Title: System for measuring the duration of a telephone call

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Abstract: A system for use in a telephone exchange to measure the duration of a telephone call includes an electrical power source from which pulses of constant frequency are applied to first and second pulse generating circuits for generating pulses at selected frequencies representative of a call initial time rate and a call overtime rate, respectively. Each of the pulse generating circuits can be programmed independently to generate pulses at different selected frequencies representative of different call time rates. The pulses from the generating circuits are applied to a plurality of pulse counting circuits through respective pulse count control circuits. At the beginning of a telephone call, one of the pulse counting circuits is seized by associated circuitry of the telephone exchange and the respective count control circuit first passes initial time rate pulses to the counting circuit while blocking overtime rate pulses. When the counting circuit determines that a maximum initial time period for the call initial time rate has been reached, a signal from the counting circuit causes the control circuit to change state and to pass overtime rate pulses while blocking the passage of initial time rate pulses. During the call the counting circuit performs the normal auxiliary control functions in the associated circuitry of the telephone exchange.


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