JPH0690240B2 - Clamp sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a clamp sensor using a Hall element,
More specifically, the present invention relates to a clamp sensor in which a control current composed of two components, a direct current and an alternating current, is made to flow through a Hall element so that the current and power of a measured line can be detected at the same time.

[Prior Art] When a current is applied to a Hall element placed in a magnetic field from a certain direction, it is proportional to the applied current and the strength of the magnetic field in the direction perpendicular to the direction of this current due to the effect called the Hall effect. It is known to generate a voltage called a Hall voltage. Using this multiplication function, a clamp sensor that incorporates a Hall element in a magnetic core that has an opening / closing mechanism that allows the measured electric wire to be wrapped outside the conventional so-called clamp type wattmeter that measures line power in a live state. It is used.

The current flowing from a certain direction to the Hall element of the clamp sensor is usually called a control current, and depending on whether the measurement target is a current value or a power value, this control current is either a constant DC current or a line voltage of the measured line. An alternating current of proportional magnitude is made to flow. In the case of AC power measurement, the phase of the control current is, of course, the same as the phase of the line voltage, so that measurement error due to phase mismatch does not occur.

When measuring electric power using such a clamp type power meter, if the line current is also known, the power factor of the load can be easily calculated. This is extremely preferable for the user side. However, in the above-mentioned conventional wattmeter using the Hall element, it is actually difficult to measure the line current when measuring the electric power. Therefore, in such a case, a separate clamp type ammeter is prepared. There was a need.

[Object of the Invention] The present invention has been made in view of the above points, and an object thereof is to pass a control current composed of two components, a direct current and an alternating current, through one Hall element to thereby reduce the current and power of a line. It is to realize a clamp sensor capable of simultaneously detecting.

[Structure of the Invention] Hereinafter, the present invention will be described in detail with reference to embodiments shown in the accompanying drawings.

FIG. 1 shows the principle of the clamp sensor according to the present invention. Referring to the figure, a ring-shaped magnetic core 2 is provided so as to surround the measured line 1, and a Hall element 3 is provided in a magnetic gap provided in a part of a magnetic path formed by the magnetic core 2. It is installed. The actual size of the Hall element 3 is set within the cross section of the magnetic core 2. However, in FIG. 1, the Hall element 3 is enlarged and shown as a cross-shaped plate for convenience of explanation. There is. The Hall element 3 has a pair of terminals X and X to which lead wires are respectively connected in a cross shape as shown in the figure, and another terminal orthogonal to the pair of terminals X and X.
A pair of terminals Y, Y is provided.

Now, the measurement line 1 is an AC line, the line voltage e _0, the line current and i _0, the line current to the line voltage e ₀
If i ₀ is delayed by the phase angle θ, it can be set as e ₀ = Emsin ωt (1) i ₀ = Imsin (ωt−θ) (2).

With this line current i ₀ is assumed that the magnetic flux B is induced, since the magnitude of the magnetic flux B is proportional to the magnitude of the line current _{i 0, B = k 1 i} 0 = k 1 Imsin (ωt-θ) (3) (k ₁ is a constant). In this case, it is assumed that the entire magnetic flux B passes through the magnetic core 2 and intersects the Hall element 3 in a direction orthogonal to the XY plane, that is, in the Z direction.

Next, in the present invention, a control current i different from that of the conventional clamp sensor is applied between the terminals X and X. This control current i is obtained by adding an alternating current ic to a constant level direct current Ic, i = Ic + ic (4) '. In this case, the phase of the alternating current ic is in phase with the line voltage e ₀ , and its current level is proportional to the magnitude of the line voltage e _0. ic = k ₂ e ₀ = k ₂ Emsinωt (k ₂ is a constant ) Has been set.

Therefore, the control current i becomes i = Ic + k ₂ Emsinωt (4) according to the equation (4) ′.

A Hall voltage Vh obtained by multiplying the equations (3) and (4) by the Hall effect appears between the terminals Y and Y.

That is, Vh = B × i = k ₁ Imsin (ωt−θ) × (Ic + k ₂ Emsinω
t) = k ₁ IcImsin (ωt−θ) + k ₁ k ₂ EmImsin ωt × sin (ωt−θ) If the intermediate process is omitted, Vh = k ₁ IcImsin (ωt−θ) + (1/2) k ₁ k ₂ EmImcos θ − (1/2) k ₁ k ₂ × EmImcos (2ωt−θ) (5) In the above equation, when ω = 2π / T and the average value in one cycle of the first term is examined, from a simple calculation, It turns out that

Similarly for the third term, Becomes

Regarding the second term, Becomes However, Has been replaced by the effective value.

Therefore, the average value of the Hall voltage Vh shown in the formula (5) in one cycle is equal to the value of the formula (6) as follows.

That is, From the above, in the equation (5), the DC signal voltage of the second term which does not include the frequency component represents the active power supplied to the load or the like via the measured line 1, and the first term and the third term
It shows that the AC signal voltage in the section has nothing to do with the supplied power. Note that, focusing on the first term, since the line current i ₀ = Imsin (ωt−θ) shown in the equation (2) is included, it is understood that this term represents the line current. Therefore, if the AC signal voltage including the fundamental wave of the first term and the DC signal voltage of the second term are detected from the Hall voltage Vh, the line current and the active power can be measured at the same time. In this case, since k ₁ × Ic of the first term and k ₁ × k ₂ of the second term are both known constants, signal processing may be performed so as to correct the detected signal. Since the frequency of the AC signal voltage of the third term is double that of the fundamental signal voltage of the first term, it is not possible to separate this signal from the signals of the first and second terms. You can easily.

The above is a description of the principle of detecting the power and the current in the AC line, but the concept is almost the same in the case of detecting the power and the power of the DC line as well, and the outline thereof will be described below.

If the line voltage of the DC line is Em ', the flowing current is Im', and the magnetic flux B'is induced by this current Im ',
Following the equation (3), B ′ = k ₁ ′ Im ′ (8) can be set. Here, k ₁ ′ is a constant.

Next, assuming that the control current is i ', this control current i'is the same as in the case of the above-mentioned AC line, the DC current Ic' and the AC current ic '.
, And I '= Ic' + ic '(9). In this case, the alternating current ic' is an appropriately set constant level alternating current, for example, ic ' = I ₀ ′ sinω′t (10)

On the other hand, the magnitude of the DC current Ic 'is the line voltage of the DC line.
'In proportion to, Ic' Em is the _{= k 2 'Em' ...... (} 11). Here, k ₂ ′ is a constant.

Therefore, the control current i'is obtained by substituting the equations (10) and (11) into the equation (9), i '= i ₀ ′ sinω′t + k ₂ ′ Em ′ (12).

Assuming that the hole appearing between the terminals Y and Y is the voltage Vh ',
This Hall voltage Vh 'intended multiplied by the equation (9) into equation (8), Vh' is = B '× i' = k 1 'Im' × (Ic '+ ic'), formula (12) When rewritten using

Vh ′ ＝ k ₁ ′ k ₂ ′ Em′Im ′ + k ₁ ′ Im ′ × i ₀ ′ sinω′t (13) As in the case of equation (5) in the AC line, the above equation (13)
If you look up the average value of Therefore, it can be seen that the DC signal voltage of the first term in equation (13) represents DC power. In this case, the AC signal voltage of the second term becomes zero and does not contribute to the power, but the DC current flowing through the line can be measured by performing the signal processing and detecting the DC component Im '.

FIG. 2 shows an embodiment in which the clamp sensor according to the present invention is applied to a power meter. Referring to the figure, a pair of magnetic cores 2 having an opening / closing mechanism (not shown) is externally included in the measured line 1, and a Hall element 3 is incorporated in the magnetic gap. This Hall element 3
The control current generator 4 is connected to one of the control current input terminals X and X via a lead wire, and the other hall voltage output terminals Y and Y are similarly connected to the detection unit 5 via a lead wire. Are connected. An instruction unit 6 is provided after the detection unit 5, and the output signal from the detection unit 5 is digitally processed here, for example, and the measured value is displayed on a numerical display or the like. It is like this.

Next, the configuration of each section will be described.
Includes a DC power supply 7 and an AC power supply 8 as current sources for forming DC and AC control currents. The DC power supply 7 is a DC power supply of a power meter body paired with the clamp sensor. You may use it. The AC power supply 8 includes, for example, a voltage transformer, an amplifier, and a relatively low frequency oscillator including a commercial power supply frequency.
It is internally switched to use voltage transformers and amplifiers when measuring AC power and current, and oscillators and amplifiers when measuring DC power and current. In this case, a switch 9 for switching the input and output of the DC power supply 7 and the AC power supply 8 is provided. That is, when the switch 9 is tilted to the contact a side for AC measurement, the induced voltage of the pickup loop 10 arranged so as to be electromagnetically coupled to the line 1 to be measured causes the switch 9A in the AC power source 8. Entered through. This input voltage is applied to the voltage setting device 11 from the switching device 9B via the voltage transformer and the amplifier in the AC power supply 8.

In the case of this embodiment, the voltage setting device 11 is composed of, for example, an amplifier whose voltage amplification factor is variable, and the voltage input from the AC power source 8 is proportional to the level of the line voltage. It is adapted to be set to relevant voltage levels. The voltage setting device 11 may be composed of an amplifier having a constant voltage amplification factor and a variable attenuator, and the input voltage from the AC power supply 8 may be switched by the attenuator.

The AC voltage thus set to have a constant proportional relationship with the line voltage is input from the voltage setter 11 to the adder 12 via the switch 9D. In this case, the DC voltage from the DC power supply 7 is also input to the adder 12 via the voltage setter 13 and the switch 9E, but this DC voltage is irrelevant to the level of the line voltage. It is set to a certain level of voltage. Both the AC and DC voltages are added to the above-mentioned adder 12
And the voltage / current converter 14 in the next stage
After being converted into a current in, a control current is applied to the Hall element 3. The adder in this embodiment
Both 12 and the voltage / current converter 14 are general circuits configured by using an ordinary operational amplifier, but the phase of the AC component in the control current output from the voltage / current converter 14 is Is noted to be in phase with the line voltage.

When measuring DC power and current, the switch 9 may be tilted to the contact point b side for DC measurement. As a result, the oscillator built in the AC power supply 8 oscillates. After the output of this oscillator is appropriately amplified by the built-in amplifier,
It is applied to the voltage setting device 15 via the contact b of the switching device 9B and is made into an AC voltage of a constant level. In addition, the voltage of the measured line 1 taken in via the pickup loop 10 is the switching device 9A.
The voltage is applied to the voltage setter 16 via the contact b of the above, and the level thereof is set to the direct current voltage having a constant proportional relationship according to the level of the line voltage, as in the case of the alternating current measurement. Although not shown, in this embodiment, the pickup loop 10 is provided with a probe, and the probe is brought into contact with the measured line 1 at the time of measuring the DC power and the current, so that the measured line 1 is measured. The voltage of 1 is detected. The constant level AC voltage output from the voltage setting unit 15 and the DC voltage having a level proportional to the line voltage output from the voltage setting unit 16 are respectively changed by the switching unit 9D.
Is input to the adder 12 via each contact b of the switch 9E, added as in the case of the AC power and current measurement, and then converted into a control current in the voltage / current converter 14. In this embodiment, the voltage setters 15 and 16 are composed of circuits substantially similar to the voltage setters 13 and 11, respectively.

The detection unit 5 separates and extracts a signal corresponding to the active power in the Hall voltage output from the Hall element 3 and a signal corresponding to the line current. Terminals Y, Y of the Hall element 3 above
The Hall voltage appearing at is input to the buffer amplifier 20 constituted by, for example, an operational amplifier via a lead wire. The output voltage of the buffer amplifier 20 is input to the low-pass filter 21 so that a signal voltage having a frequency twice that of the line voltage, which is unnecessary for AC power and current measurement, is removed. In this case, the line voltage frequency is, for example, 50H.
Of course, the cutoff frequency of the low-pass filter 21 can be switched accordingly if it covers z, 60 Hz, or any other frequency. The low-pass filter 21 preferably has a steep cutoff characteristic, and for example, an active filter formed by using an operational amplifier is suitable. If the line to be measured is a DC line, a voltage component having twice the frequency does not occur, so
The input voltage is output as it is through the low pass filter 21.

The output voltage of the low-pass filter 21 is further input to the low-pass filter 22 on the one hand, but is also input to the rectifier / smoother 24 via the DC blocking capacitor 23 on the other hand, and the output of the rectifier / smoother 24 is It is designed to be sent to the instruction section. As a result, the output voltage of the low-pass filter 22 becomes a direct current with the AC component canceled. This DC voltage and the DC voltage output from the rectifier / smoothing device 24 are
The indicator 6 digitally performs signal processing and displays the measured value on a numerical display or the like. In each of the voltage setters 11, 13, 15, and 16, the constant set when forming the control current is sent to the instruction unit as a reference signal for correcting the detection signal, and The correct measurement value is displayed.

[Operation] Next, the operation of the clamp sensor will be described with reference to FIGS. 3 and 4 together. Note that, in FIG. 2, the same reference numerals are given to the portions where the signal waveforms shown in FIG. 3 or 4 appear.

First, the case of detecting AC power and current will be described with reference to FIG.
The line voltage e ₀ having a sinusoidal waveform as shown in Fig. ₆ is applied, and a line current i ₀ with a phase angle delayed by θ as shown in (b) flows with respect to this line voltage e ₀ . It is assumed that A part of the line voltage e ₀ is taken out by the pickup loop 10 and amplified through the AC power source 8 and then proportional to the magnitude of the line voltage e ₀ as shown in (c) in the voltage setting device 11. To the specified voltage. on the other hand,
The DC power supply 7 is set to a voltage of a constant level of (+) by the voltage setting device 13 as shown in (D) of its polarity. These two voltages are sent to the adder 12 via the switches 9D and 9E, respectively, and are added there to shift the center line to the (+) side by the DC component of the above (d) as shown in (e). It becomes AC voltage. This AC voltage is the voltage of the next stage /
After being converted into a current in the current converter 14, X, X of the Hall element 3 is obtained as the control current i shown in the above equation (4).
It is washed by the terminal. The waveform of the control current i is similar to the voltage waveform of (e) as shown in (f).

Although the Hall voltage Vh shown in the above equation (5) appears at the Y and Y terminals of the Hall element 3, for the sake of simplicity, if the amplitude of the fundamental wave signal voltage and the amplitude of the double frequency signal voltage are substantially equal, The waveform of the Hall voltage Vh is as shown in (g), for example. This Hall voltage Vh is input to the low-pass filter 21 via the buffer amplifier 20, and the signal voltage of the double frequency as shown in (H) is removed. The composite signal voltage of the fundamental wave signal voltage and the direct current signal voltage appears at the output of the low pass filter 21 as shown in (i), but the fundamental wave signal voltage is converted to direct current through the capacitor 23 and the rectifier / smoothing device 24. After being converted, it is sent to the instruction unit 6 and used for the measurement of the line current i ₀ shown in the equation (2).
In this case, the voltage sent from the rectifier / smoothing device 24 is
For example, a DC voltage corresponding to the magnitude of the fundamental wave signal voltage is obtained as shown in FIG. On the other hand, low-pass filter 22
In, the fundamental wave signal voltage is further removed from the output signal voltage of the low pass filter 21 shown in (i) above,
A DC signal voltage as shown in (L) is output. This signal voltage is used for measuring the active power of the line in the indicator.

Next, referring to FIG. 4, the case of detecting DC power and current will be described. The switching device 9 is tilted to the contact b side and the AC power supply 8 is operated as an oscillator. Line voltage
Em ′ and line current Im ′ are shown in the figures (e) and (wa), respectively.
As shown in. In this case, the voltage setter 15 emits an AC signal voltage of a constant frequency ω'at a properly set constant voltage level, as shown in (f), for example. As shown in (Y), the voltage setter 16 outputs a DC signal voltage having a magnitude proportional to the line voltage Em '. This DC signal voltage is added to the AC signal of the constant level in the adder 12 to become a signal voltage as shown in (T), which is shown in (L) by the voltage / current converter 14 as in the case of the AC line. Is converted into a control current i '.

In this case, the Hall voltage Vh 'has a waveform as shown in (b), for example, and does not include a signal voltage having a doubled frequency, as was made clear in the explanation of the principle of the clamp sensor. Therefore, a signal voltage having the same waveform as the waveform of the Hall voltage Vh 'shown in (S) above appears on the output side of the low-pass filter 21, as shown in (T). The DC voltage component is removed from this signal voltage via the capacitor 23, and further passed through the rectifier / smoothing device 24 to be a DC signal voltage as shown in (N), which is sent to the instructing unit 6 and the line current Im. ′ Is used for measurement. In the low-pass filter 22, the AC voltage component is removed from the signal voltage of the low-pass filter 21 shown in (T) above, and its output side has a DC signal voltage as shown in (N) as in the case of the AC line. Is obtained. This DC signal voltage is sent to the indicator 6 and used for power measurement of the line.

FIG. 5 shows a modified embodiment of the clamp sensor. In this modified embodiment, the configuration of the control current generator is different from that of the embodiment shown in FIG. That is, in the control current generator 25 of this modified embodiment, the DC power supply 7 and the AC power supply 8 respectively generate a DC voltage and an AC voltage of a constant level that are not directly related to the voltage and current of the line under test 1, and the voltage setting device. 26 and 27 are the measured line 1 respectively
The AC voltage and the DC voltage having a magnitude proportional to the voltage are generated and transmitted.

For example, when the object to be measured is an AC line, the switch 9 is switched to the contact a side as shown in the figure, and a DC voltage of a constant level is supplied from the DC power supply 7 to one of the adders 12 via the switch 9A (a). AC voltage of a magnitude proportional to the line voltage is applied from the voltage setter 26 to the input terminal of the switch 9c (a).
Is added to the other input terminal of the adder 12 via. Further, when the measurement target is a DC line, the switch 9 is connected to the contact b.
And a constant level AC voltage of the AC power source 8 and a DC voltage proportional to the line voltage of the voltage setter 27 are applied to the adder 12 via the switches 9A (b) and 9C (b), respectively. . The output voltages of the voltage setters 26 and 27 are also applied to the instruction section 6 for calculating the measured values.

As described above, the DC power supply 7 and the AC power supply 8 in the modified embodiment are the DC power supply 7 and the DC constant voltage setter 13 and the AC power supply 8 and the AC constant voltage setting of the embodiment shown in FIG. 2, respectively. It also has the functions of device 15.

[Effect of the Invention] As described in detail above, according to the present invention, not only the active power supplied from the measured line 1 to the load but also the line current can be measured at the same time. Therefore, it is not necessary to prepare a clamp type ammeter as in the past, and since the power factor can be easily calculated from the measured power and line current values, it can be easily used for power factor improvement etc. Is.

[Brief description of drawings]

The attached drawings are all related to an embodiment of a clamp sensor according to the present invention. FIG. 1 is a diagram for explaining the principle thereof, and FIG. 2 is a block diagram when the clamp sensor according to the present invention is applied to a power meter, FIG. FIG. 4 is a signal waveform diagram for explaining the operation, and FIG. 5 is a block diagram showing a modified embodiment of the above FIG. In the figure, 1 is a line to be measured, 2 is a magnetic core, 3 is a Hall element, 4 and 25 are control current generators, 5 is a detector, 7 is a DC power supply, 8 is an AC power supply, 9A to 9E are switching devices, 11,13,15,16,
26 and 27 are voltage setting devices, 12 is an adder, 14 is a voltage / current converter, 21 and 22 are low-pass filters, 23 is a capacitor, and 24 is a rectifying / smoothing device.

Claims (1)

[Claims] 1. A pair of magnetic cores 2 provided with an opening / closing mechanism capable of enclosing a measured line 1; a Hall element 3 disposed in a magnetic path formed by the magnetic cores 2; and a Hall element. In the clamp sensor having the control current generators 4 and 25 for supplying a control current to the sensor 3, and the detector 5 for detecting the power and current of the measured line 1 by the output of the Hall element 3, the control current generator 4,25 includes a DC power supply 7 and an AC power supply 8, and an AC voltage having a magnitude proportional to the line voltage of the line to be measured 1 and a line output from the DC power supply 7 when measuring AC power and current. A control current obtained by adding a constant DC voltage irrelevant to the voltage by the adder 12 is supplied to the control current input terminals X, X of the Hall element 3, and at the time of DC power and current measurement, the measured current is measured. DC voltage whose magnitude is proportional to the line voltage of line 1 The AC constant independent of the line voltage output from the power source 8 the magnitude of the AC voltage and the adder 12
The control current added at is supplied to the control current input terminals X, X of the Hall element 3, and the detection unit 5 is included in the output signals of the voltage output terminals Y, Y of the Hall element 3. First filter means 21 for removing a frequency-doubled signal to obtain a combined signal including an AC fundamental signal voltage and a DC signal voltage; and a DC for power measurement by removing the AC fundamental signal voltage from the combined signal. Second filter means 22 for obtaining a signal voltage,
Rectifying and smoothing means 24 for obtaining a DC signal voltage for current measurement by rectifying and smoothing the AC fundamental wave signal voltage after removing the DC signal voltage in the combined signal by AC coupling. And a clamp sensor.