JPH04240572A - Electronic type watthour meter - Google Patents

Abstract

PURPOSE:To correct the error and offset of the gain of a voltage and current converter at the time of the full load of an object to be measured by correcting the reference voltage of an A/D converter whose conversion ratio is prescribed by reference voltage to the optimum value. CONSTITUTION:Voltage whose value corresponds to full load and is converted to voltage Vmax0 when a voltage converter 2 is accurately prepared is applied to the voltage input terminal 1 of the voltage converter 2. The voltage Vmax1 after conversion is converted to a digital value by an A/D converter 6 through a multiplexer 5. A CPU 7 issues a command to the bias circuit 11 in a correction means 20 while monitoring the digital value. The circuit 11 outputs the signal corresponding to the command to a reference voltage circuit 8 and, for example, in the case of Vmax1 >(<)Vmax0, the reference voltage Vr of the A/D converter 6 is increased (decreased) not only to increase (decrease) voltage per one bit but also to reduce (increase) the digital value so as to bring the same to the value corresponding to Vmax0. By this method, the error and offset of the gain of the converter are corrected.

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 an electronic watt-hour meter having a function of correcting errors in voltage converters and current converters using an A/D converter.

0002

2. Description of the Related Art FIG. 2 is a block diagram of an electronic watt-hour meter using a conventional A/D converter. In the figure, reference numeral 1 denotes a voltage input terminal to which a voltage to be measured (not shown) is applied. 2 is a voltage converter that converts the voltage applied to the voltage input terminal 1 into a small voltage signal, and includes a transformer,
Consists of resistors, etc. 3 is a current input terminal to which a current to be measured is supplied. 4 is a current converter that converts the current supplied to the current input terminal 3 into a small voltage signal;
, Hall element, etc.

Reference numeral 5 denotes a multiplexer which switches the voltage signal from the voltage converter 2 or the current converter 4 and passes either one to the next stage, and has input terminals X0, X1, Y0, Y1.
have. 6 is an A/D converter that receives the output signal of multiplexer 5 and converts it into a digital value; 7 is an A/D converter;
a CPU that calculates the amount of electric power based on the product of the digital values output from the D converter 6 and issues instructions to each part of the system;
8 is a reference voltage circuit that provides the A/D converter with a reference voltage Vr that defines a conversion rate when the A/D converter 6 converts an analog value into a digital value. 9 is voltage converter 2
and a reference power source used when measuring the error of the current converter 4, and its output voltage is V0. 10 is a RAM that stores offset data of the voltage converter 2 and current converter 4, and the like.

Next, the operation of the conventional electronic watt-hour meter shown in FIG. 2 will be explained. First, in order to measure the offset of the voltage converter 2, a known voltage is applied to the voltage input terminal 1. This voltage is a small value corresponding to a light load, and is set to a value that would be converted into a voltage signal equal to the voltage V0 in an ideal case where the voltage converter 2 is manufactured accurately. However, the voltage V1 of the voltage signal after actually being converted
is somewhat different from V0 due to errors in the voltage converter 2. The voltage V1 of the voltage signal is applied to the input terminal X0 of the multiplexer 5, and the reference power supply 9 is applied to the input terminal X1.
A voltage V0 is applied. The CPU 7 gives a command to the multiplexer 5 to calculate the error V1-V0 between the voltage V1 applied to the input terminal X0 and the voltage V0 applied to the input terminal X1.
is input to the A/D converter 6. The voltage error V1-V0 is converted into digital error data by the A/D converter 6 and input to the CPU 7. The CPU 7 converts the error data into offset data representing the offset of the voltage converter 2, and stores this in the RAM 10.

Similarly, a small known current corresponding to a light load is applied to the current input terminal 3, and the error in the current converter 4 is measured. The CPU 7 sends this error data to the current converter 4.
The offset data is converted into offset data and stored in the RAM 10.

[0006] Next, the operation of this prior art electronic watt-hour meter when measuring electric energy will be explained. The voltage and current to be measured are supplied to a voltage input terminal 1 and a current input terminal 3, respectively. These voltages and currents are converted into small voltage signals by voltage converter 2 and current converter 4, and are input to input terminals X0 and Y0 of multiplexer 5, respectively. The multiplexer 5 sequentially converts the voltage signals input to the input terminals X0 and Y0 into A according to a command from the CPU 7.
/D converter 6. At this time, input terminals X1, Y
1 are both disabled. The A/D converter 6 sequentially receives these voltage signals, converts them into digital values, and inputs the digital values to the CPU 7. The CPU 7 converts the digital value of the voltage signal into a value obtained by correcting the offsets of the voltage converter 2 and the current converter 4 using offset data in the RAM 10. Further, the CPU 7 multiplies each corrected digital value to obtain data representing the amount of electric power. At this time, the reference voltage circuit 8 applies the reference voltage Vr to the A/D converter 6 to define the voltage per bit, so that when the A/D converter 6 converts an analog value to a digital value. Define the conversion rate of In the prior art, this conversion rate is kept constant.

[0007]

[Problems to be Solved by the Invention] As described above, the conventional electronic watt-hour meter corrects only the offset among the errors of the voltage converter 2 and the current converter 4, and it is not necessary to correct the gain. I can't. In addition, the voltage V0 that determines the amount of correction was set to be most effective at light loads where both voltage and current are small, so there is an error when measuring for a full load where both voltage and current are large. The problem was that it became large.

The present invention was made to solve the above-mentioned problems, and it is an object of the present invention to provide an electronic watt-hour meter that corrects not only the offset but also the gain error and has less error at full load. With the goal.

[0009]

[Means for Solving the Problems] The electronic watt-hour meter according to the present invention uses an A/D converter to correct gain errors and offsets of a voltage converter and a current converter when the object to be measured is at full load. The present invention is characterized in that a correction means is provided to set the reference voltage to an optimum value.

0010

[Operation] In this invention, gain errors and offsets of voltage converters and current converters are corrected, and
Reduces the measurement error of electric energy when the measurement target is fully loaded.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention, and 1 to 4, 6, and 10 are the same as those described above. In this case, the multiplexer 5 switches the output signals of the voltage converter 2 and the current converter 4 and passes one of them to the next stage, and has only input terminals X0 and Y0. Further, the CPU 7 calculates the amount of electric power from the output signal of the A/D converter 6, and issues commands different from conventional ones to each part of the system. Reference numeral 11 denotes a bias circuit that changes the reference voltage Vr generated from the reference voltage circuit 8. Reference numeral 20 denotes a correction means composed of a reference voltage circuit 8 and a bias circuit 11, which adjusts the reference voltage Vr to correct the gain error and offset of the voltage converter 2 and current converter 4 when the measurement target is fully loaded. It is set to the optimum value. A voltage Vma corresponding to the full load is stored in the RAM 10.
x0 is stored in advance.

Next, the operation of the embodiment of the present invention shown in FIG. 1 will be explained. First, in order to correct the gain error and offset of the voltage converter 2, a known voltage is applied to the voltage input terminal 1. This voltage is a large value corresponding to the full load, and is set to a value that would be converted to the voltage Vmax0 in an ideal case where the voltage converter 2 is manufactured accurately. The converted voltage Vmax1 is somewhat different from Vmax0 due to an error in the voltage converter 2. The converted voltage Vmax1 is input to the A/D converter 6 via the multiplexer 5 and converted into a digital value. Here, C.P.
While monitoring this digital value by U7, a command is given to the bias circuit 11 in the correction means 20. The bias circuit 11 outputs a signal according to the command to the reference voltage circuit 8 to change the reference voltage Vr of the A/D converter 6. As described above, the reference voltage Vr determines the conversion rate when the A/D converter 6 converts an analog value into a digital value, that is, it defines the voltage per bit. Therefore, for example, if Vmax1 is larger than Vmax0, the voltage per bit is increased by increasing the reference voltage Vr, and the digital value is decreased until it becomes a value corresponding to Vmax0. Conversely, if Vmax1 is smaller than Vmax0, the reference voltage Vr is decreased and the digital value is increased until it becomes a value corresponding to Vmax0.

Similarly, a large known current corresponding to the full load is applied to the current input terminal 3. The CPU 7 monitors the digital values converted by the current converter 4 and the A/D converter 6, sets the reference voltage Vr of the A/D converter 6 to an appropriate level, and corrects the error in the gain of the current converter 4. and correct the offset.

Next, the operation of the electronic watt-hour meter of this embodiment when measuring the amount of electric power will be explained. A voltage and a current to be measured for electric energy are connected to a voltage input terminal 1 and a current input terminal 3, respectively. These voltages and currents are converted into small values by a voltage converter 2 and a current converter 4, respectively, and are respectively input to the input terminal X0 of a multiplexer 5.
, Y0. The multiplexer 5 sequentially sends the signals input to the input terminals X0 and Y0 to the A/D converter 6 according to a command from the CPU 7. A/D converter 6 sequentially receives these signals and converts them into digital values. At this time, since the reference voltage Vr is optimally determined as described above, these digital values are values that have been corrected for gain errors and offsets of the voltage converter 2 and current converter 4 at full load. It has become. The CPU 7 receives these digital values and multiplies them to obtain data representing the amount of electric power.

As described above, by using the correction means 20, it is possible to correct the voltage converter and the current converter even if the gain errors and offsets are large and therefore inexpensive components are used. An inexpensive electronic wattmeter can be obtained.

In the above embodiment, the multiplexer 5 is used so that only one A/D converter 6 is required, but two A/D converters may be used, each corresponding to the voltage and current individually. . Furthermore, although the CPU 7 gives commands to the bias circuit 11 while monitoring the digital value that is the output of the A/D converter 6, this may be done manually instead of by the CPU 7.

[0017]

As described above, according to the present invention, the reference voltage of the A/D converter can be adjusted to correct the gain error and offset of the voltage converter and current converter when the measurement target is fully loaded. Since we have provided a correction means to optimize the value,
This has the effect of providing an electronic watt-hour meter with small errors at full load.

[Brief explanation of the drawing]

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

FIG. 2 is a block diagram showing a conventional electronic watt-hour meter.

[Explanation of symbols]

2 Voltage converter 4 Current converter 6 A/D converter 7 CPU 8 Reference voltage circuit 11 Bias circuit 20 Correction means Vr Reference voltage

Claims (1)

[Claims] 1. A voltage converter that converts a voltage to be measured into a voltage signal, a current converter that converts a current to be measured into a voltage signal, and a voltage signal from the voltage converter and the current converter. In the electronic watt-hour meter, the electronic watt-hour meter is equipped with an A/D converter that converts into a digital value and whose conversion rate is defined by a reference voltage, and a CPU that calculates the amount of electricity from the digital value and issues commands to each part of the system. An electronic power consumption system characterized by comprising a correction means for adjusting the reference voltage to an optimum value in order to correct gain errors and offsets of the voltage converter and the current converter when the measurement target is fully loaded. Total.