Alternating current watt transducer

An alternating current watt transducer including an integrated circuit analog multiplier, providing four quadrant multiplication, to the input terminals of which are applied alternating current signals proportional to the voltage and current determinative of the watts to be measured. The integrated circuit analog multiplier provides an alternating current output signal which being proportional to the product of the in-phase components of the input signals, is proportional to the watts being measured. The alternating current signal which is proportional to watts is transformed to a constant-current direct current output.

BACKGROUND OF THE INVENTION 
Wattmeters of various types have been employed in the past to indicate the 
amount of power passing a particular location in a circuit by measuring 
the voltage at that location, and the current passing that location. When 
measuring power in alternating current circuits, it is necessary to take 
into consideration the relative phase relationship of the current and 
voltage, such that only the in-phase components are multiplied to 
determine the number of watts of power passing a particular location in a 
circuit. 
Mechanical watt-hour meters have typically been employed in the past by 
power companies wishing to measure the amount of alternating current power 
that is used at a customer's location. With the advent of solid state 
electronic devices, watt and watt-hour meters utilizing such solid state 
devices have been disclosed. Many of these disclosed watt and watt-hour 
meters employing solid state devices utilize pulse circuit techniques. 
Such watt and watt-hour meters are disclosed in U.S. Pat. Nos. 
3,500,200--Woodhead; 3,517,311--Wasielewski et al; 3,780,273--Turrell; and 
3,953,795--Brunner et al. Still other patents showing solid state watt or 
watt-hour meters utilizing solid state devices employing pulse techniques 
are U.S. Pat. Nos. 3,976,942--Mayfield and 3,959,724--Chana et al. 
U.S. Pat. No. 4,437,059--Hauptmann is similar to the previously mentioned 
patents in disclosing a solid state wattmeter utilizing pulse techniques. 
However, the disclosure of the Hauptmann patent is directed to features of 
the magnetic coupling to the conductors in which the current flow is to be 
measured, and to the use of photoelectric devices for coupling purposes. 
It is an object of the present invention to provide a watt transducer for 
AC power measurement utilizing an integrated circuit analog multiplier 
providing four quadrant multiplication which receives two alternating 
current inputs, one proportional to the current and the other to the 
voltage associated with the alternating current power to be measured. 
It is a further object of the present invention to provide an alternating 
current watt transducer wherein the in-phase components of AC signals 
which are proportional to the AC voltage and AC current associated with 
the power to be measured, are multiplied by each other, so as to provide 
an alternating current output signal proportional to the AC power to be 
measured. 
It is a still further object of the present invention, when applied to 
multi-phase applications, to add signals representing the power in each of 
the phases to provide a signal representative of the total power being 
measured in the multi-phase circuit. Further, without regard to whether 
the watt transducer of this invention is utilized for single phase or 
multi-phase power measurements, a signal conversion circuit is provided to 
develop from an alternating current signal representative of the total 
power being measured, a constant-current DC output which is also 
indicative of the total power being measured. 
SUMMARY OF THE INVENTION 
The present invention provides an improved alternating current watt 
transducer utilizing an integrated circuit analog multiplier providing 
four quadrant multiplication, to provide an alternating current output 
signal which is proportional to the product of the in-phase components of 
the alternating current and voltage, the in-phase portions of which are a 
measure of the power to be measured. The alternating current output which 
is representative of the power being measured is converted to a DC signal 
by a solid state amplifier. In accordance with this invention, when 
multi-phase alternating current power is measured, the DC signals 
representing power in each phase are summed and supplied to a circuit, the 
output of which is a direct constant-current proportional to the total 
power being measured. Power measurements with accuracies of one-tenth of a 
percent are readily obtainable with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, a circuit diagram for a three-phase watt 
transducer in accordance with the preferred embodiment of this invention 
is shown. Since the watt transducers for each of the three phases are 
identical, like referenc numerals will be used to identify identical 
circuit components. The three-phases are indicated by the brackets labeled 
A, B, and C on the left of the Figure. The principle component of each of 
the watt transducers is an integrated circuit analog multiplier providing 
four quadrant multiplication, identified by the numeral 1. A functional 
diagram of an integrated circuit analog multiplier is shown in FIG. 2. 
The circuit shown in FIG. 2 relates specifically to an analog multiplier 
identified as the RC4200, manufactured by the Raytheon Company. A general 
description and the functional operation of the Raytheon 4200 analog 
multiplier is set forth in a six page product specification published by 
Raytheon Company entitled, Linear Integrated Circuits--Analog Multiplier 
4200, dated October, 1981. As utilized in the watt transducer of this 
invention, the desirable functional feature of this particular integrated 
circuit analog multiplier is that with alternating current voltage inputs 
applied to two of its input terminals, an alternating current output 
signal is provided at a third terminal which is the product of the two 
input voltages, taken into account any phase difference between the two 
input voltages. That is, in performing the multiplication of the two input 
alternating current voltages, out of phase components of the two voltages 
are automatically rejected, such that the multiplication is of only 
in-phase components. Thus, if a reactive load is present on any one of the 
phases, such that the current signal is displaced in time with respect to 
the voltage signal, the integrated circuit analog multiplier will take 
into account the phase angle, such that its output signal will be a true 
indication of watts. 
FIG. 2 shows a functional diagram of the Raytheon 4200 multiplier set forth 
in the above-mentioned product specification. The AC signals applied to 
terminals 1 and 8 are, as previously set forth, multiplied to provide an 
output at terminal 4 which is proportional to the product of the in-phase 
portions of the signals applied to terminals 1 and 8. While the integrated 
circuit analog multiplier, as shown, is designed to provide an output at 
terminal 4 which is proportional to the product of the inputs at terminal 
1 and 8, divided by the input at terminal 5, the divisor function is not 
used in the watt transducer of this invention. 
Referring again to FIG. 1, the integrated circuit analog multipliers 
identified by the numeral 1 are shown with eight (8) terminals, all eight 
of which are labeled to correspond with the terminals of the integrated 
circuit analog multiplier functional diagram shown in FIG. 2. Since the 
watt transducers in each of the phases A, B, and C are to a large extent 
identical, the operation of the watt transducer for phase A will be 
described with it being understood that the description also generally 
applies to the watt transducers for phases B and C. A current transformer 
CT1 has a primary winding with the current I1 flowing therethrough being 
equal or proportional to the current flow in phase A. The output of the 
secondary winding of current transformer CT1 is applied to a resistor R10 
to create a voltage output which is applied through resistor R5 to input 
terminal 1 of the analog multiplier 1. The voltage appearing in phase A 
between line L1 and the neutral N is applied across voltage dividing 
resistors R11 and R7, with the voltage at the junction thereof, being 
applied through resistor R6 to input terminal 8 of the analog multiplier. 
Apart from the input signals applied to terminals 1 and 8 of the analog 
multiplier, a bias voltage +VCC1 is applied to terminals 1, 4, 5, and 8 
through resistors R1, R3, R4, and R2, respectively. Terminals 2, 6 and 7 
of the analog multiplier 1 are grounded, while a reference voltage -VCC1 
is applied to terminal 3. The output of the analog multiplier 1 developed 
at terminal 4, which is essentially the in-phase product of the voltages 
applied to terminals 1 and 8, is applied to the negative input terminal of 
an operational amplifier A1. The positive input of operational amplifier 
A1 is grounded. A portion of the output of the operational amplifier is 
fed back to the negative input terminal through a resistor R8. The 
operational amplifier A1 converts the alternating current output signal of 
analog multiplier 1 to a DC voltage output signal which is applied through 
a resistor R9 to a summing bus 10. Similarly, the outputs of the 
operational amplifier A1 in phase B and of operational amplifier A1 in 
phase C are also applied to the summing bus 10 through resistors R9. 
A capacitor C4 connected between summing bus 10 and ground serves as an AC 
filter. The voltage appearing on summing bus 10 is applied through a 
resistor R14 to the positive input terminal of an operational amplifier 
A2. The output of operational amplifier A2 is fed back to the negative 
input, and is also provided through an adjustable resistor R15 and a 
resistor R16 to the negative input terminal of another operational 
amplifier A3. Adjustable resistor R15 is provided for the purpose of 
adjusting the gain, so as to provide a full range output. Thus, 
operational amplifier A2 serves as a voltage followerbuffer amplifier. The 
positive input of operational amplifier A3 is provided with an offset 
voltage through a resistor R18 by way of a potentiometer R20 which is 
connected in series with two resistors R19 and R21, between the negative 
VCC1 and negative VCC2 reference voltages. A constant-current proportional 
to the voltage signal present at the output terminal of operational 
amplifier A2 is developed between the terminals 12 and 14. This 
constant-current output may drive a DC ammeter or other suitable load. A 
zero current output between terminals 12 and 14 is equal to zero watts 
input as measured in phases A, B, and C. 
Adjustment of the voltage applied to the positive input terminal of 
operational amplifier A3 through resistor R18 by way of potentiometer A20 
provides a means for eliminating any offset errors occurring in any one of 
the phases with a zero current input. 
Two power supplies energized from one of the phases A, B, or C provide the 
necessary operating power and bias voltages for each of the three watt 
transducers. A primary P1 of transformer PT1 is energized from one of the 
phase voltages, with the two power supplies being energized from secondary 
windings S1 and S2. Secondary winding S1 is connected to the input 
terminals of a full wave bridge rectifier BR1. The output of BR1 is 
filtered by capacitor C7 and provided to the power supply terminals of 
operational amplifier A2. The output of the second secondary winding S2 is 
provided to the input terminals of a full wave bridge rectifier BR2. The 
output of bridge rectifier BR2 is filtered by capacitor C8 and is provided 
through resistor R12 to the emitter of regulating transistor Q1. The base 
voltage of transistor Q1 is provided by a voltage appearing at the 
junction of a resistor R13 and a zener diode VR4 which are connected in 
series across the output of bridge rectifier BR2. Three zener diodes VR1, 
VR2, and VR3 are connected in series between the collector of transistor 
Q1 and the negative output terminal of bridge rectifier BR2 to provide 
several regulated output voltages. The regulated output is further 
filtered by capacitor C1, and is then applied to the power terminals of 
amplifier A1. With the junction between zener diodes VR1 and VR2 being 
grounded, the voltage references +VCC1, -VCC2 and -VCC1 are provided by 
the series connected zener diodes. 
Finally, the two power supplies are coupled to each other through the 
parallel connected capacitor C9 and resistor R22. The reference voltages 
+VCC1, -VCC2 and -VCC1 are applied to the watt transducers at the 
terminals as indicated by the referenc voltages. If the circuit isolation 
provided by separate power supplies is not necessary, only one power 
supply need be used. 
A preferred three phase embodiment of the present invention has been 
described herein. However, it is to be understood the changes and 
modifications thereto are within the intent and spirit of the present 
invention. For instance, it is obvious that when desired, the invention 
may readily be applied to single phase applications.