JP2000187049A - Electronic watthour meter and method for setting output voltage of source apparatus thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for automatically setting a power source to a predetermined output voltage whereby the power source of an electronic watthour meter quickly rises to the predetermined output voltage and a time while an electric energy is not measured, e.g. when a service interruption is recovered or the like is shortened. SOLUTION: When a switching power supply 4 is started up to make an output voltage an operating voltage of a CPU 2, the CPU 2 reads out an output voltage set value stored in an EPROM 5, and a D/A converter 6 inputs the value as an analog value to a switching element 44. A set predetermined output voltage is thus generated. In order to set the output voltage, an external CPU 8 operates the voltage set value according to a predetermined program based on the output voltage measured by a digital voltmeter 9, writes the value to the EPROM 5 to generate an output voltage corresponding to the voltage set value and, terminates the setting operation when the output voltage becomes the predetermined output voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic wattmeter and a method for setting an output voltage of a power supply of the electronic wattmeter.

[0002]

2. Description of the Related Art FIG. 6 is a circuit block diagram of a conventional electronic watt-hour meter, for example. In the figure, reference numeral 1 denotes a power / frequency conversion circuit (W / F conversion circuit) that multiplies the voltage / current of the measured circuit input through a conversion transformer and converts the multiplied into a pulse number proportional to the amount of power. Reference numeral 2 denotes a CPU for controlling power calculation and the electronic watt-hour meter. Reference numeral 3 denotes a weighing value display section for displaying a power value obtained by calculating and summing up the pulses from the W / F conversion circuit 1. 4 is the W / F conversion circuit 1 and CPU
2. A power supply device for supplying operating power to the weighing value display section 3, which is usually supplied at a DC voltage of 5V.

The configuration of the power supply device 4 will be described below. 41
Is a transformer that reduces the voltage of the measured circuit to a control voltage,
Reference numeral 2 denotes a rectifier, which is constituted by, for example, a diode bridge. Reference numeral 43 denotes a smoothing capacitor, and reference numeral 44 denotes a switching element having a reference voltage circuit therein, and is generally called a three-terminal switching element. 45 is a diode, 4
6 is a choke coil, and 47 is a diode for preventing backflow.

Reference numeral 48 denotes an output voltage adjusting circuit, which connects an adjustable resistor 48a and a fixed resistor 48b in series, detects an intermediate potential thereof, and inputs the intermediate potential voltage to a control terminal 44a of the switching element 44 to supply the power to the power supply device 4. Output voltage is set. The adjustable resistance 48a and the fixed resistance 48b are selected to have substantially the same resistance value. 50 is a second smoothing capacitor, and 51 is a diode for preventing backflow. The DC voltage whose ripple has been reduced by the second smoothing capacitor 50 is supplied as operating power of each electronic circuit.

Next, the operation of the conventional power supply device 4 will be described. When a voltage is applied to the electronic watt-hour meter, the switching element 44 starts operating and the output voltage starts to increase.
With this output voltage, the intermediate potential voltage of the output voltage adjusting circuit 48 rises, and the output voltage rises so that the input voltage of the control terminal 44a becomes the reference voltage in the switching element 44.
When the reference voltage is exceeded, the output voltage of the switching element 44 is controlled so as to decrease, and the output voltage is increased so that the output voltage is controlled to a stable constant voltage. Also, the adjustable resistor 48 is adjusted so that the output voltage becomes a predetermined voltage (5 V).
Is adjusted externally.

[0006]

As shown in FIG. 7, the relationship between the elapsed time and the output voltage from the start of energizing the power supply 4 of such a conventional electronic watt-hour meter is represented by a saturation curve as shown in FIG. 5V). Although the voltage rises quickly at the beginning of the energization start, the rise rate decreases near the specified voltage. Generally C
PU2 can be reset at 3.5V and starts operating.
The W / F conversion circuit 1 does not start operation unless it is close to 5V. Therefore, in the conventional electronic watt-hour meter, the W / F conversion circuit 1 that performs power measurement does not start operating unless the voltage of the supplied driving power supply is higher than a predetermined voltage. For this reason, at the rise at the time of recovery from the power failure, even if the power consumption in the load circuit to be measured is started, the voltage of the power supply device 4 does not reach the predetermined voltage. Is not metered.

As a means for accelerating the rise of the voltage of the power supply 4, if the absolute value of the resistance constituting the output voltage adjusting circuit 48 is reduced to increase the energy fed back by the choke coil 46, the predetermined voltage of the power supply 4 can be reduced. Reaching (5V) is faster. However, the consumption of the output current of the switching element 44 in the resistors 48a and 48b increases, and unnecessary heat is generated. In addition, the switching element 44 needs to have a large current capacity.
And the peripheral parts also become large and expensive.

In addition, the output voltage of the power supply
Externally adjustable resistor 48 to adjust
The adjustment work of “a” was necessary and troublesome.

The present invention has been made in order to solve the above-mentioned problems, and the power supply of the switching element 44 is accelerated without lowering the resistance value of the output voltage adjusting circuit 48 so as to measure the electric power at the time of recovery from power failure. The purpose of the present invention is to reduce the leakage of water.

[0010] It is another object of the present invention to automatically adjust the output voltage of the voltage adjusting circuit 48 by a CPU so as to eliminate manual intervention.

[0011]

(1) An electronic watt-hour meter according to the present invention comprises: a CPU; calculating means for controlling the amount of power controlled by the CPU; and supplying a predetermined voltage to the CPU and the calculating means. An electronic watt-hour meter having a switching power supply device using a switching element for performing the following operations: a nonvolatile memory storing a set value of an output voltage of the power supply device, and an output of the nonvolatile memory read by the CPU when the power supply device starts up. Output voltage setting means for controlling the switching element based on the voltage set value to generate a predetermined output voltage.

(2) In the electronic watt-hour meter of (1), a load resistance inserted on the output side of the power supply unit;
Switching means for cutting off the load resistance by a rising reset signal of the CPU or for setting the resistance value to a resistance value larger than the resistance value of the load resistance is provided.

(3) The method for setting the output voltage of the power supply device of the electronic watt-hour meter according to the above (1) or (2) uses the voltage measuring means and a second CPU different from the CPU, and The second CPU rewrites the output voltage set value of the nonvolatile memory based on the output voltage of the power supply device measured by the measuring means, and generates a predetermined output voltage according to the rewritten output voltage set value. It is.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a circuit block diagram of an electronic watt-hour meter according to Embodiment 1 of the present invention. In the figure, reference numerals 1 to 4, 41 to 47 and 51 are the same as those in the above-mentioned conventional example. An output voltage setting circuit 49 connects fixed resistors 49a and 49b having substantially the same value in series, and inputs an intermediate potential to a control terminal 44a of the switching element 44. 5 is a nonvolatile memory (E
PROM) and 6 are digital / analog converters (D / A converters) which convert a digital value in the EPROM 5 into an analog voltage, superimpose on an intermediate potential of the output voltage setting circuit 49, and input it to the control terminal 44a. .

Reference numeral 7 denotes the CPU 2 and, for example, a personal computer (external CP).
U) A communication interface (communication I / F) for controlling data communication with 8. Well-known RS-232C communication means or GPIB communication means is generally used for the external CPU 8 and the I / F 7. 9 is a digital voltmeter,
The output voltage of the power supply 4 is measured through the terminal 10. And the digital voltmeter 9 is the above RS-232C,
It is connected to the external CPU 8 by GPIB communication means. In addition,
The external CPU 8 and the digital voltmeter 9 are connected only when the output voltage of the power supply 4 is adjusted and set.
It is not required during normal power metering.

First, the adjustment setting of the output voltage of the power supply device 4 of the electronic watt-hour meter according to the first embodiment will be described. As shown in FIG. 1, an external CPU 8 and a digital voltmeter 9 are connected to the electronic wattmeter, and a voltage is applied to the electronic wattmeter. Choke coil 46, diode 45, switching element 4
4, the intermediate voltage of the output voltage setting circuit 49 begins to be applied to the control terminal 44a of the switching element 44, and the output voltage of the power supply device 4 rises, exceeds the operable voltage of the CPU 2, and forms the output voltage setting circuit 49. Fixed resistance 4
The output voltage reaches the output voltage determined by the resistance value ratio of 9a and 49b. This voltage is near 5V, but the fixed resistor 49
Due to variations in the resistance values of a, 49b, etc., the values are not constant among individual electronic watt-hour meters.

Here, the resistance values of the fixed resistors 49a and 49b are selected in advance so that the output voltage becomes about 5V. Then, the CPU 2 is set to an adjustment mode described later, and the output voltage of the power supply device 4 is measured by the digital voltmeter 9. The measured value of the digital voltmeter 9 is transmitted to the external CPU 8 by communication means. The external CPU 8 receives the measured value of the output voltage from the digital voltmeter 9 and communicates with the communication I / F 7 and the CPU 2 via the communication I / F 7 and the CPU 2 so that the voltage value becomes a regular voltage value.
Write data to ROM5.

This procedure will be described with reference to the flowchart of FIG. (1) First, the communication means from the external CPU (personal computer) 8 is connected to the connection terminal of the communication I / F 7 of the electronic wattmeter, and the measurement input of the digital voltmeter 9 is connected to the terminal 10 to adjust the output voltage. Preparation is completed (S1). (2) When a voltage is applied to the electronic watt-hour meter (S2), (3) The output voltage of the power supply device 4 rises and the CPU 2 becomes operable.
Are enabled (S3).

(4) Here, C is instructed by an external CPU.
The CPU mode of PU2 is switched from the "normal mode" to the "adjustment mode" (S4). In the adjustment mode, an EPROM is executed by an internal program according to a command from the external CPU 8.
5 can be rewritten. The initial value at the time of shipment of the EPROM 5 is normally "1" (maximum value) in each bit, and the output voltage of the power supply 4 before adjustment is
Is output (usually 6 to 7 V).

(5) The digital voltmeter 9 measures the output voltage (S5). (6) If the voltage value is not within the allowable range (S6), (7) a voltage range specified by a program in the external CPU 8. (For example, 4.9 to 5.1 V), and the corresponding bits of the EPROM 5 are sequentially rewritten to “0” so as to fall within a specified voltage range (S7).

(8) When the output voltage of the power supply 4 falls within the set target voltage range (S6), (9) the EPROM 5
A command to permanently record and save the data inside is issued and fixed (S8). (10) Then, the CPU 2 is returned from the adjustment mode to the normal mode, and the voltage adjustment operation is completed (S9). (11) The power is turned off and the connection to the watt hour meter is disconnected (S9).
10, S11).

With the above adjustment, the CPU 2
In the state where has risen, the EPR adjusted and set above
Since the data of the OM 5 is sent to the D / A converter 6, a control potential at which a specified output voltage is always obtained is given to the control terminal 44 a of the switching element 44.

As described above, the measured value obtained by the digital voltmeter 9 is determined by the program in the external CPU 8, and the output voltage of the power supply device 4 is set to a specified voltage by the EPRO.
The data in M5 can be automatically set using the CPU.

In the present invention, the output voltage of the power supply device 4 is automatically set by the external CPU 8 through the communication means by using the data value of the EPROM 5 by way of the communication means. It is also possible to set the values manually.

The digital voltmeter 9 and the external CP
U8 is provided outside, but digital voltmeter is A / D
As a converter, an external CPU may be incorporated in the wattmeter as an internal CPU.

Next, a description will be given with reference to FIG. 3 showing a waveform diagram of a voltage output of the power supply device 4 at the time of recovery from a power failure. (1) The D / A converters 6 and C are activated by the operation of the choke coil 46, the diode 45, and the switching element 44 with the distribution line voltage input to the electronic watt-hour meter upon recovery from the power failure.
It rises to the operable voltage of PU2.

(2) The CPU 2 sends the data in the nonvolatile memory 5 set by the voltage adjustment to the D / A converter 6. (3) Since the D / A converter 6 directly applies the set potential to the control terminal 44a of the switching element 44, the voltage rise of the power supply device 4 by the switching element 44 rapidly rises to the specified voltage 5V, and the W / F The operating voltage of the conversion circuit 1 is reached.

As a result, the operation voltage of the W / F conversion circuit 1 reaches the operation voltage of the conventional apparatus in a short time as compared with the gradual increase during the operation of the CPU 2 from the operable voltage of the CPU 2 to the operation voltage of the W / F conversion circuit 1. Power measurement leakage can be reduced.

The output voltage adjusting element of the power supply device 4 is changed from a mechanical variable resistor to an EPROM 5 and a D / A converter 6.
Since the solid-state element is used, the fluctuation of the adjustment value due to vibration and impact can be eliminated.

Embodiment 2 FIG. FIG. 4 is a circuit block diagram of a power supply device according to a second embodiment of the present invention, and FIG. 5 is a waveform diagram of a voltage output of the power supply device according to the second embodiment. In the figure,
1 to 7, 41 to 51 are the same as those described in the first embodiment. Reference numeral 52 denotes a parallel resistor connected in parallel to the output voltage setting circuit 49, and reference numeral 53 denotes an analog switch such as a semiconductor switch, and the parallel resistor 52 is turned off by a reset signal at the rising edge of the CPU 2.

As described in the description of the conventional device, if the absolute value of the resistance of the output voltage setting circuit 49 is reduced in order to increase the energy fed back by the choke coil 46,
Although the voltage rise of the power supply device 4 becomes faster, there are problems such as heat generation and a large capacity of the switching element 44.

In the second embodiment of the present invention, when the power supply 4 rises immediately after the recovery from the power failure, the parallel resistance 53 is connected in parallel to the output voltage setting circuit 49. Can be reduced. The current of the choke coil 46 can be increased, and the voltage of the power supply device 4 rises faster. When the output voltage of the power supply 4 reaches the operating voltage of the CPU 2, the analog switch 53 is turned off by the reset signal of the CPU 2, and the current of the parallel resistor 53 is cut off.

However, since the potential of the data value of the EPROM 5 preset by the operation of the CPU 2 is applied from the D / A converter 6 to the control terminal 44 a of the switching element 44, it is influenced by the resistance value of the output voltage setting circuit 49. Without causing the output voltage of the power supply device 4 to immediately reach the specified voltage.
This state is shown in FIG.

In the second embodiment of the present invention, the time required to reach the operable voltage of the CPU 2 is shorter than in the first embodiment, and leakage of power measurement at the time of recovery from power failure can be further reduced. Further, during normal operation, the parallel resistor 52 is cut off by the analog switch 53, and the output voltage of the switching element 44 is controlled by the set potential from the D / A converter 6, so that the resistance value of the output voltage setting circuit 49 is changed. The heat generation and the power consumption in the output voltage setting circuit 49 can be suppressed.

In the above description, the analog switch 53
Is used, but a general open / close switch may be used.

The parallel resistor 52 is connected to the analog switch 5
Although the disconnection is made at 3, the resistance may be made larger than the resistance of the parallel resistor 52 without disconnecting. For example, another parallel resistor having a large resistance value of the parallel resistor 52 may be provided and switched by the analog switch 53. Further, another resistor may be inserted at both ends of the analog switch 53 so as to be connected in series with the parallel resistor 52.

[0037]

(1) As described above, according to the present invention,
Since the CPU operates to generate a predetermined output voltage based on the output voltage set value of the nonvolatile memory when the power supply device starts up, the power supply voltage rises quickly and the time during which the amount of power is not measured is shortened. be able to.

(2) Since the load resistance is inserted when the power supply device starts up, a faster rise of the power supply voltage can be achieved.

(3) Since the output voltage of the power supply device is fed back to set the output voltage set value, a predetermined output voltage can be obtained automatically.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of an electronic watt-hour meter according to Embodiment 1 of the present invention.

FIG. 2 is a flowchart of an output voltage adjustment procedure according to the first embodiment of the present invention.

FIG. 3 is a waveform diagram of a voltage output of the power supply device according to the first embodiment of the present invention.

FIG. 4 is a circuit block diagram of an electronic watt-hour meter according to a second embodiment of the present invention.

FIG. 5 is a waveform diagram of a voltage output of a power supply device according to a second embodiment of the present invention.

FIG. 6 is a circuit block diagram of a conventional electronic watt-hour meter.

FIG. 7 is a waveform diagram of a voltage output of a conventional power supply device.

[Explanation of symbols]

Reference Signs List 1 power / frequency conversion circuit (W / F conversion circuit) 2 CPU 3 weighing value display section 4 power supply device 5 EPROM 6 digital / analog converter (D / A converter) 7 communication interface (communication I / F) 8 external CPU (PC) 9 Digital voltmeter 42 Rectifier 44 Switching element 45 Diode 46 Choke coil 49 Output voltage setting circuit 49a, 49b
Fixed resistor 50 Second smoothing capacitor 51 Diode for backflow prevention 52 Parallel resistor 53 Analog switch

Claims (3)

[Claims] 1. An electronic watt-hour meter comprising: a CPU; means for calculating an amount of electric power controlled by the CPU; and a switching power supply using a switching element for supplying a predetermined voltage to the CPU and the means for calculating. A predetermined output voltage is generated by controlling the switching element based on a nonvolatile memory storing a set value of an output voltage of the power supply device and an output voltage set value of the nonvolatile memory read by the CPU when the power supply device is started up. An electronic watt-hour meter, comprising: an output voltage setting unit that causes the output voltage to be set. 2. The electronic watt-hour meter according to claim 1, wherein a load resistance inserted on an output side of the power supply unit and a CPU.
A switching means for disconnecting the load resistance by a rising reset signal or setting the resistance value to a resistance value greater than the resistance value of the load resistance. 3. A method for setting an output voltage of a power supply device of an electronic watt-hour meter according to claim 1 or 2, wherein the voltage measurement means and a second CPU different from the CPU are used to measure the voltage. A second CPU rewrites an output voltage set value of the nonvolatile memory based on the output voltage of the power supply device measured by the means to generate a predetermined output voltage. How to set the output voltage of the device.