JP2011169703A - Wattmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wattmeter for easily confirming a proper connection method of the wattmeter on the condition of an actually-measured voltage and an actually-measured current. <P>SOLUTION: The wattmeter 10 has: a meter loss calculating part 51 for calculating power consumed in a voltage input part 1 and a current input part 2; a meter loss comparing part 52 for comparing both power calculated by the meter loss calculating part 51, and outputting a signal regarding a comparison result; and directive means 71, 72 for directing that it employs at least one of the first connection method in which the voltage input part 1 is connected to the side of a load 30 of the current input part 2 and the second connection method in which the voltage input part 1 is connected to the side of a power supply 20 of the current input part 2 based on the signal. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a power meter, and more specifically, can be suitably applied to a power meter that can be used for measuring a relatively small amount of power consumption.

  Conventionally, a power meter has been widely used in fields such as power management, power supply monitoring, development of electric appliances, evaluation, and quality assurance. For example, in the development, production, and inspection of electrical equipment, minute power consumption is measured.

  The wattmeter includes a voltage input circuit (voltmeter) and a current input circuit (ammeter) inside, and can measure the power consumption of the load by connecting a power source and a load. Since the input resistance exists in each of the voltage input circuit and the current input circuit, the power consumption value of the load displayed by the wattmeter is either the power consumed by the voltage input circuit itself or the current input circuit itself, So-called instrument loss is always included.

  As a wiring method for connecting the power source and the load to the wattmeter, a method in which the voltage input circuit is placed on the load side of the current input circuit as shown in FIG. 8A, and a voltage as shown in FIG. There is a method in which the input circuit is on the power supply side of the current input circuit.

  In general, when the measured current is relatively large, it is recommended to use a connection method in which the voltage input circuit is connected to the load side of the current input circuit because the instrument loss is reduced. That is, when this connection method is adopted, the current input circuit measures the sum of the current flowing through the load and the current flowing through the voltage input circuit. In general, since the input resistance of the voltage input circuit is larger than the resistance of the load, the current flowing through the voltage input circuit is small. Therefore, the influence of the current flowing through the voltage input circuit on the measurement accuracy of the power meter is reduced.

  On the other hand, when the measured current is relatively small, it is recommended to use a connection method in which the voltage input circuit is connected to the power supply side of the current input circuit because the instrument loss is reduced. That is, when this connection method is adopted, the voltage input circuit measures the sum of the voltage drop due to the load and the voltage drop due to the current input circuit. Generally, since the input resistance of the current input circuit is smaller than the resistance of the load, the voltage drop due to the current input circuit is small. Therefore, the influence of the voltage drop caused by the current input circuit on the measurement accuracy of the power meter is reduced.

  There is also a wattmeter equipped with a circuit that measures meter loss and cancels it (Patent Document 1).

Japanese Patent Laid-Open No. 2005-69860

  Since the power consumed by the voltage input circuit itself or the current input circuit itself varies depending on the measurement voltage and measurement current, it is troublesome for the user to calculate the instrument loss at each measurement. Also, since the instrument loss is generally small compared to the measurement accuracy of the wattmeter, it is often ignored.

  However, in recent years, from the viewpoint of energy saving, it is important to measure minute power consumption such as power consumption in standby mode and off mode of electrical equipment, so-called standby power. Therefore, appropriate wiring is necessary because the instrument loss affects the measured value.

  As mentioned above, some wattmeters have a circuit that cancels meter losses. However, by adopting an appropriate wiring method, it is possible to suppress the influence of the instrument loss on the measurement accuracy of the power meter with a simple configuration. There is no power meter that can easily confirm the connection method based on the above.

  Accordingly, an object of the present invention is to provide a wattmeter that can easily confirm an appropriate connection method of the wattmeter under conditions of actual measurement voltage and measurement current.

  The above object is achieved by a power meter according to the present invention. In summary, the present invention includes a voltage input unit connected to a power source and a load, and a current input unit connected to the power source and the load, and the voltage input to the voltage input unit and the current In a wattmeter that measures the power consumption of the load based on the current input to the input unit; an instrument loss that calculates the power consumed by the voltage input unit and the power consumed by the current input unit A calculator that compares the power consumed by the voltage input unit and the power consumed by the current input unit calculated by the meter loss calculating unit and outputs a signal related to the result of the comparison; A loss comparison unit; based on the signal, the first connection method for connecting the voltage input unit to the load side with respect to the current input unit should be adopted or the voltage input unit is used as the current input unit The second connection connected to the power supply side A power meter characterized by having a process wherein the instruction means for instructing at least one of the effect that should be adopted.

  According to the present invention, it is possible to easily confirm an appropriate connection method of the wattmeter under the actual measurement voltage and measurement current conditions.

It is a schematic block diagram of a power meter according to an embodiment of the present invention. It is a connection diagram which shows the connection state of the wattmeter at the time of a measurement, (a) shows the 1st connection method and (b) shows the 2nd connection method. It is a general | schematic functional block diagram for the control which instruct | indicates the connection method according to this invention. It is a flowchart of the control which instruct | indicates the connection method according to this invention. It is a schematic diagram which shows the example of the instruction | indication means which instruct | indicates the connection method. It is a schematic diagram which shows an example of the connector which connects an wattmeter to a power supply and load. It is a connection diagram of the wattmeter in the measurement of three-phase electric power. It is a conceptual diagram for demonstrating the connection method of a wattmeter.

  Hereinafter, the power meter according to the present invention will be described in more detail with reference to the drawings.

Example 1
An embodiment of a power meter according to the present invention will be described. In the present embodiment, the wattmeter is a single-phase wattmeter that can be used for measuring minute power consumption such as standby power of an electric device. FIG. 1 is a schematic configuration block diagram of a wattmeter 10 of the present embodiment. FIG. 2 is a connection diagram showing a connection state of the wattmeter 10 at the time of measurement.

  As shown in FIG. 1, a wattmeter 10 includes a voltage input circuit 1 that is a voltage input unit, a current input circuit 2 that is a current input unit, a first converter 3 for the voltage input circuit 1, and a current input circuit. 2, a CPU 5 as a control unit, a memory 6 as a storage unit, and a display unit 7 for displaying measurement values and the like.

Referring also to FIGS. 2A and 2B, the voltage input circuit 1 is connected to the power supply 20 in parallel with the load 30 through terminals 11 and 12. The voltage input circuit 1 has an input resistance (internal resistance) R _V. The current input circuit 2 is connected in series with the load 30 with respect to the power source 20 by terminals 21 and 22. The current input circuit 2 has an input resistance (internal resistance) _RA .

  The first converter 3 performs A / D conversion and effective value conversion on the input to the voltage input circuit 1. The second converter 4 performs A / D conversion and effective value conversion on the input to the current input circuit 2.

The CPU 5 calculates the power consumption of the load 30 based on the digital signal of the effective value of the voltage and the effective value of the current respectively input from the first and second converters 3 and 4. As will be described in detail later, the CPU 5 uses power consumption of the voltage input circuit 1 (hereinafter referred to as “first instrument loss”) W _V and power consumption of the current input circuit 2 (hereinafter referred to as “second instrument loss”). called.) calculation of W _a, a comparison of the calculation results, performs like the output of the signal corresponding to the comparison result.

  The memory 6 stores programs executed by the CPU 5, data, and the like. The CPU 5 performs various arithmetic processes based on programs and data stored in the memory 6.

  The display unit 7 displays a measured value of the power consumption of the load 30 calculated by the CPU 5 based on a signal from the CPU 5. Further, as will be described in detail later, a display for instructing the connection method of the wattmeter 10 is performed on the display unit 7.

  As described above, as a connection method for connecting the power source 20 and the load 30 to the wattmeter 10, as shown in FIG. 2A, the voltage input circuit 1 is placed on the load side with respect to the current input circuit 2 (hereinafter, referred to as “the current input circuit 2”). (Referred to as “first connection method”), as shown in FIG. 2B, a method in which the voltage input circuit 1 is set on the power supply side with respect to the current input circuit 2 (hereinafter referred to as “second connection method”). There is. When the first connection method shown in FIG. 2A is adopted, the power consumption of the voltage input circuit 1 is added to the power consumption value of the load 30. On the other hand, when the second connection method shown in FIG. 2B is adopted, the power consumption of the current input circuit 2 is added to the power consumption value of the load 30. In general, when the measurement current is relatively large, the instrument loss is smaller and the influence on the measurement accuracy is smaller when the first connection method shown in FIG. Generally, when the measurement current is relatively small, the instrument loss is smaller and the influence on the measurement accuracy is smaller when the second connection method shown in FIG.

  However, since the power consumed by the voltage input circuit 1 itself or the current input circuit 2 itself varies depending on the measurement voltage and measurement current, the wattmeter 10 has a function of the actual meter loss under the actual measurement voltage and measurement current conditions. Selecting the connection method is important for high-precision measurements. In particular, when measuring minute power consumption such as standby power of electrical equipment, the influence of instrument loss on the measurement accuracy of the wattmeter 10 increases, so it is very important to select an appropriate connection method. is important.

Therefore, in this embodiment, the first meter loss W _V and the second meter in the wattmeter 10 under the conditions of the actual measurement voltage and measurement current with the wattmeter 10 connected to the power source 20 and the load 30. It obtains a loss W _a, thereof with first instrument loss W _V is compared with the second meter loss W _a, first the effect should be adopted connection method or the second wiring method based on the comparison result Indicate at least one of the facts that should be adopted. This will be described in more detail below.

  FIG. 3 is a schematic functional block diagram of control for instructing a connection method of the wattmeter 10. FIG. 4 is a flowchart of control for instructing the connection method of the wattmeter 10.

  First, the user connects the wattmeter 10 to the power source 20 and the load 30 by, for example, the first connection method shown in FIG. And electric power is supplied to the circuit of the said measurement system as conditions of a predetermined measurement voltage and measurement current. At this time, the wattmeter 10 may be connected to the power source 20 and the load 30 by the second connection method.

The voltage input to the voltage input circuit 1 is converted into a digital signal having an effective voltage value by the first converter 3 and then input to the CPU 5. Then, in the instrument loss calculation unit 51 of the CPU 5, the first instrument loss W _V consumed in the voltage input circuit 1 is calculated (step 1). When the effective value of voltage is V and the known input resistance of the voltage input circuit 1 is R _V , the first instrument loss W _V is calculated by the following equation.
W _V = V ² / R _V (1)

The current input to the current input circuit 2 is converted into a digital signal having an effective current value by the second converter 4 and then input to the CPU 5. Then, the CPU5 instruments loss calculation unit 51, second meter loss W _A consumed by the current input circuit 2 are calculated (step 1). When the effective value of the current I, a known input resistance of the current input circuit 2, R _A, second meter loss W _A is calculated by the following equation.
W _A = I ² × R _A (2)

When the first instrument loss W _V and the second instrument loss W _A are calculated in the instrument loss calculation unit 51, the instrument loss comparison unit 52 of the CPU 5 performs the first instrument loss W _V and the second instrument loss W _A. And a signal related to the comparison result is output (step 2).

When W _V > W _A, the power consumption of the voltage input circuit 1 is large, so that the power consumption of the current input circuit 2 is included in the power consumption value of the load 30 displayed by the wattmeter 10 as shown in FIG. The second connection method shown in FIG. In the case of W _V <W _A, the power consumption of the current input circuit 2 is large, so that the power consumption of the voltage input circuit 1 is included in the power consumption value of the load 30 displayed by the wattmeter 10 as shown in FIG. The first connection method shown in FIG.

For example, when 600 V and 20 A are measured when the input resistance of the voltage input circuit 1 is 2 MΩ and the input resistance of the current input circuit 2 is 2 mΩ, the first instrument loss W _V is 0.18 VA from the above equation (1). second meter loss W _a from the equation (2) it becomes 0.8VA. In this case, since W _V <W _A , the first connection method is desirable. On the other hand, when 600 V and 1 A are measured when the input resistance of the voltage input circuit 1 is 2 MΩ and the input resistance of the current input circuit 2 is 2 mΩ, the first instrument loss W _V is 0. 18VA, second meter loss W _a from the equation (2) becomes 0.002VA. In this case, since W _V > W _A , the second connection method is desirable.

  The display unit 7 has instruction means for instructing at least one of whether to adopt the first connection method or the second connection method based on the signal input from the instrument loss comparison unit 52. is doing.

In this embodiment, the instrument loss comparing unit 52, a first meter loss W _V and second meter loss W _A is determined whether satisfies the following relationship, according to the comparison result, the instruction A signal designating which connection method should be instructed to the means is output as a signal related to the comparison result.
W _V > W _A (3)

Referring also to FIG. 5A, in the present embodiment, the display unit 7 displays characters (such as “load side” and “connection 1”) that can identify the first connection method as the instruction means. ) And a second lamp 72 that lights in association with a display (characters such as “power supply side” and “connection 2”) that can identify the second connection method. Is provided. Then, when the above formula (3) is satisfied (W _V > W _A ), the second lamp 72 is turned on to instruct that the second connection method should be adopted (step 4). On the other hand, when the above formula (3) is not satisfied (that is, W _V ≦ W _A ), the first lamp 71 is turned on to instruct that the first connection method should be adopted (step 3).

In this embodiment, when W _V = W _A , the second connection method is instructed. However, in this case, the first connection method is instructed. In this case, the connection method may not be specified. As another method, one of the connection methods may be instructed only when the difference between the first instrument loss W _V and the second instrument loss W _A is equal to or greater than a predetermined value.

  In the present embodiment, the first and second lamps 71 and 72 for indicating the first and second connection methods are provided as the instruction means, but the first and second connection methods are identified. One of the lamps 71 and 72 that are lit in association with the display to be obtained may be provided. For example, when a lamp that is lit in association with a display that can identify the first connection method is provided, lighting of the lamp indicates the first connection method, and turning off the lamp indicates the second connection method. Can be.

That is, the instructing means (i) performs the first connection when the input signal indicates that the second instrument loss W _A is larger than the first instrument loss W _V (W _V <W _A ). Indicates that the method should be adopted, or (ii) the input signal indicates that the first instrument loss W _V is greater than the second instrument loss W _A (W _V > W _A ) Or (iii) the input signal is greater in the second instrument loss W _A than in the first instrument loss W _V (W _V < (W _A ) indicates that the first connection method should be adopted, and the input signal is greater in the first instrument loss W _V than in the second instrument loss W _A ( When W _V > W _A ), it can be instructed that the second connection method should be adopted.

  Further, the instruction means is not limited to the presence or absence of lighting of the lamp, and the connection method may be displayed as characters (documents) or as a connection diagram, and appropriate connection for the user. Any device that can instruct the method is acceptable. For example, FIG. 5B shows an example in which a connection method is displayed with characters on a liquid crystal display 73 as an instruction means of the display unit 7, and FIG. 5C shows an example in which a connection diagram is displayed on the liquid crystal display 73. Indicates.

In the present embodiment, the CPU 5 exhibits a function of a power consumption calculation unit that calculates the power consumption of the load 30 by reading a program stored in the memory 6. In the present embodiment, the CPU5 is, by reading a program stored in the memory 6, exhibit the function of the meter loss calculation unit 51 for calculating a first instrument loss W _V and the second instrument loss W _A In addition, the function of the instrument loss comparison unit 52 that compares the first instrument loss W _V and the second instrument loss W _A is exhibited. As described above, in this embodiment, the CPU 5 has the function of the power consumption calculation unit, the function of the instrument loss calculation unit 51, and the function of the instrument loss comparison unit 52, but the present invention is limited to this. Instead, the power consumption calculation unit, the instrument loss calculation unit 51, and the instrument loss comparison unit 52 may be configured as separate circuits and elements, respectively.

  Here, the user connects the terminal of the voltage input circuit 1 of the wattmeter 10 to the load 30 as necessary in order to adopt any one of the first and second connection methods according to the instruction by the instruction means. Side or power source 20 side. FIG. 6 shows an example of a connector 40 that facilitates connection of the wattmeter 10 to the power supply 20 and the load 30. FIG. 6A shows a connection tool 40 when the first connection method is adopted, in which a plug 41 connected to a commercial power source or the like and a device under test (load) for measuring standby power or the like are connected. Plug receiver 42, electric wire 43 connecting plug 41 and plug receiver 42, terminals 44, 44 for connecting voltage input circuit 1 connected in the middle of electric wire 43, and current connected to electric wire 43 The terminals 44 and 44 for connecting the voltage input circuit 1 are connected to the plug receiver 42 rather than the terminals 45 and 45 for connecting the current input circuit 2. On the side. FIG. 6B shows a connection tool 40 in the case of adopting the second connection method, which has the same configuration as that of FIG. 6A, but the terminals 44 and 44 for connecting the voltage input circuit 1 are shown in FIG. The terminal 41 is provided closer to the plug 41 than the terminals 45 and 45 for connecting the current input circuit 2. By using these connectors 40, the wattmeter 10 can be easily connected to the power source 20 and the load 30 by a desired connection method. In addition, the connector 40 connects the terminals 44 and 44 for connecting the voltage input circuit 1 to both the plug receiver 42 side and the plug 41 side with respect to the terminals 45 and 45 for connecting the current input circuit 2. It may be possible to use either one selectively.

  As described above, according to the present embodiment, it is possible to easily confirm an appropriate connection method of the wattmeter under the actual measurement voltage and measurement current conditions. And since the connection method of a wattmeter can be confirmed easily, it becomes possible to perform a highly accurate measurement on the conditions where the influence of the instrument loss with respect to measurement accuracy is small.

Example 2
In the first embodiment, the present invention is described as applied to the measurement of single-phase power. In measurement of three-phase power, the measurement current is often relatively large, and the influence of instrument loss on measurement accuracy is often small. However, the present invention can be applied to measurement of three-phase power if desired. .

  In the present embodiment, a method for instructing a connection method in a three-phase power meter having a circuit pair (power measurement circuit) of a plurality of voltage input circuits and current input circuits will be described.

  For example, as shown in FIGS. 7A and 7B, the power of the three-phase three-wire is summed using two power measuring circuits (that is, two pairs of voltage input circuits and current input circuits). Can be obtained from 7A shows the case where the voltage input circuits U1 and U2 are connected to the load side from the current input circuits I1 and I2, and FIG. 7B shows that the voltage input circuits U1 and U2 are powered from the current input circuits I1 and I2. When connected to the side.

  In this case as well, as in the first embodiment, the power consumption of each voltage input circuit U1, U2 and each current input circuit I1, I2 is obtained under the conditions of the actual measurement voltage and measurement current, and the circuit U1 and circuit I1 are obtained. The magnitude relationship of the power consumption is compared for each of the circuit U2 and the circuit I2. Similarly to the first embodiment, when the current input circuit consumes more power than the voltage input circuit for each of the circuit U1 and the circuit I1, and the circuit U2 and the circuit I2, the voltage input is performed in the circuit pair. When it is instructed that the first connection method for connecting the circuit to the load side should be adopted and the power consumption of the voltage input circuit is larger than that of the current input circuit, the voltage input circuit is connected to the power supply side in the circuit pair. Instructs that the second connection method to be connected to should be adopted.

  Further, as shown in FIG. 7C, the power of the three-phase three-wires is obtained by using three power measurement circuits (that is, three pairs of voltage input circuits and current input circuits). It can also be measured by measuring. Also in this case, the power consumption of each voltage input circuit U1, U2, U3 and each current input circuit I1, I2, I3 is obtained, and each of circuit U1 and circuit I1, circuit U2 and circuit U2, and circuit U3 and circuit I3. Comparing the magnitude relationship of power consumption, depending on the comparison result, either the first connection method or the second connection method is adopted for each circuit pair in the same manner as in the case of using the two power measurement circuits. You should tell what to do.

  As described above, according to the present embodiment, even in the case of measuring three-phase power, it is possible to easily confirm the proper connection method of the wattmeter under the conditions of the actual measurement voltage and measurement current, and the measurement accuracy can be measured. It becomes possible to perform highly accurate measurement under conditions where the influence of loss is small.

1 Voltage input circuit (voltage input section)
2 Current input circuit (current input section)
5 CPU
7 Display Unit 10 Wattmeter 51 Meter Loss Calculation Unit 52 Meter Loss Comparison Unit 71 First Lamp (Instruction Unit)
72 Second lamp (instruction means)

Claims (3)

A voltage input unit connected to a power source and a load; and a current input unit connected to the power source and the load; a voltage input to the voltage input unit and a current input to the current input unit; In a wattmeter that measures the power consumption of the load based on
An instrument loss calculator that calculates power consumed by the voltage input unit and power consumed by the current input unit;
An instrument loss comparison unit that compares the power consumed by the voltage input unit and the power consumed by the current input unit, calculated by the instrument loss calculation unit, and outputs a signal related to the result of the comparison; ,
Based on the signal, the first connection method for connecting the voltage input unit to the load side with respect to the current input unit should be adopted or the voltage input unit to the current input unit on the power source side Instruction means for instructing at least one of the fact that the second connection method to be connected to
A wattmeter characterized by comprising: The instruction means includes
(I) whether the first connection method should be adopted when the signal indicates that the power consumed by the current input unit is greater than the power consumed by the voltage input unit; ,
(Ii) Whether the second wiring method should be adopted when the signal indicates that the power consumed by the voltage input unit is larger than the power consumed by the current input unit Or (iii) indicates that the first connection method should be adopted when the signal indicates that the power consumed by the current input unit is greater than the power consumed by the voltage input unit. And if the signal indicates that the power consumed by the voltage input unit is greater than the power consumed by the current input unit, indicates that the second connection method should be adopted. ,
The wattmeter according to claim 1.   The instructing means instructs a connection method to be adopted among the first connection method and / or the second connection method by lighting a lamp, displaying characters, or displaying a connection diagram. The wattmeter according to claim 2.

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