TELEPHONE DIAL-INBOUND DATA ACQUISITION SYSTEM WITH DEMAND READING CAPABILITY

摘要

TELEPHONE DIAL-INBOUND DATA ACQUISITION SYSTEM WITH DEMAND READING CAPABILITY A telephone dial-inbound data acquisition system with demand reading capability. The system has particular application for remotely reading utilitymeters. A remote data unit (RDU) dials up a host computer on a periodicbasis. The RDU is assigned a callback start time by the host computer. TheRDU calculates an actual callback time based on the callback start time and arandomly generated time delay. The RDU dials up the host computer via a modemwhen the local time, as shown by an on-board real-time clock at the RDU, equalsthe calculated actual callback time. Meter reading data is then transferred tothe host computer. The RDU also contains circuitry for detecting a pollingsignal generated by the host computer. Upon detection of this polling signal,the RDU immediately dials back the host computer and transfers utility meterreading data to the host computer. The RDU will also immediately dial back thehost computer if an alarm condition occurs, e.g. tampering or a low batterycondition. The RDU contains circuitry for characterizing the on-hook andoff-hook electrical characteristics of the telephone line to ensure that theRDU does not interfere with normal operation of a customer's telephone line.