JPWO2008047428A1 - Electronic energy meter - Google Patents

Abstract

Conventional electronic watt-hour meters cannot sufficiently reduce the size and cost of products. In the present invention, the detection output of the voltage sensor 13 and the current sensor 14 and the reference potential of the current sensor 14 are differentially amplified by the differential amplifier 23 by the software processing unit 25, and the A / D converter 24 performs A / D by ΔΣ modulation. Converted. Then, the A / D converted reference potentials are removed from the detection outputs of the A / D converted voltage sensor 13 and current sensor 14, respectively, and the power consumption of the measurement target is calculated. The process for correcting the absolute error of the power consumption is performed only by the gain adjustment process. The calculated power consumption is displayed on the liquid crystal display unit 6 under the control of the liquid crystal driver 5 and is output to the LED 15 as a pulse signal.

Description

  The present invention relates to an electronic watt-hour meter that calculates the amount of power to be measured based on a digital signal converted by an A / D (analog / digital) conversion means.

  The measurement accuracy guarantee range of the electronic watt-hour meter is generally in a wide range of 6 to 1/40 times the rated value while the voltage is about ± 10% of the rated value. For this reason, in order to measure the current within the measurement accuracy guarantee range with an accuracy of ± 1%, 1/240 × 1% = 1 / 24,000, that is, a resolution of 1 / 24,000. The A / D converter requires a resolution of about 15 bits. However, A / D converters incorporated in microcomputers (hereinafter referred to as microcomputers) that are widely used as arithmetic processing units generally have a resolution of 10 bits and at most 12 bits. An electronic watt-hour meter that uses the power will lack resolution. For this reason, in the conventional electronic watt-hour meter, the current to be measured is amplified at an amplification factor corresponding to the magnitude thereof in order to compensate for the resolution that is insufficient with the A / D converter with a built-in microcomputer. For example, in the conventional electronic watt-hour meter disclosed in Patent Document 1, the amplification factor is automatically adjusted based on the level of the rectified and averaged measurement current and the rated level of the amplification unit. The output of the current sensor is amplified based on the adjusted amplification factor. There is also a conventional electronic watt-hour meter in which a plurality of amplifiers are provided in multiple stages as shown in FIG. 1 so that the measurement current can be amplified with various amplification factors according to the magnitude of the measurement current.

This electronic watt-hour meter includes a general-purpose microcomputer 1. The microcomputer 1 is provided with a successive approximation A / D converter 2 and a software processing unit 3 that performs an operation based on digital data converted by the A / D converter 2. The A / D converter 2 is connected to four stages of amplifiers 9, 10, 11, and 12 that amplify an input signal five times through a selection switch 7. A voltage sensor 13 and a current sensor 14 are connected to the first-stage amplifier 9 via a selection switch 8. The selection switch 8 is selectively switched to one of the terminals 8a, 8b, and 8c. When switched to the terminal 8a, the voltage signal from the voltage sensor 13 is selected, when switched to the terminal 8b, the current signal from the current sensor 14 is selected, and when switched to the terminal 8c, the reference potential of the detection output of each sensor 13, 14 is selected and measured. Is done. When the selection switch 7 selects the number of stages of amplifiers used to amplify the current signal detected by the current sensor 14, the connection is selectively switched to one of the terminals 7a, 7b, 7c, and 7d. It is done. When switched to the terminal 7a, the one-stage amplifier 9 is selected, and the input signal is amplified five times. When switched to the terminal 7b, the two-stage amplifiers 9 and 10 are selected. When switched to the terminal 7c, the three-stage amplifiers 9 to 11 are selected. When switched to the terminal 7d, the four-stage amplifiers 9 to 12 are selected. each ^{5 twice, 5 three} times and amplified in ^{5 four} times.

  The software processing unit 3 is connected to an LED (light emitting diode) 15 and a liquid crystal driver 5 that controls display on the liquid crystal display unit 6. The software processing unit 3 calculates power by multiplying the voltage value and current value converted into digital data by the A / D converter 2 and cumulatively adds this power to calculate the power amount. The calculated amount of power is displayed on the liquid crystal display unit 6, and a pulse signal proportional to the amount of power used is generated based on the calculated amount of power, and the LED 15 blinks.

  FIG. 2 is a flowchart showing an outline of the calculation process of the electric energy in the software processing unit 3.

  In this power amount calculation process, first, a current dummy A / D conversion process is performed (see FIG. 2, step (hereinafter referred to as S) 1). In this process, the digital data of the current value that is first converted by the A / D converter 2 when the selection switch 8 is switched to the terminal 8b is discarded in order to increase the current measurement accuracy. Next, a current pre-A / D conversion process is performed (S2). In this process, a measurement process is performed to determine the optimum number of stages of amplifiers used for amplifying the current signal from among the amplifiers 9-12. Next, current production A / D conversion processing is performed (S3). In this process, the amplifier having the number of stages determined in S2 is selected by switching the selection switch 7, and the detection signal output from the current sensor 14 is amplified by the selected amplifier, and then converted into digital data by the A / D converter 2. Processing is performed. Next, a voltage dummy A / D conversion process is performed (S4). In this process, as in the current dummy A / D conversion process of S1, the digital data of the voltage value that is first converted by the A / D converter 2 when the selection switch 8 is switched to the terminal 8a increases the voltage measurement accuracy. Thrown away. Next, a voltage production A / D conversion process is performed (S5). In this process, the one-stage amplifier 9 is selected by switching the selection switch 7, the detection signal output from the voltage sensor 13 is amplified by the amplifier 9, and then converted into digital data by the A / D converter 2. Done.

  Next, the offset obtained in the process of S13 described later is removed from the current value obtained in S3 and the voltage value obtained in S5, and power (instantaneous power) is calculated (S6). The offset is a voltage output from the A / D converter 2 when the inputs of the amplifiers 9 to 12 are zero. The power calculation formula in S6 is (voltage value−offset) × (current value−offset). Represented.

  Next, a gain adjustment process (S7) is performed. That is, the gain adjustment is performed by multiplying the power calculation result obtained in S6 by a predetermined number according to the amplification factor by the amplifier of the number of stages determined in S2. Subsequently, gain error correction processing is performed (S8). That is, processing for removing an error generated in the power calculation result due to an error of the internal resistance that determines the amplification factor in each of the amplifiers 9 to 12 is performed. Next, processing for calculating the amount of power by accumulating (integrating) the power data obtained by the processing of S6 to S8 is performed (S9). Based on the amount of power calculated in this power accumulation process, a pulse signal proportional to the amount of power used is output to the LED 15 (S10), and the calculated amount of power is displayed on the liquid crystal display unit 6.

Next, an offset dummy A / D conversion process is performed (S11). In this process, the offset data initially obtained by the A / D converter 2 when the selection switch 8 is switched to the terminal 8c is discarded in order to increase the offset measurement accuracy of each of the amplifiers 9-12. Next, an offset production A / D conversion process is performed (S12). In this process, the offset for each stage of the amplifiers 9 to 12 is sequentially measured by switching the selection switch 7, and the measured offset is converted into digital data by the A / D converter 2. The offset is measured several times, and the average value of the offset is calculated based on the measurement result (S13). Based on the offset thus obtained, the next power calculation process (S6) is performed as described above.
JP 2004-177228 A (paragraphs [0025] to [0031])

  However, since the conventional electronic watt-hour meter shown in FIG. 1 has a configuration in which the amplifiers 9 to 12 are connected in multiple stages, the optimum stage number of the amplifier is determined by the current pre-A / D conversion process of S2. , The offsets of the amplifiers 9 to 12 at each stage are measured by the offset dummy A / D conversion process of S11, or the offset values measured several times by the offset actual A / D conversion process of S12 are measured for each stage of the amplifiers 9 to 12. You must remember every time. Further, it is necessary to adjust the gain for each of the amplifiers 9 to 12 in each stage by the gain adjustment process in S7, or to correct the resistance error for each of the amplifiers 9 to 12 in the gain error correction process in S8. Therefore, the conventional electronic watt-hour meter shown in FIG. 1 requires a large amount of processing, increases the scale of software, and requires a large data storage capacity. Therefore, a microcomputer having a large memory size is required. Become.

  Further, since the processing amount increases, the operation clock frequency of the microcomputer 1 must be increased to improve the processing speed, and the current consumption of the microcomputer 1 increases. Further, since the amplifiers 9 to 12 are connected in multiple stages, the scale of the analog circuit portion is increased, the substrate size is increased, and the current consumption in the analog circuit portion is also increased. Therefore, the conventional electronic watt-hour meter shown in FIG. 1 cannot use a small power source. Further, as the current consumption increases, the fluctuation range of the output voltage from the power supply also increases. Therefore, the conventional electronic watt-hour meter shown in FIG. 1 requires circuit components for stabilizing the output voltage of the power supply. Incurs an increase in cost. Further, when the operation clock frequency of the microcomputer 1 is increased, the influence of the radiation electric field intensity due to electromagnetic noise generated from the microcomputer 1 increases. For this reason, in the conventional electronic watt-hour meter shown in FIG. 1, measures, such as an electromagnetic shield for improving noise proof performance (EMC), are needed, and this also costs.

  As a result, the conventional electronic watt-hour meter shown in FIG. 1 cannot sufficiently reduce the size and cost of the product.

The present invention has been made to solve such problems,
A voltage sensor for detecting a voltage to be measured; and
A current sensor for detecting a current to be measured;
A selection switch that selectively selects and outputs either the detection output of the voltage sensor or the current sensor or the reference potential of the detection output;
Amplifying means for amplifying at least the detection output of the current sensor;
The detection output of the voltage sensor and current sensor output by the selection switch, the A / D conversion means for converting the reference potential from an analog signal to a digital signal, and the digital signal converted by the A / D conversion means. In an electronic watt-hour meter provided with an arithmetic processing unit incorporating a calculation means for calculating the power consumption of a measurement target,
The amplification means is composed of differential amplification means for differentially amplifying the input signal,
The A / D conversion means converts the input signal from an analog signal to a digital signal by ΔΣ modulation,
The calculating means removes the reference potential converted by the A / D conversion means from the detection output of the voltage sensor and current sensor converted by the A / D conversion means, and calculates the power consumption of the measurement target. It is characterized by.

  According to this configuration, the detection output of the voltage sensor, the detection output of the current sensor, and the reference potential of these detection outputs are converted from an analog signal to a digital signal by ΔΣ modulation in the A / D conversion means. By removing the reference potential converted into the digital signal from the detection outputs of the voltage sensor and the current sensor converted into the digital signal by the arithmetic means, the differential amplification means from the detection outputs of the voltage sensor and the current sensor. And the offset of the A / D conversion means is removed. The power consumption of the measurement target is calculated using the detection outputs of the voltage sensor and current sensor from which the offset has been removed.

  The conversion from an analog signal to a digital signal in the A / D conversion means is finely sampled by oversampling at the time of ΔΣ modulation and performed with a high resolution, so that A / D conversion is performed as in a conventional electronic watt-hour meter. There is no need to configure the amplification means in multiple stages in order to supplement the resolution of the means. For this reason, the detection output of the current sensor that requires a wide range of measurement accuracy guarantee can be measured with high accuracy over a wide range without configuring the amplification means in multiple stages. In addition, since it is not necessary to configure the amplification means in multiple stages, it is possible to determine the optimum number of amplifiers, measure the offset of the amplifiers in each stage, and measure the number of times measured, as in conventional electronic watt-hour meters. Need not be stored for each stage of the amplifier. Further, it is not necessary to adjust the gain for each amplifier at each stage by the gain adjustment process, or to correct the resistance error for the amplifier at each stage by the gain error correction process. Accordingly, the amount of processing is reduced, the size of software is reduced, and the data storage capacity is also reduced, so that the memory size required for the arithmetic processing unit can be reduced. In addition, since the amount of processing is reduced, the operation clock frequency of the arithmetic processing unit can be kept low, and the current consumption can be reduced. Further, since it is not necessary to configure the amplifying means in multiple stages, the scale of the analog circuit portion can be reduced, the substrate size can be reduced, and the current consumption in the analog circuit portion can also be reduced. Therefore, a small power source can be used as the power source of the electronic watt-hour meter. In addition, since the current consumption can be reduced and the fluctuation range of the output voltage from the power supply can be reduced, a circuit component for stabilizing the output voltage of the power supply, such as a conventional electronic watt-hour meter, is not required and the cost is reduced. Can be suppressed. In addition, since the operation clock frequency of the arithmetic processing device can be kept low, the influence of the radiation electric field intensity caused by electromagnetic noise generated from the arithmetic processing device can be reduced, and the cost for measures against noise resistance can be suppressed. As a result, the electronic watt-hour meter according to the present invention can sufficiently reduce the size and cost of the product.

  Further, since the differential amplification means is used as the amplification means, it is possible to apply a bias voltage to at least the detection signal output from the amplification means from the current sensor. For this reason, even if the detection signal of the current sensor swings in the negative range, it is converted into a signal that fluctuates in the positive range by applying a bias voltage, and the detection signal of the current sensor is amplified by the amplification means. It can be converted into a digital signal by the / D conversion means. Further, since the differential amplifying means is used as the amplifying means, even if noise is applied to the input terminal, it is canceled and the influence of the noise can be eliminated, so that the input signal can be amplified with high accuracy.

  Further, according to the present invention, the arithmetic means corrects the absolute error of the used power amount by multiplying the used power amount by a predetermined value or by adjusting the threshold value of the pulse output corresponding to the used power amount. It is characterized by.

  According to this configuration, the absolute error of the calculated power consumption is corrected by multiplying the calculated power consumption by a predetermined amount according to the amplification factor of the amplification means. In addition, by adjusting the pulse output threshold according to the calculated power consumption, the pulse output timing is adjusted, and the pulse is output according to the actual power consumption. The absolute error of the used electric energy is corrected. Therefore, it is possible to correct the absolute error of the calculated power consumption by multiplying it by a predetermined value or by adjusting the threshold value of the pulse output. Increase.

  Further, according to the present invention, when the calculation means makes the reference potential of the detection output of the current sensor different from the reference potential of the detection output of the voltage sensor, the reference potential converted by the A / D conversion means It is characterized by removing from only one of the detection output and the detection output of the voltage sensor.

  According to this configuration, the power value calculated from the detection output of each sensor is composed of a direct current component, but the offset of the amplification means and the A / D conversion means appearing in the detection output on which the reference potential has not been removed is The AC component appears evenly in the positive and negative voltages, and is removed by the integration process in the process of integrating the amount of power used. Therefore, the removal of the reference potential converted by the A / D conversion means is performed only for either the detection output of the current sensor or the detection output of the voltage sensor, and the amplification means and The offset of the A / D conversion means can be removed. For this reason, the calculation process of the power consumption of the measurement target is simplified, the software scale is further reduced, the memory size of the arithmetic processing device is further reduced, and the operation clock frequency is further reduced. The current consumption can be further reduced.

  Further, according to the present invention, the arithmetic processing unit switches the selection switch immediately after the conversion by the A / D conversion means for any of the detection output of the voltage sensor and the current sensor and the reference potential of the detection output is completed. After performing the above, the next conversion by the A / D conversion means is performed after a while.

  According to this configuration, when the conversion by the A / D conversion unit with respect to either the detection output of the voltage sensor and the current sensor and the reference potential of the detection output is completed, the selection switch is immediately switched, and after that, after a period of time, Conversion by the A / D conversion means is performed on the signal input by the switched selection switch. For this reason, each conversion by the A / D conversion means starts after a certain amount of time has elapsed after the selection switch is switched and the signal input to the A / D conversion means is stable. Therefore, the cause of the measurement error is removed, and each conversion by the A / D conversion means is performed accurately.

  Further, according to the present invention, the arithmetic processing unit stops the operation of the A / D conversion unit immediately after the completion of each conversion by the A / D conversion unit, and prepares to start the next conversion by the A / D conversion unit. It is characterized by making it.

  According to this configuration, when the conversion of the detection output of the voltage sensor and the current sensor and the reference potential of the detection output is completed, the operation of the A / D conversion unit stops immediately, and the next conversion by the A / D conversion unit is performed. Preparation for starting is performed. For this reason, each conversion by the A / D conversion means is promptly executed from a state where the A / D conversion means is stopped. Therefore, when the conversion is continuously performed without stopping the operation of the A / D conversion means, the start of the next conversion is delayed by waiting for the completion of the conversion operation before the A / D conversion means at the start of conversion. Thus, although each conversion cannot be started at a constant cycle, this configuration can be performed at a constant cycle. As a result, the measurement timing of the voltage and current of the measurement target and the offset measurement timing are performed at regular intervals, and the calculation process of the power consumption of the measurement target can be performed accurately.

  Further, the present invention is characterized in that the reference voltage of the A / D conversion means is set to the same potential as the operating voltage of the arithmetic processing unit.

  According to this configuration, the power source that supplies the reference voltage to the A / D converter and the power source that supplies the operating voltage to the arithmetic processing unit can be shared. For this reason, it is not necessary to separately prepare a power source for supplying the reference voltage to the A / D conversion means, and further downsizing and cost reduction of the product can be achieved.

  According to the present invention, as described above, it is possible to provide an electronic watt-hour meter that can sufficiently reduce the size and cost of a product.

It is a block diagram which shows the outline of the circuit structure of the conventional electronic watt-hour meter. It is a flowchart which shows the outline of the calculation process of the electric energy in the electronic watt-hour meter shown in FIG. It is a block diagram which shows the outline of the circuit structure of the electronic watt-hour meter by one Embodiment of this invention. FIG. 4 is a partial detailed circuit diagram of the block diagram shown in FIG. 3. It is a flowchart which shows the outline of the calculation process of the electric energy in the electronic watt-hour meter shown in FIG. It is a flowchart which shows the detail of the calculation process of the electric energy shown in FIG. It is a block diagram which shows the outline of the circuit structure of the electronic watt-hour meter by the 1st modification of this invention. It is a block diagram which shows the outline of the circuit structure of the electronic watt-hour meter by the 2nd modification of this invention. It is a block diagram which shows the outline of the circuit structure of the electronic watt-hour meter by the 3rd modification of this invention. It is a figure which shows the relationship between the electric energy used cumulatively added, and the pulse signal produced | generated in the electronic watt-hour meter by the 4th modification of this invention. It is an internal circuit diagram of the A / D converter used for the electronic watt-hour meter by the 5th modification of this invention.

  Next, the best mode for carrying out the present invention will be described.

  FIG. 3 is a block diagram showing an outline of a circuit configuration of the single-phase two-wire electronic watt-hour meter according to the present embodiment. FIG. 4 is a partial detailed circuit diagram of the block diagram shown in FIG. In FIGS. 3 and 4, the same or corresponding parts as those in FIG.

The electronic watt-hour meter according to the present embodiment includes a voltage sensor 13, a current sensor 14, a general-purpose microcomputer 21, and a liquid crystal display unit 6. The microcomputer 21 constituting the arithmetic processing unit includes a selection switch 22, a differential amplifier 23, an A / D converter 24, a software processing unit 25, a liquid crystal driver 5, and an LED 15. The circuit ground (GND) is 0. is connected to a reference voltage V _SS of [V].

The voltage sensor 13 includes a voltage dividing circuit that divides the voltage V · sinωt input between the power supply terminals P0 and P1 by the resistors 13a, 13b, and 13c, and the divided voltage E _V · that appears at both ends of the resistor 13c. Detect sinωt as a voltage to be measured and output it. As the signal ground to which the resistor 13c is connected, a bias voltage V _COM (1.8 [V]) which is a half of the operating voltage V _DD (3.6 [V]) of the microcomputer 21 is shown in FIG. is the potential applied to the reference potential V _SS to. The current sensor 14 includes a shunt resistor 14a, and detects a voltage E _I · sinωt appearing across the shunt resistor 14a as a current to be measured by a load current I · sinωt flowing between the load terminals 1S and 1L. ,Output. Power terminals P1 and the load terminal 1S is connected to the same 0 [V] with a reference voltage V _SS of the microcomputer 21, the 0 [V] has a reference potential of the detection output of the current sensor 14. Thus, in this embodiment, the reference potential of the detection output of the current sensor 14 and the reference potential of the detection output of the voltage sensor 13 are set to 0 [V] and 1.8 [V], respectively, and are different. .

  The selection switch 22 is selectively switched to one of the terminals 22a, 22b, and 22c. When switched to the terminal 22a, the detection output of the voltage sensor 13 is selected, when switched to the terminal 22b, the detection output of the current sensor 14 is selected, and when switched to the terminal 22c, the reference potential of the current sensor 14 is selected. Accordingly, the selection switch 22 alternatively selects and outputs either the detection output of the voltage sensor 13 or the current sensor 14 or the reference potential of this detection output.

The differential amplifier 23 is connected to the sensors 13 and 14 via the selection switch 22 and outputs the amplified output to the A / D converter 24. The differential amplifier 23 and the A / D converter 24 use, as a reference potential, a potential obtained by adding a bias voltage V _COM (1.8 [V]) generated by the power supply 26 to the circuit ground (0 [V]). The microcomputer 21 operates by being supplied with the operating voltage V _DD (3.6 [V]) of the microcomputer 21.

  As shown in FIG. 4, the inverting input terminal (−) of the differential amplifier 23 is connected to the output terminal of the selection switch 22 via a resistor 23 a, and is connected to each sensor 13, 14 selected by the selection switch 22. Detection output and its reference potential are input. The non-inverting input terminal (+) is connected to the reference potential of 0 [V] of the current sensor 14 through the resistor 23b and the power supply 26 through the resistor 23c. Further, a resistor 23d is provided between the inverting input terminal (−) and the output terminal of the differential amplifier 23, and negative feedback is applied. The differential amplifier 23 constitutes an amplifying unit that amplifies at least the detection output of the current sensor 14 selected by the selection switch 22, and is input to the inverting input terminal (−) and the non-inverting input terminal (+). It constitutes differential amplifying means for differentially amplifying the signal.

An A / D converter 24 is connected to the output terminal of the differential amplifier 23. The microcomputer 21 switches the selection switch 22 at regular time intervals to cause the A / D converter 24 to perform the conversion of the detection outputs of the voltage sensor 13 and the current sensor 14 and the reference potential of the detection outputs at regular time intervals. . The A / D converter 24 converts the signal input from the differential amplifier 23 from an analog signal to a digital signal by ΔΣ modulation with reference to the reference voltage V _ref . The A / D converter 24 constitutes A / D conversion means for converting the detection output of the voltage sensor 13 and the current sensor 14 and the reference potential of the current sensor 14 from an analog signal to a digital signal by ΔΣ modulation.

  A software processing unit 25 is connected to the output side of the A / D converter 24. Connected to the software processing unit 25 are an LED 15 that outputs a pulse signal proportional to the amount of power used, and a liquid crystal driver 5 that controls display on the liquid crystal display unit 6. The software processing unit 25 multiplies the detection output of the voltage sensor 13 and the detection output of the current sensor 14 converted into a digital signal by the A / D converter 24 to calculate the power, and cumulatively adds the calculated power to the target. Calculate the power consumption to be measured. The calculated power consumption is displayed on the liquid crystal display unit 6 under the control of the liquid crystal driver 5. In addition, the software processing unit 25 generates a pulse signal proportional to the calculated power consumption. When the generated pulse signal is output, a current flows through the LED 15 and the LED 15 emits light. The light emitted from the LED 15 is detected by a light receiving sensor, and a pulse signal proportional to the amount of power used is used to perform a verification process of power amount measurement accuracy. The software processing unit 25 constitutes a calculation unit that calculates the power consumption of the measurement target based on the digital signal converted by the A / D converter 24.

  FIG. 5 is a flowchart showing an outline of a calculation process of power consumption by the software processing unit 25 described above.

  In the calculation process of the used electric energy in the present embodiment, first, a current A / D conversion process is performed (see FIG. 5 and S21). In this process, the selection switch 22 is switched to the terminal 22b, and the detection output of the current sensor 14 amplified by the differential amplifier 23 is converted from an analog signal to a digital signal by ΔΣ modulation of the A / D converter 24. . Subsequently, a voltage A / D conversion process is performed (S22). In this processing, the selection switch 22 is switched to the terminal 22a, and the detection output of the voltage sensor 13 amplified by the differential amplifier 23 is converted from an analog signal to a digital signal by ΔΣ modulation of the A / D converter 24. .

  Next, the offset converted into the digital signal in the process of S27 described later was removed from the current value converted into the digital signal in S21 and the voltage value converted into the digital signal in S22, and the offset was removed. Power is calculated from the current value and the voltage value (S23). The offset is a voltage that appears at the output of the A / D converter 24 when the input of the differential amplifier 23 is zero, and the power calculation formula in the processing of S23 is (voltage value−offset) × (current value−offset). Is represented as

  Next, a gain adjustment process is performed (S24). In this process, the absolute error of the instantaneous power is corrected by multiplying the power data calculated in S23 by a predetermined factor according to the amplification factor of the differential amplifier 23. Next, the power data obtained in the processes of S23 and S24 is cumulatively added to calculate the power consumption (S25), and the calculated power consumption is displayed on the liquid crystal display unit 6. In addition, a pulse signal proportional to the calculated power consumption is generated, and the generated pulse signal is output to the LED 15 (S26).

  Next, an offset A / D conversion process is performed (S27). In this processing, the connection of the selection switch 22 is switched to the terminal 22c, and a reference potential of 0 [V] is input to the differential amplifier 23 to be differentially amplified. Then, the differentially amplified reference potential is converted into a digital signal by ΔΣ modulation of the A / D converter 24, and the offset of the differential amplifier 23 and the A / D converter 24 is calculated. In the next power calculation process of S23, the offset obtained by the offset A / D conversion process of S27 is removed from the voltage value and the current value as described above, and the power is calculated.

  FIG. 6 is a flowchart showing details of the above-described calculation process of the power consumption. The calculation process of the power consumption is performed as a timer interrupt process of the microcomputer 21.

When the time measured by the timer that measures the interrupt timing of the timer interrupt process reaches T _SS (= 500 [μs]), the timer interrupt process is started. In this timer interrupt process, the microcomputer 21 first determines whether or not the _TS2 flag is set (see S31 in FIG. 6). The _TS2 flag is set in S39 as will be described later while the voltage A / D conversion process (see FIG. 5, S22) is performed. When this determination is “No”, it is next determined whether or not the V _OFF flag is set, that is, whether or not the offset of the differential amplifier 23 and the A / D converter 24 is being measured. It discriminate | determines (S32). The V _OFF flag is set in S45 as will be described later while the offset A / D conversion process (see FIG. 5, S27) is performed. If the offset A / D conversion process is not performed and the determination in S32 is “No”, the microcomputer 21 sets the time of T _S1 (= 93 [μs]) in the timer (S33), and the time T The timing of _S1 is started. While the time T _S1 is being measured, the following series of processing up to S39 is performed. Further, due to the timer set in S33, after the time T _S1 elapses, the next timer interrupt is generated and the voltage ΔΣ A / D conversion in S41 is started. Next, the microcomputer 21 starts current A / D conversion processing (see FIG. 5, S21) (S34). At this time, the selection switch 22 has already been switched to the terminal 22b from which the detection output of the current sensor 14 is output to the A / D converter 24 in the process of S56 described later. Next, the microcomputer 21 determines whether or not the current A / D conversion process started in S34 is completed (S35). When this determination is “Yes”, the operation of the A / D converter 24 is immediately performed. Stop (S36). Then, the selector switch 22 is switched to the terminal 22a to set the detection output of the voltage sensor 13 to be input to the differential amplifier 23 (S37), and preparation for starting the next voltage ΔΣ A / D conversion (see S41). Do.

Next, the offset value (V _OFF value) already converted into the digital signal in S55 described later is removed from the detection output value (AD value) of the current sensor 14 converted into the digital signal in the processing of S34 and S35. The value (current value-offset) is set in a work data storage area (not shown) of a RAM (random access memory) built in the microcomputer 21 as a current value used for power calculation (S38). Next, the microcomputer 21 sets the _TS2 flag (S39) and ends the timer interrupt process.

_Also, if the determination in S31 have _{T S2} flag is set is "Yes", the microcomputer 21, _T S2 the timer _{(= T SS -T S1 = 500-93} = 407 [μs]) set the time (S40), and the timing of this time T _S2 is started. While the time T _S2 is being measured, the following series of processing up to S49 is performed. Further, due to the timer set in S40, after the time T _S2 elapses, the next timer interrupt is generated and the V _OFF ΔΣ A / D conversion in S52 is started. Next, the microcomputer 21 starts a voltage A / D conversion process (see FIG. 5, S22) (S41). At this time, the selection switch 22 has already been switched to the terminal 22a from which the detection output of the voltage sensor 13 is output to the A / D converter 24 in the process of S37. Next, the microcomputer 21 determines whether or not the voltage A / D conversion process started in S41 is completed (S42). When this determination is “Yes”, the operation of the A / D converter 24 is immediately performed. Stop (S43). Then, the selection switch 22 is switched to the terminal 22c to set the reference potential of the current sensor 14 to be input to the differential amplifier 23 (S44), the V _OFF flag is set (S45), and the next V Preparation for starting _OFF ΔΣ A / D conversion (see S52) is performed.

Next, the offset value (V _OFF value) already converted into the digital signal in S55 described later is removed from the detection output value (AD value) of the voltage sensor 13 converted into the digital signal in the processing of S41 and S42. The value (voltage value-offset) is set as a voltage value used for power calculation in a work data storage area (not shown) of the RAM built in the microcomputer 21 (S46). Next, the T _S2 flag set in S39 is cleared (S47). Subsequently, the current value set in the work data storage area in S38 is multiplied by the voltage value set in the work data storage area in S46 to obtain power. Calculate (S48). The power data calculated in S48 is subjected to the above-described gain adjustment processing (see FIGS. 5 and 24) and power accumulation processing (see FIGS. 5 and 25) to calculate the amount of power used and its absolute error. Is corrected. Next, based on the calculated power consumption, a pulse signal proportional to the power consumption is generated (S49), and the timer interrupt process is terminated. The generated pulse signal is output to the LED 15 as described above (see S26 in FIG. 5).

If the flag during V _OFF is set and the determination in S32 is “Yes”, the microcomputer 21 sets a time of T _SS (= 500 [μs]) in the timer (S51), and the time T _SS Start timing. While counting the time T _SS is performed, a series of processes from S57 described below is performed. Also, the timer setting of _S51, after a time lapse of _{T SS,} current Delta-Sigma A / D conversion step S34 in the next timer interrupt is generated is started. Next, the microcomputer 21 starts an offset A / D conversion process (see FIG. 5, S27) (S52). At this time, the selection switch 22 has already been switched to the terminal 22c from which the reference potential of the current sensor 14 is output to the A / D converter 24 in the process of S44. Next, the microcomputer 21 determines whether or not the offset A / D conversion process started in S52 is completed (S53). When this determination is “Yes”, the operation of the A / D converter 24 is immediately performed. Stop (S54). Subsequently, the offset value (V _OFF value) converted into the digital signal by the processing of S52 and S53 is set in the work data storage area of the RAM built in the microcomputer 21 (S55). Then, the selector switch 22 is switched to the terminal 22b to set the detection output of the current sensor 14 to the differential amplifier 23 (S56), and preparation for starting the next current ΔΣ A / D conversion (see S34) is made. Do. Next, the V _OFF flag set in S45 is cleared (S57), and the timer interrupt process is terminated.

  According to the electronic watt-hour meter according to the present embodiment, as described above, the detection output of the voltage sensor 13, the detection output of the current sensor 14, and the reference potential of these detection outputs are obtained by ΔΣ modulation in the A / D converter 24. The analog signal is converted to a digital signal (see FIGS. 5, S21, S22, S27, FIGS. 6, S34, S41, S52). Then, the reference potential converted into the digital signal is removed from the detection outputs of the voltage sensor 13 and the current sensor 14 converted into the digital signal by the calculation in the software processing unit 25 (FIGS. 6, S38, S46). The offset of the differential amplifier 23 and the A / D converter 24 is removed from the detection outputs of the voltage sensor 13 and the current sensor 14. The power consumption of the measurement target is calculated using the detection outputs of the voltage sensor 13 and the current sensor 14 from which the offset has been removed (see FIGS. 5, S23, S25, FIGS. 6, S48).

  The conversion from the analog signal to the digital signal in the A / D converter 24 is finely sampled by oversampling at the time of ΔΣ modulation and is performed with high resolution. Therefore, like the conventional electronic watt-hour meter, the A / D converter In order to compensate for the resolution of 24, there is no need to configure the amplification means in multiple stages. For this reason, the detection output of the current sensor 14 that requires a wide range of measurement accuracy guarantee can be measured with high accuracy over a wide range without configuring the amplification means in multiple stages. In addition, since it is not necessary to configure the amplification means in multiple stages, it is possible to determine the optimum number of amplifiers, measure the offset of the amplifiers in each stage, and measure the number of times measured, as in conventional electronic watt-hour meters. Need not be stored in the RAM for each stage of the amplifier. Further, it is not necessary to adjust the gain for each amplifier at each stage by the gain adjustment process, or to correct the resistance error for the amplifier at each stage by the gain error correction process. Accordingly, the amount of processing is reduced, the size of software in the software processing unit 25 is reduced, and the data storage capacity of the RAM built in the microcomputer 21 is also reduced, so that the memory size of the RAM required for the microcomputer 21 is reduced. It will be enough. Further, since the amount of processing is reduced, the operation clock frequency of the microcomputer 21 can be kept low, and the current consumption can be reduced. In addition, since it is not necessary to configure the amplification means in multiple stages, the scale of the analog circuit part is reduced, the board size of the electronic circuit board built in the electronic watt-hour meter is reduced, and the current consumption in the analog circuit part is also reduced. Can be small. Therefore, a small power source can be used as the power source of the electronic watt-hour meter. In addition, since the current consumption can be reduced and the fluctuation range of the output voltage from the power supply can be reduced, a circuit component for stabilizing the output voltage of the power supply, such as a conventional electronic watt-hour meter, is not required and the cost is reduced. Can be suppressed. In addition, since the operation clock frequency of the microcomputer 21 can be kept low, it is possible to reduce the influence of the radiated electric field intensity due to electromagnetic noise generated from the microcomputer 21 and to reduce the cost for countermeasures against noise resistance. As a result, the electronic watt-hour meter according to the present embodiment can sufficiently reduce the size and cost of the product.

Further, since the differential amplifier 23 is used as the amplification means, the bias voltage V _COM can be applied to the detection signals from the voltage sensor 13 and the current sensor 14 output from the differential amplifier 23. For this reason, even if the detection signals of the voltage sensor 13 and the current sensor 14 fluctuate in the negative voltage range, by applying the bias voltage V _COM , a signal that fluctuates in the positive range is obtained. The detection signal of the current sensor 14 can be amplified by the differential amplifier 23 and converted into a digital signal by the A / D converter 24. Further, since the differential amplifier 23 is used as the amplifying means, even if noise is applied to the inverting input terminal (−) and the non-inverting input terminal (+), it is canceled and the influence of the noise can be eliminated. , 14 can be amplified with high accuracy.

In the present embodiment, the current ΔΣ A / D start in FIG. 6, S 34, the voltage ΔΣ A / D start in S 41, and the V _OFF ΔΣ A / D start in _S 52 are T _S1 + T _S2 + T _SS (= 1000 [μs], respectively. ) At regular time intervals. When the conversion by the A / D converter 24 is completed for any of the detection outputs of the voltage sensor 13 and the current sensor 14 and the reference potential of the detection output, the selection switch 22 is immediately switched (FIGS. 6, S37, S44, At a later time, the signal input by the switched selection switch 22 is converted by the A / D converter 24 (see FIGS. 6, S34, S41, and S52). For this reason, each conversion by the A / D converter 24 is started in a state in which a signal input to the A / D converter 24 is stable after a certain amount of time has elapsed after the selection switch 22 is switched. . Therefore, the cause of the measurement error is removed, and each conversion by the A / D converter 24 is performed accurately.

  Further, in this embodiment, when the conversion of the detection output of the voltage sensor 13 and the current sensor 14 and the reference potential of the detection output is completed, the operation of the A / D converter 24 is immediately stopped (FIG. 6, S36, S43). , S54), preparation for starting the next conversion by the A / D converter 24 is performed. For this reason, each conversion by the A / D converter 24 is promptly executed from a state in which the A / D converter 24 is stopped. Therefore, when the conversion is continued without stopping the operation of the A / D converter 24, the start of the next conversion is delayed by waiting for the completion of the previous conversion operation of the A / D converter 24 at the start of conversion. Thus, although each conversion cannot be started at a constant cycle, according to the present embodiment, it can be performed at a constant cycle of 1000 (= 93 + 407 + 500) [μs] (FIG. 6, S34, S41, S52). reference). As a result, the measurement timing of the voltage and current of the measurement target and the offset measurement timing are performed at regular intervals, and the calculation process of the power consumption of the measurement target can be performed accurately.

  In the above embodiment, the case where the power calculation is performed by the equation (voltage value−offset) × (current value−offset) has been described (see FIGS. 5, S23, 6, S38, S46, and S48). The present invention is not limited to this. When the reference potential (0 [V]) of the detection output of the current sensor 14 is different from the reference potential (1.8 [V]) of the detection output of the voltage sensor 13 as in the above embodiment, software processing The calculation in the unit 25 is configured to remove (offset cancel) the reference potential of the detection output of the current sensor 14 converted by the A / D converter 24 from only the detection output of the current sensor 14 converted by the A / D converter 24. It is also possible.

  That is, in this configuration, the processing of FIG. 6 and S46 for removing the offset from the voltage value detected by the voltage sensor 13 is not performed, and the power is calculated by the equation (voltage value) × (current value−offset). Thus, even if only offset cancellation on the current side is performed and offset cancellation on the voltage side is not performed, the power consumption is accurately calculated as described below.

The voltage between the power supply terminals P0 and P1 in FIG. 4 is V · sinωt, the signal ground of the voltage sensor 13 is V _COM , the offset by the differential amplifier 23 and the A / D converter 24 is V _OFF , and the resistances of the resistors 13a, 13b, and 13c. When the values are R ₁ , R ₂ , R ₃ and α = R ₃ / (R ₁ + R ₂ + R ₃ ), respectively, the voltage measured by the voltage sensor 13 based on the voltage E _V · sinωt appearing at both ends of the resistor 13c. The A / D conversion result of
E _V・ sinωt + V _OFF
= (V · sinωt-V _COM ) x α + V _OFF
It becomes. In addition, since the voltage E _I · sinωt appears at both ends of the shunt resistor 14a due to the current I · sinωt flowing between the load terminals 1L and 1S, the A / D conversion result of the current measured by the current sensor 14 is
E _I · sinωt + V _OFF
It becomes. Accordingly, power is calculated as shown below.
Power = (Voltage value) x (Current value-Offset)
= (E _V · sinωt + V _OFF ) × (E _I · sinωt + V _OFF − V _OFF )
= {(V · sinωt - V COM) × α + V OFF} × (E I · sinωt + V OFF - V OFF)
= (Α · V · sinωt - α · V COM + V OFF) × E I · sinωt
= Α · V · E _I · sin ² ωt-E _I (α · V _COM -V _OFF ) sin ωt

In this case, the power value calculated from the detection outputs of the sensors 13 and 14 is composed of the DC component (α · V · E _I · sin ² ωt) of the first term, but the reference potential was not removed. The offset V _OFF of the differential amplifier 23 and the A / D converter 24 that appears in the detection output of the voltage sensor 13 becomes the AC component E _I (α · V _COM −V _OFF ) sinωt that swings positive and negative in the second term, 5 and 0 by the integration process in the power accumulation process of S25. Therefore, the effect of V _OFF is automatically removed during power calculation without performing offset cancellation on the voltage side. That is, when the α · _V = E V in the above formula, using the amount of power calculated during the time 0~t is calculated by the following equation. Here, it is converted to sin ² ωt = − (cos2ωt−1) / 2. In addition, since ω = 2πf = 2π / t, it is converted to t = 2π / ω.

Here, since E _V and E _I are peak values, the above-described electric power consumption is expressed by an effective value as follows.

In this way, the effect of V _OFF is automatically removed during power calculation without performing voltage-side offset cancellation.

  According to the above configuration, the reference potential converted by the A / D converter 24 is removed only for the detection output of the current sensor 14, and the differential amplifier 23 and the A / D are calculated from the calculated power consumption. The offset of the D converter 24 can be removed. For this reason, the calculation process of the power consumption of the measurement target is simplified, the software scale is further reduced, the memory size of the microcomputer 21 is further reduced, and the operation clock frequency is further reduced and consumed. The current can be further reduced.

Further, in the above configuration, as shown in FIGS. 3 and 4, the reference potential of the detection output of the current sensor 14 and the reference potential of the detection output of the voltage sensor 13 are 0 [V] and 1.8 [V], respectively. In the above description, the reference potential of the detection output of the current sensor 14 converted by the A / D converter 24 is removed from only the detection output of the current sensor 14 converted by the A / D converter 24. The invention is not limited to this. For example, the reference potential of the detection output of the current sensor 14 is the reference potential of the signal ground (for example, 1.8 [V]), and the reference potential of the detection output of the voltage sensor 13 is the reference potential V _SS of the circuit ground (for example, 0 [V]). and sets to), and connect the terminal 22c of the selecting switch 22 to the reference potential V _SS of the circuit ground, the reference potential of the detection output of the voltage sensor 13 is converted by the a / D converter 24, the a / D converter It is also possible to adopt a configuration in which only the detection output of the voltage sensor 13 converted at 24 is removed.

  As described above, the power value calculated from the detection outputs of the sensors 13 and 14 is composed of a DC component, but the differential amplifier 23 and the A / D converter appearing in the detection output from which the reference potential has not been removed. The offset 24 becomes an AC component that appears evenly in the positive and negative voltages, and is removed by the integration process (see S25 in FIG. 5) in the process of integrating the power consumption. Therefore, the removal of the reference potential converted by the A / D converter 24 is performed only for one of the detection output of the current sensor 14 or the detection output of the voltage sensor 13 and is different from the calculated power consumption. The offset of the dynamic amplifier 23 and the A / D converter 24 can be removed. For this reason, the calculation process of the power consumption of the measurement target is simplified, the software scale is further reduced, the memory size of the microcomputer 21 is further reduced, and the operation clock frequency is further reduced and consumed. The current can be further reduced.

  In the above embodiment, the case where one set of voltage sensor 13 and current sensor 14 is configured to be connected to the differential amplifier 23 via the selection switch 22 has been described. It is also possible to employ a multi-element instrument with a current sensor.

  FIG. 7 is a block diagram showing an outline of a circuit configuration of an electronic watt-hour meter including three sets of voltage sensors and current sensors. In the figure, the same or corresponding parts as in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted.

  In the multi-element electronic watt-hour meter according to this configuration, the voltage sensors 13A, 13B, 13C and the current sensors 14A, 14B, 14C are connected to the differential amplifier 23 built in the microcomputer 41 via the selection switch 42. ing. Each current sensor 14A-14C is comprised by the current transformer or the Rogowski coil, and the electric power calculation by the software process part 25a is performed for every element of each set. Except for these points, the configuration is the same as that of the above embodiment. Even in this configuration, the same operation and effect as the electronic watt-hour meter in the above embodiment can be obtained.

  In the above embodiment, the case where the detection outputs of both the voltage sensor 13 and the current sensor 14 are amplified by the differential amplifier 23 has been described, but the present invention is not limited to this. The voltage to be measured does not have a wide measurement accuracy guarantee range compared to the current to be measured, and the detection signal has a larger amplitude than the current to be measured. For this reason, as shown in FIG. 8, the voltage sensor 13 can be directly connected to the A / D converter 24 without using the differential amplifier 23. In the figure, the same or corresponding parts as in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted.

  In this configuration, the voltage sensor 13 is connected to the A / D converter 24 without using the differential amplifier 23 using the two selection switches 22 and 52, and the processing in the software processing unit 25b is performed according to these configurations. Except for the differences, the configuration is the same as that of the above embodiment.

  When the detection output of the voltage sensor 13 is input to the A / D converter 24 and converted into a digital signal, the selection switches 22 and 52 are respectively switched to terminals 22a and 52a as shown in FIG. 13 detection outputs are directly input to the A / D converter 24 via the selection switches 22 and 52. When the detection output of the current sensor 14 is input to the A / D converter 24 and converted into a digital signal, the selection switches 22 and 52 are switched to the terminals 22b and 52b, and the detection output of the current sensor 14 is The signal is amplified by the differential amplifier 23 and then input to the A / D converter 24. When the reference potential of the current sensor 14 is input to the A / D converter 24 and converted into a digital signal, the selection switches 22 and 52 are switched to the terminals 22c and 52b, respectively, and the reference potential of the current sensor 14 is changed. Is differentially amplified by the differential amplifier 23 and then input to the A / D converter 24. Therefore, also in this configuration, the same operational effects as the electronic watt-hour meter in the above embodiment can be obtained.

  In the above embodiment, the case where the differential amplifier 23 is built in the stage preceding the A / D converter 24 inside the microcomputer 21 has been described, but the present invention is not limited to this. The differential amplifier 23 may be built in the microcomputer 21 or may be provided outside the microcomputer 21.

  FIG. 9 is a block diagram showing an outline of a circuit configuration of an electronic watthour meter in which the differential amplifier 23 is provided outside the microcomputer 21. In the figure, the same or corresponding parts as in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted.

  The microcomputer 61 in this configuration is a general-purpose microcomputer including an amplifier 63, and the amplifier 63 is connected to the A / D converter 24 via the selection switch 62. The current sensor 14 is connected to the selection switch 22 inside the microcomputer 61 via a selection switch 65 and a differential amplifier 64 provided outside the microcomputer 61. Except for these points and the point that the processing in the software processing unit 25c differs according to these configurations, the configuration is the same as that of the above embodiment.

  When the detection output of the voltage sensor 13 is input to the A / D converter 24 and converted into a digital signal, the selection switches 22 and 62 are switched to terminals 22a and 62a, respectively, as shown in FIG. The detection output of the voltage sensor 13 is directly input to the A / D converter 24 via the selection switches 22 and 62. In addition, when the detection output of the current sensor 14 is input to the A / D converter 24 and converted into a digital signal, the selection switches 65, 22, and 62 are switched to the terminals 65a, 22b, and 62b, respectively. The detection output of the current sensor 14 is amplified by the differential amplifier 23 and the amplifier 63 and then input to the A / D converter 24. When the reference potential of the current sensor 14 is input to the A / D converter 24 and converted into a digital signal, the selection switches 65, 22, and 62 are switched to the terminals 65b, 22c, and 62b, respectively. The reference potential of the current sensor 14 is amplified by the differential amplifier 23 and the amplifier 63 and then input to the A / D converter 24. Therefore, also in this configuration, the same operational effects as the electronic watt-hour meter in the above embodiment can be obtained.

  In the above-described embodiment, the case where the absolute error of the used power amount is corrected by multiplying the instantaneous power by a predetermined value in the gain adjustment processing (see FIG. 5, S24) has been described, but the present invention is limited to this. is not.

  FIG. 10 is a diagram illustrating the relationship between the accumulated power consumption (see FIG. 5, S25) and the pulse signal output from the software processing unit 25 to the LED 15. (A) in the figure shows the amount of power used cumulatively added over time, and (b) in the figure shows the output when the amount of power used shown in (a) reaches a certain value (threshold). The output timing of the pulse signal to be performed is shown respectively. In FIGS. 4A and 4B, the horizontal axis represents the time axis.

When it is not necessary to correct the absolute error of the amount of power used, the pulse output threshold is set to α as shown by the solid line in FIG. When the used power amount cumulatively added in the software processing unit 25 reaches α, a pulse signal is output as shown in FIG. 5B, and the cumulatively used power amount is reset to “0”. Similarly, a pulse signal is output every time the amount of power used reaches the threshold value α after the time t has elapsed. The threshold value α is adjusted so that the time t becomes constant and the pulse signal frequency becomes, for example, 6.4 [Hz] when the rated voltage and the rated current are applied to the electronic watt-hour meter. However, the rate of increase in the amount of used electric power that is actually cumulatively added depends on the sensitivity and internal resistance values of the sensors 13 and 14, the value of the reference voltage V _ref applied to the A / D converter 24, and the differential amplifier 23. Depending on the accuracy of each component, such as gain error, it changes as it becomes smaller or larger like a sawtooth waveform shown by a dotted line or a one-dot chain line in FIG. When the rate of increase changes in this way, the timing at which the amount of power used reaches the threshold value α also changes, so adjusting the pulse output threshold according to the amount of power used will result in an absolute error in the amount of power used. Correct. Specifically, as shown by the dotted line in FIG. 5A, when the rate of increase in the amount of power used is small, the threshold value is changed from α to β (α> β). Further, when the increase rate of the power consumption increases as shown by the alternate long and short dash line, the threshold value is changed from α to γ (α <γ). In this way, by adjusting the threshold value, the timing of pulse output is adjusted, so that the pulse signal is output according to the actual power consumption, and the absolute error of the calculated power consumption is It is corrected.

  The absolute error of the calculated power consumption is corrected by multiplying the amplification factor of the differential amplifier 23 by a predetermined factor by adjusting the gain in FIG. 5 and S24. It is also corrected by adjusting. For this reason, the freedom degree of design of an electronic watt-hour meter increases.

  Moreover, although the case where the differential amplifier 23 is used to amplify the detection signals and reference potentials of the sensors 13 and 14 has been described in the above embodiment, the present invention is not limited to this. For example, in the electronic watt-hour meter shown in FIGS. 3 and 4, the detection signals and reference potentials of the sensors 13 and 14 are amplified by the input capacitor ratio of the A / D converter 24 instead of the differential amplifier 23. Also good. FIG. 11 is a circuit diagram showing a switched capacitor integrating circuit configured inside the A / D converter 24.

The A / D converter 24 includes an operational amplifier 71 and a comparator 72 connected to the output side thereof. The input side and the output side of the operational amplifier 71 are feedback-connected by hold capacitors 79 and 80. On the input side of the operational amplifier 71, sampling capacitors 73 and 74 having a capacity Ci for sampling an input signal and feedback capacitors 75 and 76 having a capacity Cr for feedback are connected. The change-over switches 77 and 78 are connected to the feedback capacitors 75 and 76, respectively. These switches 77 and 78 are switched by the output of the comparator 72, and the reference voltage + V _ref or −V _ref is applied to the feedback capacitors 75 and 76. Is done. The sampling capacitor 73 is connected to the selection switch 22 described above, and the detection outputs and reference potentials of the sensors 13 and 14 are input to the sampling capacitor 73 in accordance with the switching of the selection switch 22. The sampling capacitor 74 is connected to the reference potential of the current sensor 14, and a reference potential of 0 [V] is input to the sampling capacitor 74.

  In the above configuration, the signals input to the sampling capacitors 73 and 74 are differentially amplified and ΔΣ modulated by the amplification factor of the input capacitor ratio Ci / Cr, respectively, and converted from an analog signal to a digital signal. Therefore, also in this configuration, the same effects as those in the above embodiment are achieved.

  Further, in the above embodiment, the case where the voltage sensor 13 is configured by the voltage dividing resistors 13a to 13c and the current sensor 14 is configured by the shunt resistor 14a has been described, but the types of the voltage sensor 13 and the current sensor 14 are as follows. It can be changed as appropriate. For example, the current sensor 14 may be a current transformer (CT), a Rogowski coil, or the like shown in FIG.

  In the above embodiment, the A / D converter 24 performs A / D conversion in the order of the detection output of the current sensor 14, the detection output of the voltage sensor 13, and the reference potential of the current sensor 14 by switching the selection switch 22. Although the case where the processing is performed has been described (see FIGS. 5, S21, S22, and S27), the order of the A / D conversion processing for these signals can be changed as appropriate.

In the above embodiment, the case where the reference voltage V _ref applied to the A / D converter 24 is prepared separately from the operating voltage V _{DD of the} microcomputer 21 has been described, but the present invention is not limited to this. Absent. For example, A / D reference voltage _{V ref} of the converter 24 is set to the operating voltage _{V DD} and the same potential of the microcomputer 21, a power source for supplying a reference voltage _{V ref} to the A / D converter 24, the operating voltage _{V DD} to the microcomputer 21 Can be shared with the power supply for supplying the power. According to this configuration, it is not necessary to separately prepare a power source for supplying the reference voltage V _ref to the A / D converter 24, and further downsizing and cost reduction of the product can be achieved.

In the timer interrupt process of the above embodiment, the times T _S1 , T _S2 , and T _SS are set to 93 [μs], 407 [μs], and 500 [μs], respectively, and the bias voltages V _COM , The operation voltage V _DD of the microcomputer 21 has been described as 1.8 [V] and 3.6 [V], respectively, but T _S1 , T _S2 , T _SS and V _COM , V _DD are limited to these values. It is not a thing and can be changed suitably.

  In the above embodiment, the case where two resistors 13a and 13b are connected in series between the power supply terminal P0 and the resistor 13c in order to improve the withstand voltage performance of the voltage sensor 13 has been described. One resistor may be connected between P0 and the resistor 13c, and the number thereof can be changed as appropriate.

  In the above embodiment, the case where the present invention is applied to a single-phase two-wire electronic watt-hour meter has been described. However, based on the digital signal converted by the A / D conversion means, the power consumption of the measurement target It is also possible to apply to various electronic watt-hour meters such as single-phase three-wire type and three-phase three-wire type. Even when the present invention is applied to such various electronic watt-hour meters, the same effects as those of the above embodiment can be obtained.

[0005]
A current sensor for detecting a current to be measured;
A selection switch for sequentially repeating each of the detection output of the voltage sensor, the detection output of the current sensor, and the reference potential of this detection output, and alternatively selecting and outputting each;
Differential amplification means for differentially amplifying the potential of the output signal of the selection switch and the reference potential;
A / D conversion means for converting an analog signal output from the differential amplification means into a digital signal, and calculation means for calculating the power consumption of the measurement target based on the digital signal output from the A / D conversion means An arithmetic processing unit with built-in,
An electronic watt-hour meter comprising:
The A / D conversion means performs A / D conversion by ΔΣ modulation each time the selection switch is switched, stops operation after the conversion is completed, and
The computing means is an A when the selection switch selects the reference potential from the output of the A / D conversion means when the selection switch selects at least one of the detection output of the voltage sensor and the detection output of the current sensor. Based on the digital signal from which the output of the / D conversion means is removed, the power consumption of the measurement target is calculated.
[0014]
According to this configuration, the detection output of the voltage sensor, the detection output of the current sensor, and the reference potential of these detection outputs are converted from an analog signal to a digital signal by ΔΣ modulation in the A / D conversion means. By removing the reference potential converted into the digital signal by the calculating means from at least one of the detection outputs of the voltage sensor and the current sensor converted into the digital signal, the detection output from the voltage sensor and the current sensor is removed. The offset of the differential amplification means and the A / D conversion means is removed. The power consumption of the measurement target is calculated using the detection outputs of the voltage sensor and current sensor from which the offset has been removed.
[0015]
The conversion from an analog signal to a digital signal in the A / D conversion means is finely sampled by oversampling at the time of ΔΣ modulation and performed with a high resolution, so that A / D conversion is performed as in a conventional electronic watt-hour meter. There is no need to configure the amplification means in multiple stages in order to supplement the resolution of the means. For this reason, the detection output of a current sensor that requires a wide range of guaranteed measurement accuracy can be distributed over a wide range without the need to configure amplification means in multiple stages.

[0006]
Therefore, it becomes possible to measure with high accuracy. In addition, since it is not necessary to configure the amplification means in multiple stages, it is possible to determine the optimum number of amplifiers, measure the offset of the amplifiers in each stage, and measure the number of times measured, as in conventional electronic watt-hour meters. Need not be stored for each stage of the amplifier. Further, it is not necessary to adjust the gain for each amplifier at each stage by the gain adjustment process, or to correct the resistance error for the amplifier at each stage by the gain error correction process. Accordingly, the amount of processing is reduced, the size of software is reduced, and the data storage capacity is also reduced, so that the memory size required for the arithmetic processing unit can be reduced. In addition, since the amount of processing is reduced, the operation clock frequency of the arithmetic processing unit can be kept low, and the current consumption can be reduced. Further, since it is not necessary to configure the amplifying means in multiple stages, the scale of the analog circuit portion can be reduced, the substrate size can be reduced, and the current consumption in the analog circuit portion can be reduced. Therefore, a small power source can be used as the power source of the electronic watt-hour meter. In addition, since the current consumption can be reduced and the fluctuation range of the output voltage from the power supply can be reduced, a circuit component for stabilizing the output voltage of the power supply, such as a conventional electronic watt-hour meter, is not required and the cost is reduced. Can be suppressed. In addition, since the operation clock frequency of the arithmetic processing device can be kept low, the influence of the radiation electric field intensity caused by electromagnetic noise generated from the arithmetic processing device can be reduced, and the cost for measures against noise resistance can be suppressed. As a result, the electronic watt-hour meter according to the present invention can sufficiently reduce the size and cost of the product.
[0016]
Further, since the differential amplification means is used as the amplification means, it is possible to apply a bias voltage to at least the detection signal output from the amplification means from the current sensor. For this reason, even if the detection signal of the current sensor swings in the negative range, it is converted into a signal that fluctuates in the positive range by applying a bias voltage, and the detection signal of the current sensor is amplified by the amplification means. It can be converted into a digital signal by the / D conversion means. Further, since the differential amplifying means is used as the amplifying means, even if noise is applied to the input terminal, it is canceled and the influence of the noise can be eliminated, so that the input signal can be amplified with high accuracy.
Further, when the conversion of the detection output of the voltage sensor and the current sensor and the reference potential of the detection output is completed, the operation of the A / D conversion unit is stopped and preparation for starting the next conversion by the A / D conversion unit is performed. . For this reason, each conversion by the A / D conversion means is promptly executed from a state where the A / D conversion means is stopped. Therefore, when the conversion is continuously performed without stopping the operation of the A / D conversion means, the start of the next conversion is delayed by waiting for the completion of the conversion operation before the A / D conversion means at the start of conversion. Thus, although each conversion cannot be started at a constant cycle, this configuration can be performed at a constant cycle. As a result, the measurement timing of the voltage and current of the measurement target and the offset measurement timing are performed at regular intervals, and the calculation process of the power consumption of the measurement target can be performed accurately.
[0017]
Further, according to the present invention, the arithmetic means corrects the absolute error of the used power amount by multiplying the used power amount by a predetermined value or by adjusting the threshold value of the pulse output corresponding to the used power amount. It is characterized by.
[0018]
According to this configuration, the absolute error of the calculated power consumption is corrected by multiplying the calculated power consumption by a predetermined amount according to the amplification factor of the amplification means. In addition, by adjusting the pulse output threshold according to the calculated power consumption, the pulse output timing is adjusted, and the pulse is output according to the actual power consumption. The absolute error of the used electric energy is corrected. Therefore, it is possible to correct the absolute error of the calculated power consumption by multiplying it by a predetermined value or by adjusting the threshold value of the pulse output. Increase.
[0019]
The present invention also provides:
The computing means is
When the reference potential of the detection output of the voltage sensor is set to a potential different from the reference potential of the detection output of the current sensor,
A / D when the selection switch selects the reference potential only from the output of the A / D conversion means when the selection switch selects either the detection output of the voltage sensor or the detection output of the current sensor. Based on the digital signal from which the output of the conversion means is removed, the power consumption of the measurement target is calculated.
[0020]
According to this configuration, the power value calculated from the detection output of each sensor is composed of a direct current component, but the amplifying means and A / A appearing in the detection output on which the reference potential has not been removed.

[0007]
The offset of the D conversion means becomes an AC component that appears evenly in the positive and negative of the voltage, and is removed by the integration process in the process of integrating the amount of power used. Therefore, the removal of the reference potential converted by the A / D conversion means is performed only for either the detection output of the current sensor or the detection output of the voltage sensor, and the amplification means and The offset of the A / D conversion means can be removed. For this reason, the calculation process of the power consumption of the measurement target is simplified, the software scale is further reduced, the memory size of the arithmetic processing device is further reduced, and the operation clock frequency is further reduced. The current consumption can be further reduced.
[0021]
Further, according to the present invention, the arithmetic processing unit switches the selection switch immediately after the conversion by the A / D conversion means for any of the detection output of the voltage sensor and the current sensor and the reference potential of the detection output is completed. After performing the above, the next conversion by the A / D conversion means is performed after a while.
[0022]
According to this configuration, when the conversion by the A / D conversion unit with respect to either the detection output of the voltage sensor and the current sensor and the reference potential of the detection output is completed, the selection switch is immediately switched, and after that, after a period of time, Conversion by the A / D conversion means is performed on the signal input by the switched selection switch. For this reason, each conversion by the A / D conversion means starts after a certain amount of time has elapsed after the selection switch is switched and the signal input to the A / D conversion means is stable. Therefore, the cause of the measurement error is removed, and each conversion by the A / D conversion means is performed accurately.

[0008]
[0023]
[0024]
[0025]
Further, the present invention is characterized in that the reference voltage of the A / D conversion means is set to the same potential as the operating voltage of the arithmetic processing unit.
[0026]
According to this configuration, the power source that supplies the reference voltage to the A / D converter and the power source that supplies the operating voltage to the arithmetic processing unit can be shared. For this reason, it is not necessary to separately prepare a power source for supplying the reference voltage to the A / D conversion means, and further downsizing and cost reduction of the product can be achieved.
[0027]
According to the present invention, as described above, it is possible to provide an electronic watt-hour meter that can sufficiently reduce the size and cost of a product.
Brief Description of Drawings

Claims (6)

A voltage sensor for detecting a voltage to be measured; and
A current sensor for detecting a current to be measured;
A selection switch that selectively selects and outputs either the detection output of the voltage sensor or the current sensor or a reference potential of the detection output;
Amplifying means for amplifying at least the detection output of the current sensor;
A / D conversion means for converting the detection output of the voltage sensor and the current sensor output by the selection switch and the reference potential from an analog signal to a digital signal, and the digital signal converted by the A / D conversion means In an electronic watt-hour meter comprising an arithmetic processing unit with a built-in arithmetic means for calculating the power consumption of a measurement target based on
The amplifying means comprises differential amplifying means for differentially amplifying an input signal,
The A / D conversion means converts an input signal from an analog signal to a digital signal by ΔΣ modulation,
The calculation means removes the reference potential converted by the A / D conversion means from the detection output of the voltage sensor and current sensor converted by the A / D conversion means, respectively, and uses power to be measured. An electronic watt-hour meter characterized by calculating a quantity.   The arithmetic means corrects an absolute error of the used power amount by multiplying the used power amount by a predetermined value or by adjusting a threshold value of a pulse output corresponding to the used power amount. The electronic watt-hour meter according to claim 1.   The calculation means converts the reference potential converted by the A / D conversion means into the current when the reference potential of the detection output of the current sensor is different from the reference potential of the detection output of the voltage sensor. The electronic watt-hour meter according to claim 1 or 2, wherein the electronic watt-hour meter is removed from only one of the detection output of the sensor and the detection output of the voltage sensor.   The arithmetic processing unit switches the selection switch immediately after the completion of conversion by the A / D conversion unit with respect to any of the detection output of the voltage sensor and the current sensor and the reference potential of the detection output and performs the next selection. The electronic watt-hour meter according to any one of claims 1 to 3, wherein after the operation is performed, the next conversion by the A / D conversion means is performed at a time interval.   The arithmetic processing unit stops the operation of the A / D conversion unit immediately after the completion of each conversion by the A / D conversion unit, and prepares to start the next conversion by the A / D conversion unit. The electronic watt-hour meter according to claim 4.   The electronic watt-hour meter according to any one of claims 1 to 5, wherein a reference voltage of the A / D conversion means is set to the same potential as an operating voltage of the arithmetic processing unit. .

Images