pluging, an S-52 pulse generator head (25-ps rise time), and an S-6 sampling head (35-ps rise time). The SMA cable from the sampling head to the termination is about 18 inches. Glrx (talk) 02:00, 23 August 2014 (UTC)[reply]
This is a simulation, but it has the advantage of showing the near end and far end.
A SPICE simulation of 100 feet of unterminated coaxial cable driven with a step waveform from a matched source.Constant314 (talk) 04:46, 24 August 2014 (UTC)[reply]
File:Megger MTDR1 screenshot.jpg caption needs more explanation[edit]
This screen shot appears to be a two channel display, possibly comparing a good cable to a bad cable. This needs to be explained. Also, the upper channel shows multiple traces, why and what does it mean? The launched pulse is truncated. Is that the actual shape of the pulse or is it a limit of the display or the instrument? Constant314 (talk) 13:58, 26 October 2015 (UTC)[reply]
There are actually at least 3 traces; the top is doubled; there are two flat lines at the bottom. Top trace appears to be an open reflection; bottom trace a short. I suspect the launch pulse overdrove the digitizer. I'd just delete the image; the image appears to be more about showing a particular user interface than about TDRs in general. Particularly troubling are the absence of a grid (no ampltude or distance/time scale) and indication of scale or units. The distance between the markers is 595.1, but is that feet, meters, or nanoseconds? It also is confusing with the left-hand 595.1. The entire width of the bottom trace looks to be 1184 unknown units. The marker positions are poorly chosen because they don't imply anything meaningful. The 80 ns might be the pulse width, but the 3 unit separation is a mystery. I don't think the picture shows anything useful, so I'd remove it rather than try to save it. No other article uses it. Glrx (talk) 17:00, 26 October 2015 (UTC)[reply]
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A web search for reflectometric impulse measurement technique find this page, though it isn't mentioned here. As I understand it (from watching Nova), RIMT is a similar technique applied to steel cables used for prestressed concrete structures, such as bridges. RIMT can detect corrosion in steel cables in the same way as TDR detects problems in electrical cables. But that is about as much as I know, which is why I am looking it up. Gah4 (talk) 05:01, 18 October 2019 (UTC)[reply]
I was going to revert the removal of the following, and then add {{cn}}, but decided
to discuss it here, first. For one, this reminds me of RIMT (see above), which I believe
should be discussed here, or referenced to a page of its own. I will let it be discussed
here, to see what should go into the article. Gah4 (talk) 00:47, 24 October 2019 (UTC)[reply]
TDR is used to monitor a coaxial or a cable pair to look for liquid penetration that causes an impedance change along the sensor cable length. Applications include data centers, double contained piping systems, tank farms, nuclear facilities, water treatment plants, semiconductor facilities, museums, office buildings, generator rooms, hospitals and other critical facilities. The system allows detection of leaks, growing leaks, multiple leaks, breaks and shorts along the sensor cable with location of the event.[1]
TDR can detect liquid invasion of a transmission line due to impedance change. No objection to the first sentence. The rest reads like advertising copy.Constant314 (talk) 01:02, 24 October 2019 (UTC)[reply]
OK, so we need less advertising discussion, and better WP:RS. I didn't even look at the reference. Gah4 (talk) 12:38, 24 October 2019 (UTC)[reply]
