An electronic multiphase watt-hour metering system containing time-division multiplying circuitry. A duty cycle modulator and a switching device are provided for each phase of interest, the output signals of which are combined and conducted to a current-to-frequency converter. The output frequency of the current-to-frequency converter is responsive to the rate of electrical power consumption from a multiphase transmission system. In one embodiment, the current-to-frequency converter is coupled at its output to an accumulating counting system for recording the total energy supplied to a load. There may further be provided an indicator responsive to the frequency of the current-to-frequency converter for providing a visual indication of the instantaneous rate of power usage.

BACKGROUND OF THE INVENTION 
This invention relates generally to systems for measuring electrical energy 
consumption from a transmission system, and more particularly to an 
electronic system for measuring electrical energy consumption from a 
three-phase transmission system. 
A commercially available electronic watt-hour meter which is used for 
measuring the consumption of electrical energy from a single phase 
alternating current transmission system is described in German Patent 
DE-OS No. 27 47 385. The system described therein receives an electrical 
signal which corresponds to the load current of the system for controlling 
a duty cycle modulator. The output signal of the duty cycle modulator is 
applied through logic circuitry to an analog control switch which controls 
the conduction of a second input signal which corresponds to the load 
voltage. The analog switch, however, is shunted by complex amplification 
circuitry so as to produce a signal which corresponds to a preselected 
fraction of the second input signal. This signal, corresponding to the 
preselected fraction of the load voltage input signal, is conducted to a 
current-to-frequency converter which consequently controls a counting 
device. The count stored in the counting device, therefore, corresponds to 
the energy consumption of the load. 
In order to apply the energy measuring system of German Patent reference 
DE-OS No. 2747 385 to multiphase systems, the system described hereinabove 
with respect to a single phase transmission system must be replicated for 
each phase of interest. Such replication, however, is complex and 
expensive because each analog switch must be shunted by the amplification 
circuitry. 
In view of the foregoing, it is an object of this invention to produce a 
multiphase watt-hour meter which is simpler, less costly and requires less 
space than the replication of a single phase system. 
SUMMARY OF THE INVENTION 
The foregoing and other objects are achieved by this invention which 
provides a circuit having a duty cycle modulator and an analog switch 
associated with each phase of a multiphase system, the analog switch being 
responsive to an output signal of the duty cycle modulator for processing 
signals corresponding to the voltage and current associated with each 
phase conductor of the multiphase transmission system. 
Such processing produces an output signal for each phase of interest which 
corresponds to the electrical power being conducted by the respectively 
associated phase conductor to the load. The plural output signals in a 
multiphase system are combined and conducted to a current-to-frequency 
converter. The frequency converter is coupled at its output to an 
accumulating counter, the number in which corresponds to the total energy 
supplied to the load. The invention eliminates the need for amplification 
circuitry and associated resistors in shunt with each analog switch. In an 
illustrative embodiment wherein the transmission system is of the 
three-phase type, the elimination of the shunt amplification circuitry 
produces a savings of at least three operational amplifiers and nine 
resistors. Moreover, the elimination of such components reduces the 
possibility of circuit failure. Such an elimination of the shunt 
components results from the realization that, in a transmission system 
having symmetrical phase voltages, the sum of the currents flowing in the 
three shunt branches equals zero. 
In a preferred embodiment, the input signals corresponding to the load 
current are taken across measurement resistors which are serially disposed 
in each phase supply. It is, therefore, a feature of this invention that 
expensive and bulky current transformers and voltage transformers, which 
are required in known systems, can be eliminated.

DETAILED DESCRIPTION 
FIG. 1 shows an embodiment of a prior art watt-hour meter which is 
described in German Patent DE-OS No. 27 47 385 and which is useful for 
explaining the principles of the subject invention. An electronic single 
phase alternating current watt-hour meter system 1 is shown within a 
dashed line in the Figure. An input circuit 9, which is generally shown 
contained within a dashed and dotted line contains a duty cycle modulator 
2 which receives at an input terminal a signal i.sub.R which is 
proportional to the load current flowing through a conductor of a 
transmission system (not shown). Duty cycle modulator 2 is connected at an 
output terminal to an input terminal of an exclusive OR gate 3 which is 
coupled at its output to a control terminal of an analog switch 4. 
Accordingly, analog switch 4 is placed into sequential conductive and 
non-conductive states which have a duty cycle relationship with respect to 
one another which corresponds to the output signal of duty cycle modulator 
2. Analog switch 4 is coupled at an input terminal thereof to a terminal 
for receiving an input signal u.sub.R which is proportional to the load 
voltage, by means of a serial resistor 5. Thus, for any given value of 
load current signal i.sub.R, analog switch 4 provides at an output 
terminal a current signal i.sub.uR which is proportional in amplitude to 
input load voltage signal u.sub.R. The series circuit consisting of 
resistor 5 and analog switch 4 is shunted by a series circuit consisting 
of an inverting amplifier 6 which is coupled at its output to a serial 
resistor 7 and other feedback and input resistors, the value of which are 
preselected so as to produce an output current having a value negative 
i.sub.uR all divided by 2. The output current of analog switch 4 
(i.sub.uR) is combined with the current in the shunt loop 
(-1/2.times.i.sub.uR) to produce an output current which is conducted to a 
current-to-frequency converter 8, the current having a value of positive 
1/2.times.i.sub.uR when analog switch 4 is in a conductive state, and 
-1/2.times.i.sub.uR when analog switch 4 is non-conductive. 
Current-to-frequency converter 8 comprises an integrator and a comparator 
which has two limits. When one limit of the comparator is reached, the 
comparator reverses the polarity of its output signal, and the resulting 
pulse-shaped signal activates an accumulating counting device (not shown), 
the number in which corresponds to the total energy consumption. The 
pulse-shaped signal at the output of current-to-frequency converter 8 is 
also conducted to a second input terminal of exclusive OR gate 3. The 
output signal of current-to-frequency converter 8 which is conducted to 
exclusive OR gate 3 corresponds to the inverted signal of duty cycle 
modulator 2, thereby causing the integrator in the current-to-frequency 
converter 8 to change direction of integration. As the integrator 
approaches a second limit of the comparator, the output signal of the 
comparator is reversed again. This operation causes the integrator to be 
sequentially charged and discharged. The output frequency of the 
current-to-frequency converter is proportional to the product of the 
load-current proportional input signal i.sub.R, and the load-voltage 
proportional input signal u.sub.R. 
An electronic three-phase watt-hour meter which is commercially available 
and which operates according to the principle explained above with respect 
to single phase watt-hour meter system 1 is shown schematically in FIG. 1. 
Each of the three transmission system phases R, S and T are assigned to a 
respective one of input circuits 9, 10 and 11. Input circuits 10 and 11 
are but replications of input circuit 9 described hereinabove and in 
German Patent reference DE-OS No. 27 47 385. Thus, each such input circuit 
comprises a duty cycle modulator, an analog switch and amplification 
circuitry connected in shunt across the analog switch. The output signals 
of the input circuits 9, 10 and 11 are combined at a point 12 and 
conducted to the commonly shared current-to-frequency converter 8. As is 
the case with the hereinabove described single phase watt-hour meter 
system 1, current-to-frequency converter 8 is connected at its output to 
an accumulating device (not shown) for determining the energy consumption. 
FIGS. 2A and 2B show a multiphase watt-hour metering system which operates 
in accordance with the principles of the invention to measure the total 
energy delivered to a load by a transmission network having phase 
conductors R, S and T. A neutral conductor O is shown as part of the 
transmission system, but is not connected to the watt-hour meter system. 
As shown in FIG. 2A, input circuits 101, 201 and 301, are each associated 
with a respective one of phase conductors R, S and T. Input circuit 101 
which is associated with phase conductor R contains circuit components 
identified by reference numerals in a 100 series; input circuit 201 which 
is associated with a phase conductor S contains circuit components which 
are designated with reference numerals in a 200 series; and input circuit 
301 which is associated with phase conductor T has circuit components 
which are designated with reference numerals in a 300 series. Since input 
circuits 101, 201 and 301 are identical to one another in design and 
operation, the descriptions hereinbelow pertaining to input circuit 101 
should be construed to be applicable to all input circuits. 
Phase conductors R, S and T each have serially disposed therein a 
respective one of low resistance measuring resistors 100, 200 and 300. 
Input circuit 101 is coupled by serial resistor 102 to the load side of 
measuring resistor 100 so as to provide at an inverting input terminal of 
a preamplifier 106 an input signal i.sub.R which corresponds to the load 
current. Diode 103 and 104 which serve for overvoltage protection are 
connected in parallel, but poled for forward conduction in opposite 
directions, between the inverting input terminal of preamplifier 106 and a 
reference potential which is obtained at the transmission network side of 
measuring resistor 100. The potential at the transmission network side of 
measuring resistor 100 also serves as a reference potential for a duty 
cycle modulator 105. 
Duty cycle modulator 105 receives load current input signal i.sub.R, as 
indicated, at the inverting input terminal of a preamplifier 106, which is 
constructed with an operational amplifier. Preamplifier 106 is coupled at 
its output to an inverting input terminal of an astable multivibrator 108, 
by means of a serial resistor 107. 
The duty cycle of astable multivibrator 108 is a function of the magnitude 
of load current input signal i.sub.R. The astable multivibrator comprises 
an operational amplifier 109 which has its output terminal coupled to its 
inverting input terminal by a feedback resistor 110. A capacitor 111 is 
connected between the inverting input of operational amplifier 109 and the 
reference potential of the phase conductor R at line 112. A non-inverting 
input terminal of operational amplifier 109 is connected to line 112 by a 
resistor 113. The output signal of operational amplfier 109 is coupled to 
the non-inverting input terminal by a feedback resistor 114. The output 
terminal of operational amplifier 109 is further coupled to the reference 
potential at line 112 by the parallel combination of reference diodes 115 
and 116, which are poled for forward conduction in opposite directions. 
The output signal of astable multivibrator 108, which is also the output 
signal of duty cycle modulator 105, is conducted by a resistor 117 to an 
optical coupler 118 which operates to isolate the reference potential from 
ground. A diode 119 is connected in parallel to the light emitting diode 
of optical coupler 118, but is poled for forward conduction in an opposite 
direction. Diode 119 insures that currents can flow through reference 
diode 116 if the output signal of operational amplifier 109 is inverted. 
Although duty cycle modulator 105 is referenced in potential to the 
voltage at phase conductor R, the duty cycle is converted by optical 
coupler 118 so as to be referenced to ground. In operation, the current 
from the output of operational amplifier 109 which flows through the light 
emitting diode of optical coupler 118 is also conducted through reference 
diode 115. This provides the advantage of minimizing the supply current 
drain by duty cycle modulator 105. 
The output signal of optical coupler 118 is conducted to an input terminal 
of an exclusive OR gate 120. Exclusive OR gate 120 is coupled at its 
output to a control terminal of a field effect transistor 122 which 
operates as an analog switch. The combination of exclusive OR gate 120, 
analog switch 122 and duty cycle modulator 105 operates as a time-division 
multiplier which is assigned to the transmission network phase on phase 
conductor R. Similarly, the time-division multiplier assigned to phase S 
consists of duty cycle modulator 205, an exclusive OR gate, and an analog 
switch 222; and the time-division multiplier assigned to phase T consists 
of a duty cycle modulator 305, an exclusive OR gate 320, and an analog 
switch 322. 
Analog switch 122 in input circuit 101 chops the voltage-proportional input 
current signal i.sub.uR in accordance with the duty cycle which is 
determined by the duty cycle modulator 105. Diodes 124 and 125, which are 
connected in parallel and poled for conduction in opposite directions, are 
connected between the input terminal of analog switch 122 and ground. 
These diodes serve to limit the amplitude of the signal applied to the 
input of analog switch 122. The output signal of analog switch 122 on line 
126 is a time-division multiplication signal which is power-proportional 
to the signal taken from phase conductor R. The output signals of analog 
switches 122, 222 and 322, are combined at a summing node 27. 
It is evident from the foregoing that the input circuits shown in FIG. 2A 
do not contain a shunting branch across the respective analog switches, as 
mentioned in the embodiment of FIG. 1. As previously indicated, the 
omission of the shunting branches is enabled by the fact that the current 
through such branches would sum to zero at any instant, for a symmetrical 
three-phase system. 
The combined output signals at node 27 are conducted to a commonly shared 
current-to-frequency converter 28. Current-to-frequency converter 28 
contains an integrator 29 which is constructed with an operational 
amplifier having an output terminal which is coupled by a voltage divider 
circuit consisting of resistors 30 and 31 to an inverting input terminal 
of an operational amplifier 33 of a comparator 32. The output signal of 
comparator 32 is connected to ground by a resistor 34 and the parallel 
combination of reference diodes 35 and 36 which are poled for conduction 
in opposite directions. A non-inverting input of operational amplifier 33 
is connected to ground by a resistor 37 and to reference diodes 35 and 36 
by a variable resistor 38. Variable resistor 38 is advantageously 
adjustable to preselect two threshold limits of comparator 32. 
Additionally, such limits can be modified by the advantageous selection of 
reference diodes 35 and 36. 
The output signal of comparator 32 at the output terminal of operational 
amplifier 33 is conducted by a diode 39 to input terminals of exclusive OR 
gates 120, 220 and 320 which are contained in respective input circuits 
101, 201 and 301. Diode 39 suppresses the negative signal component of 
operational amplifier 33. In a first state of the output signal of 
comparator 32, analog switches 122, 222 and 322 are activated in response 
to the output signals of duty cycle modulators 105, 205 and 305 so as to 
produce at summing node 27, a current which is proportional to the sum of 
the powers of the transmission network phases at phase conductors R, S and 
T. This produces a slow charging of an integration capacitor 40 in 
integrator 29 until the output signal of integrator 29 reaches a first 
limit of comparator 32. At that moment, comparator 32 changes the state of 
its output signal. Thereby permitting only the inverted output signals of 
the duty cycle modulators 105, 205 and 305 to drive the analog switches. 
This produces a power-proportional current responsive to the three phases 
at summing node 27, but with a reverse polarity. Consequently, integration 
capacitor 40 slowly discharges until a second limit of comparator 32 is 
reached, whereupon the output signal once again reverses its state. The 
frequency of the changes in signal at the output of comparator 32 is 
proportional to the total power taken from the transmission network by 
means of phase conductors R, S and T. 
A summation of the signal changes at the output of comparator 32 over a 
given period of time corresponds to the energy drawn from the transmission 
network during the same time interval. In this embodiment of the 
invention, the output signal of comparator 32 is conducted to a frequency 
divider 41 in an accumulating counting system 48. Frequency divider 41 is 
coupled at its output to the base terminal of a switching transistor 43 by 
means of a resistor 42. Switching transistor 43 switches a pulse relay 44 
which is supplied by parallel capacitor 45. Capacitor 45 is connected 
between a positive supply voltage u.sub.O and ground. Frequency divider 41 
steps down the output frequency of comparator 32 by a predetermined 
fraction, because the frequency of the comparator is too high for 
operating electromechanical counting mechanisms. A light emitting diode 47 
is connected by a resistor 46 to the output of comparator 32 and provides 
a visual indication of the signal changes of the comparator, and 
consequently, of the rate of power usage. 
In the above described embodiment of the invention, load current-responsive 
and voltage-responsive input signals to the input circuits 101, 201 and 
301, from respectively associated phase conductors R, S and T, are 
obtained by direct connection to the phase conductors across respective 
measuring resistors 100, 200 and 300. It is to be understood, however, 
that the principles of the inventions are applicable to systems wherein 
such input signals are obtained from current and voltage transformers. It 
should further be noted that although the hereinabove described embodiment 
of the invention conducts a voltage responsive signal to an analog switch, 
and a current responsive signal to a duty cycle modulator, such inputs 
signals may be interchanged so as to provide the voltage proportional 
input signal to the duty cycle modulator and the load current proportional 
input signal to the time-division multiplier containing the analog switch. 
Thus, it is to be understood that although the inventive concept disclosed 
herein has been described in terms of specific embodiments and 
applications, other applications and embodiments will be obvious to 
persons skilled in the pertinent art without departing from the scope of 
the invention. The drawings and descriptions of specific embodiments of 
the invention in this disclosure are illustrative of applications of the 
invention and should not be construed to limit the scope thereof.