JP2006343175A - Magnetic field measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic field measuring device which requires a small-scaled circuit configuration because high speed sampling is unnecessary, and comprises an effective value operation means requiring only a small consumption current. <P>SOLUTION: The magnetic field measuring device contains a magnetic sensor (for example, a coil) 11 for outputting a voltage proportional to the flux density of the magnetic field to be measured, an A/D converter 14 for converting the output voltage of the magnetic field sensor 11 into digital data, and an operation control means 15 calculating the effective value of specific parameters of the field to be measured, based on the digital data. In the prestage of the A/D converter 14, an RMS/DC converter 13 for converting the output voltage of the field sensor 11 to the effective value converted voltage is provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic field measurement device that measures a magnetic field radiated from a power transmission system, home appliances, and the like, and more specifically, relates to an effective value calculation unit that calculates an effective value such as a detected magnetic flux density and an exposure amount. is there.

  Magnetic fields (electromagnetic fields) in an extremely wide frequency band are radiated in unspecified directions from household electrical appliances such as power lines, transformers, microwave ovens, and personal computer displays that are in daily contact with the human body. There are concerns about adverse effects on the human body.

  Therefore, the International Commission on Non-Ionizing Radiation Protection (International Commission on Non-Ionizing Radiation Protection; abbreviation ICNIRP) announced in April 1998 that “Guidelines for limiting exposure to time-varying electric and magnetic fields and electromagnetic fields (up to 300 GHz). ) ”, And the guideline provides reference levels for each mode of occupational and public exposure.

  Note that since the reference value of the magnetic field in the low frequency region varies greatly depending on the frequency, when the magnetic field frequency generated by the electrical device is a wide band, the measured value cannot be directly compared with the reference level. Therefore, in order to be able to collate with the reference level, a method for normalizing the measurement magnetic field to a reference frequency such as 50 Hz or 60 Hz, for example, by a weighting function for the frequency is defined as a standard evaluation method. It is called Time domain evaluation).

In addition, TCO (the latest version of TCO '03FPD), an international integrated standard for the safety, ergonomics, electromagnetic radiation, energy saving, and environment of office equipment under the jurisdiction of TCO Development owned by the Swedish Employers' Federation. A4 emissions; A4.3 AC magnetic field measurement, as a requirement for the monitor screen,
(Low frequency): 5 Hz to 2 kHz; front 30/50 cm, ≦ 200 nT
(High region): 2 kHz to 400 kHz; 30 cm in front and 50 cm in circumference, ≦ 25 nT
Is defined as (units of Tesla, 1 Tesla (T) = 10 ⁴ gauss (G)).

  Among these, Patent Document 1 discloses an exposure amount measuring apparatus that measures the exposure amount of a magnetic field to be measured based on a reference level (hereinafter referred to as an ICNIRP reference level) indicated in the ICNIRP guidelines. .

  At the reference level of ICNIRP, as an example, the magnetic flux density B (exposure amount) is low in the low frequency range and the high frequency range in the frequency range of 10 Hz to 400 kHz, and is low in the intermediate frequency range. Regardless of whether it is specified to be almost constant.

  Therefore, the exposure amount measuring apparatus described in Patent Document 1 uses an evaluation filter composed of the reciprocal of the reference level of ICNIRP. That is, an output signal having a substantially constant amplitude regardless of the frequency of the magnetic field is obtained by passing a detection signal having an amplitude proportional to the magnetic field strength of the X-axis component, the Y-axis component, and the Z-axis component detected by the magnetic field detection means. The exposure amount is calculated from digital data obtained by A / D converting the output signal.

JP 2001-235396 A

  By the way, since the magnetic field changes with time, in the magnetic field measurement, the measured value is usually displayed as an effective value and compared with a predetermined threshold value by the effective value. Incidentally, the value of the reference level of ICNIRP is defined by the effective value.

  Therefore, conventionally, an X-axis component, a Y-axis component, and a Z-axis component are sampled at high speeds to obtain instantaneous values, the effective values of the respective axis components are obtained from the sampling data of the instantaneous values, and the effective values of the respective axis components are further determined. The composite effective value is obtained from the value.

For example, assuming that the instantaneous value of the X-axis component is X _n1 , X _n2 ,... X _nN , the effective value X _nRMS is obtained by the following equation (1).

If the effective values of the Y-axis component and Z-axis component obtained in the same manner are Y _nRMS and Z _nRMS , the combined effective value R (t) _RMS of the X-axis, Y-axis, and Z-axis is obtained by the following equation (2). It is done.

However, this effective value calculation requires high-speed sampling of, for example, about 1 MHz, and sampling of three axes (X axis, Y axis, Z axis) when obtaining instantaneous values X _n , Y _n , Z _n. Is important. Therefore, the circuit configuration becomes large and the current consumption is large. Many of the magnetic field measuring devices require a portable power source for the battery, so that it is not preferable that the current consumption be large.

  Accordingly, an object of the present invention is to provide a magnetic field measuring apparatus provided with an effective value calculating means that requires a high-speed sampling and that requires a small circuit configuration and that consumes less current.

  In order to solve the above-mentioned problems, a first aspect of the present invention provides a magnetic field sensor that outputs a voltage proportional to the magnetic flux density of a magnetic field to be measured, and an A / D converter that converts the output voltage of the magnetic field sensor into digital data. And a calculation control means for calculating an effective value of a predetermined parameter of the magnetic field to be measured based on the digital data, the output voltage of the magnetic field sensor is effectively output before the A / D converter. An RMS / DC converter for converting to a value converted voltage is provided.

  According to a second aspect of the present invention, in the first aspect, when the integration time Tb inherent to the RMS / DC converter is shorter than the integration time Ta required for the calculation of the effective value, the calculation control means Until the integration time Ta is reached, the effective value converted voltage digital data output from the RMS / DC converter is taken in, and then the effective value is calculated.

  According to a third aspect of the present invention, in the first or second aspect, the magnetic field sensor includes three coils of an X-axis coil, a Y-axis coil, and a Z-axis coil, and the RMS / A DC converter is included, and the output voltage of each coil is converted into an effective value converted voltage by the RMS / DC converter and converted into digital data by the A / D converter. The combined effective value of the magnetic field to be measured is calculated from the square root of the root mean square of the digital data of the coil.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the predetermined parameter of the magnetic field to be measured is a magnetic flux density and / or an exposure amount that has passed through an evaluation filter.

  According to the first aspect of the present invention, since the output voltage of the magnetic field sensor is converted into an effective value converted voltage by the RMS / DC converter, the number of samplings can be reduced to 1 / N compared to the conventional example. Thus, since high-speed sampling is not required, the circuit configuration becomes small and current consumption is reduced.

  The RMS / DC converter has a unique integration time (integration interval) Tb. When the integration time Tb is shorter than the integration time Ta (usually 1 second) necessary for the calculation of the effective value, the operation control means determines the effective value converted voltage output from the RMS / DC converter until the integration time Ta is reached. According to the second aspect of the present invention in which digital data is taken in and an effective value is calculated thereafter, the integration time Tb unique to the RMS / DC converter can be arbitrarily set by a constant multiple. Therefore, the RMS / DC converter can be applied to the effective value calculation without any trouble.

  The magnetic field sensor includes three coils, an X-axis coil, a Y-axis coil, and a Z-axis coil, each of which has an RMS / DC converter, and the output voltage of each coil is converted into an effective value by the RMS / DC converter. 4. The voltage is converted into digital data by an A / D converter, and the arithmetic control means calculates a combined effective value of the magnetic field to be measured based on the square root of the root mean square of the digital data of each coil. According to the invention described in (1), the combined effective value of the magnetic field to be measured can be obtained without processing a large amount of data.

  According to the invention described in claim 4, since the predetermined parameter of the magnetic field to be measured is the magnetic flux density and / or the exposure amount that has passed through the evaluation filter, the magnetic flux density measurement according to the TCO standard and the exposure according to the ICNIRP guidelines Quantity measurements can be made.

  Next, an embodiment of the present invention will be described with reference to FIGS. 1 and 2, but the present invention is not limited to this. FIG. 1 is a block diagram schematically showing a circuit configuration of a magnetic field measuring apparatus according to the present invention, and FIG. 2 is a flowchart showing steps of effective value calculation.

  As shown in FIG. 1, the magnetic field measuring apparatus 10 includes a magnetic field detection coil 11 as a magnetic field sensor. In this example, the coil 11 includes three coils: an X-axis coil 11x, a Y-axis coil 11y, and a Z-axis coil 11z. These three coils 11x, 11y, and 11z are arranged in a spherical sensor casing (not shown), preferably in a plane orthogonal to each other sharing a central point. In the following description, the coil 11 is simply referred to when the axis is not particularly questioned. A magnetoelectric conversion element such as a Hall element may be used instead of the coil.

  For each measurement system of the X, Y, and Z axes, integrators 12x, 12y, and 12z (in particular, simply referred to as integrator 12 if the axis is not specified), RMS / DC converters 13x, 13y, and 13z (particularly axes) And the A / D converters 14x, 14y and 14z (simply referred to as the A / D converter 14 when the axis is not particularly questioned), and the coil 11 Is supplied to the arithmetic control means 15 comprising a microcomputer, for example, via the integrator 12, the RMS / DC converter 13, and the A / D converter 14.

Here, the output voltage V1 of the coil 11 is
V1 = k · B · N · f (k is a constant, B is a magnetic flux density, N is the number of turns, and f is a frequency)
Even when the peak magnetic flux density B is constant, it has a differential characteristic of increasing in proportion to the frequency f.

The integrator (CR integrator) 21 is used to flatten the output voltage V1 of the coil 11. That is, the output voltage V2 of the integrator 21 is
V2 = 1 / CR∫V1dt (CR is an integral constant)
Since the output decreases with frequency, the output voltage V1 of the coil 11 is flattened by the frequency effect of the integrator 21, and a voltage proportional to the magnetic flux density is obtained.

  An RMS / DC converter (Root Mean Squared to Direct Current converter) 13 squares the output voltage V2 of the integrator 21, takes an average value thereof, and outputs an effective value conversion voltage equal to a value obtained by taking the square root. To do.

The effective value converted voltage output from the RMS / DC converter 13x will be described by taking the X axis as an example. When the instantaneous value at time t is X (t) and the effective value (effective value converted voltage) is X (t) _RMS , the effective value X (t) _RMS is expressed by the following equation (3) (where Tb is The integration time (integration interval) inherent to the RMS / DC converter, where n is a variable of the number of samplings).

For the Y-axis and the Z-axis, RMS values DC (t) _RMS and Z (t) _RMS are output from the RMS / DC converters 13y and 13z in the same manner, and these _RMS values X (t) _RMS and Y (t _RMS , Z (t) _RMS is converted into digital data by A / D converters 14x, 14y, 14z, respectively, and is supplied to the arithmetic control means 15.

The arithmetic control unit 15 calculates √ {(X (t) _RMS ) ² + (Y (t) _RMS ) according to each effective value X (t) _RMS , Y (t) _RMS , Z (t) _RMS (digital value). ^The combined effective value R (t) _RMS is calculated by performing an operation of ² + (Z (t) _RMS ) ² }. Then, in accordance with a display instruction from an operation unit (not shown), the composite effective value R (t) _RMS , each effective value X (t) _RMS , Y (t) _RMS , Z (t) _{RMS and the} like are displayed on the display unit 16. .

Thus, according to the present invention, since the measured voltage output from the coil 11 is converted into an effective value by the RMS / DC converter 13, high-speed sampling is not required as in the conventional example, and the sampling is performed. The number of times is only 1 / N compared to the conventional example. Therefore, the circuit configuration may be small and current consumption can be reduced. Furthermore, the calculation control means 15 only _needs to calculate the combined effective value R (t) _RMS , and the number of calculations is reduced.

  For example, by inserting an evaluation filter based on the time domain evaluation method consisting of the reciprocal of the reference level of ICNIRP between the integrator 12 and the RMS / DC converter 13, the exposure amount can be measured according to the ICNIRP guidelines. it can.

  Further, for example, by inserting a high-pass filter and a low-pass filter in parallel between the integrator 12 and the RMS / DC converter 13, a low-frequency measurement in the 5 Hz to 2 kHz band defined by the TCO magnetic flux density measurement, and a 2 kHz It is possible to perform high-frequency measurement in a ~ 400 kHz band.

  By the way, when the effective value is calculated by the magnetic field measurement, the integration time (Ta) is normally set to 1 second, but the RMS / DC converter 13 has a specific integration time (integration section), and The integration time Tb cannot be changed arbitrarily.

  Generally, the integration time Tb of the RMS / DC converter 13 is shorter than the integration time Ta required for calculating the effective value. Therefore, in the present invention, the integration time Tb of the RMS / DC converter 13 can be arbitrarily set by a constant multiple as follows.

A description will be given by taking an X-axis measurement system as an example. First, an instantaneous value at time t input to the RMS / DC converter 13 is X (t), and an effective value converted by the RMS / DC converter 13 is _XnRMS . Further, the number of actually performing sampling N, the variable n (provided that, 1 ≦ n ≦ N) When, _{X nRMS} effective value is expressed by the following equation (4).

If the square root of Formula (4) is opened, Formula (4) can be converted into following Formula (5).

Since the integral equation of equation (5) means that {X _nRMS } ² is sequentially added from 1 to N, equation (5) can be rewritten into the following equation (6).

Next, when both sides of the equation (6) are multiplied by 1 / N · Tb, the following equation (7) is obtained.

Accordingly, the effective value X (t) RMS in the interval [t-NTb] is expressed by the following equation (8).

  As can be seen from equation (8), the actual integration time of the RMS / DC converter 13 is N × Tb, which is N times longer. As an example, if the sampling time per time of the RMS / DC converter 13 is 2.5 mS, the sampling time (N) is set to 400 times, so that the integration time required for calculating the effective value is 1S. be able to.

The same applies to the Y-axis and Z-axis, and the combined effective value R _nRMS for each instantaneous value is obtained by the following equation (9), and the combined effective value R (t) _RMS over the integration time (N × Tb) is _expressed by the following equation (9) 10).

  The actual effective value calculation is performed by the calculation control means 15, and a schematic flowchart of the calculation process is shown in FIG. This will be briefly described. Data obtained by converting the three axes of the X axis, the Y axis, and the Z axis into effective values by the RMS / DC converter 13 and A / D conversion by the A / D converter 14. Is squared, and the square value is added until the integration time (for example, 1S) required for calculating the effective value is reached to obtain the sum of squares. Thereafter, the effective value of each axis (X-axis, Y-axis, Z-axis) is calculated from the square sum, and the combined effective value is obtained from the effective value of each axis.

The block diagram which shows typically the circuit structure of the magnetic field measuring apparatus by this invention. The flowchart which shows the step of the effective value calculation in this invention.

Explanation of symbols

11 (11x, 11y, 11z) Coil 12 (12x, 12y, 12z) Integrator 13 (13x, 13y, 13z) RMS / DC converter 14 (14x, 14y, 14z) A / D converter 15 Arithmetic control means 16 Display vessel

Claims (4)

A magnetic field sensor that outputs a voltage proportional to the magnetic flux density of the magnetic field to be measured, an A / D converter that converts the output voltage of the magnetic field sensor into digital data, and a predetermined parameter of the magnetic field to be measured based on the digital data In a magnetic field measuring apparatus including a calculation control means for calculating an effective value,
A magnetic field measuring apparatus comprising an RMS / DC converter for converting an output voltage of the magnetic field sensor into an effective value converted voltage in a preceding stage of the A / D converter.   When the integration time Tb inherent to the RMS / DC converter is shorter than the integration time Ta necessary for the calculation of the effective value, the calculation control means is configured to start from the RMS / DC converter until the integration time Ta is reached. The magnetic field measuring apparatus according to claim 1, wherein the digital data of the effective value converted voltage to be output is taken, and then the effective value is calculated.   The magnetic field sensor includes three coils, an X-axis coil, a Y-axis coil, and a Z-axis coil, each of which includes the RMS / DC converter, and the output voltage of each coil is the RMS / DC converter. Is converted into an effective value converted voltage and converted into digital data by the A / D converter, and the arithmetic control means synthesizes the magnetic field to be measured based on the square root of the root mean square of the digital data of the coils. The magnetic field measuring apparatus according to claim 1, wherein an effective value is calculated. The magnetic field measuring apparatus according to claim 1, wherein the predetermined parameter of the magnetic field to be measured is a magnetic flux density and / or an exposure amount that has passed through an evaluation filter.

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