JPH0534384A - Watthour meter - Google Patents

Abstract

PURPOSE:To enable the compensation of an error ratio in a light load area. CONSTITUTION:This apparatus is provided with a potential divider 3 for dividing a load voltage, a shunt 4 for shunting a load current, a waveform shaping circuit 8 for shaping a waveform of an output of the potential divider 3. a power/frequency conversion circuit 6 which multiplies an output of the potential divider 3 and a sum output of the shunt 4 and the waveform shaping circuit 8 to output a pulse train having a frequency proportional to a power, and a counter 7 for counting the frequency. This enables the compensation of an error ratio in a light load area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic watt hour meter, and more particularly to compensating an error of the watt hour meter.

[0002]

2. Description of the Related Art The structure of a conventional example will be described with reference to FIG. FIG. 4 is a block diagram showing a conventional watt hour meter. In the figure, a conventional watt-hour meter is connected to a load voltage input terminal 1, a load current input terminal 2, a load voltage input terminal 1 and a voltage divider 3 which is, for example, PT, and a load current input terminal 2, for example. CT shunt 4, voltage divider 3 and multiplier 5 connected to shunt 4, and voltage / frequency conversion circuit (V / F conversion circuit) 6 connected to this multiplier 5.
And a counter 7 connected to the voltage / frequency conversion circuit 6.

Next, the operation of the above conventional example will be described with reference to FIG. FIG. 5 is a characteristic diagram showing an error rate of a conventional watt hour meter. First, the load voltage is divided by the voltage divider 3 from, for example, about 100 V (AC) to about 5 V, and the load current is divided by the shunt 4 from 120 A to 2 mA, for example, and supplied to the multiplier 5. The multiplier 5 multiplies the divided voltage and divided load voltage and load current to obtain electric power. Then, a DC voltage proportional to the obtained electric power is output. The voltage / frequency conversion circuit 6 converts the DC voltage into a frequency, and the counter 7 counts the frequency,
Finally, the integrated power can be obtained. However, in the conventional watt-hour meter, as shown in FIG. 5, the error rate is large in the negative direction in the region where the load current is small. This is because the shunt (CT) 4 essentially has an exciting current component, so that the error rate in the small current region is large and the multiplier 5
This is because the offset in the small current region is large.

[0004]

As described above, the conventional watt hour meter has a problem that the error rate is large in the light load region. The present invention has been made to solve the above problems, and an object thereof is to obtain a watt hour meter capable of compensating for an error rate in a light load region.

[0005]

A watt hour meter according to the present invention is provided with the following means. (1) A voltage divider that divides the load voltage. (2) A shunt that divides the load current. (3) A waveform shaping circuit that shapes the output of the above voltage divider. (4) A multiplier that multiplies the output of the voltage divider and the added output of the current divider and the waveform shaping circuit. (5) A voltage / frequency conversion circuit that converts the output of this multiplier into a frequency. (6) A counter that counts the above frequencies.

[0006]

In the present invention, by the waveform shaping circuit,
The output of the voltage divider that divides the load voltage is waveform shaped. In addition, the multiplier multiplies the output of the voltage divider by the addition output of the shunt that divides the load current and the waveform shaping circuit. Furthermore, by the voltage / frequency conversion circuit,
The output of the multiplier is converted to frequency. Then, the frequency is counted by the counter and the electric power is integrated.

[0007]

【Example】

Example 1. The configuration of an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a block diagram showing an embodiment of the present invention, in which the load voltage input terminal 1 or the counter 7 is exactly the same as that of the conventional instrument. In FIG. 1, an embodiment of the present invention is the same as that of the conventional instrument described above, and a waveform shaping circuit 8 connected to a voltage divider 3.
, One input side is connected to the shunt 4, the other input side is connected to the waveform shaping circuit 8, and the output side is the multiplier 5
And an adder 9 which is, for example, an OP amplifier.

FIG. 2 is a circuit diagram showing an embodiment of the waveform shaping circuit 8 and the adder 9 in the above configuration. In the figure, the waveform shaping circuit 8 includes an operational amplifier 81 having an inverting input terminal connected to the voltage divider 3 and a non-inverting input terminal connected to a resistor 82 connected to a reference potential, and the operational amplifier 81.
A resistor connected between the non-inverting input terminal and the output terminal of
And a resistor 84 connected to the output terminal of the operational amplifier 81. The adder 9 has an inverting input terminal connected to the resistor 84 and the shunt 4 of the waveform shaping circuit 8, a non-inverting input terminal connected to the reference potential, and an output terminal connected to the multiplier 5. The amplifier 91 and this operational amplifier 91
Of the resistor 92 connected between the inverting input terminal and the output terminal.

Next, the operation of the above embodiment will be described with reference to the characteristic diagram (FIG. 3) showing the error rate. That is, the load voltage to be measured is almost constant, but it still fluctuates by about ± 10%, and the load current greatly changes depending on the load. However, the basic operation is the same as that of the conventional example, and therefore its explanation is omitted. The waveform shaping circuit 8 waveform-shapes the output voltage of the voltage divider 3 based on the reference potential and supplies a rectangular wave to the adder 9. Since the amplitude of this rectangular wave is determined by the power supply voltage range of this circuit even if the output voltage of the voltage divider 3 fluctuates, the amplitude remains substantially constant. The adder 9 adds the output current of the shunt 4 and the rectangular wave of the waveform shaping circuit 8 and supplies the result to the multiplier 5. The multiplier 5 multiplies the divided load voltage and the addition current of the adder 9 to obtain electric power. Then, a DC voltage proportional to the obtained electric power is output. By doing this, as shown in FIG. 3, the error rate in the small current (light load) region is improved, and the error rate becomes almost constant. This is because the smaller the current is, the more the error rate is compensated by constantly adding the rectangular waves having the substantially constant amplitude.

Since one embodiment of the present invention is provided with the waveform shaping circuit 8 as described above, the voltage component is input to the current input circuit as a rectangular wave of the same phase, and the influence of the fluctuation of the load voltage is small. Load compensation can be performed. That is, there is an effect that the linearity of the error rate can be improved. Further, the watt-hour meter can be configured with an inexpensive CT / OP amplifier or the like. Furthermore, it is possible to prevent latent movement (creep). The same function can be obtained even if the multiplier 5 and the voltage / frequency conversion circuit 6 are integrated into a power / frequency conversion circuit.

[0011]

As described above, the present invention includes a voltage divider for dividing a load voltage, a shunt for dividing a load current, and
A waveform shaping circuit that shapes the output of the voltage divider, and a power / frequency conversion that outputs a pulse train having a frequency proportional to the power by multiplying the output of the voltage divider and the addition output of the shunt and the waveform shaping circuit. Since the circuit and the counter that counts the frequency are provided, it is possible to compensate the error rate in the light load region.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a waveform shaping circuit and an adder according to an embodiment of the present invention.

FIG. 3 is a characteristic diagram showing an error rate of an embodiment of the present invention.

FIG. 4 is a block diagram showing a conventional watt hour meter.

FIG. 5 is a characteristic diagram showing an error rate of a conventional watt hour meter.

[Explanation of symbols]

 1 load voltage input terminal 2 load current input terminal 3 voltage divider 4 current divider 5 multiplier 6 voltage / frequency conversion circuit 7 counter 8 waveform shaping circuit 9 adder

Claims (1)

Claims: 1. A voltage divider for dividing a load voltage, a divider for dividing a load current, a waveform shaping circuit for shaping the output of the divider, an output of the divider and the divider. An electric energy meter, comprising: a power / frequency conversion circuit that multiplies a summed output of a waveform shaping circuit and outputs a pulse train having a frequency proportional to electric power; and a counter that counts the frequency.