JPS63231272A - Power-factor meter - Google Patents

Abstract

PURPOSE:To obtain such a digital power-factor meter that its output has linear characteristics and its measured value is easy to read by measuring the digital converted value of a phase difference signal and finding a power-factor. CONSTITUTION:The voltage component and current component of a cable run 1 to be measured are detected by a voltage detector 22 and a current detector 27 and applied to a phase difference detector 25 and a polarity detector 26 through an attenuator 23, a current/voltage converter 28, and waveform shaping devices 24 and 29. Then a DC phase signal Vphi from the phase difference detector 25 is digitized by an A/D converter 30 and applied to a cosphi computing element 32, whose output is displayed numerically as a power-factor on a display device 36. The calculated value of a 1-cosphi calculator 32, on the other hand, is inputted to a D/A converter 33; when the phase difference phi is a delay phase, the analog value of 1-cosphi is sent out as it is through an output switch 34 and when the phase difference indicates a leading phase, the analog value whose polarity is inverted by an inverting amplifier 35 is sent out of the output switch 34 and applied to a recorder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital power factor meter, in particular, for measuring the power factor of three-phase AC power lines, etc.

[Conventional technology]

Conventionally, an analog power factor meter has generally been used, a typical example of which is shown in FIG.

That is, the voltage component of the electrical circuit under test 1 is detected by, for example, a voltage detector 2, adjusted to an appropriate level by an attenuator 3, and then shaped into a square wave voltage by a waveform shaper 4. is added to the detector 6. Further, the current component of the electrical circuit under test 1 is detected, for example, by a current detector 7, converted to an appropriate voltage level via a current/voltage converter 8, and then converted into a square wave voltage by a waveform shaper 9 in the same manner as above. and is added to the phase difference detector 5 and polarity detector 6.

The phase difference detector 5 detects the phase difference φ at the time of rising, for example, between one square wave voltage representing the applied voltage component and the other wave voltage representing the current component, and detects this phase difference φ. A phase difference signal ■φ whose magnitude is proportional to is sent out. In addition, in polarity detection: i) 6, for example, it is detected whether the rise time of the other square wave voltage representing the current component is ahead or behind the rise time of one square wave voltage representing the voltage component. Correspondingly, a − or 10 phase polarity signal is sent to the adder/subtractor 11.

The phase difference signal Vφ sent from the phase difference detector 5 is converted into a direct current through a filter 10, for example, and the adder/subtractor 1
Added to 1. This adder/subtractor 11 is supplied with, for example, a predetermined reference voltage ■. is set, and if the phase difference signal Vφ has a leading phase, V. -Vφ is subtracted, and if it is a delayed phase, it is V. An addition of +Vφ is applied, and the meter 12 is made to swing with the output.

The scale plate of this meter 12 has a center value of 1 as shown in FIG.
The value of φ is graduated. For example, if this meter has a full scale of 100 mV, its median value 1 is 50 mV.
Corresponds to V. Therefore, this meter 12 has, for example, 50
An offset voltage of mV is applied to indicate the median value 1 when there is no signal. In this case, the reference voltage of the adder/subtractor 11 is set to ■. is set to 50mV,
Further, the maximum level of the phase difference signal Vφ when the phase difference φ=π/2 is also adjusted to 50 mV in advance. Note that the power factor scale for measuring the three-phase electric circuit is shifted by 30°.

[Problem that the invention seeks to solve]

This conventional device has the advantage that the circuit is relatively simple, since the phase difference between the voltage and current in the electrical path to be measured is converted into the power factor by meter scale processing.

However, since the output is non-linear, it is difficult to read the measured values when recorded on a recorder, etc., and generally a reading scale such as the one shown in Figures 7 (A) and (B) is used. It was necessary to prepare several types to match the paper width of the recorder.

In addition, recently, digital measuring instruments equipped with microcomputers, for example, have become commonly used to measure other electrical quantities such as the voltage of the electrical circuit under test, so at least analog measuring instruments are available for on-site use. It is necessary to prepare two power factor meters and other digital measuring instruments, which is particularly inconvenient when working outdoors.

The present invention has been made in view of the above points, and its first purpose is to realize a digital power factor meter whose output has linear characteristics and whose measured values are easy to read. Also,
A second object of the present invention is to provide a power factor meter that can be incorporated into, for example, another digital measuring instrument and can perform measurements by sharing its microcomputer.

[Structure of the invention]

Referring to FIG. 1, which shows an embodiment of the present invention, in the power factor meter of 1, for example, a phase difference signal Vφ having a magnitude proportional to the phase difference φ output from the phase difference detector 25 is shown.
an A/D converter 30 that digitally converts the value, and e0 that calculates the value of cosφ from this digital conversion value V'φ.
8φ operator 31 and a 1,000-cosφ operator (hereinafter referred to as r1-co) that subtracts the value of cosφ from 1.
It is called "sφ operator". ) 32, and a D/A converter 33 that converts the subtraction result into, for example, an analog value;
It includes an output switch 34 that outputs the analog conversion value as is or inverted, an inverting amplifier 35, and a polarity detector 26 that controls the switching operation of the output switch 34.

[Measurement principle]

Since the phase difference signal ■φ output from the phase difference detector 25 has a level proportional to the phase difference φ between the voltage and current of the circuit under test 1 as described above, Vφ=k・φ
・・・・・・・・・・・・(1). However, is a constant of proportionality.

Here, since the maximum value Vφmax of Vφ is when φ=π/2, Vφmax=k・π/2 ・・・・・・・・・・・・
(2), which is known.

Therefore, from equations (1) and (2), Vφ/Vφmax=φ/(π/2) From the above equation, φ=(π/2)vφ/Vφmax・・・・・・・・・(
3) is obtained.

From equation (3), the value of the phase difference φ can be found by measuring Vφ.

The power factor cosφ is determined from this value of φ, and 1-cosφ is calculated.For example, as shown in the first quadrant of FIG. 2,
Expressing the value of the power factor CO3φ by a straight line OA on a graph having a horizontal axis representing the power factor on an evenly spaced scale with the origin as 1 and a vertical axis representing the output 1-COSφ on the equally spaced scale with the origin as O. Can be done.

In this case, if the straight line OA in the first quadrant is, for example, the power factor in the lagging phase, the power factor in the leading phase becomes a straight line ○B' that is symmetrical with respect to the vertical axis, as shown by the dotted line in the second quadrant. , it is unlucky at the origin ○.

Therefore, in this embodiment, as shown in the third quadrant, the output 1-cosφ of the leading phase is inverted to make the straight line OB' the straight line OB, and there is no discontinuity point between the leading phase and the lagging phase. The power factor cosφ is represented by a straight line.

Note that the straight line AOB representing the power factor cosφ is shown as an example inclined at 45 degrees with respect to the horizontal axis to make it easier to see, but the slope can be changed by making the scale intervals of the vertical and horizontal axes different. Needless to say.

〔Example〕

Referring again to FIG. 1, the manual section of this power factor meter includes, for example, a voltage detector 22, an attenuator 23, a waveform shaper 24, a phase difference detector, and the like as in the conventional device shown in FIG. Vessel 25. Polarity detector 26. It also includes a current detector 27, a current/voltage converter 28, a waveform shaper 29, and the like. In this embodiment, the phase difference detector 25 is also equipped with a filter that converts the phase difference signal Vφ into a direct current and outputs the DC signal, for example. Furthermore, the polarity detector 26 is adapted to apply, for example, a - or ten phase polarity signal to the output switch 34 and the display 36, indicating the lead or lag of the phase difference φ.

The DC phase difference signal ■φ sent from the phase difference detector 25 is converted into a digital signal by, for example, an A/D converter 30, and the converted digital signal V′φ is added to a cosφ calculator 31 to obtain a value of cosφ. The value is now required. This value of cosφ is applied to, for example, a 1-cosφ calculator 32 and a display 36, and is displayed as a power factor on a numeric display or the like in the display 36. In this case, when the displayed power factor value is in a leading phase, a display of 1 is given by the phase polarity signal from the polarity detector 26, for example.

” In the 1-cosφ calculator 32, 1-cosφ
is calculated, and this calculated value is used, for example, by the D/A converter 33.
After being analog-converted at , it is applied to an output switch 34 and an inverting amplifier 35 . In this embodiment, when the phase difference φ is a lagging phase, the analog value of 1-cosφ is sent out as it is, for example, via the output switch 34, and when it is a leading phase, the polarity is changed by the inverting amplifier 35. The inverted analog value is sent out from the output switch 34. This output is applied to a recorder (not shown), for example, and is used to record the power factor of the electrical circuit 1 to be measured. In this case, the switching operation of the output switch 34 is controlled by a phase polarity signal applied from the polarity detector 26, for example.

FIG. 3 shows an example in which three electrical circuits to be measured are measured on a recording paper 37 having equally spaced scales using a recorder (not shown). For example, the recorder is set so as to indicate the center position of the recording width of the recording paper 37 when there is no input, and the recording paper 37 has a lag phase (+) on each side of the recording paper 37, with the center position being 1. Appropriate equally spaced scale 0.8.0.6 so that the phase (-) can be seen.・・・・・・
...0 is added. For example, the measured values are shown in (a) or c), but it can be intuitively read that (a) is a power factor of 0.8, (b) is 0.9, and (c) is 0.7. Can be done. If you want to read more precisely, or if you are using recording paper that does not have scale lines, prepare a ruler with scale lines written on thick paper to match the recording width, as shown in Figure 4. do it.

〔Effect of the invention〕

As explained in detail above, this power factor meter measures, for example, the digital conversion value V'φ of the phase difference signal Vφ, which has a magnitude proportional to the phase difference φ between the voltage of the electrical circuit to be measured and the current stop. Find the phase difference φ and calculate cosφ by 1”J′J cos
A φ calculation unit, a 1-cosφ calculation unit that calculates 1-cosφ using the value of cosφ, and an analog conversion value of this calculation result, which is sent out as it is when the phase difference φ is a lagging phase, and a leading phase. In the case of
is controlled by the phase polarity signal.

Therefore, according to this power factor meter, the leading or lagging phase difference φ
Using the power factor value cosφ of the nonlinear characteristic according to 1-cos
φ is calculated, and the horizontal axis represents the power factor with equally spaced scale lines with the origin as 1, and the vertical axis represents the value of 1-cosφ with equally spaced scale lines with the origin as O. When the actually measured calculated value of 1-cosφ is plotted on a graph consisting of the above, the value of the power factor cosφ can be represented by a straight line passing through the origin.

Therefore, by recording this calculated value on recording paper using a recorder, for example, the power factor of the electrical circuit to be measured can be visually and intuitively read, making it possible to provide a highly accurate digital power factor meter that is extremely easy to use. .

In addition, this power factor meter can be incorporated into other digital measuring instruments,
For example, by sharing the microcomputer, it is possible to realize a relatively low-cost, multifunctional on-site measuring instrument equipped with a power factor meter.

[Brief explanation of the drawing]

1 to 4 relate to an embodiment of the power factor meter according to the present invention, FIG. 1 is a block diagram showing an example of its configuration, FIG. 2 is a diagram explaining the measurement principle, and FIG. 3 is a recorder 4 is an explanatory diagram of power factor measurement, 4th is an explanatory diagram of a power factor reading ruler, 5 is a block diagram of a conventional device, 6 is an explanatory diagram of its power factor scale, 7 (A) and 7 Figure (B) is an explanatory diagram of a power factor reading ruler. In the figure, 1 is the electrical circuit to be measured, 22 is the voltage detector, 24°29
25 is a phase difference detector, 26 is a polarity detector, 27 is a current detector, and 30 is an A/D converter. 31 is a cosφ operator, 32 is a 1-cosφ operator, 3
3 is a D/A converter, 34 is an output switch, 35 is an inverting amplifier, φ is a phase difference, Vφ is a phase difference signal, and V'φ is a digital conversion value.

Claims (1)

[Claims] A phase difference detector that detects the voltage and current of the electrical circuit to be measured, shapes the waveforms into square wave voltages, and forms a phase difference signal having a voltage proportional to the phase difference φ. , a polarity detector that forms positive and negative phase polarity signals in response to the lead and lag of the phase difference φ, and an arithmetic unit that determines the power factor cosφ from the digital conversion value of the phase difference signal and calculates 1-cosφ. and the above calculated value 1
- an output switching device that selectively switches the analog conversion value of cosφ or its inverted analog conversion value using the phase polarity signal from the polarity detector, and outputs the value of the power factor cosφ as a linear characteristic over positive and negative sides; A power factor meter characterized by comprising: