larry@uunet.uu.net (Larry Lippman) (10/17/89)
In article <telecom-v09i0448m05@vector.dallas.tx.us> H.Shrikumar{shri@ncst.in} writes: > >> ... The usual system of billing > >> calls elsewhere is with "metering pulses". Each pulse is worth so much > >> money. On a local call, the pulses go by very slowly and on an > >> international call the pulses come rapid-fire. > In India too, where we have these metering pulses, most places dont > not get itemized billing. However, the new electronic exchanges that > are now being set up provide metering pulses only as a sort as > "backward compatibility" to the local exchanges that demand it. > BTW, these metering pulses cause havoc with dial-up data-comm. They > are audible right through the subscribes phone set. We have spent a > good amount of time with various combinations of modems and metering > pulse rates. Metering pulses generated by central office apparatus in various European and Asian countries may be a problem for data communication users. There are different metering pulse schemes in use throughout the world, but I believe the most common method uses simplex pulses of 50 Hz AC. Using a repeating coil in a trunk circuit, 50 Hz is pulsed through a single primary winding. There are two secondary windings, one of which is placed in series with the tip side of the line, and the other is placed in series with the ring side of the line. The secondary windings are arranged so that their phases are *opposed*, which means that no 50 Hz tone will be audible in the station instrument. The meter is an electromechanical counter which is sensitive to 50 Hz signals, and is connected with one side to ground, and the other side connected to BOTH tip and ring using two series capacitors. While the meter is located in the central office, the system is intended that "private meters" can be used at subscriber premises. The effective method of signaling as described above is simplex. However, the inaudibility of the 50 Hz metering pulse is only as good as the longitudinal balance of the cable plant. Cable plant in poor condition, especially that which may be subject to effects of moisture will result in a longitudinal imbalance, thereby increasing the detected level of these metering pulses. An appropriately designed impedance network located at the station may be used to correct for longitudinal imbalance of the cable plant and thereby reduce the level of the metering pulse. I have an off-the-wall suggestion for such a crude, but perhaps effective balance network. Obtain a 2,500 ohm wirewound potentiometer and two 0.22 uF non-polarized capacitors rated for 200 WVDC. Connect the wiper arm of the potentiometer to a GOOD earth ground. Connect the tip side of the telephone line to one side of the potentiometer using the first 0.22 uF series capacitor; connect the ring side of the telephone line to the other side of the potentiometer using the second 0.22 uF capacitor. Adjust the potentiometer for minimum audible level of the metering pulses. While I have not had firsthand experience with metering pulses in the U.S. (where they are not used), I did acquire some knowledge of the topic back in 1977 when I was involved with a project for the government of Egypt. <> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp. <> UUCP {allegra|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> TEL 716/688-1231 | 716/773-1700 {hplabs|utzoo|uunet}!/ \uniquex!larry <> FAX 716/741-9635 | 716/773-2488 "Have you hugged your cat today?"