A variable gain analog to digital compression encoder apparatus and method is operational for `on the fly` gain adjustments without introducing significant distortion or noise in telephone conversation. An incoming analog signal is fixed gain reproduced as a first stabilized mid-operating point analog signal. A second stabilized mid-operating point analog signal is produced in inverse proportion to the first stabilized mid-operating point analog signal, in response to a signal tapped along a signal division of a difference between the first and second signals. The second signal is compression encoded at a predetermined rate to produce pulse code modulated signal samples. The tap may be varied to change the encoding gain, at any time, in accordance with operating requirements of a telephone apparatus.

An analog-digital converting circuit comprises an analog amplifying circuit having different amplification factors and an input connected to an analog signal input terminal. A first selector is connected at a corresponding number of inputs to receive the plurality of amplified analog signals, respectively. The first selection circuit outputs one analog signal selected from the received amplified analog signals, to an analog-digital converter. A second selector is connected at its an input to receive a digital signal from the analog-digital converter and has a plurality of outputs for outputting the received digital signal from one sequentially alternatively selected from the plurality of outputs. A coefficient multiplying circuit is connected to the outputs of the second selector, and generates multiplied digital signals obtained by multiplying the outputs of the second selector by different coefficeints. A third selector is connected at its corresponding number of inputs to the plurality of outputs of the coefficient multiplying circuit so as to output, as a digital signal, one selected from the plurality of outputs of the coefficient multiplying circuit. A controller is connected to receive the plurality of outputs of the second selector for monitoring respective levels of the plurality of outputs of the second selector and for supplying a selection signal to the third selector so as to cause to select, from the plurality of outputs of the coefficient multiplying circuit, one multiplied digital signal in correspondence to a level of the analog signal inputted to the analog signal input terminal. y

A circuit for converting input analog signals to output digital signals including an analog-to-digital converter having an analog input, an offset input and a digital output that represents the value of a signal at the analog input offset by an amount related to the value of the signal at the offset input, signal conditioning circuitry for receiving the input analog signal and providing it to the analog input via one of a plurality of different paths or under one of a plurality of different conditions, the different paths or different conditions providing different offsets to the input analog signal, and an offset correction memory storing offset correction characteristics for respective paths or conditions and being connected to provide an offset signal based on the characteristic for a path or condition to the offset input.

An electronic watthour meter is digitally configurable to operate as several different types of watthour meters for metering electrical energy from a variety of different electric utility services. Automatic scaling of line input currents is provided to scale the voltage input to an analog to digital converter over selected ranges such that low level and high level input signals are measured in an optimum range. A digital signal processor is employed to calculate values for metered electrical energy and output pulses, each proportional to a quantum of energy flowing in the circuit being metered. The processor calculates the value of DC offset errors inherent in the various analog circuits of the meter and uses that value in the calculation of metered electrical energy to compensate for such offset errors. The meter employs automatic and manually initiated test functions for testing the operation of the processor and other critical circuits in the meter.

An electrical overcurrent circuit provides both digital based modeling and analog based modeling of the temperature of an electrical conductor to simulate the conductor temperature during all expected operating conditions including a condition when electrical power is unavailable to the electrical overcurrent circuitry. When electrical power is available to the circuitry, the conductor temperature is calculated from the sensed load currents to form the digital based model. During such a condition, the analog based model is forced to track the digital based model. Once the temperature of the electrical conductor exceeds its maximum safe operating temperature, the electrical overcurrent circuitry initiates a trip of the circuit breaker. Since the overcurrent circuitry is powered either by the sensed load currents or derived from the circuit breaker output, the circuit breaker trip will result in a loss of electrical power to the electrical overcurrent circuitry. This causes the digital based model to be reset to a cold conductor temperature value. However, the analog based model continues to operate to simulate the conductor temperature during this condition. When electrical power is restored to the circuit, for example, when the circuit breaker is closed, the digital model is initialized with the value from the analog model.