KR20070043514A - Wattmeter for voltage, current and power measurement - Google Patents

Abstract

The present invention relates to a precision current, voltage and power measuring device for developing a multi-function power meter capable of accurately measuring voltage, current, and power based on a thermoelectric converter and configuring the power meter. To this end, the transformer 60 and the current meter 72 for outputting a predetermined current and voltage, respectively; A predetermined DC voltage source 74; First switch 62, 68, 70 for switching between measurement mode connected to transformer 60 and current meter 72 and calibration mode connected to DC voltage source 74: First switch 62, 68, 70 Second switches 64 and 66 respectively connected to each other to switch one of voltage mode, current mode and power mode; First amplifying means having an adding means (80) for adding each output signal of the second switches (64, 66) and a subtracting means (82) for subtracting; Third and fourth thermoelectric transducers 84 and 86 each receiving an amplified signal amplified by the first amplifying means and connected in series; Second amplifying means for amplifying the output signals of the third and fourth thermoelectric transducers 84 and 86 to produce an output value proportional to the input; And feedback means for feeding back to the second switch 66 amplified by the second amplifying means.

Thermoelectric transducers, power, measurement, current, voltage, feedback, precision, calibration

Description

Precision current, voltage and power measurement

1 is a block diagram showing a schematic configuration of a thermoelectric converter used as a heat transfer element;

FIG. 2 is a graph showing the relationship between the heater 10 current and the output voltage in the thermoelectric converter shown in FIG. 1;

3 is a circuit diagram illustrating a principle of measuring input voltage and current using a thermoelectric converter;

4 is a circuit diagram illustrating a principle of measuring a power value using a thermoelectric converter according to the present invention;

5 is a circuit diagram of an electronic circuit for realizing voltage, current, and power measurement according to an embodiment of the present invention;

Figure 6 is a graph showing the experimental results of measuring the voltage using the measuring device according to the present invention,

7 is a graph showing the experimental results of measuring the current using the measuring device according to the present invention;

8 is a graph showing an experimental result of measuring power using the measuring apparatus according to the present invention.

<Description of the symbols for the main parts of the drawings>

10: heater,

12: thermocouple,

15: voltmeter,

16: insulator,

20: first amplifier,

22: second amplifier,

24: third amplifier,

25: thermoelectric transducer for signal measurement,

26: thermoelectric transducer for balance,

40: an adder,

42: subtractor,

44: fourth amplifier,

46: first thermoelectric transducer,

48: second thermoelectric transducer,

60: transformer,

62: first switch,

64: second switch,

66: second switch,

68: the first switch,

70: first switch,

72: current transformer,

74: direct current voltage source,

80: fifth amplifier,

84: third thermoelectric transducer,

86: fourth thermoelectric transducer,

90: second switch,

92: transistor,

96: second switch,

98: voltage-to-power converter,

100: second switch,

102: second switch,

104: second switch.

The present invention relates to a precision current, voltage and power measuring device, and more specifically, based on a thermoelectric converter, develop a multi-function power meter capable of measuring voltage, current, and power precisely, and the precision current constituting the power meter, It relates to a voltage and power measuring device.

In general, there are largely mechanical and electronic methods for precisely measuring AC electricity amount that changes over time, but most of them have recently been changed to electronic methods. Unlike the mechanical type, the electronic type can be operated by the development of the electronic device, and has the advantage of being able to perform several functions simultaneously.

Even in the case of electronic type, accuracy, measuring range, function, etc. vary depending on the type of electronic device used. A / D converters are widely used for measuring AC power due to high speed and improved resolution. However, the accuracy of the electricity measurement and the performance of the device are still insufficient.

For accurate and accurate measurement of AC electricity, thermoelectric transducers such as thermistors are used, which have the ability to convert alternating current into thermoelectric power. AC calorimeters made using thermoelectric transducers are used mostly as standard class power meters for calibrating power meters with high accuracy. However, when measuring voltage, current, power, and power factor using a thermoelectric converter, it is difficult to manufacture and there is a technical difficulty in compensating the characteristics of the thermoelectric converter. In addition, the measurement frequency is limited to the power supply frequency.

Accordingly, the present invention has been made to solve the above problems, an object of the present invention, to develop a multi-function power meter capable of precisely measuring voltage, current, power based on a thermoelectric converter and to configure a power meter To provide a precision current, voltage and power measuring device.

An object of the present invention as described above, the transformer 60 and the current transformer 72 for outputting a predetermined current and voltage, respectively;

A predetermined DC voltage source 74;

First switches 62, 68, 70 for switching between measurement mode connected to transformer 60 and current meter 72 and calibration mode connected to DC voltage source 74:

Second switches 64 and 66 connected to the first switches 62, 68 and 70, respectively, to switch one of voltage mode, current mode and power mode;

First amplifying means having an adding means (80) for adding each output signal of the second switches (64, 66) and a subtracting means (82) for subtracting;

Third and fourth thermoelectric transducers 84 and 86 each receiving an amplified signal amplified by the first amplifying means and connected in series;

Second amplifying means for amplifying the output signals of the third and fourth thermoelectric transducers 84 and 86 to produce an output value proportional to the input; And

Feedback means for feeding back to the second switch 66 amplified by the second amplification means; it can be achieved by a precision current, voltage and power measuring device.

The transformer 60 is a constant voltage selected from 15, 30, 60, 120, 240, and 480 V, and the current meter 72 is selected from 0.5, 1, 2, 2.5, 5, 10, 25, and 50 A. May be a constant current.

In addition, the DC voltage source 74 includes a 1 V supply DC voltage source used for calibration and a calibrator that can be adjusted from 0 to 1 V.

Among the first switches 62, 68, and 70, the measurement mode of the first switches 62 and 68 is connected to the transformer 60.

The measurement mode of the first switch 70 is connected to the current meter 720,

The calibration mode of the first switch 62, 70 is connected to the calibrator of the DC voltage source 74,

The calibration mode of the first switch 68 may be connected to the 1 V supply DC voltage source of the DC voltage source 74.

In addition, among the second switches 64 and 66, the voltage mode V of the second switch 64 is connected to the first switch 62.

The current mode I of the second switch 64 is connected to the first switch 70,

The power mode P of the second switch 64 is connected to the first switch 68,

The voltage mode V and the current mode I of the second switch 66 are connected to the feedback means,

The power mode P of the second switch 66 may be connected to the first switch 70.

In addition, the second amplifying means may include a transistor 92 connected in series with the output terminal of the sixth amplifier 94 and the sixth amplifier 94.

When the second switches 64 and 66 are in the voltage mode or the current mode, the feedback signal of the feedback means is preferably connected to the fourth thermoelectric transducer 86 through the subtraction means 82.

In addition, when the second switches 64 and 66 are in the power mode, it is most preferable that the second amplifying means further includes a voltage-to-power converter 90.

Other objects, specific advantages and novel features of the invention will become more apparent from the following detailed description and the preferred embodiments described in conjunction with the accompanying drawings.

The invention will now be described in detail with reference to the accompanying drawings, in which preferred embodiments are shown. In particular, it develops a multifunctional power meter that can measure voltage, current, and power precisely based on thermoelectric converters, and describes the development and characterization of measurement methods for voltage, current, and power that make up the power meter.

The device that converts input voltage to low voltage uses precision transformer with high accuracy and the electronically compensated two-stage current transformer as the device that converts input current to low current and has a change ratio error of 0.005%. In the case of voltage measurement, the measurement range was 15 V to 480 V, frequency 60 Hz to 3 kHz, and accuracy ± 0.05% .The current was measured at 0.5 A to 50 A, frequency 60 Hz to 3 kHz, and accuracy ± 0.08%. Characteristics. In case of power, the frequency of input voltage and current can be measured up to 1 kHz, and the performance of accuracy is ± 0.05% at 60 Hz, power factor 1, and ± 0.08% at power factor 0.5 (ground, phase).

First, the configuration and operation of the thermoelectric converter will be described. The thermoelectric converter used as a heat transfer element is used as an element for measuring alternating current and is composed of a heater 10 and a thermocouple 12. 1 is a block diagram showing a schematic configuration of a thermoelectric converter used as a heat transfer element. As shown in Fig. 1, the current supplied from the input of the thermoelectric converter generates heat in the heater 10 composed of a high resistance wire. Heat generated in the heater 10 generates thermoelectric power in the thermocouple attached while maintaining electrical insulation by the insulator 16 at the heater intermediate point. When the generated thermoelectric power is connected as shown in FIG. 1 and measured by a voltmeter 15, electrical output characteristics as shown in FIG. 2 are shown.

FIG. 2 is a graph illustrating a relationship between a heater 10 current and an output voltage in the thermoelectric converter illustrated in FIG. 1. As shown in FIG. 2, the output e of the thermoelectric converter is represented by Equation 1 below.

Represented by Where n is the thermal conversion constant of the thermoelectric converter, and I _heater represents the current flowing to the heater 10. That is, as can be seen from [Equation 1] and Figure 2, the output of the thermoelectric converter has a characteristic proportional to the square of the heater 10 current.

Single-junction thermoelectric converters using a single thermocouple use a multiple junction thermoelectric converter in one embodiment of the present invention because the output thermoelectric power is small and the heat transfer error is large compared to a multi-junction thermoelectric converter using a large number of thermocouples. . The thermoelectric converter uses TEM-6, purchased from a Russian standard body. The thermoelectric converter has two heaters 10 composed of multiple junctions. The heater 10 has a resistance of 100 Ω and a conversion error of AC and current of 5 × 10 ⁻³ %.

Hereinafter, the AC effective voltage and current measuring principle applied in the present invention will be described. First, in order to measure AC signals mixed with various waveforms to the most accurate value, they should be read as RMS values. The effective value (I _rms ) of the alternating current is shown in [Equation 2].

Since it is equal to the square root of the current squared mean value, the output characteristics of the thermoelectric converter can be used.

3 is a circuit diagram illustrating a principle of measuring input voltage and current using a thermoelectric converter. As shown in FIG. 3, the low voltage or low current signal Vac converted through a transformer or a current transformer is supplied to the thermoelectric converter 25 through the first amplifier 20. In this case, the first amplifier 20 should have a broadband characteristic for a quick response when the frequency of the input voltage is fast while acting as a buffer between the thermoelectric converter 25 for signal measurement and a transformer or a current transformer. The third amplifier 24 is a direct current amplifier but has the same performance as the first amplifier 20. In other words, the gains of the two first and third amplifiers 20 and 24 are equal, so that the outputs of the thermoelectric converter 25 for signal measurement and the thermoelectric converter 26 for balance are the same. The second amplifier 22 requires a DC amplification characteristic with low drift characteristics and excellent performance. Since the output voltage of the thermoelectric converters 25 and 26 is low voltage, the second amplifier 22 amplifies the signal to a high multi-volt signal and feeds it back. To gain is 10 ⁶ or more.

The output voltage E1 of the thermoelectric converter 25 for signal measurement is connected to the non-inverting input terminal of the second amplifier 22, and the output voltage E2 of the balance thermoelectric converter 26 influences the current fed back. It is connected to the inverting input terminal after receiving. The output voltage E2 is exactly equal to the magnitude of the output voltage E1. If the output voltage E2 is less than the output voltage E1, the output of the second amplifier 22 is increased, and the heater current of the balance thermoelectric converter 26 is increased to be adjusted to be equal to the output voltage E1. . On the contrary, if the output voltage E2 is larger than the output voltage E1, the output of the second amplifier 22 is reduced, and the heater current of the balance thermoelectric converter 26 is simultaneously reduced, so that the magnitude of the output voltage E1 is reduced. Becomes the same as This is expressed as the following equation. That is, the converted voltage and current signal Vac passing through the first amplifier 20 have the following outputs in the thermoelectric converters 25 and 26.

If the gain of the second amplifier 22 is very high,

In the process

Becomes N ₁ and n ₂ represent the conversion constants of the thermoelectric converters 25 and 26, respectively. If n ₁ ≠ n ₂ can be achieved by adjusting the resistance (R1). Therefore, the output DC voltage Vdc of the third amplifier 24 has an effective value proportional to the input AC voltage Vac. In both cases of voltage and current, the same measurement principle is used, and the use of transformers and current transformers, which are the elements used in the input conversion, is different.

Hereinafter will be described with respect to the measuring principle of the power adopted in the present invention. Power measurement using thermoelectric transducers applies principles using basic mathematical laws. Mathematically, the product of two variables can be expressed by the terms squared to the sum and difference, respectively, as shown in [Equation 7].

In other words, when A = U _u and B = U _i in Equation 7, Equation 8 is obtained. U _u is the signal voltage converted through the transformer, and U _i is the signal current converted by the current transformer. Respectively. As shown in Equation 8, U _u ㆍ U _i = Vp, which is a multiplication of two signals expressed as power, is represented as a power value by using a thermoelectric converter.

4 is a circuit diagram illustrating a principle of measuring a power value using a thermoelectric converter in the present invention. As shown in Figure 4, Equation 8] cheotjjaehang first thermal type by supplying the converter (46) (U _u + U _i) ² is realized by adding the U _u and U _i signal from the adder 40, The second term realizes (U _u -U _i ) ² by subtracting the U _u and U _i signals from the subtractor 42 and supplying them to the thermoelectric converter of the second thermoelectric converter 48. By connecting the output polarities of the two thermoelectric converters 46 and 48 opposite to each other, the value of the first term to the second term is subtracted. It is represented by the power value represented by the output V _p = U _u ㆍ U _i of the fourth amplifier 44 thus obtained.

Hereinafter, a detailed configuration of a voltage and current power measurement circuit according to an embodiment of the present invention will be described. 5 is a circuit diagram of an electronic circuit for realizing voltage, current, and power measurement according to an embodiment of the present invention. In order to increase the accuracy of the measurement, a transformer 60 and a current transformer 72 which can select an input measurement range were used. The converted voltage and current signals are supplied to the circuit through the first switches 62, 68 and 70, and the first switches 62, 68 and 70 allow selection of measurement and calibration functions. The measurement range selection of the transformer 60 was selected to measure the value to be measured by setting the measurement range to 6 ranges including 15, 30, 60, 120, 240, 480 V. In the case of the current transformer 72, measurement ranges of 0.5, 1, 2, 2.5, 5, 10, 25, and 50 A are provided. At this time, the maximum signal size converted according to the measurement range selected at the input of the transformer 60 and the current transformer 72 is 1V. If the calibration function is selected, the measurement circuit is calibrated. The 1 V supply DC voltage source (DC, Ref.V. 1 V) used for calibration and the calibrator adjustable from 0 to 1 V use the Fluke 5520A and are all housed in the DC voltage source 74 together. Used as a supply DC voltage source, the Fluke 5520A has an uncertainty characteristic of 0.001% at 1 V DC. When the measuring circuit is fully calibrated, this function is absent and only the measuring function is maintained for future calibration of the circuit.

When measuring the voltage, the first switch 62, 68, 70 is in the "measurement" position as shown in Figure 5, the second switch 64, 66, 90, 96, 100, 102, 104 is in the "V" position Put it. The measured voltage signal is connected from the fifth amplifier 80 to the third thermoelectric converter 84 via the second switch 64. At this time, the AC signal is converted into a DC signal and fed back through the sixth amplifier 94 and the transistor 92. This signal is connected to a fourth thermoelectric converter 86 via a second switch 66 and a second switch 100. In addition, the output obtains a value proportional to the input AC voltage through the sixth amplifier 94.

The current measurement is the same as the voltage, except that the positions of the second switches 64, 66, 90, 96, 100, 102, and 104 used at this time are different from "I".

In the case of power measurement, the input voltage and the input current are supplied to the transformer 60 and the current transformer 72. The second switches 64, 66, 90, 96, 100, 102, 104 are all placed in the position of "P". The output voltage of the sixth amplifier 94 is converted into power, and the value measured by power is output in proportion to the input voltage and the input current and the phase between the input voltage and the current.

Hereinafter, an operation method and an experimental method of the precision current, voltage, and power measuring device having the above configuration will be described. First, the following experiment was repeated to measure the voltage using the circuits of FIG. 5 described above. That is, the input voltage was measured at 15, 30, 60, 120, 240, and 480 V by supplying frequencies 60, 100, 400, 1,000, and 3,000 Hz. The input voltage was converted to low voltage using a precision voltage transformer (conversion ratio error: 0.005%). The voltage source used for the test was ROTEK 8000 (accuracy: 0.02% in the 15-600 V range) and the output was read with a digital voltmeter Keithley 182 (0.01% accuracy). Experimental results are shown in FIG. 6, and as shown in FIG. 6, it can be seen that the relative error of the voltage output falls within a range of ± 0.05% over the full range of frequencies. In other words, the relative error of the voltage output was good.

In addition, the following experiment was repeated to measure the current using the circuit of FIG. 5 described above. Measurement currents were measured from 0.5 A to 50 A and measured at 0.5, 1, 2, 2.5, 5, 10, 25, 50 A. The frequency was measured by supplying 60, 100, 400, 1,000, and 3,000 Hz in the same manner as the voltage.

Current was used with an electronically compensated precision current meter (current ratio error: ± 0.005%). The voltage source used for the test was ROTEK 8000 (accuracy: 0.02% from 0.5 to 50 A) and the output was measured with a digital voltmeter Keithley 182 (accuracy 0.001%). This measurement result is shown in FIG. That is, Figure 7 is a graph showing the experimental results of measuring the current using the measuring device according to the present invention. As shown in FIG. 7, it can be seen that the relative error is in the range of ± 0.01%.

Hereinafter, an experiment of measuring power using the above-described circuit of FIG. 5 will be described. 8 shows the result of measuring the input voltage at 240 V and measuring the current from 0.5 A to 50 A among the results of the power measurement. The power factor was measured at 1, 0.5 (ground) and 0.5 (true phase), and the frequency was 60, 100, 400, and 1,000 Hz with the same voltage to measure the power values for each. The measurement results show that the input voltage and current frequency can be measured up to 1 kHz, with accuracy of ± 0.05% at 60 Hz and 100 Hz, power factor 1, and ± 0.08% at power factor 0.5 (ground, true phase).

Therefore, according to one embodiment of the present invention as described above, it is possible to provide a power meter capable of accurately measuring voltage, current, and power based on a thermoelectric converter. The ideal thermoelectric converter has the same response characteristics for alternating current and direct current, and the output thermoelectric power has a square output proportional to the input signal, which can be used to measure voltage, current, and power. In the case of power, a power meter capable of measuring the measurement frequency range up to 1 kHz was manufactured and its characteristics were evaluated. In addition to power, voltage and current can be measured precisely, and the frequency range can be measured up to 3 kHz.

Although the present invention has been described in connection with the above-mentioned preferred embodiments, it will be readily apparent to those skilled in the art that various other modifications and variations can be made without departing from the spirit and scope of the invention. It is obvious that all modifications fall within the scope of the appended claims.

Claims (9)

A transformer 60 and a current transformer 72 for outputting a predetermined current and voltage, respectively; A predetermined DC voltage source 74; First switches 62, 68, 70 for switching between a measurement mode connected with the transformer 60 and the current transformer 72 and a calibration mode connected with the DC voltage source 74: Second switches (64, 66) connected to the first switches (62, 68, 70), respectively, to switch one of voltage mode, current mode, and power mode; First amplifying means having an adding means (80) for adding each output signal of said second switch (64, 66) and a subtracting means (82) for subtracting; Third and fourth thermoelectric transducers 84 and 86 each receiving an amplified signal amplified by the first amplifying means and connected in series; Second amplifying means for amplifying the output signals of the third and fourth thermoelectric transducers 84 and 86 to generate an output value proportional to the input; And And feedback means for feeding back to the second switch (66) amplified by the second amplifying means. The device of claim 1, wherein the transformer (60) is a constant voltage selected from 15, 30, 60, 120, 240, and 480 V. The device of claim 1, wherein the current meter (72) is a constant current selected from 0.5, 1, 2, 2.5, 5, 10, 25, 50 A. 2. The apparatus of claim 1, wherein the direct current voltage source (74) comprises a 1 V supply direct current voltage source used for calibration and a calibrator capable of adjusting from 0 to 1 V. The method of claim 4, wherein, among the first switches 62, 68, 70, The measurement mode of the first switch 62, 68 is connected to the transformer 60, The measurement mode of the first switch 70 is connected to the current meter 720, The calibration mode of the first switch 62, 70 is connected to the calibrator of the DC voltage source 74, The calibration mode of the first switch (68) is a precision current, voltage and power measuring device, characterized in that connected to the 1 V supply DC voltage source of the DC voltage source (74). The method of claim 1, wherein the second switch (64, 66), The voltage mode V of the second switch 64 is connected to the first switch 62, The current mode I of the second switch 64 is connected to the first switch 70, The power mode P of the second switch 64 is connected to the first switch 68, The voltage mode V and the current mode I of the second switch 66 are connected to the feedback means, The power mode (P) of the second switch (66) is a precision current, voltage and power measuring device, characterized in that connected to the first switch (70). The method of claim 1, wherein the second amplifying means, Sixth amplifier 94 and Precision current, voltage and power measurement device, characterized in that consisting of a transistor (92) connected in series with the output terminal of the sixth amplifier (94). The method of claim 1, When the second switch (64, 66) is in voltage mode or current mode, the feedback signal of the feedback means is connected to the fourth thermoelectric transducer (86) through the subtraction means (82) Current, voltage and power measuring devices. The method of claim 1, And the second amplifying means further comprises a voltage-to-power converter (90) when the second switch (64, 66) is in power mode.

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