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Call Logging Circuit

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monolog99

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Hi,

I am trying to understand how a particular telephone line monitoring solution works. The monitor sits across the telephone pair in the exchange, and monitors the line voltage to determine the status of the line.

This all works well and good, however, I have read that in certain circumstances (e.g. high line resistances), voltage sensing alone is inadequate. A better method is to introduce a measure of current sensing as well, using a relay (http://www.electro-tech-online.com/custompdfs/2009/04/5042.pdf).

My question is this. I can see how the coil of the relay could be inserted into either leg of the line, which would operate the contacts when the line is seized. I'm puzzled what to do with the contacts and how the line monitor would make use of/connect into, the relay in order to make its voltage sensing more reliable on long lines. If it helps, the monitor is located in the exchange and has an exchange earth connected to it for reference purposes.

Thanks.
 

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Hero999

Banned
I hope it is only your phone they you're planning to log and that anyone who uses it is aware of the logging?

If not then you're probably breaking the law.
 

monolog99

New Member
This is all theoretical, purely to satisfy my curiosity. The information taken from a publicly available journal published in April 1989. I don't possess a physical logger/exchange etc. and not planning to log anything myself.
 
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