mikectrcdd
IS-IT--Management
Please advise. I say it is not pass/fail, but a characterization of the installed fiber. Power meter tests can be pass/fail. Very interested in the facts.
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OTDR ..is it pass/fail?
- Thread starter mikectrcdd
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Servamatic
IS-IT--Management
An OTDR is primarily a troubleshooting tool, but it can be used for Pass/Fail. Why would you think it couldn't be?
While we generally use a LS & PM for certification, that is due mostly to cost. You can purchase a LS & PM for less than 10% of what some OTDR's cost.
If all you need to know is the insertion loss or attenuation of a given section of fiber and its associated connectors use a LS & PM, if you need to know exactly where the events are on that fiber use an OTDR.
An OTDR trace can be very beneficial as it possible to overlay an old trace with a new trace and graphically see what has changed since installation.
An OTDR can also show you things a LS & PM can not. Such as Ghosts and Gainers.
Richard S. Anderson, RCDD
While we generally use a LS & PM for certification, that is due mostly to cost. You can purchase a LS & PM for less than 10% of what some OTDR's cost.
If all you need to know is the insertion loss or attenuation of a given section of fiber and its associated connectors use a LS & PM, if you need to know exactly where the events are on that fiber use an OTDR.
An OTDR trace can be very beneficial as it possible to overlay an old trace with a new trace and graphically see what has changed since installation.
An OTDR can also show you things a LS & PM can not. Such as Ghosts and Gainers.
Richard S. Anderson, RCDD
My opinion, an OTDR and PM/LS are two different tools.
We require the use of both on all our fiber testing. The PM/LS gives the performance of the installed fiber by measuring the loss of signal. We as an OTDR gives an indication of the quality of the installation. A marginal splice will still give you a pass, but not tell you why. The OTDR will show you where.
I too see OTDR's as troubleshooting devices, not as certification.
Justin T. Clausen
Physical Layer Implementation
California State University, Monterey Bay
We require the use of both on all our fiber testing. The PM/LS gives the performance of the installed fiber by measuring the loss of signal. We as an OTDR gives an indication of the quality of the installation. A marginal splice will still give you a pass, but not tell you why. The OTDR will show you where.
I too see OTDR's as troubleshooting devices, not as certification.
Justin T. Clausen
Physical Layer Implementation
California State University, Monterey Bay
daronwilson
Vendor
Most specs I deal with require an OTDR shot of the final project, loss budgets, and power meter measurements. I too use the OTDR for troubleshooting, but generally the customer wants light loss measurements provided from a calibrated light source and receiver.
Good Luck!
It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com
Good Luck!
It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com
- Thread starter
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Servamatic
IS-IT--Management
Jeff
Are you saying an OTDR will not give accurate loss measurements?
Richard S. Anderson, RCDD
Are you saying an OTDR will not give accurate loss measurements?
Richard S. Anderson, RCDD
daronwilson
Vendor
I believe an OTDR will give accurate loss estimates. However, since it is not injecting a light at one end and measuring the received signal at the other, it is not measuring the loss as a power source and light meter would.
In a typical fiber circuit, you could screw up the connector on the distant end in the polishing process and not actually see that screw up with the OTDR, but you would definately see that loss if using a light meter with a power source.
Again, since the OTDR shoots the fiber from one end, unterminated, I do not believe you can accurately measure the loss of the circuit/connectors without using a light meter and power source.
Good Luck!
It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com
In a typical fiber circuit, you could screw up the connector on the distant end in the polishing process and not actually see that screw up with the OTDR, but you would definately see that loss if using a light meter with a power source.
Again, since the OTDR shoots the fiber from one end, unterminated, I do not believe you can accurately measure the loss of the circuit/connectors without using a light meter and power source.
Good Luck!
It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com
<<In a typical fiber circuit, you could screw up the connector on the distant end in the polishing process and not actually see that screw up with the OTDR, but you would definately see that loss if using a light meter with a power source. >>
this is why we require OTDR traces from both ends. I agree though that a PM/LS give a more acurate measured loss reading, because the OTDR is interpitating the loss from measuring the relections. You measure the loss of a splice based on the reflections the OTDR sees from the splice.
In practice, I'll put an PM/LS on a fiber to see what the loss is, if it's over -2db, (after cleannig and retesting) I'll put a OTDR on to find where the problem is.
Justin T. Clausen
Physical Layer Implementation
California State University, Monterey Bay
this is why we require OTDR traces from both ends. I agree though that a PM/LS give a more acurate measured loss reading, because the OTDR is interpitating the loss from measuring the relections. You measure the loss of a splice based on the reflections the OTDR sees from the splice.
In practice, I'll put an PM/LS on a fiber to see what the loss is, if it's over -2db, (after cleannig and retesting) I'll put a OTDR on to find where the problem is.
Justin T. Clausen
Physical Layer Implementation
California State University, Monterey Bay
Richard,
Not my words exactly. I recalled from an instructional manual as "accurate" being the word to describe the role of the OLTS for end to end testing. Perhaps not as accurate is better.
I say each device has a role. While the OTDR can provide end to end loss, the primary tool for this test is the OLTS. I contend an OTDRs reading is more of an estimated loss and therefore less accurate than an OLTS. My experience has been that an OTDR end to end reading could show less loss end to end than an OLTS. Maybe the OLTS is more accurate since it has a stablized light source and you don't have to compensate for a dead zone.
Not my words exactly. I recalled from an instructional manual as "accurate" being the word to describe the role of the OLTS for end to end testing. Perhaps not as accurate is better.
I say each device has a role. While the OTDR can provide end to end loss, the primary tool for this test is the OLTS. I contend an OTDRs reading is more of an estimated loss and therefore less accurate than an OLTS. My experience has been that an OTDR end to end reading could show less loss end to end than an OLTS. Maybe the OLTS is more accurate since it has a stablized light source and you don't have to compensate for a dead zone.
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