TELEMETRY DEVICE INCLUDING A DYNAMIC OFF-HOOK DETECTOR

The telemetry device of the present invention overcomes the wide variation in operating parameters found in the telephone system by automatically tuning itself to the operating conditions sensed on the telephone line. More particularly, the invention dynamically adjusts the subscriber loop current to compensate for the variety of line conditions encountered. The telemetry device collects data at a remote location and transmits that data over a phone line back to a central station. The device includes a power supply which is coupled to the phone line to derive a power supply voltage therefrom to power the device. When the device enters an active state, it seizes the phone line before transmitting the collected data back to the central station. Upon entering the active state, a pre-loading circuit in the device progressively loads the device down until the power supply voltage within the device decreases to a first predetermined voltage level. The telemetry device also includes a voltage drop detector which is coupled to said power supply for detecting when the power supply voltage decreases to a second predetermined voltage level less than the first predetermined voltage level, thus indicating that a contending telephone device coupled to the phone line has come off-hook during the active state. When this occurs, the telemetry device immediately disengages from the phone line.