Abstract: A pay telephone unit is disclosed that derives all operating power from the tip and ring conductors of the telephone line without the need for a battery. All data is stored in nonvolatile memory requiring no power for data retention, even when disconnected from the telephone line. The unit employs an interrupt architecture that advantageously reduces current consumption in comparison with prior art polling arrangements. In addition, stored power from operational circuitry is diverted to keep the real-time clock operating during momentary disruptions in line power. Diverted power may also be used to permit certain parameter settings, when initiated by the real-time clock, to be changed while the telephone unit is in an on-hook condition.

Abstract: High temperature oxidation resistance of an aluminide diffusion overcoated MCrAlY coating system is substantially improved by CVD over-aluminizing the MCrAlY type overlay coating under CVD conditions that result in reduced concentrations of such tramp impurities as S and P in the aluminized MCrAlY overlay coating region of the coating system. The CVD aluminizing conditions yield an outwardly grown aluminide over-coat on the underlying MCrAlY type coating.

Abstract: A low power consuming signal detection device for attachment to a telephone line. The device has an impedance of at least five megohms across the telephone lines. The device includes a power supply having an input impedance of least five megohms and an amplifier powered by the power supply for amplifying tone interrogation signals present on the telephone line. A phase-locked-loop is responsive to the amplifier signals for determining when the frequency of the amplified signals are within a predefined bandwidth. Phase locking of the phase-locked-loop to the amplified signals is detected by a lock detector when the frequency of the signals falls within a predetermined bandwidth for a predetermined period of time. the lock detection signal is used to place meter reading circuitry in an "off-hook" condition and for effecting the transfer of data from meter data collection apparatus over the telephone line back to a remote location.