JPH0792210A - Watthour meter - Google Patents

Abstract

PURPOSE:To make it possible to display an integrated amount of power in the case where it is small and display of an integrated power high resolution by a method wherein CPU switches over a display resolution automatically on the basis of an integrated value and time of integration. CONSTITUTION:AC voltage (v) and current (i) are inputted to A/D converters 21 and 22 through input circuits 11 and 12 and converted into digital signals, respectively. DSP(digital signal processor) 30 taking in these signals determines an instantaneous power and an integrated power for a prescribed time on the basis of the two input data and transfers them to CPU 40. The CPU 40 determines the position of a decimal point and others on the basis of data on the integrated power and a time of integration and a display digit of a display device 50 and then displays the value of the integrated power in the display device 50. On the occasion, the CPU 40 changes the digit when the time of integration needs the change of the digit, while it determines the position of the decimal point and unit on the basis of the data on the integration when the time does not yet reach the time of integration necessitating the change of the digit, and makes the display device 50 display them. In other words, the CPU can switch over a display resolution automatically and display an integrated electric energy with a high resolution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrating wattmeter, and more particularly to an integrating wattmeter provided with a means for automatically switching the resolution in integrated display.

[0002]

2. Description of the Related Art In an integrated wattmeter for obtaining an integrated value of electric power, it is necessary to switch the display resolution to an appropriate value according to the integrated value. In the conventional watt-hour meter, for example, the decimal point position and unit were set so that the integrated value one hour after the range rated input could be displayed, but these decimal point position and unit are fixed. Therefore, when the integration time was short and the integration amount was small, the value could not be displayed with sufficient resolution. In addition, an integrating wattmeter is also known in which a dip (DIP) switch is used as a display resolution switching means, and the system is set by the user with the dip switch. However, the conventional switching method using the DIP switch has a problem that the switching operation is troublesome, and an appropriate resolution cannot be set when the integrated amount is unknown. In order to eliminate these drawbacks, a method has been devised in which the resolution automatically switches depending on the integrated value, but when the input is small, the error that increases with the passage of time is displayed. There is.

[0003]

SUMMARY OF THE INVENTION The present invention has been made to eliminate the drawback of the display resolution in the conventional integrating wattmeter, and its purpose is to display the value even when the integrated amount is small. In addition, the display resolution is automatically switched so that the display value of the error does not increase with the passage of time, and it is to realize a wattmeter equipped with a means capable of displaying the integrated electric energy with high resolution. .

[0004]

SUMMARY OF THE INVENTION The present invention is an analog-to-digital converter for converting an alternating voltage and a current into digital signals, respectively, and outputs of both analog-to-digital converters are taken in and multiplied by both digital signals to instantly A digital signal processor that obtains electric power and sequentially integrates the instantaneous power, and a decimal point of the integrated power value displayed on the display unit based on the integrated power value and the integrated time by receiving the calculation result of the digital signal processor. It is equipped with a microprocessor adapted to determine the position and unit.

[0005]

In the present invention as described above, the microprocessor functions to automatically switch the display resolution based on the integrated power value and the integrated time.

[0006]

The present invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration diagram of an embodiment of the present invention. In the figure, v
Is an AC voltage in the power circuit to be measured, and i is also a current. Input circuits 21 and 22 receive voltage v and current i, respectively, and normalize them.
Is an analog / digital converter (hereinafter referred to as an A / D converter) that converts the outputs of the input circuits 21 and 22 into digital signals. Reference numeral 30 captures the outputs of the A / D converters 21 and 22, multiplies both input data, and instantaneous power P _n =
In a digital signal processor (hereinafter referred to as DSP) having a function of calculating v _n × i _n ( _n is the number of samples) and sequentially integrating the value (ΣP _n ), the integrated power data is stored in the next stage. Microprocessor (hereinafter CPU
Called) 40. 50 is a display. CP
U40 determines the position and unit (mWh, Wh, kWh, MWh, etc.) of the decimal point based on the integrated power data, integrated time data and the display digit of the display 50, and the decimal point is displayed on the display 50. Display integrated power value by position and unit.

Here, in order to automatically switch the display resolution, two elements, that is, the integrated power value when the digit changes and the integration time when the digit changes are necessary. The element of is the value obtained from the maximum value of the rating display, and the element of is the input 100
When the value is%, it indicates the time when the integrated value exceeds and the time when the digit changes at the rated input. In Figure 2, CPU40 is DSP3
It shows a flow for receiving data from 0 and automatically determining the decimal point position and unit based on the above elements and.

As shown in this flow, the CPU 40
When the integrated data is received from the DSP 30, it determines whether or not it is "integrated time for digit change" based on the received data. If it is the accumulated time when the digit changes, the CPU 40 changes the digit. On the other hand, if the integrated time at which the digit changes has not been reached, the CPU 40 obtains the decimal point position and unit from the integrated data received from the DSP 30, and causes the display 50 to display the decimal point position and unit for which the integrated power value was obtained. .

[0009]

According to the present invention, the CPU is configured to automatically switch the display resolution from the two factors of the integrated value and the integrated time based on the data received from the DSP. It is possible to obtain an integrating wattmeter capable of displaying even when the minute and integrated amount are small, and capable of performing high-resolution integrated display without displaying an error that increases with the passage of time.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of the circuit of FIG.

[Explanation of symbols]

 11,12 Input circuit 21,22 Analog-to-digital converter 30 Digital signal processor 40 Microprocessor 50 Display

Claims (1)

[Claims] 1. An analog-digital converter for converting an AC voltage and a current into a digital signal respectively, and outputs of both analog-digital converters are taken in to multiply both digital signals to obtain an instantaneous power and the instantaneous power is obtained. A digital signal processor that sequentially integrates, and receives the calculation result of this digital signal processor, and determines the decimal point position and unit of the integrated power value displayed on the display based on the integrated power value and the integrated time. Integrated wattmeter with a microprocessor.