JPH0651002A - Adding circuit for electric power measuring value - Google Patents

Abstract

PURPOSE:To eliminate restriction on the range setting through attainment of a correct adding result by furnishing the resistance at each output with a resistance element for changing over whose resistance value is selectively controlled in reverse proportion to the electric power range to be set on power measuring parts. CONSTITUTION:Because the output voltages V1-V3 of electric power measuring parts 11-13 are all emitted in one volt, switches S1-S5 are opened and closed on the basis of a control signal given by a control part 18 so that a resistance value in reverse proportion to the power range set on the measuring parts 11-13 is obtained among resistance elements Ra-Re for changing over at the corresponding resistances R1-R3, and thereby the resistance element which becomes effective is selected. Among the power ranges set on the measuring parts 11-13 in currently service, therefore, the addition output with the max. range made full scale relatively is always acquired at an addition power output terminal T3. In whichever combination the power range set condition on the measuring parts 11-13 is, a correct adding result is obtained at all times, and restriction on the power range setting on the measuring parts 11-13 can be eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for adding measured power values, and more particularly to a circuit for adding measured power values in a digital power meter such as a digital AC meter having a plurality of power measuring units.

[0002]

2. Description of the Related Art A digital power meter such as a digital AC meter is mainly used for low-frequency AC power, power amount,
It measures voltage, current, etc., and displays them digitally. Since only single-phase power can be measured, three-phase three-wire system,
Some even measure three-phase four-wire three-phase power.

FIG. 2 shows a conventional digital power meter having three power measuring units capable of measuring not only single-phase power but also three-phase three-wire and three-phase four-wire three-phase power. 2 shows an example of an addition circuit of measured power values adopted by

According to the figure, the whole of the adder circuit for the measured power values has a voltage input terminal T1 and a current input terminal T2, respectively.
And three electric power measurement units 1, 2, and 3, which are respectively provided with
A first operational amplifier 4 in which the outputs from the power measuring units 1, 2 and 3 are input to the inverting input terminal side via resistors R1, R2 and R3 connected in series, and the first operational amplifier 4
The output from the operational amplifier 4 is input to the side of the inverting input terminal via the resistor R5 connected in series, and is configured with the second operational amplifier 5 including the output terminal T3 of the added power on the output side thereof. Is provided with a negative feedback circuit 6 formed by a resistor R4, and the second operational amplifier 5 is provided with a negative feedback circuit 7 formed by a resistor R6.

For the sake of convenience of description, the relationship between the resistors in the figure is R1 = R2 = R3 = 3 × R4, and R5
= R6, the power range of each power measuring unit 1, 2, 3 is
All of them are set to 1000 W (full scale), and the output of each of the power measuring units 1, 2, and 3 is a DC voltage proportional to the measured power. Here, in the power range full scale (1000 W). On the other hand, it is assumed to be 1V.

In this case, when the measured electric power of each electric power measuring unit 1, 2, 3 is 1000 W (full scale), the output of each electric power measuring unit 1, 2, 3 becomes 1V, respectively.
The voltage Va on the output side of the operational amplifier 4 is obtained by the following equation. Va =-(1VxR4 / R1 + 1VxR4 / R2 + 1VxR4 / R3) =-1V

Therefore, the output of 1V is obtained at the output terminal T3 for the added power by passing through the second operational amplifier 5 in the next stage.

That is, if the power ranges of the three power measuring units 1, 2 and 3 are the same, the output of the added power is 1000
This means a DC voltage with W × 3 as the full scale.

[0009]

By the way, according to the conventional example shown in FIG. 2, the total power (for example, three-phase four-wire is measured if the measurement of the three-phase four-wire line is performed under a simple circuit configuration. A DC voltage proportional to the total power) is obtained.

However, in the case of individually measuring, for example, three-channel single-phase power using the individual power measuring units 1, 2, and 3, the power ranges set in the respective power measuring units 1, 2, and 3 are set. As a result, the apparent added value is obtained at the output terminal T3 of the added power located on the output side of the second operational amplifier 5, but the correspondence with the set power range is unknown. Therefore, there was a problem that the data became virtually meaningless.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems found in the prior art. The structural feature of the present invention is that a plurality of power measuring units and these power measuring units are used. Each of the outputs of the first operational amplifier is input to the side of the inverting input terminal through the respective resistances connected in series, and the output from the first operational amplifier is input to the side of the inverting input terminal via the series connected resistance. And a second operational amplifier arranged so that the output thereof can be provided, and a negative feedback circuit formed by each of the first operational amplifier and the second operational amplifier being provided with a negative feedback circuit is provided. And
Each of the resistors on each output side of the power measurement unit is formed separately by providing a plurality of switching resistance elements whose resistance values are selectively controlled in inverse proportion to the power range set in the corresponding power measurement unit. However, the resistance in the negative feedback circuit of the second operational amplifier is the switching resistance element that is selectively controlled so as to have a resistance value corresponding to the maximum power range in the power range set by each power measurement unit. This is because the switching resistance element having the same configuration is provided.

[0012]

Therefore, on the output terminal side of the added power, of the power range set in the power measuring unit currently in use,
Since the addition output with the maximum range relative to the full scale is always obtained, the correct addition result can be obtained regardless of the combination of the setting states of the power ranges of the power measurement units. As a result, the restriction on range setting can be eliminated.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory view showing an embodiment of the present invention. As a whole, three power measuring units 11 and 12 each having a voltage input terminal T1 and a current input terminal T2 are provided. , 13 and these power measuring units 11, 12, 1
The respective resistors R1 in which the respective outputs from 3 are connected in series
A first operational amplifier 14 that is input to the side of the inverting input terminal via R2 and R3, and an output from this first operational amplifier 14 is input to the side of the inverting input terminal via a resistor R5 that is connected in series, and to the output side thereof. The second operational amplifier 15 is provided with an output terminal T3 for added power, and the first operational amplifier 1
4 is provided with a negative feedback circuit 16 formed by a resistor R4, and the second operational amplifier 15 is provided with a negative feedback circuit 17 formed by a resistor R6.

In this case, the resistors R1, R2 and R3 and the resistor R
6 and the corresponding switches S1 and S
By connecting in parallel switching resistance elements Ra, Rb, Rc, Rd, Re which are controlled to be opened / closed by 2, S3, S4, S5, the resistance values can be switched freely.

The three power measuring units 11, 12, 13 are also provided.
Are controlled by a range control signal sent from the control unit 18 via the control line 19 such that the power range can be automatically switched.
The resistance values of 1, R2 and R3 are selectively set in a relationship inversely proportional to the size of the set power range.

Each power measuring unit 11 set in this case,
Each of the power ranges of 12 and 13 is 200
5 of 0W, 1000W, 500W, 200W, 100W
Each type of power measuring unit 11, 12, 1 has a kind of power range.
Each of the outputs V1, V2 and V3 from 3 will be described as being 1V with respect to the full scale of the power range.

Further, the resistance values of the resistors R1, R2 and R3 selected in correspondence with the power ranges set in the respective power measuring units 11, 12 and 13, that is, the switching resistance element R.
The values of a, Rb, Rc, Rd, and Re are selected in a relationship that is inversely proportional to the set power range as shown in Table 1, and R4 = 1 and R5 = 1. It should be noted that the switching resistance elements Ra and R that form the resistor R6.
b, Rc, Rd and Re are also resistors R1, R2 and R3
It is assumed that the resistance value can be set under the same correspondence relationship as in the case.

[0019]

[Table 1]

Therefore, the power measuring units 11, 12, 13
For each power range in, the power measuring unit 11 as the channel 1 is set to 2000 W, the power measuring unit 12 as the channel 2 is set to 500 W, and the power measuring unit 13 as the channel 3 is set to 100 W to set the power corresponding to the full scale. If it is measuring, the power measuring unit 11, 1
Each of the output voltages V1, V2 and V3 of 2 and 13 is 1V.

That is, under the above setting conditions, the resistors R1 = Ra = 1, R2 = Rc = 4, R3 = Re according to Table 1.
The range control signal is output from the control unit 18 so that = 20.

Thus, the voltage Vo at the output terminal T3 of the added power is obtained by the equation (1) of Vo = -R6 * V4 / R5.

In the circuit of FIG. 1, the first operational amplifier 14
The output voltage V4 on the output side is V4 = −R4 × V1
/ R1-R4 x V2 / R2-R4 x V3 / R3 (2)
Calculated by the formula, based on Table 1, R1 is "1", R
By substituting “4” for 2 and the numerical value of “20” for R3, V4 = −1.3V is obtained.

On the other hand, regarding the resistor R6, there are three power measuring units 11, 12, 1 according to the control signal from the control unit 18.
Among the three, the resistance value corresponding to the setting range of any one in which the relatively maximum power range is set is controlled so that the resistance R6 = Ra under the above setting conditions. = 1.

Then, Vo = -R which is the above-mentioned formula (1).
By substituting R6 = R5 = 1 and V4 = −1.3V into 6 × V4 / R5, the voltage Vo at the output terminal T3 of the added power is obtained.
= 1.3V will be obtained.

Here, the set power range 200
Considering that the voltage Vo at the output terminal T3 of the added power is 1 V with respect to 0 W (full scale), Vo is 1.3.
In the case of V, the electric power corresponds to 2600 W, which is equal to the total power (2000 W + 500 W + 100 W) measured by the three power measuring units 11, 12, and 13.

Since the present invention is configured as described above, each of the output voltages V1, V2, V3 from the power measuring units 11, 12, 13 will be output at 1V. The switching resistance elements Ra, Rb, Rc, Rd, and R are provided in the respective resistors R1, R2, and R3.
Based on the control signal from the control unit 18, the switches S1, S2, S3, S4, S5 are provided so that a resistance value inversely proportional to the power range set in the power measurement units 11, 12, 13 is obtained from e. The switching resistance element that is controlled to be opened and closed and becomes effective is selected.

Therefore, on the side of the output terminal T3 for the added power, the addition of the maximum range of the power ranges currently set in the power measuring units 11, 12, and 13 as the full scale is added. The output will always be available.

Therefore, each power measuring unit 11, 12, 1
Since the correct addition result can be obtained regardless of the combination of the setting states of the power range of No. 3,
It is possible to eliminate the restriction on the range setting such that the respective power ranges of the power measuring units 11, 12, and 13 must be equal.

[0030]

As described above, according to the present invention, on the output terminal side of the added power, a relatively maximum range among the power ranges set in the power measuring unit currently in use is full. The scaled addition output is always obtained. Therefore, the correct addition result can be obtained regardless of the combination of the setting states of the power ranges of the power measurement units. The constraint can be removed.

[Brief description of drawings]

FIG. 1 is an explanatory circuit diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a power measurement value addition circuit for a conventional example.

[Explanation of symbols]

 Reference Signs List 11 power measuring unit 12 power measuring unit 13 power measuring unit 14 first operational amplifier 15 second operational amplifier 16 negative feedback circuit 17 negative feedback circuit 18 control unit 19 control line T1 voltage input terminal T2 current input terminal T3 added power output terminal S1 switch S2 Switch S3 switch S4 switch S5 switch Ra switching resistor element Rb switching resistor element Rc switching resistor element Rd switching resistor element Re switching resistor element

Claims (1)

[Claims] 1. A plurality of power measuring units, a first operational amplifier in which outputs from the power measuring units are input to the inverting input terminal side via respective resistors connected in series, and the first operational amplifier. A second operational amplifier arranged so that its output can be output by being input to the inverting input terminal side through a resistor connected in series, and each of the first operational amplifier and the second operational amplifier has a resistor. In the addition circuit of the measured power value, which is provided with a negative feedback circuit formed by
Each of the resistors on each output side of the power measurement unit is formed separately by providing a plurality of switching resistance elements whose resistance values are selectively controlled in inverse proportion to the power range set in the corresponding power measurement unit. However, the resistance in the negative feedback circuit of the second operational amplifier is the switching resistance element that is selectively controlled so as to have a resistance value corresponding to the maximum power range in the power range set by each power measurement unit. An addition circuit of measured power values, which is formed by providing switching resistance elements having the same configuration.