OTDR TestingGN Netttest CMA4000 OTDROTDR (Optical Time Domain Reflectometer) technology is designed to provide a single ended test of any cable. Utilizing sophisticated algorithms, the equipment is able to calculate exact length and approximate loss of “events” along the cable span.
OTDR Testing 1. Generates a baseline trace: A “visual” of the link. 2. Can identify and evaluate specific events in the link. 3. Cable acceptance tool. 4. Fault location tool. 5. Excellent documentation capabilities. 6. Limited use in short length networks. <50ftNoyes M600 OTDR
Fault-Locate (Using an OTDR)Work Area PC Telecom Horizontal Outlet Cross-connect Telecom Room MM Main Network Cross-connect Equipment Launch Equipment Room Cable OTDR
Assorted Troubleshooting Tools VFI Talk Set OTDR
OTDR Types Wavetek MTS5100FlukeOptiFiber Most common OTDRs use a “console” design allowing the user to upgrade or swap between MM and SM modules. These offer similar analytical features to the lab qualityOTDRs, but are more rugged and field portable. Files can be saved to various media and later downloaded to a PC.
OTDR Types Anritsu CMA5000 ExfoFTB-150 More common console OTDRs. Files can be saved to various media and later downloaded to a PC.
OTDR Types Noyes M200 Noyes OFL200 OTDR Noyes M100 OTDR OTDR Micro-OTDRs are the next generation of fast, economicaltest sets for field use. These models offer fewer features than the larger console design and are currently not upgradeable. Many manufacturers are focusing on development of these types of OTDRs for size and weight reasons.
OTDR FunctionalityBasic OTDR function LCD Display Control Unit Splitter Laser Transmitter Fiber under Test Detector OTDR Connector
OTDR Trace Analysis Physical cable plant as displayed onLoss OTDR screen Network under test
Launch CablesLaunch cables vary from simple reel (or “ring style”) through larger “lunch box” style suitcases. Most modern OTDRs don’t require a launch suppression longer than 250-500’, but many older models needed delay lines of 1000’ or more.
Using an OTDR w/ Launch CableUse of a launch cable assures the user that the front end connector of the network will be accurately measured. If the launch cable is too short, the front end connector will be consumed in the deadzone. Likewise, a receive cable assures the technician that the far end connector is not broken and the span has continuity. Cable under test End Launch Cable EventOTDR Launch Noise Port event Receive Floor Cable
OTDR Trace AnalysisOTDR Panel Splice Closure Panel Launch Cable Receive CableConnect the OTDR to a launch (suppression/reference) cable. The secondary end of the launch cable will be connected to an access panel at one end of the fiberoptic span under test. Optionally, a receive cable can be attached at the far end.
OTDR Trace Analysis Power Loss Network Under Test Splice Distance ScaleOTDR Launch Cable Receive Cable
OTDR Trace Analysis Most commonly, users manipulate two cursors, “A” and “B”, toillustrate what is referred to as “two point loss” on an OTDR result. This can be used to show loss in a single event or in a group of events. These cursors can be individually moved left and right to specific points on the result. A B
OTDR Trace AnalysisPower Loss A B Distance Scale Use cursor/markers to isolate individual events, such as the repair splice location (above)…
OTDR Trace AnalysisPower Loss A B Distance Scale …or the two point loss (attenuation) of an entire network span (above)…
OTDR Trace AnalysisPower Loss A B Distance Scale …or the physical length of a fiber span (above).
OTDR Setup - Range OTDRs have four basic setup requirements regardless of brand:Range/Resolution, Pulse Width, Index of Refraction and Time (number ofaverages). If any of these settings contradicts another, the results will be poor. The first one to consider is “Range” or distance of fiber to test.Many OTDRs have automatic length detection functions, but if the lengthis known, the user can set the range manually. The range setting should be adjusted to no less than 1.5 to 2x the fiber span under test. 2975’ span under test Set to >6000’
OTDR Setup - Range: SummaryToo short: less than Good: about 1.5x to Too long: much largerlink length 2x link length than link length Link Link LinkCan’t see entire link – Good trace – can Trace is “squashed”unpredictable results see end of fiber. into left side of display.
OTDR Setup - Pulse WidthLonger pulse widths are used for longer range tests. As distanceincreases, pulse width must go up, otherwise traces will appear“noisy” and rough. Similarly, short traces will be inconclusive if longpulse widths are used (events may be missed or clipped). Long cablespan=longer pulse width, Short cable span= short pulse width “Short”Fiber rununder test >6500’ “Long”Fiber rununder test >10,000’
OTDR Setup - Pulse Width: SummaryToo narrow: About right: Too wide: Link Link Link Where is this this event?Trace “disappears” Events can be seen Can’t resolve eventsinto noise floor. and trace is smooth.
Index of Refraction (IOR)In review, the Index of Refraction is a way of measuring the speed of light in a material. Light travels fastest in a vacuum, such as outer space. The actual speed of light in a vacuum is 300,000 kilometers per second, or186,000 miles per second. Index of Refraction is calculated by dividing the speed of light in a vacuum by the speed of light in some other medium (such as glass in the case of fiber optics!). Medium Typical Index of Refraction Speed Vacuum 1.0000 Faster Air 1.0003 Water 1.33 Cladding 1.46 Core 1.48 Slower Speed of Light in a Vacuum Index of Refraction = Speed of Light in a Medium
OTDR Setup – Index Of Refraction Each different optical glass fiber has a different refractive index profile consistent with it’s type and manufacture process. TypicalG.652.B singlemode fiber from Draka has an index number of 1.467 @ 1310nm and 1.468 @ 1550nm. Note that the longer the wavelength, the faster the light travels through the core. The user must set the OTDR to the proper GIR (Group Index of Refraction). If the GIR is not set to the proper number, the OTDRmay overestimate or underestimate linear cable footage. Since the index is a measure of the speed of light, if the GIR is not set properly, the OTDR cannot calculate the proper footage. If the actual index is not known, use the machine’s default or the following guidelines: MM 850nm – 1.496 MM 1300nm – 1.491 (Corning SMF28e) SM 1310nm - 1.4677 (Corning SMF28e) SM 1550nm – 1.4682
Index Of Refraction: Summary As discussed earlier, Index of Refraction is a measure of thespeed of light in a medium. If the Group Index of Refraction (GIR) setting in the OTDR does not match that of the fiber under test, the results will show incorrect distances as a result. GIR set at Launch OTDR thinks 1.462 Cord Footage is 9,800’ 10,000’ of fiber GIR 1.4677 @ 1310nm
OTDR Averaging Time Averaging time refers to how long the user allows the device to take samples (a.k.a. how long the test “runs”). The longer thetesting/averaging time allowed, the better the result. Eventually, enough data is averaged for a good test and continuing to test won’t yield any more of an accurate result. Corning OV1000 MUTOA Launch Cord
OTDR Setup - Averages: Summary Too few: About right: Too many Link Link LinkTrace is noisy – noise Trace is smooth. Trace is smooth butfloor is too high. waste of time.
OTDR Trace Analysis LSA lines are an effective method of getting more accurate testresults. Most OTDRs have loss estimation based on the simple 2-point method, but use of LSAs obtain better accuracy through events bycalculating lead-in slope and tail-out slope. See below for an example: Lead in Area Tail out Area A B