JPH0534385A - 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 first potential divider 3 for dividing a load voltage. a second potential divider 8 for dividing outputs of a shunt 4 for shunting a load current and the first potential divider 3, a power/ frequency conversion circuit 6 which multiplies an output of the first potential divider 3 and sum output of the shunt 4 and the second potential divider 8 to output 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. 3 is a block diagram showing a conventional watt hour meter. In FIG. 3, 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, the flow divider 4 which is CT and the voltage divider 3
And a multiplier 5 connected to the shunt 4 and the multiplier 5
Voltage / frequency conversion circuit (V / F conversion circuit) connected to
6 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. 4 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 5 V, and the load current is divided by the shunt 4 from 120 A to 2 mA, for example, and is 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 can count the frequency and finally obtain the integrated power. However, in the conventional watt hour meter, as shown in FIG. 4, 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 the error rate in the small current region is large, and the multiplier 5 also has a large offset in the small current region.

[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) The first voltage divider that divides the load voltage. (2) A shunt that divides the load current. (3) A second voltage dividing circuit that divides the output of the voltage divider. (4) A power / frequency conversion circuit that multiplies the output of the first voltage divider and the added output of the current divider and the second voltage divider circuit to output a frequency proportional to the power. (5) A counter that counts the above frequencies.

[0006]

In the present invention, the output of the voltage divider for dividing the load voltage is further divided by the voltage dividing circuit. Further, the multiplier multiplies the output of the voltage divider by the addition output of the current divider and the voltage divider circuit that divide the load current. Further, the output of the multiplier is converted into a frequency proportional to the electric power, and the counter counts the frequency to obtain the electric power integration.

[0007]

【Example】

Example 1. The configuration of the embodiment of the present invention will be described with reference to FIG. 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 above-mentioned conventional instrument, a voltage divider 8 connected to a voltage divider 3 and, for example, a fixed resistor, and one input side connected to a current divider 4. The other input side is connected to the voltage divider 8 and the output side is connected to the multiplier 5 and is composed of an adder 9 which is, for example, an OP amplifier.

Next, the operation of the above embodiment will be described with reference to the characteristic diagram (FIG. 2) showing the error rate. That is, the load voltage to be measured is almost constant, and the load current changes greatly depending on the load. Therefore, the basic operation is the same as that of the conventional example, and therefore the description thereof is omitted. Voltage divider 8
Further divides the output voltage of the voltage divider 3, for example 5V,
A minute current flowing, for example, about 2 μA is supplied to the adder 9. Since the load voltage of this minute current is substantially constant, the minute current is also substantially constant. The adder 9 adds the output current of the shunt 4 and the minute current of the voltage divider 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. If this is done, FIG.
As shown in, the error rate in the small current region is improved to a substantially constant error rate. This is because the error rate is compensated as the current becomes smaller by constantly adding a substantially constant minute current.

Since one embodiment of the present invention is provided with the voltage divider 8 as described above, a part of a substantially constant load voltage is input to the current input circuit and a constant effective product (electric power) output component is obtained. Can be supplied to the multiplier 5 for light load compensation.
That is, the linearity can be improved. In addition, inexpensive CT. An electric power meter can be configured with an OP amplifier or the like.

Embodiment 2. In the above embodiment, the voltage divider 8
Although it is composed of a fixed resistor, the same operation can be expected even if a variable resistor is used, and it also has a function of an adjusting device such as an error rate. Further, 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 the first voltage divider for dividing the load voltage, the current divider for dividing the load current, and the second voltage divider for dividing the output of the voltage divider. A power / frequency conversion circuit for multiplying the output of the first voltage divider and the added output of the current divider and the second voltage divider to output a frequency proportional to the power, and a counter for counting the frequency Therefore, it is possible to compensate the error rate in the small current region, that is, 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 characteristic diagram showing an error rate of an embodiment of the present invention.

FIG. 3 is a block diagram showing a conventional power meter.

FIG. 4 is a characteristic diagram showing an error rate of a conventional watthour 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 voltage divider 9 adder

Claims (1)

Claims: 1. A first voltage divider for dividing a load voltage, a current divider for dividing a load current, a second voltage divider for dividing an output of the first voltage divider, and the first voltage divider. A power / frequency conversion circuit that multiplies the output of the voltage divider and the added output of the current divider and the second voltage divider to output a pulse train having a frequency proportional to the power, and a counter that counts the frequency. Electricity meter characterized by.