Sensitivity Analysis of the 47A Signal

Proper coin telephone performance results in the transmission of coin deposit information to the central office. Simply stated, if a coin passes a series of tests at the coin telephone station set, it is determined to be valid and its denomination, also detected at the station set, constitutes the information transmitted to the central office. This validation and detection process is statistical not only because of the complex interaction of mechanical and electrical subsystems at the station, but also because of the random nature of coin deposits. The 1747 physical attributes of the coins, as well as the introduction of the customer's deposit action, lends a statistical quality to coin deposits. As a result of this random feature, coin telephone and coin telephone subsystem designs are usually proven-in via large-scale experimentation involving the deposit of tens of thousands of coins. ID-type electronic coin telephone sets use the 47A Signal to initiate the transmission of coin deposit information to the central office. During the initial production of this Signal, manufacturing difficulties surfaced. While testing these early units for compliance with performance criteria, it was determined that an unacceptable number of Signals in fact failed to meet that criteria. Production was halted, and Bell Laboratories was faced with investigating whether a design change