#reflectogram

[teardownit]

Search for intermittent faults, and Pupin coils using a reflectometer.

Intermittent faults ('floating' defects) are damages that manifest themselves periodically and are caused by poor-quality core connections or reduced insulation resistance. Customer complaints about short-term connection losses are evidence of defects of this kind. Such defects may appear due to mechanical damage to the cable (for example, in the event of vibration from heavy vehicles, rotary equipment, etc., nearby).

Typically, when a technician encounters this type of damage, he has to wait patiently for it to manifest itself, hoping the effect will last long enough to determine its location. There is no guarantee that the damage will reveal itself while the technician is on duty. The use of reflectometers allows one to automate this process and maximize productivity.

Some reflectometers have a special function for detecting intermittent faults. The device connected to the line accumulates all reflectograms over a certain period and displays them superimposed on each other. Where the reflectogram differs, the intermittent fault is located.

Finding intermittent faults

For example, consider the following situation: a particular pair of cables works fine for the better part of the day, but there is a momentary failure out of the blue.

We get two reflectograms for the same pair (with different gain settings) when checked. In the first one, with a gain of 12 dB, a surge of positive polarity is observed on the reflectogram of a working pair at a distance of 6760 feet, corresponding to the end of the cable. In the second one, when the gain increases by 14 dB, an additional spike appears on the reflectogram, the nature of which indicates the presence of a coupling in the cable at a distance of 3280 feet. By further increasing the vertical gain level, the reflectogram will not reveal the slightest sign of damage along the entire length of the cable being tested.

We will need the 'intermittent fault detection' function mentioned above. By continuously monitoring the pair's condition, the OTDR shows any deviations from the cable's rated impedance, allowing the location of intermittent faults to be pinpointed.

The reflectometer display will show the current reflectograms obtained during testing. Periodic inspections allow one to determine whether signs of malfunction have appeared. Once the non-persistent damage has been captured, the result should look approximately as shown in the figure.

The differences will be evident if one compares it with the previous one. A noticeable drop appears where there was nothing before. The location of the fault can be determined by simply moving the cursor to the front of the pulse reflected from the break and reading the distance from the display.

Random vibrations or other irregular events cause the connections to loosen and electrical contact to be temporarily lost, resulting in a fault similar to a partial break. Note that at the moment this fault occurs, the pulse reflected from the far open end of the line decreases because, due to a poor connection in the cable coupling, the magnitude of the electrical signal reaching the end of the cable is reduced.

What conclusions can be drawn? Almost every type of cable system is susceptible to intermittent faults. Such damage creates severe problems for users and technicians. The intermittent fault detection mode of reflectometers allows one to continuously monitor the cable over a long period, so the technician does not have to waste working hours waiting for the damage to manifest itself.

Pupin coils

Pupin coils can still be found on an analog telephone line. Pupin coils disrupt the homogeneity of the copper pair, turning it into an ideal low-pass filter with more substantial high-frequency attenuation.

Therefore, a prerequisite for using any xDSL technologies on existing phone lines is the removal of Pupin coils, which have been found to have extensive applications in US telephone networks. Servicing xDSL systems can always result in such a problem. In this case, one will need a reflectometer with a function for searching and counting Pupin coils.

Searching for installation locations of Pupin coils

A reflectometer is the only device that allows one to simply and accurately determine the location of Pupin coils. Since the pulses sent by the reflectometer are high-frequency, they are reflected from the Pupin coil, a low-pass filter. The coil on the reflectogram looks like a significant increase in the cable impedance, i.e., similar to the reflectogram of a line break.

As you can see, the outline of the pulse reflected from the Pupin coil is more rounded than the pulse reflected from the cable brake, and the coil itself is located at a distance of about 5600 feet. In Eastern Europe, there are several Pupinization systems: medium, light, extra light, and broadcasting light. All systems have the same pitch of 1.7 km and differ in the inductance of the coils, the bandwidth of the transmitted frequencies, and the distance between the amplifiers. Unfortunately, the reflectogram shows only the first coil.

Counting the number of Pupin coils

The reflectometer can also be used as an auxiliary device when taking resistive bridge measurements. The presence of Pupin coils introduces inaccuracy into the readings since each of them adds about 4 ohms to the resistance value obtained during the measurement. Using a Pupin coil counter allows one to approximately estimate the number of coils installed on the line and determine the error of measurements made using a resistive bridge.

For example, 4 ohms corresponds to approximately 500 feet of 20 AWG cable. This means that with each installed Pupin coil, the measurement values obtained using a resistive bridge will be almost 500 feet longer. If one suspects the results may contain an error, use a Pupin coil counter.

[agnesdelmotte]

Infrared reflectogram of the Madonna of the Yarnwinder by Leonardo da Vinci, Lansdowne version.

source wikimedia

[rothgalleries]

Colorful houses at Lake Winnipesaukee with early fall foliage. Good light and happy photo making! www.RothGalleries.com . . . #lakewinnipesaukee #whitemountainsnh #reflectogram #reflection #granitestate  #newhampsire_igers  #YesWhiteMountains  #outdoors   #riseandshineon7  #newenglandlife #ipulledoverforthis  #fineartphotography   #morning #artwork #wallart   #newengland_igers  #NewEngland  #fallvibes   #mynewengland #hiking #nature #fall #fallfoliage #autum #photography #country #rurallife #newenglandfall #riseandshineon7 (at Lake Winnipesaukee, New Hampshire) https://www.instagram.com/rothgalleries/p/CVP0tgWgoyN/?utm_medium=tumblr

[rerika2564]

Фотография месячной давности 🤔 Я часто пересматриваю старые фотографии и каждый раз долго думаю, стоит ли их выкладывать 🤷🏻‍♀️ Бывают моменты, когда я выкладываю и сразу удаляю 😅 А вообще, у меня осталась ещё неделя отпуска и надо выбраться и поснимать что-нибудь. Я чувствую, что мне это нужно 😅🤷🏻‍♀️ Если есть идеи - внимательно слушаю 👌🏻 . . . . #instagood #follow #followme #life #photo #photooftheday #amazing #likes #like4like #sky #reflectogram #fatalframes #way2ill #killeverygram #aov #agameoftones #createcommune #nikon #nikonrussia #urbanromantix #mood #streets_vision #folkgood #nature #town #sunset #moscow #sunset_vision #macro #bokeh

[glenesis]

Rochester. Color-matched to reality, Tone-matched too. #cityscape #reflectogram #December2020 (at Downtown Rochester) https://www.instagram.com/p/CIodSmbp5a2/?igshid=ox3nekfpdcp4

[littlegoldboat]

Truckin’ #greatfuldead #tiedie #reflectogram #mylagunabeach #sometimesthelightsallshiningonme #likethedodahman #whatalongstrangetripitsbeen #songlyrics #rockoncalifornia #whoawhoababy (at Laguna Beach, California) https://www.instagram.com/p/BwF8ecpBR7d/?utm_source=ig_tumblr_share&igshid=kn7ewz10b6ks

[rob-lix-me]

• open • • • • • #bokeh #bokehphotography #bokehfan #bokehlicious #night #nightshot #nightshotz #nightkiller #bokehkillerz #bokeh_kings #nightbokeh #neon #neonphotography #neonphotoshoot #sunglasses #reflection #reflection_shotz #reflection_shots #reflectogram #nightreflection #neonnights #cityphotography • • • • #rob_lix (hier: Vienna, Austria) https://www.instagram.com/p/BvPruNPh-93/?utm_source=ig_tumblr_share&igshid=cueys1aum054

[aeonmagnus]

Transformers G1 Reflector: Spectro, Viewfinder and Spyglass.

[devicfotos]

[volpevolpe96-blog]

6AM

[ofmothsandme]

We had a sunny spell a little while ago and I shot a tonne of film in the space of a few days. Just got them back so feels like my birthday. 

[teardownit]

Finding branches using a reflectometer

As you know, a data cabling system consists of different segments. To connect them all and bring the data connection to the end user, it is necessary to make a certain number of crossings. Often, staff forgets to disconnect "old" lines. As a result, over time, parallel branches appear, and their presence can have a detrimental effect on the quality of services.

BRANCHES AS A SOURCE OF PROBLEMS

Parallel branches can make it difficult to serve clients and ensure system functionality. With the introduction of digital systems, the search for parallel branches becomes an increasingly important task since they negatively affect the operation of digital transmission systems and, even if in most cases they are relatively short in length, nevertheless lead to significant problems. The bramch creates a second path for digital signals transmitted on the main line, which travel along the branch and are reflected from its open end. Reflected signals (echoes) enter the main line, where they are mixed with "good" digital signals and negatively affect the quality of the transmitted data. Therefore, to ensure correct operation of the digital line, the branches must be disconnected completely.

When connecting to analog lines, branching also creates problems. For example, if there is a fault on such a branch, it may show itself in the form of a decrease in the quality of the transmitted signal.

Finally, unknown branches can affect the accuracy of diagnostic equipment, for example, when measuring cable capacitance and estimating the distance to a break using a capacitive bridge. An unknown branch increases the combined capacitance of the cable pair and causes a measurement error: for the tested pair, the calculated length will be greater than the actual length.

It is very important to have full information about all the parallel branches available on the line in order, if necessary, to select the correct algorithm for troubleshooting and eliminating the problem.

SEARCHING FOR THE LOCATION OF THE BRANCH CONNECTION

The capacitive bridge is the device most often used to measure the length of a cable that is open at the far end. Unfortunately, it only allows one to estimate the total length of a cable pair, including all parallel branches.

Using multi-function devices (combining a capacitive and resistive bridge), it is possible to calculate the length of the branch cable due to the ability to compare the length values obtained from measuring the cable capacitance and the resistance of the loop.

Pic main_img_p7621_thumb.png

In this case, an OTDR is the most optimal and, moreover, the only device that allows one to find the locations of branching, measure the lengths of the branches, and determine the distance to them.

However, in practice, cable analyzers that combine the functions of a reflectometer and a multi-function instrument are more convenient. The implementation of two measurement methods (reflectometric and bridge) in one device allows for comparison of the results obtained for more accurate fault localization.

The classic branch reflectogram is similar to the one for testing a damaged cable, the only difference being that the reflection of the signal from the branch is a straight line rather than a curve.

As an explanation, let's look closely at the reflectograms for an open-ended cable section without a branch and a cable section with one (it is located at a distance of 3385 ft). The corresponding measurement results using a capacitive bridge were transferred to the reflectometer for direct comparison and accounted for. Note how the presence of a branch affects the measurement results of a capacitive bridge—in particular, how the cable section with a branch distorts the pulse reflected from the open end of the cable at a distance of 6500 feet. This occurs because part of the energy of the reflectometer signal was lost passing through the branch. The ideal way to view these graphs simultaneously is to use a dual-channel OTDR to connect and compare the "good" and "bad" cable pairs back-to-back.

Just as echoes affect digital signal transmission, parallel branches affect cable reflectograms. Interpretation of the reflectogram becomes significantly more difficult if two or more branches are connected to the pair under test.

The following graph is similar to the one shown in the previous figure, but in this case there is an additional branch at a distance of approximately 5400 feet.

The open end of the cable at a distance of 6500 feet is almost invisible on this reflectogram since the energy of the reflectometer test pulse is spent on passing two branches. If there are multiple branches connected to the cable under test, the best strategy is to locate the first one, access its location, and only then locate the next branch. This procedure should be repeated until the locations of all branches have been found.

Let's get to conclusions. Branches obstruct the operation of digital systems. The search for branches and their subsequent removal is extremely important to ensure the high quality of the digital services provided.

In order to make sure that the distance to the nearest branch corresponds to the standard for digital lines (maximum and total length of branches), one can use the following algorithm:

Check the distance to the nearest branch.

Check the length of the cable branch.

Check the total length of all branches found.

[otttokaji]

[blackbird-cris]

[rerika2564]

🌸 . . . . #instagood #follow #followme #life #photo #photooftheday #amazing #likes #like4like#reflectogram #fatalframes #way2ill #killeverygram #aov #agameoftones #createcommune #nikon #nikonrussia #urbanromantix #streets_vision #folkgood #moscow #macro #winter #lights #nature

[glenesis]

Sunset & Moonrise Yesterday 28th November 2020 . I hope all of you are well and happy :) . #sunset #moonrise #reflectogram (at West Henrietta, New York) https://www.instagram.com/p/CIL9j1ZpEO-/?igshid=153oj8bulydbk