telecommunications Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...

, metering pulses are telephone signals sent by

telephone exchanges telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syste ...

to metering boxes and

payphones A payphone (alternative spelling: pay phone) is typically a coin-operated public telephone, often located in a telephone booth or in high-traffic outdoor areas, with prepayment by inserting money (usually coins) or by billing a credit or debit ...

aimed at informing the latter of the cost of ongoing telephone calls. Metering pulses are also known as ''billing pulses'' and ''tax pulses''. The properties of metering signals differ between the telephone administrations in various countries. Some systems use alternating current pulses superimposed on the direct current (battery) levels of the local loop, while others may use a reversal of tip-ring polarity of the wire pair. Common frequencies of the A.C. pulses are 50 Hz, 12 kHz, and 16 kHz, with typical durations of the signal varying from several tens to hundreds of milliseconds. 50 Hz pulses are applied to the telephone circuit as

common-mode signal Common-mode signal is the voltage common to both input terminals of an electrical device. In telecommunication, the common-mode signal on a transmission line is also known as longitudinal voltage. In most electrical circuits the signal is transferr ...

s with respect to ground, as applying them differentially would make them audible for the talking parties as buzzing tones. The pulse amplitude (RMS voltage) is high enough to distinguish them from signals induced from

mains electricity Mains electricity or utility power, power grid, domestic power, and wall power, or in some parts of Canada as hydro, is a general-purpose alternating-current (AC) electric power supply. It is the form of electrical power that is delivered to h ...

. 12- and 16 kHz metering pulses are applied differentially across the telephone circuit, as these frequencies cannot be heard by listeners with conventional telephone instruments. Each pulse represents an incremental cost. For calls with higher billing rates, the exchange equipment generates metering pulses at a higher rate than during calls to cheaper destinations, or during periods of lower billing rates. On residential telephone lines, metering pulses are not used to generate billing records, but serve to inform the calling subscriber with a visual display in form of a counter or advancing dial connected to the telephone instrument. In commercial pay station telephones and coin collectors, A.C. signaling pulses operate coin control.J.G. Pearce, ''Telecommunications Switching'', Plenum Press & Springer Science, N.Y. (1981), , p.96.

References

{{DEFAULTSORT:Metering Pulse Telephony signals

See also

References