An electronic circuit arrangement for producing an output signal representative of the average value of an alternating voltage in a power transmission system, composed of: at least one circuit unit composed of a pulse width modulator (6) connected to derive, from the alternating voltage, a train of pulses modulated in width as a function of the amplitude of the alternating voltage and with a defined phase relation to the alternating voltage, an electronic circuit (4,8) connected to derive, from the alternating voltage, an alternating signal which varies in frequency with the alternating voltage and which has the defined phase relation to the alternating voltage, and a signal multiplying device (14) connected to receive the train of pulses modulated in width and the alternating signal for multiplying the pulses and the alternating signal to produce a product signal having an amplitude proportional to the average magnitude of the alternating voltage; and a signal to frequency converter (16) connected to derive from the product signal a train of output pulses having a repetition rate proportional to the amplitude of the product signal and constituting the output signal (18).

BACKGROUND OF THE INVENTION 
The present invention relates to circuits for producing volt-hour readings 
for polyphase power systems. 
It is common practice in the art to derive volt-hour (Vh) readings from the 
output of a volt-squared-hour (V.sup.2 h) meter, which requires a certain 
amount of data processing. At present, there are no electromechanical 
polyphase V.sup.2 h or Vh meters. 
Polyphase V.sup.2 h metering would require three single phase V.sup.2 h 
meters and an appropriate summing device. 
While polyphase Vh and V.sup.2 h meters presently exist, they are 
relatively expensive and are incapable of accepting low-level "electronic" 
inputs. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an inexpensive 
polyphase Vh meter circuit. 
Another object of the invention is to provide a circuit of this type which 
is capable of acting on low-level electronic input signals. 
Another object of the invention is to provide a polyphase volt-hour 
indicating circuit which can alternatively be used for single-phase power 
systems. 
The above and other objects are achieved, according to the present 
invention, by an electronic circuit arrangement for producing an output 
signal representative of the average value of an alternating voltage in a 
power transmission system, comprising: 
at least one circuit unit composed of pulse width modulator means connected 
to derive, from the alternating voltage, a train of pulses modulated in 
width as a function of the amplitude of the alternating voltage and with a 
defined phase relation to the alternating voltage, electronic circuit 
means connected to derive, from the alternating voltage, an alternating 
signal which varies in frequency with the alternating voltage and which 
has the defined phase relation to the alternating voltage, and signal 
multiplying means connected to receive the train of pulses modulated in 
width and the alternating signal for multiplying the pulses and the 
alternating signal to produce a product signal having an amplitude 
proportional to the average magnitude of the alternating voltage; and 
signal to frequency converter means connected to derive from the product 
signal a train of output pulses having a repetition rate proportional to 
the amplitude of the product signal and constituting the output signal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A preferred embodiment of a circuit according to the present invention is 
illustrated in FIG. 1 and includes an input terminal 2 connected to inputs 
of a square wave generator 4 and a pulse width modulator 6. Square wave 
generator 4 produces an output square wave having a pulse rate equal to 
the frequency of the signal applied to input terminal 2 and delayed in 
phase by 90.degree.. relative to that input signal. Pulse width modulator 
6 produces a train of output pulses modulated in width as a function of 
the amplitude of the signal applied to input terminal 2. 
The output signal produced by square wave generator 4 is applied to the 
control input of a set of transmission gates 8 which are additionally 
supplied with positive and negative dc potentials having precisely fixed 
amplitudes. Gates 8 apply the dc potentials alternatingly and in phase 
opposition to outputs 10 and 12 under control of the square wave signal 
supplied by generator 4. 
The output of pulse width modulator 6. and outputs 10 and 12 of gates 8 are 
supplied to a multiplying circuit 14 which produces a unidirectional 
output voltage proportional to the average value of the voltage applied to 
terminal 2. In effect, circuit 14 operates in a known manner to multiply 
the pulse width modulated signal portion representative of each positive 
half-wave of the signal at terminal 2 by a positive constant and to 
multiply the pulse width modulated signal portion representative of each 
negative half-wave of the signal at terminal 2 by a negative constant, the 
constant being represented by the dc potentials. A multiplying circuit of 
this type is disclosed, for 
example, in U.S. Pat. No. 4,596,951. The output voltage from circuit 14 is 
to the input of a voltage-to-frequency converter 16 to produce, at output 
terminal 18, a train of square wave pulses having a repetition rate which 
is directly proportional to the average amplitude value of the voltage 
applied to input terminal 2. Converter 16 could, for example, be 
constituted by a circuit as disclosed an illustrated in U.S. Pat. No. 
4,182,983 and identified therein as circuit 60. 
A volt-hour indication can be obtained simply by counting the output pulses 
at terminal 18 during a selected time interval. 
Square wave generator 4 is composed essentially of a differential amplifier 
20 having its inverting input connected to input terminal 2 to receive 
input signal A, shown in FIG. 2a, and provided with a feedback connected 
capacitor 22 to function as an integrator. The output signal from 
differential amplifier 20 is applied to one input of a second differential 
amplifier 24 having its other input connected to ground and thus connected 
to function as a comparator. Amplifier 24 produces, at its output, a 
square wave signal B which, as shown FIG. 2b, differs in phase by 
90.degree. relative to signal A. It will be noted that the output signal 
from amplifier 20 is inverted by comparator 24. 
Signal B controls transmission gates 8 in such a manner as to produce, at 
outputs 10 and 12, square wave signals C and D as shown in FIGS. 2c and 
2d, respectively. 
Reverting to FIG. 1, pulse width modulator 6 is constructed in a manner 
similar to square wave generator 4 in that modulator 6 is composed of a 
first differential amplifier 30 having its inverting input connected to 
input terminal 2 and provided with a feedback connected capacitor 32 to 
function as an integrator. However, the inverting input of amplifier 30 is 
additionally supplied with a square wave clock signal supplied by 
multiplying circuit 14, the clock signal having, as shown in FIG. 3b, a 
repetition rate which is several times the frequency of the voltage 
applied at input terminal 2. Thus, integrator 30, 32 produces a triangular 
output signal E, shown in FIG. 3c whose peak amplitude varies as a 
function of the change in amplitude of the voltage applied to input 
terminal 2 with a phase shift of 90.degree.. The output signal E is 
applied to a second differential amplifier 34 which is connected to 
function as a comparator and which, because it has a very high gain and 
effects a polarity reversal, produces an output signal F constituted, as 
shown in FIG. 3d, by a train of square wave pulses modulated in width as a 
function of variations in amplitude, relative to ground, of the triangular 
signal E. FIG. 3a illustrates the voltage wave form applied to input 
terminal 2. All of FIGS. 3 relate to the same time scale, which is 
enlarged compared to the time scale of FIGS. 2. 
As FIGS. 3 illustrate, the amplitude of each peak of triangular wave E 
relative to ground (0) is proportional to the instantaneous value of 
change of the voltage applied to input terminal A, with a phase shift of 
90.degree. or, in other terms, is proportional to the time integral of 
that voltage. Comparator 34 acts to produce the modulated pulse train F 
having an average repetition rate equal to that of the clock signal but 
composed of pulses which vary in width as a function of the peak amplitude 
of each cycle of triangular wave E. 
Multiplying circuit 14 multiplies the pulse width modulated signal F 
produced by modulator 6 under control of the two pulse trains C and D 
provided by gates 8 and, with the aid of converter 16, derives from the 
product signal an output pulse train having a repetition rate proportional 
to the average amplitude value of the voltage applied at input terminal 2. 
The circuit arrangement described thus far and illustrated in FIG. 1 will 
provide an output which can produce volt-hour indication for a single 
phase input signal. In order to produce a corresponding indication for a 
three-phase signal, a separate circuit unit can be provided for each 
signal phase, and as shown in FIG. 4, the output signals from multipliers 
14, 14' and 14" of these three units can then be applied to a summing 
circuit 40, which can be an analog adder, producing an output voltage 
equal to the sum of the product voltages produced by the three multipliers 
14, 14' and 14". The sum voltage provided by summing circuit 40 can then 
be applied directly to converter 16 so that the repetition rate of the 
output pulses appearing at terminal 18 will be representative of the sum 
of the three phase voltages. 
Output terminal 18 can be connected to a suitable counting circuit 42, 
which may be of a known type, controlled to produce an output signal 
representative of the number of pulses appearing at terminal 18 during 
successive time intervals of fixed duration. The output signal from 
counting circuit 42 will thus provide a Vh indication. Circuit 42 could, 
of course, be connected to output terminal 18 of the circuit shown in FIG. 
1. 
In an exemplary circuit arrangement according to the invention for 
monitoring a 60 Hz power voltage, the period of the output pulses 
appearing at terminal 18 could vary about a center value of the order of 
100 ms. 
The illustrated circuit could be modified to provide an output signal 
proportional to the square of the input voltage, for use in deriving a 
V.sup.2 h indication, by replacing square wave generator 4 and gates 8 by 
a suitable integrator and amplifier arrangement which will provide an 
output voltage proportional in amplitude to the voltage applied to 
terminal 2 and having the correct phase position relative to pulse width 
modulated signal F. 
While the description above shows particular embodiments of the present 
invention, it will be understood that many modifications may be made 
without departing from the spirit thereof. The pending claims are intended 
to cover such modifications as would fall within the true scope and spirit 
of the present invention. 
The presently disclosed embodiments are therefore to be considered in all 
respects as illustrative and not restrictive, the scope of the invention 
being indicated by the appended claims, rather than the foregoing 
description, and all changes which come within the meaning and range of 
equivalency of the claims are therefore intended to be embraced therein.