JP2000338150A - Watthour meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure accurate electric energy while preventing an electric energy data from being lost at the time of generation of electric power interruption. SOLUTION: An electric energy data is written into an EEPROM 22 by an operation circuit 21 when electric power interruption of an alternating current power source AC is detected by a power interruption power restoration detecting circuit 1. The electric energy data found by the circuit 21 is written thereby into the EEPROM 22 before the writing for writing the electric energy data by the operation circuit 21 gets impossible actually after the interruption is detected. As the result, the electric energy data is prevented from being lost at the time of generation of power interruption, and the accurate electric energy is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a watt-hour meter which is attached to a power supply path to a load on an AC wiring path and displays the amount of power supplied to the load.

[0002]

2. Description of the Related Art As a watt-hour meter of this type, there has recently been provided a watt-hour meter which obtains a power amount by multiplying a voltage value and a current value of an AC wiring line and integrating over time (that is, integration). In this type of watt-hour meter, a voltage value between the probes is obtained by connecting a probe to each line of the AC wiring path, and a current passing through the AC wiring path is obtained by using a current sensor. As the current sensor, a current transformer in which a winding for detection is wound around an annular core and a part of the annular core can be opened and closed is widely used. This type of current sensor closes the annular core after opening the annular core and introducing the AC wiring path into the annular core,
The AC wiring path is constrained so as to pass through the annular core, and in this sense, it is called a clamp sensor.

Since the instantaneous values of the voltage value and the current value can be obtained with the probe and the current sensor, the amount of power can be obtained by multiplying the voltage value and the current value by an arithmetic means using a microcomputer and integrating over time. . In addition, the watt hour meter is provided with a display means for displaying the obtained electric energy. As described above, this kind of watt hour meter uses the arithmetic means and the display means. A power supply is required to supply power to the power supply, and in general, a battery is built in the watt-hour meter, or power is supplied from an AC wiring line via an adapter provided separately from the watt-hour meter. .

[0004] However, in the case where the battery is built-in as described above, maintenance for managing the life of the battery and appropriately replacing the battery is required. In the case where a separate adapter is provided, a probe to the AC wiring path is required. In addition, the connection of the adapter is required in addition to the connection, and the connection work is troublesome.

Accordingly, the present applicant has already proposed a watt-hour meter provided with a power supply circuit for generating an internal power supply using power taken from an AC wiring path via a probe. In a watt-hour meter equipped with such a power supply circuit, it is possible to supply internal power only by connecting a probe necessary for detecting a voltage value, which not only simplifies connection work but also reduces the internal power supply. Since the battery is obtained from the AC wiring path, there is no need to incorporate a battery, and there is an advantage that battery replacement is unnecessary and maintenance becomes easy.

[0006]

In the above-described conventional watt-hour meter, the data of the power amount obtained by the arithmetic means is written in the EEPROM at predetermined time intervals, and the data is stored in the EEPROM until the next data is written. If a power failure occurs within a certain time, there is a problem that data that was not written before the power failure occurred is lost without being stored at all.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a power supply capable of measuring an accurate power amount without losing power amount data when a power failure occurs. To provide a meter.

[0008]

According to a first aspect of the present invention, there is provided a probe connected to an AC wiring path, a current sensor for detecting a current passing through the AC wiring path, and
Calculating means for calculating the amount of power passing through the AC wiring path using the voltage value and the current value of the AC wiring path detected by the probe and the current sensor; and the data of the power amount obtained by the calculating means is changed every predetermined time. EEPROM to be written
A display means for displaying data of the amount of power written in the EEPROM; and a power supply for generating an internal power supply including a power supply for the calculation means and the display means using the power taken from the AC wiring path via the probe. And a power meter, the power supply circuit outputs an intermediate output such that the power is reduced at a predetermined rate of time change when the power supply from the AC wiring path is stopped using the power taken from the AC wiring path. Means for generating the internal power from the intermediate output, wherein the level of the intermediate output is at least higher than a limit value at which the arithmetic means can write power value data to the EEPROM. When a power failure is detected and the intermediate output level exceeds the threshold when the intermediate output level falls below the threshold as compared with the threshold set to To provide a power failure, power recovery detection means for detecting a power recovery, the calculating means, the power amount data when a power failure is detected by the power failure, power recovery detection unit EE
Writing the data of the electric energy obtained by the arithmetic means to the EEPROM before the data writing by the arithmetic means becomes impossible after the power failure is detected by the power failure / recovery detecting means; Therefore, it is possible to accurately measure the power amount without losing the data of the power amount when a power failure occurs.

According to a second aspect of the present invention, in the first aspect of the present invention, the arithmetic means continues the arithmetic processing for calculating the electric energy even if the power failure is detected by the power failure / recovery detection means. In addition to the effect of the first aspect, the measurement of the electric energy can be continued even when an instantaneous power failure occurs.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the power supply circuit stops the power supply from the power supply circuit, and the power failure / recovery detection means detects a power recovery. In addition to the operation of the invention according to claim 1 or 2, the arithmetic processing of the electric energy is not restarted after the power is restored from the power outage. Can be determined.

According to a fourth aspect of the present invention, in the first or second aspect of the present invention, the arithmetic means performs an arithmetic processing for calculating an amount of power when power recovery is detected after power supply from the power supply circuit is stopped. 3. The method according to claim 1, wherein the processing is restarted.
In addition to the operation of the invention, it is possible to automatically restart the measurement of the electric energy after the power is restored without any manual operation, and there is no possibility that the electric energy data is lost due to the operation of restarting the measurement. .

[0012]

(Embodiment 1) Embodiment 1 of the present invention will be described with reference to FIGS. In the following description, as shown in FIG. 2, three lines L connecting an AC power supply AC and a load LD, such as a single-phase three-wire system or a three-phase three-wire system, are used.
An AC wiring path L including 1 to L3 is assumed. In the present embodiment, three probes P1 to P3 that are connected to the lines L1 to L3 of the AC wiring path L and detect line voltage, and two lines L1 and L3 of the AC wiring path L are It has two current sensors CT1 and CT2 penetrated. Each of the current sensors CT1 and CT2 uses a current transformer having an openable and closable annular core as described in the conventional example.

As shown in FIG. 1, the probes P1 to P3 constitute a part of the voltage input section 11, and the current sensors CT1 and C3
T2 constitutes a part of the current input unit 12. Voltage input 1
1 and a current input unit 12 are provided with a filter for removing a frequency component unnecessary for detecting power supplied from the AC power supply AC to the load LD through the AC wiring path L, and a gain set according to the input value. And a current-voltage conversion circuit are provided as appropriate. The voltage value and the current value detected by the voltage input unit 11 and the current input unit 12, respectively, are input to the preprocessing circuit 13 before performing the calculation for the electric energy, and the polarity and the absolute value of the voltage value and the current value are determined. Desired. That is, the preprocessing circuit 13 includes polarity detection circuits 14a and 14b for detecting the polarities of the voltages of the other probes P1 and P3 when the voltage applied to the probe P2 is set to the reference potential (0 V). Rectifier circuits 15a and 15b for full-wave rectifying the voltage are provided. The pre-processing circuit 13 includes a polarity detection circuit 1 that detects the polarities of the currents detected by the two current sensors CT1 and CT2, respectively.
6a and 16b, and rectifier circuits 17a and 17b for full-wave rectification of both currents.

Each of the polarity detection circuits 14a, 14b, 16a,
16b is configured to detect a zero-cross point of a voltage waveform or a current waveform, and generate a binary signal corresponding to the polarity between adjacent zero-cross points. Therefore, the probes P1 to P3 or the current sensors CT1,
If the AC voltage or AC current detected by CT2 is, for example, a sine wave as shown in FIG. 3 (a), the output of each polarity detection circuit 14a, 14b, 16a, 16b is shown in FIG.
A rectangular wave signal as shown in FIG. In addition, the rectifier circuit 15
The outputs of a, 15b, 17a, and 17b have a pulsating waveform as shown in FIG.

The polarity detection circuits 14a, 14b, 16a, 1
The polarity of the AC voltage or the AC current detected by 6b and the absolute value of the AC voltage or the AC current detected by the rectifier circuits 15a, 15b, 17a and 17b are each provided with an arithmetic circuit 21 having a microcomputer as a main component. Is input to the calculating means 20. The arithmetic circuit 21 includes the rectifier circuits 15
A, 15b, 17a, and 17b have the function of A / D converting the output, and the digital value after A / D conversion has a code corresponding to the polarity detected by the polarity detection circuits 14a, 14b, 16a, 16b. Will be added.

Here, since the target of the A / D conversion is a pulsating flow waveform, the AC waveform (see FIG. 3A) can be converted into an A / D converter without changing the dynamic range of the A / D converter.
As compared with the case where the / D conversion is performed, the step width per bit can be reduced, and as a result, the resolution is increased. The thus obtained AC voltage and AC instantaneous value are multiplied by a signed digital value corresponding to the instantaneous value.
Here, the sampling cycle at the time of A / D conversion is set appropriately (to a cycle sufficiently shorter than the cycle of the AC power supply AC), and after the sum of the multiplied values for one cycle of the AC power supply AC is obtained, When divided by the number of samplings, this value corresponds to the active power (average power). Further, the power amount in the desired period is obtained by converting the integrated value of the active power per unit time into an average value per hour and adding the average value.

FIG. 4 shows a procedure for calculating the power in the arithmetic circuit 21. That is, the outputs of the rectifier circuits 15a and 15b corresponding to the absolute value of the AC voltage are converted to A / D
After the conversion (S1), the code detected by the polarity detection circuits 14a and 14b is input (S2), and a code is added to the digital value obtained by the A / D conversion (S3). Also,
After the A / D conversion of the outputs of the rectifier circuits 17a and 17b corresponding to the absolute value of the alternating current (S4), the polarity detection circuit 16
a, the code detected by 16b is input (S5), and A
A sign is added to the digital value obtained by the / D conversion (S6). When the values V1 and I1 corresponding to the voltage value and the current value of the AC power supply are obtained in steps S3 and S6 in this way, the calculating means 10 instantaneously calculates the multiplication value (= V1 × I1) of these values V1 and I1. (S
7). The obtained instantaneous values W1 are sequentially added (S8). After obtaining an added value W0 of the instantaneous value W1 for one cycle of the voltage waveform of the AC power supply AC (S9), the added value W0 is divided by the number of samples N. (S10). The division value thus obtained corresponds to active power (average power).

The electric energy is often obtained within a fixed period, such as weekly, daily, or hourly, and these periods are measured by a clock unit 23 provided in the arithmetic means 20. That is, when the operation is started, a signal indicating a break of week, day, and time is input to the arithmetic circuit 21 by the clock unit 23, and when this signal is input to the arithmetic circuit 21, the power amount within the corresponding period is reduced. Data is written to the EEPROM 22, and old and unnecessary data is erased from the EEPROM 22. The clock unit 23 also has a function of measuring the elapsed time from the start of the measurement of the electric energy. The arithmetic means 20 includes a liquid crystal display 31 and a keypad 32 as display means.
Is connected.

By the way, the preprocessing circuit 13, the arithmetic means 2
0, the internal power supply of the display operation unit 30 and the like is a probe P1,
It is supplied from the AC wiring path L through P2. That is,
A power supply circuit 40 is connected to the probes P1 and P2, and a constant DC voltage is output from the power supply circuit 40 and used as an internal power supply. This power supply circuit 40 is, as shown in FIG.
Is connected to the voltage input unit 11 via a power switch SW (not shown), and the AC voltage input through the high-frequency blocking filter circuit F is subjected to full-wave rectification by a rectifier DB composed of a diode bridge, and thereafter, by a smoothing capacitor C1. Smooth. A series circuit of a switching element Q1 composed of a MOSFET and a resistor R1 for current detection is connected between both ends of the smoothing capacitor C1 via a primary winding of a transformer T1. Therefore, if the switching element Q1 is turned on / off at a high frequency, an AC output can be obtained on the secondary side of the transformer T1, and a DC voltage is generated by rectifying the AC output on the secondary side. . This type of circuit configuration is known as a DC-DC converter.

The secondary output of the transformer T1 is taken out of three secondary windings, and one secondary winding is provided with a center tap. That is, in the pre-processing circuit 13, the polarity detection circuits 13a, 13b, 15a, and 15b are provided, and this type of circuit is generally configured using an operational amplifier. Since a positive / negative bipolar power supply (for example, ± 12 V) is required, the secondary winding of the portion for supplying power to the preprocessing circuit 13 is provided with a center tap so that a positive / negative bipolar power supply can be easily configured.
The power supply to the arithmetic means 20 and the display / operation unit 30 is set to, for example, 5V. Preprocessing circuit 13, arithmetic means 20,
Since the display operation unit 30 requires a constant DC voltage,
Rectifier diodes D2 to D2 are provided on the secondary side of the transformer T1.
4 and the smoothing capacitors C2 to C4 as well as the constant voltage circuits 41a to 41c for stabilizing the voltage across the capacitors C2 to C4 to stabilize the supply voltage.

The remaining secondary winding provided in the transformer T1 is
The control circuit CN is provided to supply power to a control circuit CN for turning on and off the switching element Q1, and the control circuit CN is provided with a control power supply circuit 42 to which power is supplied from the transformer T1. However, since power cannot be supplied to the control power supply circuit 42 through the transformer T1 before the on / off of the switching element Q1 is started, power is supplied from the smoothing capacitor C1 to the control power supply circuit 42 through the resistor R2 and the switch SW at startup. It can be supplied. The switch SW is turned on only at the time of startup by the switch control circuit SC, and is turned off when power is supplied through the transformer T1. This prevents useless power from being consumed by the resistor R2 during normal operation. The control circuit CN basically includes an oscillation circuit 43 that generates a pulse signal that determines the on / off timing of the switching element Q1, and a drive circuit 44 that generates a signal that allows the switching element Q1 to be turned on and off from the output of the oscillation circuit 43. Further, a feedback circuit 45 for keeping the input voltage to the constant voltage circuit 41c substantially constant, and a current flowing through the switching element Q1 are monitored by a voltage across the resistor R1 to monitor the switching element Q1.
And a current limiter circuit 46 for limiting the current flowing to the control circuit CN. The feedback circuit 45 includes a voltage detection circuit 47 for monitoring the input voltage of the constant voltage circuit 41c.
Is input via the photocoupler PC. That is, the on / off timing of the switching element Q1 is feedback-controlled so that the input voltage to the constant voltage circuit 41c is kept substantially constant.

As described above, the power is supplied to the power supply circuit 40 for generating the internal power from the AC wiring line L through the probes P1 and P2. It is not necessary to separately provide an adapter, and the connection work to the AC wiring path L is facilitated. Moreover, in order to stabilize the secondary output of the transformer T1, a circuit configuration for feedback-controlling the ON / OFF timing of the switching element Q1 is employed, and furthermore, since the constant voltage circuits 41a to 41c are provided, the voltage of the AC power supply AC is reduced. Constant voltage circuits 41a to 41
The output voltage of c is maintained at a constant voltage, so that even if the specifications of the AC power supply AC are different, it is possible to cope with the same configuration.

Incidentally, the AC power supply AC may cause a power failure, and if the power supply to the clock unit 23 is stopped when the power failure occurs, it is necessary to reset the time of the clock unit 23 when the power is restored. It is something that takes. Therefore, a backup power supply circuit 48 is provided so that power can be supplied to the clock unit 23 even when the power supply from the power supply circuit 40 to the arithmetic unit 20 is stopped. The backup power supply circuit 48 uses a secondary battery, and this secondary battery is charged by the output voltage of the power supply circuit 40 during normal operation, and supplies power to the clock unit 23 during a power failure. Therefore, even during a power failure, the clock unit 23 operates normally, and it is not necessary to set the time when the power is restored. In addition, since the secondary battery is a secondary battery, it does not need to be replaced for a long time. Further, since the secondary battery is normally charged, it is not necessary to separately charge the secondary battery.

By the way, when a power failure of the AC power supply AC occurs, the power supply to the arithmetic circuit 21 is stopped before the power amount data obtained before the power failure and not written in the EEPROM 22 is written in the EEPROM 22. In this case, the power amount data is lost, and accurate power amount measurement cannot be performed. On the other hand, since the power supply circuit 40 includes capacitance components such as the smoothing capacitors C1 and C4, the input voltage Vx to the constant voltage circuit 41c is
As shown in (a), when a power failure occurs, the voltage gradually decreases at a predetermined rate of change over time. The constant voltage circuit 41c is
As shown in FIG. 6C, when the input voltage Vx is equal to or higher than the limit value Vm, the output voltage Vo can be maintained at a constant value (+5 V). If the value falls below this range, power cannot be supplied to operate the arithmetic circuit 21 correctly, and the operation of the arithmetic circuit 21 stops.

Therefore, a power failure / recovery detection circuit 1 for detecting a power failure / recovery of the AC power supply AC is provided, and when the power failure / recovery detection circuit 1 detects a power failure, an arithmetic circuit 21 is provided.
Write the electric energy data to the EEPROM 22. As shown in FIG. 5, the power failure / recovery detection circuit 1 sets the input voltage (hereinafter referred to as “detection voltage”) Vx to the constant voltage circuit 41c to a threshold value set to a level higher than the limit value Vm. Vr, the detected voltage Vx is equal to the threshold V
A power outage / recovery detection signal is output to the arithmetic circuit 21 when it exceeds the threshold voltage r and goes to the H level, and when the detection voltage Vx falls below the threshold value Vr, it goes to the L level (see FIG. 1). The threshold value Vr is set so that the time required for the arithmetic circuit 21 to write the electric energy data to the EEPROM 22 can be secured from the time when the detection voltage Vx starts to decrease in accordance with the time change rate to the time when the detection voltage Vx reaches the limit value Vm. (See FIG. 6A). The power failure / recovery detection circuit 1 having such a function can be realized by a conventionally well-known technique using a comparator or the like, so that detailed illustration and description of the circuit configuration are omitted.

Next, the operation when a power failure occurs will be described with reference to the flowchart of FIG. As shown in FIG. 6A, assuming that the AC power supply AC fails at time t = t1, the detected voltage Vx gradually decreases after that time, and when the detected voltage Vx falls below the threshold Vr at time t = t2, the power failure occurs. The power recovery detection circuit 1 detects the power failure, and changes the power failure / recovery detection signal from H level to L level as shown in FIG. 6B (S1). When the power failure / restoration detection signal changes from the H level to the L level, the arithmetic circuit 21 starts an operation of writing the obtained electric energy data into the EEPROM 22 as shown in FIG.
2). If the return (recovery) of the AC power supply AC is not detected by the power failure / recovery detection circuit 1 during the write operation (S3), the writing of the electric energy data by the arithmetic circuit 21 is completed (S4). As shown in FIG. 6E, at that time (time t = t3), the arithmetic circuit 21 stops the operation of measuring the electric energy. Thereafter, when the detection voltage Vx falls below the limit value Vm (time t = t4), the arithmetic circuit 21 stops operating (S5). Further, the arithmetic circuit 21 stops its operation until the power failure is detected by the power failure / restoration detection circuit 1 (S6).
No. 1 does not restart the operation of measuring the electric energy (S7, S8).

On the other hand, as shown in FIGS. 8A to 8D, when the detection voltage Vx exceeds the threshold value Vr and the power is restored during the operation of writing the electric energy data into the EEPROM 22 by the arithmetic circuit 21, that is, In the case of a momentary power failure, the arithmetic circuit 2
Reference numeral 1 indicates that when the power failure is detected by the power failure / recovery detection circuit 1 and the power failure / recovery detection signal changes from the L level to the H level, the writing operation of the electric energy data is interrupted, and the measurement operation is continued ( S10).

As described above, the power failure / recovery detection circuit 1 is provided, and when the power failure of the AC power supply AC is detected by the power failure / recovery detection circuit 1, the EEPRO
Since the writing of the electric energy data into the M22 is performed, before the electric power data can no longer be written by the arithmetic circuit 21 after the power failure is detected by the power failure / recovery detection circuit 1, the arithmetic circuit 21 Can be written to the EEPROM 22. As a result, the power amount data is not lost when a power failure occurs, and the accurate power amount can be measured.

In the present embodiment, the power supply circuit 4
Power failure / recovery detection circuit 1 after power supply from 0 stops
When the power recovery is detected, the arithmetic circuit 21 does not restart the arithmetic processing for calculating the electric energy.
After the power is restored from the power failure, the calculation processing of the electric energy is not restarted,
This makes it possible to determine that a power failure has occurred. For example, when an electric clock that receives power supply from an AC power supply AC as the load LD or an electric device that has a timer function and does not have a timer compensation function due to a power failure is connected to the AC wiring line L, When there is a power outage and the above-mentioned electric clock or the clock of electric equipment is delayed, whether the cause is a power outage or whether the time of the electric clock or the clock powered by the battery is correct Can be easily determined. In other words, if the watt-hour meter operates normally, it is considered that the time of a clock or the like powered by a battery not receiving power supply from the AC power supply AC is incorrect, and the watt-hour meter must be operating. If
It is considered that the time of the electric clock was delayed due to a power failure.

(Embodiment 2) In Embodiment 1 described above, after the power supply from the power supply circuit 40 is stopped,
When the power recovery is detected by the power recovery detection circuit 1, the arithmetic circuit 21 does not restart the arithmetic processing for obtaining the electric energy. However, in this embodiment, the arithmetic circuit 2
1 restarts the calculation for obtaining the electric energy, which is a feature of the present embodiment. Note that the configuration and basic operation of the present embodiment are the same as those of the first embodiment, and illustration and description of the common configuration and operation will be omitted.

The operation at the time of the occurrence of a power failure, which is a feature of this embodiment, will be described with reference to the flowchart of FIG. Here, as shown in FIG. 9, the operations of Steps 1 to 7 are common to those of the first embodiment, and thus detailed description is omitted.
In the present embodiment, when the power failure / recovery detection circuit 1 detects power recovery after the detection voltage Vx falls below the limit value Vm and the arithmetic circuit 21 stops operating, the arithmetic circuit 21 measures the power amount. The operation is restarted (S11). In this case, the arithmetic circuit 21 reads the electric energy data written in the EEPROM 22 before the operation is stopped, and restarts the measurement from the continuation.

As described above, when a power failure is detected after the power failure / recovery detection circuit 1 detects a power failure, the arithmetic circuit 21 restarts the arithmetic processing for obtaining the electric energy. It is possible to automatically restart the measurement of the electric energy regardless of the simple operation, and there is no possibility that the operation of restarting the measurement is forgotten and the electric energy data is lost, thereby improving the usability.

[0033]

According to a first aspect of the present invention, a probe connected to an AC wiring path, a current sensor for detecting a current passing through the AC wiring path, the probe and the current sensor are provided. Calculating means for calculating the amount of electric power passing through the AC wiring path using the detected voltage value and current value of the AC wiring path; an EEPROM in which data of the electric energy obtained by the calculating means is written at predetermined time intervals;
Display means for displaying data of the amount of electric power written in the OM; and a power supply circuit for generating an internal power supply including a power supply for the calculation means and the display means using the power taken from the AC wiring path via the probe. In the watt hour meter provided, the power supply circuit obtains an intermediate output that decreases at a predetermined time rate of change when power supply from the AC wiring path is stopped using power taken from the AC wiring path. Means for generating the internal power supply from the intermediate output, wherein the level of the intermediate output is set to at least a value higher than a limit value at which the arithmetic means can write power value data to the EEPROM. A power failure is detected when the intermediate output level is lower than the threshold value, and a power recovery is detected when the intermediate output level exceeds the threshold value. Power failure / recovery detection means is provided, and the arithmetic means writes power amount data to the EEPROM when the power failure is detected by the power failure / recovery detection means, so that the power failure is detected by the power failure / recovery detection means. Before the data can no longer be written by the arithmetic means after the data is written, the data of the electric energy obtained by the arithmetic means can be written to the EEPROM, and the data of the electric energy can be accurately stored without loss in the event of a power failure. There is an effect that a large amount of power can be measured.

According to a second aspect of the present invention, in the first aspect of the present invention, the arithmetic means continues the arithmetic processing for calculating the electric energy even if the power failure is detected by the power failure / recovery detecting means. In addition to the effects of the invention, there is an effect that the measurement of the electric energy can be continued even when an instantaneous power failure occurs.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the arithmetic unit detects a power recovery by the power failure / power recovery detection unit after the power supply from the power supply circuit is stopped. Since the calculation processing for calculating the electric energy is not restarted, in addition to the effect of the invention according to claim 1 or 2, the arithmetic processing for the electric energy is not restarted after the power recovery from the power failure, thereby causing the power failure. This has the effect of making it possible to determine.

According to a fourth aspect of the present invention, in the first or second aspect of the present invention, the arithmetic means performs an arithmetic process for calculating an amount of power when power recovery is detected after power supply from the power supply circuit is stopped. Since restarting, in addition to the effects of the invention of claim 1 or 2, the measurement of the electric energy can be automatically resumed after the power is restored without any manual operation. There is no danger that data will be lost, and the usability is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment.

FIG. 2 is a schematic diagram showing a usage pattern of the above.

FIG. 3 is an operation explanatory diagram of the above.

FIG. 4 is an operation explanatory view of the above.

FIG. 5 is a circuit diagram showing a power supply circuit used in the power supply circuit;

FIG. 6 is an operation explanatory view of the above.

FIG. 7 is an operation explanatory view of the above.

FIG. 8 is an operation explanatory view of the above.

FIG. 9 is an operation explanatory view of the above.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power failure / restoration detection circuit 21 Operation circuit 22 EEPROM 40 Power supply circuit 41a to 41c Constant voltage circuit CT1, CT2 Current sensor L AC wiring path P1 to P3 Probe

Claims (4)

[Claims] A probe connected to an AC wiring path, a current sensor for detecting a current passing through the AC wiring path, and an AC using a voltage value and a current value of the AC wiring path detected by the probe and the current sensor. Calculating means for calculating the amount of power passed through the wiring path; an EEPROM in which data of the amount of power determined by the calculating means is written at predetermined time intervals;
Display means for displaying data of the amount of electric power written in the EPROM; and a power supply circuit for generating an internal power supply including a power supply for the arithmetic means and the display means using the power taken from the AC wiring path via the probe. In the watt hour meter provided, the power supply circuit obtains an intermediate output that decreases at a predetermined time rate of change when power supply from the AC wiring path is stopped using power taken from the AC wiring path. ,
Means for generating the internal power supply from the intermediate output, wherein the level of the intermediate output is set at least to a value higher than a limit value at which the arithmetic means can write power value data to the EEPROM. A power failure / recovery detection means for detecting a power failure when the intermediate output level falls below a threshold value as compared with a threshold value and detecting a power recovery when the intermediate output level exceeds the threshold value And the calculating means converts the electric power data to the EEPRO when the power failure is detected by the power failure / recovery detecting means.
A watt-hour meter characterized by writing to M. 2. The watt hour meter according to claim 1, wherein said calculating means continues the calculation processing for calculating the electric energy even when the power failure is detected by said power failure / recovery detecting means. 3. The power supply circuit according to claim 2, wherein the power supply circuit stops power supply from the power supply circuit, and does not restart the power supply calculation processing when the power outage / power recovery detection means detects power recovery. The watt hour meter according to claim 1 or 2, wherein 4. The arithmetic unit according to claim 1, wherein the arithmetic unit restarts an arithmetic process for calculating an amount of power when a power recovery is detected after the power supply from the power supply circuit is stopped. Watt hour meter.