MULTIPLIER USING HALL ELEMENT
The invention relates to a multiplier for calculating the product of current and voltage by using a Hall ele- 5 ment and more particularly to the one useful for watthour meters.
Watt-hour meters now commonly used are classified into DC type and AC type ones; induction watt-hour .meters, mercury-motor watt-hour meters, and commu- 10 tator watt-hour meters for DC type and induction watthour meters for AC type. In these type watt-hour meters, the product of current and voltage, i.e. measured power, is applied to a motor to develope a drive torque corresponding thereto to rotate the motor at the corre- 15 sponding speed. The amount of the rotation of the motor is measured of power consumption. With such a construction, they suffer inherent problems such as demagnetization of an electromagnet for speed control, wear of the rotational parts such bearings, gears, and 20 the like, possibly causing measurement error and poor reliability. Further, when it is applied to automatic meter inspection with attendant remote display of measurement values, they need complex signal converting apparatus. Further, now available watt-hour meters 25 have the best precision of measurement at most up to 0.5%, followed by bulkiness of meters.
Accordingly, the primary object of the invention is a multiplier permitting realization of watt-hour meters which uses a Hall element as means to obtain the prod- 30 uct of current and voltage, and maintains high reliability for long time use, with high precision but simple construction.
According to the invention, there is provided a multiplier comprising at least one Hall element with a pair of 35 control current input terminals and a pair of Hall output voltage terminals, ah electromagnet for converting load current into magnetic field and for applying the magnetic field to the Hall element, means for converting load voltage into control current and for feeding the 40 control current to the control current input terminals. The Hall element produces Hall output voltage corresponding to the product of the load current and the load voltage across the pair of Hall output terminals.
The invention will be better understood from the 45 following description taken in connection with the accompanying drawings, in which:
FIG. 1 shows a block diagram of a watt-hour meter constructed by using a multiplier using a Hall element according to the invention; 50
FIG. 2 shows a circuit diagram of an embodiment of the invention;
FIG. 3 is a circuit diagram of another differential amplifier circuit in FIG. 2;
FIG. 4 is a circuit diagram of another embodiment of 55 the invention;
FIG. 5 is a circuit diagram when the invention is applied to a three-phase watt-hour meter;
FIG. 6 is a graph for illustrating the relation between the flux density of the bias magnetic field of a common 60 type Hall element and the Hall output voltage thereof;
FIGS. 7 and 8 are diagrams for illustrating the way to remove the misalignment voltage by connecting in series two Hall elements;
FIG. 9 is a circuit diagram showing still another 65 embodiment of the invention;
FIG: 10 is a circuit diagram showing a modification of the embodiment of FIG. 2;
FIG. 11 is a circuit diagram showing another embodiment of the invention;
FIG. 12 is a circuit diagram showing yet another example of the power-voltage converter in FIG. 11; and FIG. 13 is a circuit diagram when the principle of the FIG. 12 embodiment is applied to a three-phase watthour meter.
Referring now to the drawings where like numerals designate identical or corresponding parts throughout the several views, the invention will be given about an embodiment that the invention is applied to a watt-hour meter. FIG. 1 shows a block diagram illustrating the entire of a watt-hour meter using a current/voltage multiplier according to the present invention. A load current I/, and a load voltage Vz, are applied to a powervoltage converter of the multiplier. The power-voltage converter is designated by numeral 1. In the converter, the load current Iz. is converted into a bias magnetic field and the load voltage Vz, into a control current. These converted ones are applied into a Hall element which in turn produces a Hall output voltage V# proportional to the load power, i.e. Iz.XVz.. The output voltage V#is applied to a differential amplifier circuit 2 comprised of three operational amplifiers 21, 22 and 23 where the in-phase component thereof is removed, and amplified. The output voltage of the differential amplifier circuit 2 is fed to a voltage-frequency (V-F) converter 3 which produces pulses with the frequency corresponding to the output voltage of the amplifier circuit 2. The pulses obtained are fed to a counter memory 4 where they are counted and stored. The counted value is then displayed in a light emission diode (LED) 5. The displayed counted value indicates the consumed power, i.e. the product of the load current Iz. and the load voltage Vz,. The counter memory 4 may be constructed by a non-volatile semi-conductor memory or a mechanical counter using a stepping motor or the like.
The power-voltage converter 1 in FIG. 1 corresponds to the multiplier using a Hall element of the invention. An embodiment of the multiplier is shown in FIG. 2. A control current supply circuit included in the power-voltage converter 1 is comprised of a coil 12 to be applied with a bias magnetic field corresponding to a single phase load current Iz, to a Hall element 11, a boosting transformer 13 for feeding a fixed current corresponding to the load voltage Vz. to the control current input terminals of the Hall element, a variable resistor 14 and a fixed resistor 15. The load voltage Vz, is applied to the primary winding of the transformer 13 and a high voltage current induced in the secondary winding thereof is processed by the combination of the variable resistor 14 and the fixed resistor 15 into a constant current to be directed to the control current input terminal of the Hall element 11.
As well known, the Hall element 11 is fabricated in such a manner, for example, that an epitaxial layer of GaAs is grown on a semi-insulating GaAs substrate and the layer is photo-etched to form a pair of control current input terminals and a pair of Hall voltage output terminals. A Hall element used as the Hall element 11 of the example has, for example, the internal resistance between Hall voltage output terminals 1200 ohms and the Hall output voltage VH of 22 mV/KG mA. The winding T of the electromagnet coil has 18 turns, for example. The coil is designated by numeral 12. The load current Iz. is fed to the coil 12 to develope a bias magnetic field which is in turn applied to the Hall element 11. The load voltage Vz. is boosted by the transformer