|
(204) Sun 3 Nov 91 15:03 By: Peter Knoppers To: All Re: Re: Need Information on European Metering Pulses St: ------------------------------------------------------------------------------ @PTH 1:340/201.0@Fidonet From: knop@duteca4.et.tudelft.nl (Peter Knoppers) Newsgroups: comp.dcom.telecom Subject: Re: Need Information on European Metering Pulses Organization: Delft University of Technology, Dept. of Electrical Engineering moon@gdc.com writes: > I am looking for information on the "metering pulses" that are used in > many European countries. In the Netherlands metering pulses are available at a price if you are connected to a computerized telephone exchange, or free if you are connected to an old-style exchange. (The telco cannot suppress the signal in old-style exchanges.) The signal is a 50Hz common mode signal of approximately 60 Volts. The signal lasts about 400 ms (but this varies a lot). Each pulse corresponds to DFL 0.15 on your phone bill (about US $ 0.08). To count the pulses a special (rather expensive) counter is used that contains the following circuit: a b a and b are connected parallel to the phone(s) | | (These wires are called tip and ring in the US) | | * > ||| < This is a kind of transformer that only passes > ||| < through common mode AC and DC current. > ||| < * | | | | These capacitors block DC current, preventing === === 0.3 uF an off-hook condition that would otherwise occur. | | Only common mode AC current gets beyond this point. |_____| | | === 0.5 uF Don't know why this capacitor is needed. | | / \ 1.2 .. 2.2 kOhm Resistor. / \ | __|__ |__/__| 2400 Ohm Coil that controls the mechanical counter. | | e This wire must be connected to ground. In computerized exchanges additional equipment must be connected to the subscriber circuits that are to receive metering pulses. This equipment is very expensive and takes up a similar amount of space as 4 subscriber line circuits. It is possible to replace the resistor in the counter with a bridge rectifier and a small relay. This relay closes shortly when a metering pulse is received and can be used to drive other circuits. Such modifications are probably not appreciated by the phone company ... > My particular problem is determining the requirements for a modem in > this scenario, in particular, I need to know the maximum signal level > of the metering pulses at the modem's input. As you can see, the metering pulse signal reaches the phone or modem completely intact. The modem should therefore be capable of normal operation with a 50 Hz 60 Volt common mode signal superimposed on the normal line voltage. (The audio signal is differential mode.) Test signals used by the phone company to test subscriber circuits use much higher voltages (a few 100 Volts). While this does not happen while the line is off-hook, a modem should survive such signals when on-hook. Hope this helps, Peter Knoppers - knop@duteca.et.tudelft.nl --- Fred-Uf 1.8(L)[BETA] * Origin: Megabyte BBS, UUCP, Fidonet, IMEx, total messaging (1:340/201.0) @Path: softwords!news.UVic.CA!ubc-cs!van-bc!zaphod.mps.ohio-state.edu!think.com!spool.mu.edu!telecom-request @Message-ID: <telecom11.884.3@eecs.nwu.edu> @Date: 3 Nov 91 15:03:40 GMT @PID: FredMail 1.8-BETA @PATH: 340/201