Optical Time Domain Reflectometer

Hello all, want to ask.

1. What is the used of microprocessor at OTDR? And please be spesific.

2. How can the OTDR shows the graphic dB vs km as the result?
Because as I know, the backscatter and reflected pulse that detected by Avalanche Photodiode is changed to current, then the current is changed to voltage by I-V Converter. Then the voltage is sent to ADC to convert it to bit. Is there any correlation between the power (dB) and the voltage?

Hello all, I want to ask,
1. What does a microprocessor contained in the OTDR do?
2. How can OTDR get the graph dB vs km?
3. Is it true that the microprocessor do logarithmic function? 20 log (Va / Vb), with Va is the present voltage and Vb is the voltage before?
4. If the OTDR do logarithmic function, then, at the beginning of the light pulse delivered by OTDR, there will be a dead zone on the OTDR graphic due to the use of connector to connect the fiber optic cable with OTDR, How does the OTDR do to process that reflective power? Since it is the first input that OTDR will receive and no voltage before to compare with.
5. As I know, at the OTDR receiver, there is Avalanche Photodiode (APD), I-V Converter and Analog to Digital Converter (ADC). Backscatter and reflected pulse is detected by the APD and converted into photocurrent, then the photocurrent is converted into voltage by I-V Converter, which will then be given to the ADC to be converted into bits that can be processed by a microprocessor. Which part is responsible to form the graph on the OTDR?

Thank you

have you though of getting a service manual for an OTDR and reading up on how it works directly from the literature ?

would seem the obvious thing to do ;)

Dave

Actually I'm already read some literatures, but some of them are just telling that OTDR works based on Rayleigh Scattering and Fresnel Reflection.
And not very clear of how the microprocessor convert the bits produced by ADC to dB that shown in the OTDR graphic.

And for the service manual for an OTDR, I don't have any, could you please share some if you have?

Thanks.

google for an OTDR then search for its service manual you may have to go through several makes and models till you find one that has an available manual online .... a service manual will give a detailed description on how the system works

Dave

Ok then I'll search them.. Thanks..

Just want to know, is there any explanation there in the service manual about how the microprocessor do so OTDR can get the graphic?