Measuring device and measuring method

A measuring device (1) includes a first signal generation section (3) and a first removal section (5). The first signal generation section (3) generates a first source signal (x1(t)) including a fundamental and a plurality of harmonics based on a first physical quantity (p1) and a second physical quantity (p2). The first removal section (5) removes some or all of the harmonics from the first source signal (x1(t)). The first source signal (x1(t)) is a periodic signal, and one period of the first source signal (x1(t)) includes a first signal (p1), a second signal (p2), and a reference signal (pr). The first signal (p1) has a first duration (w1) and indicates the first physical quantity (p1). The second signal (p2) has a second duration (w2) and indicates the second physical quantity (p2). The reference signal (pr) has a third duration (w3) and indicates the reference physical quantity (pr).

TECHNICAL FIELD

The present invention relates to measuring devices and measuring methods.

BACKGROUND ART

In general optical measurement such as spectroscopic measurement and voltage measurement, a ratio between a physical quantity x0and a physical quantity x1is determined. The spectroscopic measurement for example refers to measurement of wavelength dependency of optical properties of a measurement target sample through determination of a ratio between an intensity (physical quantity x1) of light that has interacted with the sample (typically, light transmitted through the sample) and an intensity (physical quantity x0) of light that has not interacted with the sample. The voltage measurement for example refers to measurement of a ratio between a reference voltage (physical quantity x0) and a measurement voltage (physical quantity x1).

Consider now the case where temporal variation of the physical quantity x0and the physical quantity x1is negligible as against the time required for the measurement, that is, the case where a random error can be reduced by any amount by averaging. When a ratio between the physical quantity x0and the physical quantity x1is to be determined precisely, improvement of precision of the measurement may be difficult due to non-linearity of a measuring device, that is, non-linearity of a relationship between measured amounts and measurement results. That is, measurement results include a non-linearity error. The non-linearity error refers to an error that occurs due to non-linearity of the measuring device.

Generally, multipoint calibration is performed in order to reduce influence of non-linearity of the measuring device. Regarding optical measurement, for example a light measuring apparatus described in Patent Literature 1 performs multipoint calibration. Specifically, the light measuring apparatus includes a calculation controlling circuit, a light receiving sensor array, and correction light emitting diodes (LEDs). The correction LEDs irradiate light onto the light receiving sensor array. The calculation controlling circuit calculates correction values at a plurality of known illuminance levels based on sensor output levels expected at the respective illuminance levels and actual sensor output levels while successively turning the correction LEDs on at the illuminance levels. At the time of an actual light measurement, the calculation controlling circuit corrects each sensor output level using a corresponding correction value. As a result, influence of non-linearity of the measuring apparatus is reduced. Regarding voltage measurement, for example multipoint calibration of a voltage ratio is performed by a voltage source including a Josephson device.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, in order to reduce influence of non-linearity by multipoint calibration,a standard is needed that has linearity comparable to or higher than linearity desired to be achieved. It is technically difficult to prepare a standard having high linearity at least in spectroscopic measurement and voltage measurement. Multipoint calibration to a precision of for example 10 parts per million (ppm) in spectroscopic measurement or multipoint calibration to a precision of for example 10 parts per billion (ppb) in voltage measurement involves complicated procedures, takes significant time, and requires large-scale equipment.

The present invention has been achieved in consideration of the above problems and an objective thereof is to provide a measuring device and a measuring method that allow easy reduction of influence of non-linearity on measurement results.

Solution to Problem

A measuring device according to a first aspect of the present invention includes a first signal generation section and a first removal section. The first signal generation section generates a first source signal including a fundamental and a plurality of harmonics based on a first physical quantity and a second physical quantity. The first removal section removes some or all of the plurality of harmonics from the first source signal.

Preferably, in the measuring device according to the present invention, the first source signal is a periodic signal. Preferably, one period of the first source signal includes a first signal having a first duration and indicating the first physical quantity, a second signal having a second duration and indicating the second physical quantity, and a reference signal having a third duration and indicating a reference physical quantity.

Preferably, the measuring device according to the present invention further includes a measurement section, and the first removal section includes a first summing section, a harmonic generation section, a first Fourier transform section, and a first control section. The first summing section sums the first source signal and a harmonic signal having the same frequency as a removal target harmonic among the plurality of harmonics to output a first summed signal. The measurement section outputs the first summed signal in analog form as a first measurement signal in digital form. The harmonic generation section generates the harmonic signal. The first Fourier transform section calculates a plurality of harmonics included in the first measurement signal. The first control section causes the harmonic generation section to adjust either or both of an amplitude and a phase of the harmonic signal so that a harmonic that matches the removal target harmonic is removed from the first measurement signal.

Preferably, in the measuring device according to the present invention, each of the first physical quantity and the second physical quantity is a voltage, and each of the first source signal and the harmonic signal is an electric signal. Preferably, the measurement section includes an analog-digital conversion section. The analog-digital conversion section converts the first summed signal being an analog signal to a digital signal and outputs the digital signal as the first measurement signal.

Preferably, in the measuring device according to the present invention, each of the first physical quantity and the second physical quantity is an optical intensity, and each of the first source signal and the harmonic signal is an optical signal. Preferably, the measurement section includes a photoelectric conversion section and an analog-digital conversion section. The photoelectric conversion section converts the first summed signal being an optical signal to an electric signal. The analog-digital conversion section converts the electric signal being an analog signal to a digital signal and outputs the digital signal as the first measurement signal.

Preferably, in the measuring device according to the present invention, the measurement section includes a phase calculating section and a first ratio calculating section. The phase calculating section calculates a phase of a fundamental in the first measurement signal. The first ratio calculating section calculates a value of a ratio of the second physical quantity to the first physical quantity based on the phase of the fundamental in the first measurement signal.

Preferably, in the measuring device according to the present invention, the measurement section further includes a delay calculating section that calculates a delay time of the first measurement signal relative to the first summed signal. Preferably, the first ratio calculating section calculates the value of the ratio in accordance with an equation (1).

r represents the value of the ratio.

p1represents the first physical quantity.

p2represents the second physical quantity.

pr represents a reference physical quantity.

θ represents the phase of the fundamental in the first measurement signal.

f represents a frequency of the fundamental in the first measurement signal.

τ represents the delay time.

Preferably, the measuring device according to the present invention has a non-linearity error measurement mode including a first mode and a second mode. Preferably, in each of the first mode and the second mode, the first signal generation section outputs the first source signal in which the first physical quantity is maintained constant and the second physical quantity is changed in a stepwise manner. Preferably, in the first mode, the first summing section sums the harmonic signal and the first source signal to output the first summed signal, and the measurement section outputs the first measurement signal from which the harmonic has been removed. Preferably, in the first mode, the first ratio calculating section calculates the value of the ratio for each second physical quantity based on the first measurement signal from which the harmonic has been removed. Preferably, in the second mode, the first summing section outputs the first source signal as the first summed signal without summing the harmonic signal and the first source signal, and the measurement section outputs the first measurement signal from which none of the harmonics has been removed. Preferably, in the second mode, the first ratio calculating section calculates the value of the ratio for each second physical quantity based on the first measurement signal from which none of the harmonics has been removed. Preferably, the measurement section further includes a first difference calculating section and a storage section. The first difference calculating section calculates a difference between the value of the ratio calculated in the first mode and the value of the ratio calculated in the second mode for each second physical quantity. The storage section stores therein the difference in association with the value of the ratio calculated in the second mode for each second physical quantity.

Preferably, the measuring device according to the present invention further includes a second signal generation section and a second removal section. The second signal generation section generates a second source signal including a fundamental and a plurality of harmonics and having a waveform of the first source signal with the first physical quantity and the second physical quantity interchanged. The second removal section removes some or all of the plurality of harmonics from the second source signal.

Preferably, the measuring device according to the present invention further includes a second signal generation section and a second removal section. The second signal generation section generates a second source signal including a fundamental and a plurality of harmonics and having a waveform of the first source signal with the first physical quantity and the second physical quantity interchanged. The second removal section removes some or all of the plurality of harmonics from the second source signal. Preferably, the second removal section includes a second summing section, a harmonic generation section, a second Fourier transform section, and a second control section. The second summing section sums the second source signal and a harmonic signal having the same frequency as a removal target harmonic among the plurality of harmonics in the second source signal to output a second summed signal. The measurement section outputs the second summed signal in analog form as a second measurement signal in digital form. The harmonic generation section generates the harmonic signal that is summed with the second source signal. The second Fourier transform section calculates a plurality of harmonics included in the second measurement signal. The second control section causes the harmonic generation section to adjust either or both of an amplitude and a phase of the harmonic signal that is summed with the second source signal so that a harmonic that matches the removal target harmonic in the second source signal is removed.

Preferably, in the measuring device according to the present invention, the measurement section includes a phase difference calculating section and a second ratio calculating section. The phase difference calculating section calculates a phase difference between a fundamental in the first measurement signal and a fundamental in the second measurement signal. The second ratio calculating section calculates a value of a ratio of the second physical quantity to the first physical quantity based on the phase difference.

Preferably, in the measuring device according to the present invention, the measurement section further includes a delay difference calculating section. The delay difference calculating section calculates a delay time difference between the first measurement signal and the second measurement signal. Preferably, the second ratio calculating section calculates the value of the ratio in accordance with an equation (2).

r represents the value of the ratio.

p1represents the first physical quantity.

p2represents the second physical quantity.

pr represents a reference physical quantity.

Δθ represents the phase difference.

f represents a frequency of the fundamental in the first measurement signal.

Δτ represents the delay time difference.

Preferably, the measuring device according to the present invention has a non-linearity error measurement mode including a first mode and a second mode. Preferably, in each of the first mode and the second mode, the first signal generation section generates the first source signal in which the first physical quantity is maintained at a constant level and the second physical quantity is changed in a stepwise manner. Preferably, in each of the first mode and the second mode, the second signal generation section generates the second source signal in which the first physical quantity is maintained at the constant level and the second physical quantity is changed in a stepwise manner. Preferably, in the first mode, the first summing section sums the harmonic signal and the first source signal to output the first summed signal, and the measurement section outputs the first measurement signal from which the harmonic has been removed. Preferably, in the first mode, the second summing section sums the harmonic signal and the second source signal to output the second summed signal, and the measurement section outputs the second measurement signal from which the harmonic has been removed. Preferably, in the first mode, the second ratio calculating section calculates the value of the ratio for each second physical quantity based on the first measurement signal from which the harmonic has been removed and the second measurement signal from which the harmonic has been removed. Preferably, in the second mode, the first summing section outputs the first source signal as the first summed signal without summing the harmonic signal and the first source signal, and the measurement section outputs the first measurement signal from which none of the harmonics has been removed. Preferably, in the second mode, the second summing section outputs the second source signal as the second summed signal without summing the harmonic signal and the second source signal, and the measurement section outputs the second measurement signal from which none of the harmonics has been removed. Preferably, in the second mode, the second ratio calculating section calculates the value of the ratio for each second physical quantity based on the first measurement signal from which none of the harmonics has been removed and the second measurement signal from which none of the harmonics has been removed. Preferably, the measurement section further includes a second difference calculating section and a storage section. The second difference calculating section calculates a difference between the value of the ratio calculated in the first mode and the value of the ratio calculated in the second mode for each second physical quantity. The storage section stores therein the difference in association with the value of the ratio calculated in the second mode for each second physical quantity.

Preferably, in the measuring device according to the present invention, the measurement section further includes a third ratio calculating section and a correction section. The third ratio calculating section calculates a value of a ratio of a fourth physical quantity to a third physical quantity. The correction section corrects the value of the ratio calculated by the third ratio calculating section based on the difference stored in the storage section.

A measuring method according to a second aspect of the present invention includes a step of generating a first source signal including a fundamental and a plurality of harmonics based on a first physical quantity and a second physical quantity, and a step of removing some or all of the plurality of harmonics from the first source signal.

Advantageous Effects of Invention

According to the present invention, influence of non-linearity of a measuring device on measurement results can be easily reduced by removing some or all of a plurality of harmonics, which are a cause of occurrence of a non-linearity error.

DESCRIPTION OF EMBODIMENTS

The following describes embodiments of the present invention with reference to the drawings. Elements that are the same or equivalent are indicated by the same reference signs in the drawings and description thereof is not repeated.

FIG. 1is a block diagram illustrating a measuring device1according to Embodiment 1 of the present invention. The measuring device1includes a first signal generation section3(first signal generation means), a first removal section5(first removal means), and a measurement section7(measurement means). The first signal generation section3generates a first source signal x1(t) including a fundamental and a plurality of harmonics based on a first physical quantity p1and a second physical quantity p2. In the present description, t represents time. The first removal section5removes some or all of the harmonics from the first source signal x1(t).

According to Embodiment 1, influence of non-linearity of the measuring device1(measurement section7) on measurement results can be easily reduced by removing some or all of the harmonics, which are a cause of occurrence of a non-linearity error.

The first removal section5includes N (N representing an integer greater than or equal to one) harmonic generation sections (harmonic generation means)9[1] to9[N], a first summing section11(first summing means), a first Fourier transform section13(first Fourier transform means), and a first control section15(first control means).

The number N of harmonic generation sections9[1] to9[N] is equal to the number of removal target harmonics in the first source signal x1(t) that are to be removed by the first removal section5. The harmonic generation sections9[1] to9[N] respectively generate harmonic signals h[1] to h[N].

Herein, the harmonic generation sections9[1] to9[N] will be collectively referred to as a harmonic generation section9[n] (n representing an integer greater than or equal to one), and the harmonic signals h[1] to h[N] will be collectively referred to as a harmonic signal h[n].

The harmonic signal h[n] has the same frequency as a removal target harmonic among the plurality of harmonics included in the first source signal x1(t). In the case where the removal target harmonic is a second-order harmonic, for example, the harmonic generation section9[1] generates the harmonic signal h[1] having the same frequency as the second-order harmonic.

The first summing section11sums the harmonic signal h[n] and the first source signal x1(t) to output a first summed signal y1(t). The measurement section7outputs the first summed signal y1(t), which is an analog signal, as a digital first measurement signal z1(t). The first Fourier transform section13calculates a plurality of harmonics included in the first measurement signal z1(t) through Fourier transform of the first measurement signal z1(t).

The first control section15causes the harmonic generation section9[n] to adjust either or both of an amplitude and a phase of the harmonic signal h[n] so that a harmonic that matches the removal target harmonic is removed from the first measurement signal z1(t). In the case where the removal target harmonic is a second-order harmonic, for example, the first control section15causes the harmonic generation section9[1] to adjust either or both of an amplitude and a phase of the harmonic signal h[1] having the same frequency as the second-order harmonic so that a second-order harmonic is removed from the first measurement signal z1(t).

The first summing section11sums the first source signal x1(t) and the harmonic signal h[n] having either or both of an adjusted amplitude and an adjusted phase to output the first summed signal y1(t). The first summed signal y1(t) is converted by the measurement section7to the first measurement signal z1(t), and the first measurement signal z1(t) is re-input into the first Fourier transform section13.

The Fourier transform by the first Fourier transform section13, the control of the harmonic generation section9[n] by the first control section15, the adjustment of either or both of the amplitude and the phase by the harmonic generation section9[n], the summing by the first summing section11, and the digital output by the measurement section7are repeated until harmonics that match the removal target harmonics are removed from the first measurement signal z1(t).

The following describes the first source signal x1(t), the first summed signal y1(t), and the first measurement signal z1(t) in detail with reference toFIGS. 1 to 4.FIG. 2is a waveform diagram illustrating the first source signal x1(t). The first signal generation section3generates the first source signal x1(t) based on the first physical quantity p1, the second physical quantity p2, and a reference physical quantity pr. The first source signal x1(t) is a periodic, staircase signal having a period T.

One period of the first source signal x1(t) includes a first signal p1indicating the first physical quantity p1, a reference signal pr indicating the reference physical quantity pr, and a second signal p2indicating the second physical quantity p2.

The first signal p1indicating the first physical quantity p1has a first duration w1(=(¼) period) from time0to time T/4. The reference signal pr indicating the reference physical quantity pr has a third duration w3(=( 2/4) period) from time T/4 to time3T/4. The second signal p2indicating the second physical quantity p2has a second duration w2(=(¼) period) from time3T/4 to time T.

The first source signal x1(t) has a plurality of frequency components, not shown inFIG. 2. That is, the first source signal x1(t) includes a fundamental and a plurality of harmonics. The fundamental has a frequency f (=1/T). The plurality of harmonics respectively have frequencies2f,3f,5f That is, each of the frequencies of the harmonics is a frequency that is k times the frequency f. k is an integer greater than or equal to two excluding multiples of four. Each of fundamentals of the first summed signal y1(t) and the first measurement signal z1(t) that are generated from the first source signal x1(t) has a frequency equal to the frequency f of the fundamental in the first source signal x1(t). Accordingly, the frequency of each of harmonics of the first summed signal y1(t) is a frequency k times the frequency f, and the frequency of each of harmonics of the first measurement signal z1(t) is a frequency k times the frequency f. However, k may be a multiple of four in the cases of the harmonics in the first summed signal y1(t) and the first measurement signal z1(t).

FIG. 3is a waveform diagram illustrating the first summed signal y1(t) and the first measurement signal z1(t). The first summed signal y1(t) is generated by summing the first source signal x1(t) and the harmonic signal h[n]. InFIG. 3, the harmonics remain in the first summed signal y1(t). The measurement section7measures the first summed signal y1(t) and generates the first measurement signal z1(t) as a result of the measurement. Then, Fourier transform of the first measurement signal z1(t) is performed, and in the example illustrated inFIG. 3, feed back control of the harmonic generation section9[n] is performed so that no harmonics remain. As a result, the first measurement signal z1(t) including no harmonics is obtained. That is, the first measurement signal z1(t) is a sine wave including only the fundamental.

The first measurement signal z1(t) illustrated inFIG. 3is calculated using a non-linear response function F(y1) shown inFIG. 4.FIG. 4is a diagram illustrating an example of input/output characteristics of the measurement section7. The measurement section7has non-linearity. The non-linearity of the measurement section7is represented by the non-linear response function F(y1). y1represents any input. The non-linearity of the measurement section7causes a non-linearity error G(y1). The first measurement signal z1(t) is represented by a non-linear response function F (y1(t−τ)). t represents a delay time by which the first measurement signal z1(t) is delayed relative to the first summed signal y1(t). The delay time τ is specific to the measurement section7and is frequency-independent.

The following describes a method for calculating a value r of a ratio of the second physical quantity p2to the first physical quantity p1with reference toFIGS. 3 and 5A-5B. The measurement section7calculates the value r of the ratio.FIG. 5Ais a diagram illustrating an electrical configuration of the measurement section7. The measurement section7includes a processor17, a storage section18, a detector19, and a display section20.

The processor17is for example a central processing unit (CPU), a micro controller unit (MCU), or a field-programmable gate array (FPGA). The processor17may include a digital signal processor (DSP). The storage section18is for example semiconductor memory such as random access memory (RAM), read only memory (ROM), and flash memory. The storage section18may include an auxiliary storage device such as a hard disk drive. The storage section18is an example of what may be referred to as a storage medium. The detector19detects the analog first summed signal y1(t) and outputs the first summed signal y1(t) as the digital first measurement signal z1(t). The detector19for example includes an analog-digital converter in the case of voltage measurement. The detector19for example includes a photoelectric conversion section and an analog-digital converter in the case of optical measurement. The display section20displays a measurement result (for example, the value r of the ratio). The display section20is for example a liquid crystal display.

FIG. 5Bis a functional block diagram of the measurement section7. The measurement section7includes a phase calculating section21(phase calculating means), a delay calculating section23(delay calculating means), and a first ratio calculating section25(first ratio calculating means). The processor17functions as the phase calculating section21, the delay calculating section23, and the first ratio calculating section25through execution of a computer program stored in the storage section18.

The first ratio calculating section25calculates the value r of the ratio of the second physical quantity p2to the first physical quantity p1based on a phase θ of the fundamental in the first measurement signal z1(t). That is, the phase calculating section21calculates the phase θ of the fundamental. The delay calculating section23calculates the delay time τ of the first measurement signal z1(t) relative to the first summed signal y1(t). The first ratio calculating section25calculates the value r of the ratio in accordance with an equation (1). In the equation (1), pr represents the reference physical quantity, and f represents the frequency of the fundamental in the first measurement signal z1(t). In Embodiment 1, pr=0.

As illustrated inFIG. 3, the harmonics remain in the first summed signal y1(t). However, in a configuration in which a characteristic frequency of the measurement section7is sufficiently higher than the frequency of the fundamental, an input signal that outputs a sine wave has peaks at the same positions as peak positions of a sine wave, although the delay time τ is present. Accordingly, the value r of the ratio can be calculated from the phase θ in accordance with the equation (1) as long as the delay time τ is determined in advance by measuring the phase θ on the assumption that p1=p2. In this case, at the same time, correction is performed on a reference point in the time axis for calculation of the phase θ. According to Embodiment 1, the value r of the ratio can be calculated easily by measuring the phase θ of the fundamental and using the equation (1).

The following schematically describes the equation (1) assuming the delay time τ is 0 with reference toFIGS. 6 and 7.FIG. 6is a waveform diagram for schematically describing the equation (1).FIG. 7is a diagram illustrating a vector for schematically describing the equation (1).

FIG. 6illustrates a square wave p1s only of the first physical quantity p1, a square wave p2s only of the second physical quantity p2, a fundamental p1f of the square wave p1s, a fundamental p2f of the square wave p2s, and a composite wave A. The composite wave A is a wave obtained by combining the fundamental p1f and the fundamental p2s.

As illustrated inFIGS. 6 and 7, the fundamental p1f is a sine wave having a phase β of −45 degrees and an amplitude of (√2× (p1/π)), and can be represented as a vector p1f in a complex plane. The fundamental p2f is a sine wave having a phase γ of 45 degrees and an amplitude of (√2× (p2/π)), and can be represented as a vector p2f in a complex plane. The composite wave A can be represented as a resultant vector A. An angle α is determined to be 45 degrees+θ using the phase θ of the composite vector A. The value r of the ratio is therefore represented by an equation (1A). The phase β, the phase γ, and the phase θ each include a plus or minus sign. In the example illustrated inFIG. 7, the phase β and the phase θ are each a negative value, and the phase γ is a positive value.

The following describes influence of harmonics of a staircase signal SF on a non-linearity error with reference toFIGS. 8 to 11.FIG. 8is a waveform diagram illustrating the staircase signal SF. The staircase signal SF has the same waveform as the first source signal x1(t) illustrated inFIG. 2and is generated based on the first physical quantity p1(=1), the second physical quantity p2(=0.5), and the reference physical quantity pr (=0).FIG. 9is a diagram illustrating frequency distribution of the staircase signal SF. The staircase signal SF includes a plurality of low-order to high-order harmonics.

Suppose that the staircase signal SF is measured using a non-linear measuring device. In such a situation, generally, an output signal includes a non-linearity error although the output signal is a staircase signal similar to an input signal so long as frequency dependency of the delay time of the measuring device is negligible. A height ratio r of the staircase signal SF can be calculated from the phase θ of the fundamental having the frequency f as indicated by the equation (1). Influence of non-linearity in frequency space will now be considered.

Operating a non-linear function upon the harmonics of the staircase signal SF causes mixing of harmonics, mixing of a 0th-order term (constant) with a harmonic, and mixing of a fundamental with harmonics. As a result, a new fundamental is generated. In a situation in which the new fundamental has a different phase from the original fundamental, the fundamentals are phase-shifted with respect to one another. Such fundamental phase shifting causes a non-linearity error.

A measuring device is now defined by a quadratic non-linearity function (z=x +0.5×x2). The following describes fundamental phase shifting due to mixing with harmonics in the case where the staircase signal SF is measured using the thus defined measuring device.

FIG. 10is a diagram illustrating fundamental phase shifting due to mixing with harmonics.FIG. 11is an enlarged view of a straight line v17inFIG. 10. The fundamental corresponding to a true value (the original fundamental) is represented by a straight line v1extending from the origin to point a1. The fundamental corresponding to a measurement value including all the harmonics (the new fundamental) is represented by a straight line v2extending from the origin to point a2. It can be confirmed that the fundamentals are phase-shifted with respect to one another.

A straight line v01extending from point a1to point a3corresponds to mixing of the 0th-order term with the first-order term. The first-order term represents the original fundamental. It can be confirmed that mixing of the 0th-order term with the first order term has no influence on the phase of the original fundamental.

A straight line v12extending from point a3to point a4corresponds to mixing of the first-order term with a second-order harmonic. A straight line v23corresponds to mixing of the second-order harmonic with a third-order harmonic. A straight line v56corresponds to mixing of a fifth-order harmonic with a sixth-order harmonic. A straight line v67corresponds to mixing of the sixth-order harmonic with a seventh-order harmonic. It should be noted that there is no forth-order harmonic.

It can be confirmed that mixing of the first-order term with the second-order harmonic, mixing of the second-order harmonic with the third-order harmonic, mixing of the fifth-order harmonic with the sixth-order harmonic, and mixing of the sixth-order harmonic with the seventh-order harmonic have influence on the phase of the original fundamental. Mixing of the first-order term with the second-order harmonic shifts the phase of the original fundamental to the greatest extent. Mixing of the second-order harmonic with the third-order harmonic shifts the phase of the original fundamental to the second greatest extent. That is, a lower-order harmonic has greater influence on the phase of the original fundamental, shifting the phase of the original fundamental to a greater extent.

Since the value r of the ratio is expressed using the phase θ of the fundamental as shown in the equation (1), the phase shifting of the original fundamental causes the value r of the ratio to deviate from the true value and include a non-linearity error. Since the harmonics cause phase shifting of the original fundamental, it is thought that the harmonics are a cause of the non-linearity error included in the value r of the ratio. A lower-order harmonic shifts the phase of the original fundamental to a greater extent. That is, the low-order harmonics are responsible for a majority of the non-linearity error. Generally, the non-linearity error changes only modestly relative to the measurement value. It is therefore thought that the high-order harmonics, which have a small amplitude, have little influence on the degree of the non-linearity error.

As illustrated inFIG. 9, the staircase signal SF includes higher-order harmonics than the seventh-order harmonic, but the amplitude of the higher-order harmonics is small. Accordingly, the staircase signal SF can be sufficiently reproduced using a signal S07including the 0th-order to seventh-order harmonics as illustrated inFIG. 8.

Since harmonics, particularly low-order harmonics are responsible for a non-linearity error as described above, the measuring device1reduces influence of non-linearity of the measuring device1on measurement results by removing some or all of the harmonics. Which orders of harmonics should be removed and to what degree a non-linearity error can be reduced by the harmonic removal can for example be estimated through numerical simulation assuming non-linearity of the measurement section7.

The following describes a flow of a measuring method that is performed by the measuring device1with reference toFIGS. 1, 5A-5B, and 12.FIG. 12is a flowchart illustrating the measuring method. The measuring device1performs processes in steps S1to S19. Step S3includes steps S5to S15.

In Step S1, the first signal generation section3generates the first source signal x1(t) including a fundamental and a plurality of harmonics based on the first physical quantity p1, the second physical quantity p2, and the reference physical quantity pr.

In Step S3, the first removal section5removes some or all of the harmonics from the first source signal x1(t).

That is, in Step S5, the harmonic generation section9[n] generates the harmonic signal h[n]. In Step S7, the first summing section11sums the first source signal x1(t) and the harmonic signal h[n] to output the first summed signal y1(t). In Step S9, the measurement section7(the detector19) outputs the first summed signal y1(t), which is an analog signal, as the digital first measurement signal z1(t).

In Step S11, the first Fourier transform section13calculates harmonics included in the first measurement signal z1(t) through Fourier transform of the first measurement signal z1(t). In Step S13, the first control section15determines whether or not the first measurement signal z1(t) includes a harmonic that matches a removal target harmonic. If a result of the determination is positive (Yes in Step S13), the first control section15takes the process to Step S15. If the result of the determination is negative (No in Step S13), the first control section15takes the process to Step S17.

In Step S15, the first control section15causes the harmonic generation section9[n] to adjust either or both of the amplitude and the phase of the harmonic signal h[n] so that the harmonic that matches the removal target harmonic is removed from the first measurement signal z1(t). Subsequently, the process proceeds to Step S5. The processes in Steps S5to S15are repeated until harmonics that match the removal target harmonics are removed from the first measurement signal z1(t). Through the above-described feed back control, the removal target harmonics can be removed reliably.

In Step S17, the phase calculating section21calculates the phase θ of the fundamental in the first measurement signal z1(t). In Step S19, the first ratio calculating section25calculates the value r of the ratio of the second physical quantity p2to the first physical quantity p1in accordance with the equation (1). It should be noted that the delay calculating section23calculates in advance the delay time τ based on the phase θ when p1=p2in accordance with the equation (1).

According to Embodiment 1, as described above with reference toFIGS. 1 to 12, influence of non-linearity of the measurement section7(the detector19) can be reduced by removing some or all of the harmonics from the first measurement signal z1(t). As a result, a non-linearity error included in the value r of the ratio can be reduced. It is not that non-linearity of the measurement section7is reduced, but influence of the non-linearity of the measurement section7is reduced. Therefore, the measurement section7, for example, the detector19does not need to be improved. Accordingly, even if the detector19is an existing product, the non-linearity error included in the value r of the ratio can be reduced.

According to Embodiment 1, as described with reference toFIGS. 1 and 5A-5B, the value r of the ratio is calculated from the phase θ of the fundamental in the first measurement signal z1(t) from which some or all of the harmonics have been removed. That is, reduction of non-linearity of the measurement section7is performed at the same time as the measurement. Thus, the measuring device1in Embodiment 1 is utilized in simultaneous calibration. Since reduction of influence of non-linearity is performed at the same time as the measurement, such calibration is less likely to be influenced by a drift in non-linearity of the measurement section7, unlike typical multipoint calibration. Typical multipoint calibration has a time difference between calibration and measurement. Accordingly, there may be a drift in non-linearity of the measuring device.

According to Embodiment 1, as described with reference toFIGS. 2 and 5A-5B, no other reference point than the reference physical quantity pr (i.e., zero point) is required unlike typical multipoint calibration. For example, assuming that the second physical quantity p2is measured using the first physical quantity p1as a reference signal, the measuring device1will perform calibration using two references (the reference physical quantity pr and the first physical quantity p1) as in the case of typical two-point calibration. Embodiment 1 uses only two references as in the case of two-point calibration but has the same effect as multipoint calibration, reducing influence of non-linearity on measurement results without reducing non-linearity of the measurement section7. It should be noted that according to typical two-point calibration, correction is limited to within the range of linearity, and only calibration of offset and gain is enabled.

According to Embodiment 1, as described with reference toFIG. 2, the first source signal x1(t) is generated that includes the first signal p1having the first duration w1, the reference signal pr having the third duration w3, and the second signal p2having the second duration w2. As a result, the value r of the ratio can be determined through simple calculation represented by the equation (1).

The following describes a measuring device1according to Embodiment 2 of the present invention with reference toFIGS. 1, 2, 5A-5B, and 13. As the measuring device1according to Embodiment 2, the measuring device1according to Embodiment 1 is applied to voltage measurement. Accordingly, each of the first physical quantity p1, the second physical quantity p2, and the reference physical quantity pr inFIG. 1is a voltage. Each of the first source signal x1(t), the first summed signal y1(t), the first measurement signal z1(t), and the harmonic signal h[n] is an electric signal. The measuring device1is utilized in simultaneous calibration.

FIG. 13is a block diagram illustrating the measuring device1according to Embodiment 2. The measuring device1includes a first signal generation section3(first signal generation means), a first removal section5(first removal means), and a measurement section7(measurement means). An electrical configuration of the measurement section7is the same as the electrical configuration of the measurement section7illustrated inFIG. 5A. A detector19according to Embodiment 2 includes an analog-digital converter19a(hereinafter, referred to as an “ADC19a”) (analog-digital conversion section or analog-digital conversion means). The ADC19aconverts an analog signal to a digital signal.

The first signal generation section3includes a switch12, and the switch12includes contacts4ato4d. A voltage p1is applied to the contact4aas the first physical quantity p1. A voltage p2is applied to the contact4bas the second physical quantity p2. A voltage pr is applied to the contact4cas the reference physical quantity pr. In Embodiment 2, the voltage pr is0V.

The switch12switches the contact that is connected with the contact4damong the contacts4ato4cthereby to generate the staircase first source signal x1(t). That is, as illustrated inFIG. 2, the switch12connects the contact4awith the contact4dduring an interval from time 0 to time T/4, connects the contact4cwith the contact4dduring an interval from time T/4 to time3T/4, and connects the contact4bwith the contact4dduring an interval from time3T/4 to time T. The switch12repeats such connection to generate the periodic, staircase first source signal x1(t).

The first removal section5includes N (N representing an integer greater than or equal to one) oscillators9a[1] to9a[N] (harmonic generation means), a first summer11a(first summing means), a first fast Fourier transform device13a(hereinafter, referred to as a “first FFT13a” (first Fourier transform section or first Fourier transform means), and a first control section15a(first control means).

The number N of oscillators9a[1] to9a[N] is equal to the number of removal target harmonics in the first source signal x1(t) that are to be removed by the first removal section5. The oscillators9a[1] to9a[N] respectively generate harmonic electric signals ha[1] to ha[N].

Herein, the oscillators9a[1] to9[N] will be collectively referred to as an oscillator9a[n] (n representing an integer greater than or equal to one), and the harmonic electric signals ha[1] to ha[N] will be collectively referred to as a harmonic electric signal ha[n].

The harmonic electric signal ha[n] has the same frequency as a removal target harmonic among the plurality of harmonics included in the first source signal x1(t).

The first summer11asums the harmonic electric signal ha[n] and the first source signal x1(t) to output the first summed signal y1(t). The ADC19aconverts the first summed signal y1(t), which is an analog signal, to a digital signal and outputs the digital signal as the first measurement signal z1(t). The first FFT13aperforms fast Fourier transform to calculate a plurality of harmonics included in the first measurement signal z1(t).

The first control section15acauses the oscillator9a[n] to adjust either or both of an amplitude and a phase of the harmonic electric signal ha[n] so that a harmonic that matches the removal target harmonic is removed from the first measurement signal z1(t). As in Embodiment 1, the control of the oscillator9a[n] by the first control section15a, the adjustment of either or both of the amplitude and the phase by the oscillator9a[n], the summing by the first summer11a, and the analog-digital conversion by the detector19, and the fast Fourier transform by the first FFT13aare repeated until harmonics that match the removal target harmonics are removed from the first measurement signal z1(t).

As in Embodiment 1, the measurement section7includes a phase calculating section21, a delay calculating section23, and a first ratio calculating section25. As in Embodiment 1, the measurement section7calculates the value r of the ratio in accordance with the equation (1).

Furthermore, as in Embodiment 1, the measuring device1performs the measuring method illustrated by the flowchart inFIG. 12. In the case of Embodiment 2, the harmonic generation section9[n] is replaced with the oscillator9a[n], the harmonic signal h[n] is replaced with the harmonic electric signal ha[n], the first summing section11is replaced with the first summer11a, the first Fourier transform section13is replaced with the first FFT13a, and the first control section15is replaced with the first control section15ain the illustration inFIG. 12.

According to Embodiment 2, as described above with reference toFIG. 13, influence of non-linearity of the measurement section7(the ADC19a) can be reduced by removing some or all of the harmonics from the first measurement signal z1(t) in voltage measurement. As a result, a non-linearity error included in the value r of the ratio, that is, a voltage ratio can be reduced. In addition to the above, Embodiment 2 also achieves the same effects as Embodiment 1.

Furthermore, the measuring device1according to Embodiment 2 can be applied to direct current voltage measurement. The measuring device1is effectively utilized in simultaneous calibration in direct current voltage measurement.

In direct current voltage measurement, the measuring device1can be applied to a commercially-available high-end digital voltmeter (digital multimeter) including an analog-digital converter (AD converter) adopting a double integration technique or a multiple integration technique.

A digital voltmeter having a linearity of 10 ppb can for example be achieved. Measurement of a voltage ratio (the value r of the ratio) is a basic aspect of voltage measurement. Therefore, linear voltage ratio measurement is a necessary technique for achieving a high-precision digital voltmeter. Linearity can be further improved by for example employing a commercially-available high-end digital voltmeter as the measurement section7. A digital voltmeter having a linearity of 10 ppb can be utilized for high-precision physical measurement as well as for secondary calibration. The measuring device1may be produced as a new digital voltmeter rather than being applied to an existing digital voltmeter.

In direct current voltage measurement, the measuring device1can be applied to a relatively inexpensive digital voltmeter including a delta-sigma or successive-approximation-register (SAR) AD converter. A digital voltmeter having a linearity of 1 ppm can for example be achieved. A delta-sigma or SAR digital voltmeter has a relatively high S/N ratio but does not have sufficient linearity. A low-cost digital voltmeter having a linearity of 1 ppm can for example be achieved by employing a delta-sigma or SAR digital voltmeter as the measurement section7.

Some analog band-elimination filters used in voltage measurement employ a method involving phase-inverting an output from a bandpass filter and summing the output and an original signal. The first FFT13a, the first control section15a, and the oscillator9a[h] according to Embodiment 2 achieve a multichannel band-elimination filter by phase detection using digital signal processing.

The following describes a measuring device1according to Embodiment 3 of the present invention with reference toFIGS. 1, 2, 5A-5B, and 14. As the measuring device1according to Embodiment 3, the measuring device1according to Embodiment 1 is applied to optical measurement such as spectroscopic measurement. Accordingly, each of the first physical quantity p1, the second physical quantity p2, and the reference physical quantity pr inFIG. 1is an optical intensity. Each of the first source signal x1(t), the harmonic signal h[n], and the first summed signal y1(t) is an optical signal. The first measurement signal z1(t) is an electric signal. The measuring device1is utilized in simultaneous calibration.

FIG. 14is a block diagram illustrating the measuring device1according to Embodiment 3. The measuring device1includes a first signal generation section3(first signal generation means), a first removal section5(first removal means), and a measurement section7(measurement means). An electrical configuration of the measurement section7is the same as the electrical configuration of the measurement section7illustrated inFIG. 5A. A detector19according to Embodiment 3 includes a photoelectric conversion section19b(photoelectric conversion means) and an analog-digital converter19c(hereinafter, referred to as an “ADC19c”) (analog-digital conversion section or analog-digital conversion means). The photoelectric conversion section19bconverts a received optical signal to an electric signal. The photoelectric conversion section19bis for example a photomultiplier tube or an image sensor (for example, a CCD image sensor or a CMOS image sensor). The ADC19cconverts an analog signal to a digital signal.

Light having an optical intensity p1as the first physical quantity p1, light having an optical intensity p2as the second physical quantity p2, and light having an optical intensity pr as the reference physical quantity pr are input into the first signal generation section3. The optical intensity pr according to Embodiment 3 is a level indicative of a dark state.

The first signal generation section3generates the staircase first source signal x1(t) through switching among the light having the optical intensity p1, the light having the optical intensity p2, and the light having the optical intensity pr, and outputs the first source signal x1(t) to a first summer11b. That is, as illustrated inFIG. 2, the first signal generation section3emits the light having the optical intensity p1during the interval from time 0 to time T/4, emits no light during the interval from time T/4 to time3T/4, and emits light having the optical intensity p2during the interval from time3T/4 to time T. The signal generation section3repeats such light emission to generate the periodic, staircase first source signal x1(t). The dark state is achieved through the first signal generation section3emitting no light.

The first removal section5includes N (N representing an integer greater than or equal to one) harmonic generation sections9b[1] to9b[N] (harmonic generation means), the first summer11b, a first fast Fourier transform device13b(hereinafter, referred to as a “first FFT13b”) (first Fourier transform section or first Fourier transform means), and a first control section15b(first control means).

The number N of harmonic generation sections9b[1] to9b[N] is equal to the number of removal target harmonics in the first source signal x1(t) that are to be removed by the first removal section5. The harmonic generation sections9b[1] to9b[N] respectively generate harmonic optical signals hb[1] to hb[N] and emit them to the first summer11b.

Herein, the harmonic generation sections9b[1] to9b[N] will be collectively referred to as a harmonic generation section9b[n] (n representing an integer greater than or equal to one), and the harmonic optical signals hb[1] to hb[N] will be collectively referred to as a harmonic optical signal hb[n].

The harmonic optical signal hb[n] has the same frequency as a removal target harmonic among the plurality of harmonics included in the first source signal x1(t).

The harmonic generation section9b[n] includes a light source45and a current control circuit47. The light source45is for example an LED. The current control circuit47is controlled by the first control section15band controls or chops electric current that is supplied to the light source45to control an amount of light that is emitted by the light source45. As a result, the current control circuit47can adjust either or both of the amplitude and the phase of the harmonic optical signal hb[n]. In accordance with the current control circuit47, the light source45generates a square optical signal and emits the signal as the harmonic optical signal hb[n]. The light source45may for example be a laser. In such a configuration, the harmonic generation section9b[n] for example includes an optical system instead of the current control circuit47. The optical system chops the optical signal output by the light source45and having a constant intensity to generate the square optical signal and emits the signal as the harmonic optical signal hb[n].

Non-linearity, which poses a problem when a linearity of for example 10 ppm is to be achieved, is related to intensity distribution in a detection surface of a photodetector. The harmonic generation section9b[n] therefore generates the harmonic optical signal hb[n] such that the harmonic optical signal hb[n] has the same intensity distribution as the first source signal x1(t) in a detection surface of the photoelectric conversion section19b.

The summer11bsums the harmonic optical signal hb[n] and the first source signal x1(t) to output the first summed signal y1(t).

The first summer11bis for example a bifurcated optical fiber. The bifurcated optical fiber includes a plurality of input optical fibers, an output optical fiber, and an optical coupler that connects the input optical fibers and the output optical fiber. In such a configuration, the first source signal x1(t) is input into one of the input optical fibers. The harmonic optical signal hb[n] is input into the corresponding input optical fiber. As a result, the first source signal x1(t) and the harmonic optical signal hb[n] are summed, and the first summed signal y1(t) is emitted from the output optical fiber.

Alternatively, the first summer11bfor example includes a plurality of stages of half mirror that are in a linear arrangement. In such a configuration, the first source signal x1(t) is input into a first one of the stages of half mirror. The harmonic optical signal hb[n] is input into the corresponding stage of half mirror. As a result, the first source signal x1(t) and the harmonic optical signal hb[n] are summed, and the first summed signal y1(t) is emitted from a last one of the stages of half mirror.

The first summed signal y1(t) is input into the photoelectric conversion section19bof the detector19, and the photoelectric conversion section19breceives the first summed signal y1(t). The photoelectric conversion section19bconverts the first summed signal y1(t), which is an optical signal, to an electric signal and inputs the electric signal into the ADC19c. The ADC19cconverts the input electric signal, which is an analog signal, to a digital signal and outputs the digital signal as the first measurement signal z1(t). The first FFT13bperforms fast Fourier transform to calculate a plurality of harmonics included in the first measurement signal z1(t).

The first control section15bcauses the harmonic generation section9b[n] to adjust either or both of the amplitude and the phase of the harmonic optical signal hb[n] so that a harmonic that matches the removal target harmonic is removed from the first measurement signal z1(t). As in Embodiment 1, the control of the harmonic generation section9b[n] by the first control section15b, the adjustment of either or both of the amplitude and the phase by the harmonic generation section9b[n], the summing by the first summer11a, the photoelectric conversion and the analog-digital conversion by the detector19, and the Fourier transform by the first FFT13bare repeated until harmonics that match the removal target harmonics are removed from the first measurement signal z1(t).

As in Embodiment 1, the measurement section7includes a phase calculating section21, a delay calculating section23, and a first ratio calculating section25. As in Embodiment 1, the measurement section7calculates the value r of the ratio in accordance with the equation (1).

Furthermore, as in Embodiment 1, the measuring device1performs the measuring method illustrated by the flowchart inFIG. 12. In the case of Embodiment 3, the harmonic generation section9[n] is replaced with the harmonic generation section9b[n], the harmonic signal h[n] is replaced with the harmonic optical signal hb[n], the first summing section11is replaced with the first summer11b, the first Fourier transform section13is replaced with the first FFT13b, and the first control section15is replaced with the first control section15bin the illustration inFIG. 12.

The following describes removal of a harmonic using the harmonic optical signal hb[n] in detail with reference toFIGS. 14 to 17.FIG. 15is a waveform diagram illustrating removal of a second-order harmonic.FIG. 15illustrates the first source signal x1(t), a fundamental FW in the first source signal x1(t), and the harmonic optical signal hb[1].

In order to remove the second-order harmonic included in the first source signal x1(t), the harmonic generation section9b[1] generates the harmonic optical signal hb[1] having the same frequency as the second-order harmonic and outputs the harmonic optical signal hb[1] to the first summer11b. The harmonic optical signal hb[1] is represented by shaded areas inFIG. 15.

FIG. 16is a waveform diagram illustrating removal of the second-order harmonic, a third-order harmonic, and a fifth-order harmonic. There is no fourth-order harmonic.FIG. 16illustrates the first source signal x1(t), the fundamental FW of the first source signal x1(t), and the harmonic optical signals hb[1] to hb[3].

In order to remove the second-order harmonic included in the first source signal x1(t), the harmonic generation section9b[1] generates the harmonic optical signal hb[1] having the same frequency as the second-order harmonic and emits the harmonic optical signal hb[1] to the first summer11b. In order to remove the third-order harmonic, the harmonic generation section9b[2] generates the harmonic optical signal hb[2] having the same frequency as the third-order harmonic and emits the harmonic optical signal hb[2] to the first summer11b. In order to remove the fifth-order harmonic, the harmonic generation section9b[3] generates the harmonic optical signal hb[3] having the same frequency as the fifth-order harmonic and emits the harmonic optical signal hb[3] to the first summer11b. The harmonic optical signals hb[1] to hb[3] are represented by shaded areas inFIG. 16.

FIG. 17is a diagram illustrating reduction of a non-linearity error by harmonic removal. A curve NE1represents the non-linearity error in the value r of the ratio in a case where no harmonic is removed. A curve NE2represents the non-linearity error in the value r of the ratio in a case where the second-order harmonic is removed using the harmonic optical signal hb[1] illustrated inFIG. 15. A curve NE3represents the non-linearity error in the value r of the ratio in a case where the second-order harmonic, the third-order harmonic, and the fifth-order harmonic are removed using the harmonic optical signals hb[1] to hb[3] illustrated inFIG. 16.

The non-linearity error is less in the case where the second-order harmonic is removed than in the case where no harmonic is removed. The non-linearity error is less in the case where the second-order harmonic, the third-order harmonic, and the fifth-order harmonic are removed than in the case where only the second-order harmonic is removed.

In the simulation illustrated inFIG. 17, because of non-linearity of the photoelectric conversion section19b, the non-linearity error is made proportional to the sixth power of the optical intensity of the non-linearity error, the first physical quantity p1is constant, and the second physical quantity p2(≤p1) is changed. The value r of the ratio is calculated in accordance with the equation (1).

According to Embodiment 3, as described above with reference toFIGS. 14 to 17, influence of non-linearity of the measurement section7(the photoelectric conversion section19band the ADC19c) can be reduced by removing some or all of the harmonics from the first measurement signal z1(t) in optical measurement. As a result, a non-linearity error included in the value r of the ratio, that is, an optical intensity ratio can be reduced. In addition to the above, Embodiment 3 also achieves the same effects as Embodiment 1.

The measuring device1according to Embodiment 3 can be applied to spectroscopic measurement (ultraviolet, visible, or near-infrared light region). The measuring device1is effectively utilized in simultaneous calibration in spectroscopic measurement. Linearity in double-beam spectroscopic measurement can for example be improved. The measuring device1can for example be combined with a double-beam spectrophotometer. That is, linearity in double-beam spectroscopic measurement can be improved by inputting light having, as the first physical quantity p1, an optical intensity that has interacted with a measurement sample and light having, as the second physical quantity p2, an optical intensity that has not interacted with the measurement sample into the first signal generation section3. Furthermore, a spectrophotometer having a linearity of 10 ppm can for example be achieved. Improvement in linearity of the spectrophotometer leads to improvement in precision of quantitative analysis using the spectrophotometer. Furthermore, it is possible to reduce an error in multivariate analysis, which is employed in a case where many signals overlap such as in a case of the near-infrared light region, because the multivariate analysis is performed assuming linearity of a spectrum.

The following describes a measuring device1according to Embodiment 4 of the present invention with reference toFIGS. 1 to 18.FIG. 18is a block diagram illustrating the measuring device1. The measuring device1includes a first bandpass filter4(first removal means) instead of the first removal section5of the measuring device1according to Embodiment 1. The measuring device1is utilized in simultaneous calibration.

The first bandpass filter4allows only the fundamental in the first source signal x1(t) to pass and outputs the fundamental to the measurement section7as a harmonic-removed signal y1(t) (corresponding to the first summed signal y1(t) in Embodiment1). The measurement section7converts the harmonic-removed signal y1(t), which is an analog signal, to the digital first measurement signal z1(t). The measurement section7calculates the value r of the ratio in accordance with the equation (1).

The first bandpass filter4is for example an analog filter. The first bandpass filter4has a configuration that has no influence on the phase of the fundamental in the first source signal x1(t), that is, a configuration that prevents phase shifting between the fundamental in the first source signal x1(t) and the fundamental in the harmonic-removed signal y1(t) and prevents a drift in the phase shifting.

According to Embodiment 4, influence of non-linearity of the measurement section7(the detector19) can be reduced by removing some or all of the harmonics from the first measurement signal z1(t). As a result, a non-linearity error included in the value r of the ratio can be reduced. In addition to the above, Embodiment 4 also achieves the same effects as Embodiment 1.

The measuring device1according to Embodiment 4 can be applied to voltage measurement. Accordingly, each of the first physical quantity p1, the second physical quantity p2, and the reference physical quantity pr inFIG. 18is a voltage. Each of the first source signal x1(t), the harmonic-removed signal y1(t), and the first measurement signal z1(t) is an electric signal.

The measuring device1according to Embodiment 4 can also be applied to optical measurement such as spectroscopic measurement. Accordingly, each of the first physical quantity p1, the second physical quantity p2, and the reference physical quantity pr inFIG. 18is an optical intensity. Each of the first source signal x1(t) and the harmonic-removed signal y1(t) is an optical signal. The first measurement signal z1(t) is an electric signal.

The following describes a measuring device1according to Embodiment 5 of the present invention with reference toFIGS. 1, 5A-5B, 19A-19B, and 20. The measuring devices1according to Embodiments 1 to 4 are utilized in simultaneous calibration. In contrast, the measuring device1according to Embodiment 5 is utilized not only in simultaneous calibration but also in multipoint calibration. When utilized in multipoint calibration, the measuring device1prepares a non-linearity error table in advance and corrects measurement values using the table.

The measuring device1according to Embodiment 5 includes the same configuration as the measuring device1according to Embodiment 1, and can determine the value r of the ratio while reducing influence of a non-linearity error by removing harmonics. Therefore, a difference between a measurement value determined without performing harmonic removal and a measurement value determined with performing harmonic removal represents the non-linearity error. Accordingly, the measuring device1is utilized in multipoint calibration by preparing the non-linearity error table.

The measuring device1according to Embodiment 5 has a non-linearity error reduction mode and a non-linearity error measurement mode. The measuring device1in the non-linearity error reduction mode operates in the same manner as the measuring device1according to Embodiment 1 and is utilized in simultaneous calibration. The following describes the non-linearity error measurement mode and utilization in multipoint calibration. The non-linearity error measurement mode of the measuring device1includes a first mode and a second mode.

FIG. 19Ais a block diagram illustrating the measuring device1according to Embodiment 5 of the present invention. The measuring device1includes a two-channel signal source8in addition to the configuration of the measuring device1according to Embodiment 1. The first signal generation section3, the first removal section5, and the measurement section7respectively have the same configurations as the configurations of the first signal generation section3, the first removal section5, and the measurement section7of the measuring device1according to Embodiment 1. An electrical configuration of the measurement section7according to Embodiment 5 is the same as the electrical configuration illustrated inFIG. 5A. However, the measurement section7has a different configuration from the configuration illustrated inFIG. 5B.

FIG. 20is a block diagram illustrating the measurement section7. The measurement section7includes a first difference calculating section53(first difference calculating means), the storage section18(storage means), a third ratio calculating section55(third ratio calculating means), and a correction section57(correction means) in addition to the configuration of the measurement section7illustrated inFIG. 5B.

The processor17functions as the phase calculating section21, the delay calculating section23, the first ratio calculating section25, the first difference calculating section53, the third ratio calculating section55, and the correction section57through execution of a computer program stored in the storage section18.

The following describes operation of the measuring device1in the first mode with reference toFIGS. 1, 19A, and 20. The signal source8generates a first signal p1indicating the first physical quantity p1, maintains the first physical quantity p1constant, and outputs the first signal p1to the first signal generation section3. The first signal p1is measured in advance to determine an approximate value of the first physical quantity p1. The thus determined first physical quantity p1includes not only a non-linearity error but also offset and gain errors. The determined value of the first physical quantity p1is set as an upper limit of the second physical quantity p2.

The signal source8also generates a second signal p2indicating the second physical quantity p2, changes the second physical quantity p2in a stepwise manner, and outputs the second signal p2to the first signal generation section3. Specifically, the signal source8changes the second physical quantity p2, and subsequently maintains the second physical quantity p2constant. Thereafter, once a specific period of time has elapsed, the signal source8changes the second physical quantity p2to a different value, and subsequently maintains the second physical quantity p2constant. In accordance with the predetermined number of steps for changing the second physical quantity p2, the signal source8repeats changing and maintaining of the second physical quantity p2until the second physical quantity p2reaches the upper limit. The reference signal pr indicating the reference physical quantity pr is also input into the first signal generation section3.

The ratio (p2/p1) is stable after the second physical quantity p2is maintained constant, and a drift therein within the measurement time is negligible. Accuracy of the value of the first physical quantity p1and the value of the second physical quantity p2does not need to be high. Furthermore, the ratio (p2/p1) does not need to be known in advance. It should be noted that accuracy indicates a range within which a difference between the measurement value and a standard (for example, an international standard or a national standard) falls. In contrast, precision indicates variability of measurement values when measurement of the same physical quantity is repeated.

The first signal generation section3outputs the first source signal x1(t) in which the first physical quantity p1is maintained constant and the second physical quantity p2is changed in a stepwise manner. The first summing section11of the first removal section5sums the harmonic signal h[n] and the first source signal x1(t) to output the first summed signal y1(t). Having the harmonic signal h[n] added thereto, the first summed signal y1(t) is a signal from which a corresponding harmonic has been removed. The measurement section7inputs the first summed signal y1(t) and outputs the first measurement signal z1(t) from which the harmonic has been removed. In Embodiment5, the first measurement signal z1(t) from which the harmonic has been removed is referred to as a first measurement signal z1a(t).

Based on the first measurement signal z1a(t), the first ratio calculating section25calculates the value r of the ratio of the second physical quantity p2to the first physical quantity p1for each second physical quantity p2. That is, the phase calculating section21calculates a phase θ of a fundamental in the first measurement signal z1a(t) for each physical quantity p2. The delay calculating section23calculates a delay time τ of the first measurement signal z1a(t). The first ratio calculating section25calculates the value r of the ratio in accordance with the equation (1) using the phase θ of the fundamental and the delay time τ of the first measurement signal z1a(t) for each physical quantity p2, and stores the value r of the ratio in the storage section18. The value r of the ratio includes a reduced non-linearity error, and therefore the accuracy thereof is high. Through the above, the first mode has been described.

The following describes operation of the measuring device1in the second mode. Operation of the signal source8and the first signal generation section3is the same as the operation of the signal source8and the first signal generation section3in the first mode. The harmonic generation section9[n] in the first removal section5does not generate the harmonic signal h[n]. Accordingly, the first summing section11outputs the first source signal x1(t) as the first summed signal y1(t) without summing the harmonic signal h[n] and the first source signal x1(t). Having no harmonic signal h[n] added thereto, the first summed signal y1(t) is a signal from which none of the harmonics has been removed. The measurement section7inputs the first summed signal y1(t) and outputs the first measurement signal z1(t) from which none of the harmonics has been removed. In Embodiment5, the first measurement signal z1(t) from which none of the harmonics has been removed is referred to as a first measurement signal z1b(t).

Based on the first measurement signal z1b(t), the first ratio calculating section25calculates the value r of the ratio of the second physical quantity p2to the first physical quantity p1for each second physical quantity p2. That is, the phase calculating section21calculates the phase θ of the fundamental in the first measurement signal z1b(t) for each second physical quantity p2. The delay calculating section23calculates the delay time τ of the first measurement signal z1b(t). The first ratio calculating section25calculates the value r of the ratio in accordance with the equation (1) using the phase θ of the fundamental and the delay time τ of the first measurement signal z1b(t) for each physical quantity p2, and stores the value r of the ratio in the storage section18. The value r of the ratio includes a non-linearity error that is not reduced. Through the above, the second mode has been described.

The first difference calculating section53acquires from the storage section18the value r of the ratio calculated in the first mode and the value r of the ratio calculated in the second mode for each second physical quantity p2. Subsequently, the first difference calculating section53calculates a difference Δr between the value r of the ratio calculated in the first mode and the value r of the ratio calculated in the second mode for each second physical quantity p2. The storage section18stores therein the difference Δr in association with the value r of the ratio calculated in the second mode for each second physical quantity p2.

As a result, a table associating the value r of the ratio calculated in the second mode with the difference Δr (hereinafter, referred to as an “error table”) is created. The difference Δr represents the non-linearity error, and therefore the error table is a table associating the value r of the ratio calculated in the second mode with the non-linearity error. Preferably, the second physical quantity p2is changed finely in a sufficiently large number of steps so that data in the error table is sufficiently continuous and sufficiently precise.

Since the error table is prepared, an analog signal p3indicating a third physical quantity p3and an analog signal p4indicating a fourth physical quantity p4can be input into the measurement section7. The third physical quantity p3corresponds to the first physical quantity p1, and the fourth physical quantity p4corresponds to the second physical quantity p2. The analog signal p3and the analog signal p4are optionally input and are measurement targets. The measurement section7converts each of the analog signal p3and the analog signal p4to a digital signal and calculates a value R (=p4/p3) of a ratio of the fourth physical quantity p4to the third physical quantity p3. The measurement section7then corrects the value R of the ratio using the error table and calculates a value Rc of the ratio including a reduced non-linearity error.

That is, the third ratio calculating section55calculates the value R of the ratio. Subsequently, the correction section57corrects the value R of the ratio based on the error table, that is, based on the difference Δr stored in the storage section18to calculate the value Rc of the ratio. In a case where data is not found in the error table, the non-linearity error is calculated through interpolation. In a case where a drift in the non-linearity error is negligible, the error table may be prepared before the measurement of the third physical quantity p3and the fourth physical quantity p4, or the error table may be prepared after the measurement of the third physical quantity p3and the fourth physical quantity p4.

The following describes a measuring device1according to a variation of Embodiment 5 with reference toFIG. 19B.FIG. 19Bis a block diagram illustrating the measuring device1according to the variation. The measuring device1includes a first signal source8instead of the signal source8of the measuring device1illustrated inFIG. 19A. The first signal source8is included in the first signal generation section3. According to the variation, in each of the first and second modes, the first signal source8generates and outputs the first source signal x1(t) in which the first physical quantity p1is maintained constant and the second physical quantity p2is changed in a stepwise manner.

According to Embodiment 5 (hereinafter, including the variation thereof), as described above with reference toFIGS. 19A-19B and 20, it is possible to easily determine the value r of the ratio including a non-linearity error reduced through harmonic removal and the value r of the ratio including a non-linearity error that is not reduced. Therefore, the error table for achieving utilization in multipoint calibration can be easily prepared.

Furthermore, according to Embodiment 5, the value R of the ratio can be corrected using the error table. Therefore, it is not necessary to generate the first source signal x1(t) and it is not necessary to perform harmonic removal. As a result, the third physical quantity p3and the fourth physical quantity p4, which fluctuate, can be measured.

Furthermore, the first signal generation section3, the first removal section5, and the measurement section7in Embodiment 5 can be replaced with the first signal generation section3, the first removal section5, and the measurement section7according to Embodiment 2. That is, the measuring device1according to Embodiment 5 can be applied to voltage measurement. Accordingly, for example an alternating current voltage meter or a high-speed voltage meter can be formed using the measuring device1, and thus linearity of the alternating current voltage meter or the high-speed voltage meter can be improved.

Furthermore, the first signal generation section3, the first removal section5, and the measurement section7in Embodiment 5 can be replaced with the first signal generation section3, the first removal section5, and the measurement section7according to Embodiment 3. That is, the measuring device1according to Embodiment 5 can be applied to optical measurement. It is therefore possible to for example correct non-linearity of a light measuring device using the error table. The light measuring device is for example a double-beam spectrophotometer or a multi-channel optical meter (including a camera) such as a CCD image sensor and a CMOS image sensor. Non-linearity can be evaluated through comparison between an optical detection system having high linearity and an optical detection system having low linearity. Provision of a plurality of light sources such as LEDs that enable easy switching allows utilization in multipoint calibration.

The following describes a measuring device1according to Embodiment 6 of the present invention with reference toFIGS. 21 to 24. Unlike the measuring device according to Embodiment 1, in which a one-channel staircase signal (the first source signal x1(t)) is generated, the measuring device1according to Embodiment 6 generates a two-channel staircase signal (the first source signal x1(t) and a second source signal x2(t)). The measuring device1is utilized in simultaneous calibration. The following mainly describes differences between Embodiment 6 and Embodiment 1.

FIG. 21is a block diagram illustrating the measuring device1according to Embodiment 6. The measuring device1includes a second signal generation section3B (second signal generation means) and a second removal section5B (second removal means) in addition to the configuration of the measuring device1according to Embodiment 1.

The second signal generation section3B generates the second source signal x2(t) including a fundamental and a plurality of harmonics.FIG. 22Ais a waveform diagram illustrating the first source signal x1(t).FIG. 22Bis a waveform diagram illustrating the second source signal x2(t). The second source signal x2(t) has a waveform of the first source signal x1(t) with the first physical quantity p1and the second physical quantity p2interchanged.

That is, one period of the second source signal x2(t) includes the second signal p2indicating the second physical quantity p2, the reference signal pr indicating the reference physical quantity pr, and the first signal p1indicating the first physical quantity p1. The second signal p2has the second duration w2(=(¼) period) from time 0 to time T/4. The reference signal pr has the third duration w3(=( 2/4) period) from time T/4 to time3T/4. The first signal p1has the first duration w1(=(¼) period) from time3T/4 to time T. Furthermore, the frequency of the fundamental in the second source signal x2(t) is equal to the frequency f (=1/T) of the fundamental in the first source signal x1(t). The frequencies of the harmonics in the second source signal x2(t) are respectively equal to the frequencies of the harmonics in the first source signal x1(t).

Referring back toFIG. 21, the second removal section5B removes some or all of the harmonics from the second source signal x2(t).

The second removal section5B includes N (N representing an integer greater than or equal to one) harmonic generation sections9B[1] to9B[N] (harmonic generation means), a second summing section11B (second summing means), a second Fourier transform section13B (second Fourier transform section or second Fourier transform means), and a second control section15B (second control means). Configurations of the harmonic generation sections9B[1] to9B[N], the second summing section11B, the second Fourier transform section13B, and the second control section15B are respectively the same as the configurations of the harmonic generation sections9[1] to9[N], the first summing section11, the first Fourier transform section13, and the first control section15.

That is, the harmonic generation sections9B[1] to9B[N] respectively generate harmonic signals hB[1] to hB[N].

Herein, the harmonic generation sections9B [1] to9B [N] will be collectively referred to as a harmonic generation section9B [n] (n representing an integer greater than or equal to one), and the harmonic signals hB[1] to hB[N] will be collectively referred to as a harmonic signal hB[n].

The harmonic signal hB [n] has the same frequency as a removal target harmonic among the plurality of harmonics included in the second source signal x2(t). The removal target harmonic that is to be removed by the second removal section5B is the same as the removal target harmonic that is to be removed by the first removal section5.

The second summing section11B sums the harmonic optical signal hB[n] and the second source signal x2(t) to output a second summed signal y2(t). The fundamental and the harmonics in the second summed signal y2(t) respectively have the same frequencies as the fundamental and the harmonics in the second source signal x2(t).

The measurement section7outputs the first summed signal y1(t), which is an analog signal, as the digital first measurement signal z1(t) and outputs the second summed signal y2(t), which is an analog signal, as a digital second measurement signal z2(t). An electrical configuration of the measurement section7is the same as the electrical configuration illustrated inFIG. 5A. A detector19in Embodiment 6 is a two-channel detector. The fundamental and the harmonics in the second measurement signal z2(t) respectively have the same frequencies as the fundamental and the harmonics in the second source signal x2(t).

The second Fourier transform section13B calculates a plurality of harmonics included in the second measurement signal z2(t) through Fourier transform of the second measurement signal z2(t). The second control section15B causes the harmonic generation section9B [n] to adjust either or both of an amplitude and a phase of the harmonic signal hB [n] so that a harmonic that matches the removal target harmonic is removed from the second measurement signal z2(t).

The second summing section11B sums the second source signal x2(t) and the harmonic signal hB [n] having either or both of an adjusted amplitude and an adjusted phase to output the second summed signal y2(t). The second summed signal y2(t) is converted by the measurement section7to the second measurement signal z2(t), and the second measurement signal z2(t) is re-input into the second Fourier transform section13B.

The Fourier transform by the second Fourier transform section13B, the control of the harmonic generation section9B[n] by the second control section15B, the adjustment of either or both of the amplitude and the phase by the harmonic generation section9B[n], the summing by the second summing section11B, and the digital output by the measurement section7are repeated until harmonics that match the removal target harmonics are removed from the second measurement signal z2(t).

The following describes a method for calculating the value r of the ratio of the second physical quantity p2to the first physical quantity p1with reference toFIG. 23. The measurement section7calculates the value r of the ratio.FIG. 23is a functional block diagram of the measurement section7. The measurement section7includes a phase difference calculating section61(phase difference calculating means), a delay difference calculating section63(delay difference calculating means), and a second ratio calculating section65(second ratio calculating means). The processor17functions as the phase difference calculating section61, the delay difference calculating section63, and the second ratio calculating section65through execution of a computer program stored in the storage section18.

Based on a phase difference Δθ between the fundamental in the first measurement signal z1(t) and the fundamental in the second measurement signal z2(t), the second ratio calculating section65calculates the value r of the ratio of the second physical quantity p2to the first physical quantity p1. That is, the phase difference calculating section61calculates the phase difference Δθ. The phase difference Δθ in Embodiment6represents shifting of the phase of the fundamental in the second measurement signal z2(t) relative to the phase of the fundamental in the first measurement signal z1(t). The delay difference calculating section63calculates a delay time difference2(t). The delay time difference Δτ in Embodiment 6 represents a difference between the delay time of the first measurement signal z1(t) and the delay time of the second measurement signal z2(t). The second ratio calculating section65calculates the value r of the ratio in accordance with an equation (2). In the equation (2), pr represents reference physical quantity, and f represents frequency of the fundamental in the first measurement signal z1(t). In Embodiment 6, pr=0.

The delay time difference Δτ can be determined by determining the phase difference Δθ in advance on the assumption that p1=p2in the equation (2).

The following describes a flow of a measuring method that is performed by the measuring device1with reference toFIGS. 21, 23, and 24.FIG. 24is a flowchart illustrating the measuring method. The measuring device1performs processes in steps S31to S53. The process in Step S31is the same as the process in Step S1inFIG. 12. The process in Step S33is the same as the process in Step S3inFIG. 12and includes Steps S5to S15illustrated inFIG. 12.

That is, in Step S31, the first signal generation section3generates the first source signal x1(t). In Step S33, the first removal section5removes some or all of the harmonics from the first source signal x1(t).

Meanwhile, in Step S41, the second signal generation section3B generates the second source signal x2(t). In Step S43, the second removal section5B removes some or all of the harmonics from the second source signal x2(t).

The process in Step S43includes the processes in Steps S5to S15illustrated inFIG. 12. In the case of Step S43, the harmonic signal h[n] is replaced with the harmonic signal hB[n], the first source signal x1(t) is replaced with the second source signal x2(t), the first summed signal y1(t) is replaced with the second summed signal y2(t), the first measurement signal z1(t) is replaced with the second measurement signal z2(t), the harmonic generation section9[n] is replaced with the harmonic generation section9B [n], the first summing section11is replaced with the second summing section11B, the first Fourier transform section13is replaced with the second Fourier transform section13B, and the first control section15is replaced with the second control section15B in the description of Steps S5to S15.

In Step S51, the phase difference calculating section61calculates the phase difference Δθ between the fundamental in the first measurement signal z1(t) and the fundamental in the second measurement signal z2(t). In Step S53, the second ratio calculating section65calculates the value r of the ratio of the second physical quantity p2to the first physical quantity p1in accordance with the equation (2). It should be noted that the delay difference calculating section63calculates in advance the delay time difference Δτ based on the phase difference Δθ when p1=p2in accordance with the equation (2).

According to Embodiment 6, as described above with reference toFIGS. 21 to 24, influence of non-linearity of the measurement section7(the detector19) on measurement results can be easily reduced by removing some or all of the harmonics, which are a cause of occurrence of a non-linearity error. In addition to the above, Embodiment 6 also achieves the same effects as Embodiment 1.

Furthermore, according to Embodiment 6, the value r of the ratio is calculated from the phase difference Δθ, and thus a task of searching for a reference point on the time axis for calculating the phase θ of the fundamental in the first measurement signal z1(t) can be omitted. Furthermore, there is no dead time.

The measuring device1according to Embodiment 6 can also be applied to voltage measurement and optical measurement. It is therefore possible to reduce a non-linearity error in the voltage ratio and the optical intensity ratio. In a case where the measuring device1is applied to voltage measurement, each of the first signal generation section3and the second signal generation section3B has the same configuration as the configuration of the first signal generation section3according to Embodiment 2, each of the first removal section5and the second removal section5B has the same configuration as the configuration of the first removal section5according to Embodiment 2, and the measurement section7has the same configuration as the configuration of the measurement section7according to Embodiment 2. In a case where the measuring device1is applied to optical measurement, each of the first signal generation section3and the second signal generation section3B has the same configuration as the configuration of the first signal generation section3according to Embodiment 3, each of the first removal section5and the second removal section5B has the same configuration as the configuration of the first removal section5according to Embodiment 3, and the measurement section7has the same configuration as the configuration of the measurement section7according to Embodiment 3.

The following describes a measuring device1according to Embodiment 7 of the present invention with reference toFIGS. 21 to 25.FIG. 25is a block diagram illustrating the measuring device1according to Embodiment 7. The measuring device1includes a first bandpass filter4(first removal means) and a second bandpass filter4B (second removal means) instead of the first removal section5and the second removal section5B of the measuring device1according to Embodiment 6. The first bandpass filter4has the same configuration as the configuration of the first bandpass filter4illustrated inFIG. 18.

The second bandpass filter4B has the same properties as the first bandpass filter4; the second bandpass filter4B allows only the fundamental in the second source signal x2(t) to pass and outputs the fundamental to the measurement section7as a harmonic-removed signal y2(t) (corresponding to the second summed signal y2(t) in Embodiment6).

The measurement section7converts the harmonic-removed signal y1(t), which is an analog signal, to the digital first measurement signal z1(t), and converts the harmonic-removed signal y2(t), which is an analog signal, to the digital second measurement signal z2(t). The measurement section7calculates the value r of the ratio in accordance with the equation (2).

According to Embodiment 7, influence of non-linearity of the measurement section7(the detector19) can be reduced by removing some or all of the harmonics from the first measurement signal z1(t) and some or all of the harmonics from the second measurement signal z2(t). As a result, a non-linearity error included in the value r of the ratio can be reduced. In addition to the above, Embodiment 7 also achieves the same effects as Embodiment 6. The measuring device1can also be applied to voltage measurement and optical measurement.

The following describes a measuring device1according to Embodiment 8 of the present invention with reference toFIGS. 21 and 26 to 28. As the measuring device1according to Embodiment 8, the measuring device1according to Embodiment6illustrated inFIG. 21is applied to voltage measurement. Accordingly, each of the first physical quantity p1, the second physical quantity p2, and the reference physical quantity pr inFIG. 21is a voltage. Each of the first source signal x1(t), the first summed signal y1(t), the first measurement signal z1(t), the harmonic signal h[n], the second source signal x2(t), the second summed signal y2(t), the second measurement signal z2(t), and the harmonic signal hB[n] is an electric signal. Each of the first removal section5and the second removal section5B in Embodiment8removes only a second-order harmonic. Therefore, N=1. The measuring device1is utilized in simultaneous calibration.

FIG. 26is a block diagram illustrating the measuring device1according to Embodiment 8. The measuring device1includes a function generator91(hereinafter, referred to as an “FG91”, a function generator92(hereinafter referred to as an “FG92”), a two-channel signal generator93(hereinafter, referred to as an “SG93”), an FPGA94, a digital voltmeter95(hereinafter, referred to as a “DVM95”, a switching board96(hereinafter, referred to as an “SB96”), a two-channel analog-digital converter97(hereinafter, referred to as an “ADC97”), and a personal computer98(hereinafter, referred to as a “PC98”).

The FG91supplies a base clock clk0to the FPGA94and supplies a synchronous clock clks to the FG92.

The FG2operates in synchronization with the synchronous clock clks and generates the harmonic electric signal h[1] and the harmonic electric signal hB[1]. Each of the harmonic electric signal h[1] and the harmonic electric signal hB[1] has the same frequency as the second-order harmonic. The FG92functions as the harmonic generation section9[1] and the harmonic generation section9B[1].

The SG93generates a direct current voltage p1as the first physical quantity p1and a direct current voltage p2as the second physical quantity p2. The FPGA94generates clocks clk1to clk3and a sampling clock clk4based on the base clock clk0. The DVM95is a voltmeter and measures the direct current voltage p1and the direct current voltage p2.

The SB96functions as the first signal generation section3, the second signal generation section3B, the first summing section11, and the second summing section11B. The SB96generates the first source signal x1(t) and the second source signal x2(t). The SB96further generates the first summed signal y1(t) and the second summed signal y2(t).

The ADC97converts the first summed signal y1(t), which is an analog signal, to a digital signal and outputs the digital signal as the first measurement signal z1(t) to the PC98. The ADC97also converts the second summed signal y2(t), which is an analog signal, to a digital signal and outputs the digital signal as the second measurement signal z2(t) to the PC98. The ADC97functions as the detector19(FIG. 5A).

The PC98functions as parts of the measurement section7(the phase difference calculating section61, the delay difference calculating section63, and the second ratio calculating section65). The PC98measures the first measurement signal z1(t) and the second measurement signal z2(t), and calculates the value r of the ratio in accordance with the equation (2). The PC98also functions as the first Fourier transform section13, the second Fourier transform section13B, the first control section15, and the second control section15B.

FIG. 27is a schematic diagram of a signal generation circuit81that is mounted in the SB96illustrated inFIG. 26. The signal generation circuit81functions as the first signal generation section3and the second signal generation section3B. The signal generation circuit81includes a switch section82, a switch85, and a switch86.

The switch85is driven by the clock clk3and includes contacts89ato89c. The switch86is driven by the clock clk3and includes contacts90ato90c. The contact89cis connected with the contact90c. A voltage of 0 V is applied as the reference physical quantity pr to each of the contact89cand the contact90c. That is, the contact89cand the contact90care grounded.

The switch section82is driven by the clock clk and includes a switch83and a switch84. The clock clk in Embodiment 8 includes the clocks clk1and clk2. The switch83includes contacts87ato87c. The switch84includes contacts88ato88c. The contact87b, the contact88c, and the contact89bare connected with one another. The contact87c, the contact88b, and the contact90bare connected with one another. The direct current voltage p1is applied to the contact87a, and the direct current voltage p2is applied to the contact88a.

The switch83and the switch84operate in synchronization. Thus, the switch84connects the contact88awith the contact88bwhen the switch83connects the contact87awith the contact87b. The switch84connects the contact88awith the contact88cwhen the switch83connects the contact87awith the contact87c.

The switch85and the switch86operate in synchronization. Thus, the switch86connects the contact90awith the contact90bwhen the switch85connects the contact89awith the contact89b. The switch86connects the contact90awith the contact90cwhen the switch85connects the contact89awith the contact89c.

The following describes operation of the signal generation circuit81with reference toFIGS. 22 and 27. During an interval from time 0 to time T/4, the contact87aand the contact87bare connected, the contact89aand the contact89bare connected, the contact88aand the contact88bare connected, and the contact90aand the contact90bare connected. Accordingly, the level of the first source signal x1(t) becomes the level of the direct current voltage p1, and the level of the second source signal x2(t) becomes the level of the direct current voltage p2.

During an interval from time T/4 to time3T/4, the contact89aand the contact89care connected, and the contact90aand the contact90care connected. Accordingly, the level of the first source signal x1(t) and the level of the second source signal x2(t) each become 0 V.

During an interval from time3T/4 to time T, the contact88aand the contact88care connected, the contact89aand the contact89bare connected, the contact87aand the contact87care connected, and the contact90aand the contact90bare connected. Accordingly, the level of the first source signal x1(t) becomes the level of the direct current voltage p2, and the level of the second source signal x2(t) becomes the level of the direct current voltage p1.

The following describes the SB96in detail with reference toFIG. 28.FIG. 28is a circuit diagram illustrating the SB96. The SB96includes the signal generation circuit81, the first summing section11, and the second summing section11B. The signal generation circuit81illustrated inFIG. 27is implemented as the signal generation circuit81illustrated inFIG. 28. The signal generation circuit81includes operational amplifiers A1aand A2awith a drift of 0, an operational amplifier A3awith field effect transistor (FET) input, operational amplifiers A1band A2bwith a drift of 0, an operational amplifier A3bwith FET input, switches82a,82b,85, and86, resistance elements R1ato R3a, and resistance elements R1bto R3b. The operational amplifiers A1a, A2a, A1b, and A2bfunction as non-inverting amplifiers. Each of the switches82a,82b,85, and86is an analog switch and has the same configuration as the switch section82.

The direct current voltage p2is input to an input terminal of the operational amplifier A1a, and the direct current voltage p1is input to an input terminal of the operational amplifier A1b. Output terminals of the operational amplifiers A1aand A1bare connected with input terminals j1and j3of the switch82a. The operational amplifier A2aand the resistance element Rla are connected in series between an output terminal j2of the switch82aand an input terminal j1of the switch82b. The operational amplifier A2band the resistance element R1bare connected in series between an output terminal j4of the switch82aand an input terminal j3of the switch82b.

An output terminal j2of the switch82band the resistance element R2aare connected with input terminals j1and j3of the switch85. An output terminal j2of the switch85is connected with a negative terminal of the operational amplifier A3a, and an output terminal j4thereof is grounded. The resistance element R3ais connected between an output terminal and the negative terminal of the operational amplifier A3a.

The output terminal j4of the switch82band the resistance element R2bare connected with input terminals j3and j1of the switch86. An output terminal j2of the switch86is connected with a negative terminal of the operational amplifier A3b, and an output terminal j4thereof is grounded. The resistance element R3bis connected between an output terminal and the negative terminal of the operational amplifier A3b.

The first summing section11is a summer obtained by modifying a non-inverting amplifier and includes resistance elements R4to R6and an operational amplifier A4of FET input. One terminal of each of the resistance elements R4, R5, and R6is connected with a negative terminal of the operational amplifier A4. The other terminal of the resistance element R6is connected with an output terminal of the operational amplifier A4. A positive terminal of the operational amplifier A4is grounded.

The signal generation circuit81generates the first source signal x1(t) and the second source signal x2(t) based on the direct current voltage p1and the direct current voltage p2through switching of the switches82a,82b,85, and86. The input capacitance of the operational amplifiers A2aand A2bis dependent on input voltage, and accordingly switching noise of the switch82abehaves non-linearly with respect to the direct current voltage p1and the direct current voltage p2. Embodiment 8 therefore includes switches in two stages (the switch82aand the switch82b) so that noise of the operational amplifiers A2aand A2bis not superimposed on the first source signal x1(t) and the second source signal x2(t).

The output terminal of the operational amplifier A3ais connected with the other terminal of the resistance element R4, and the harmonic electric signal h[1] is input to the other terminal of the resistance element R5. Thus, the first source signal x1(t) generated by the signal generation circuit81and the harmonic electric signal h[1] generated by the FG92are input into the first summing section11. As a result, the first summing section11sums, and inverts and amplifies the first source signal x1(t) and the harmonic electric signal h[1] to output the first summed signal y1(t).

The second summing section11B has the same configuration as the configuration of the first summing section11. However, the output terminal of the operational amplifier A3bis connected with the resistance element R4, and the harmonic electric signal hB[1] is input to the resistance element R5. Accordingly, the second summing section11B sums, and inverts and amplifies the second source signal x2(t) and the harmonic electric signal hB[1] to output the second summed signal y2(t).

According to Embodiment8, as described above with reference toFIGS. 26 to 28, influence of non-linearity of the ADC97can be reduced by removing some or all of the harmonics from the first measurement signal z1(t) and some or all of the harmonics from the second measurement signal z2(t) in voltage measurement. As a result, a non-linearity error included in the value r of the ratio, that is, a voltage ratio can be reduced. In addition to the above, Embodiment 8 also achieves the same effects as Embodiment 6.

The following describes a measuring device1according to Embodiment 9 of the present invention with reference toFIGS. 19A-19B, 21, 29A-29B, and 30. The measuring devices1according to Embodiments 6 to 8 reduce non-linearity of the measurement section7and are utilized in simultaneous calibration while performing measurement. In contrast, the measuring device1according to Embodiment 9 is not only utilized in simultaneous calibration but also utilized in multipoint calibration.

The measuring device1according to Embodiment 9 has a non-linearity error reduction mode and a non-linearity error measurement mode. The measuring device1in the non-linearity error reduction mode operates in the same manner as the measuring device1according to Embodiment 6 and is utilized in simultaneous calibration. The following describes the non-linearity error measurement mode and utilization in multipoint calibration. The non-linearity error measurement mode of the measuring device1includes a first mode and a second mode.

FIG. 29Ais a block diagram illustrating the measuring device1according to Embodiment 9. The measuring device1includes a two-channel signal source8in addition to the configuration of the measuring device1according to Embodiment 6. The signal source8has the same configuration as the configuration of the signal source8illustrated inFIG. 19A. However, the signal source8according to Embodiment 9 outputs the first signal p1indicating the first physical quantity p1to the first signal generation section3and the second signal generation section3B. The signal source8also outputs the second signal p2indicating the second physical quantity p2to the first signal generation section3and the second signal generation section3B.

The first signal generation section3, the first removal section5, the second signal generation section3B, the second removal section5B, and the measurement section7of the measuring device1according to Embodiment 9 respectively have the same configurations as the configurations of the first signal generation section3, the first removal section5, the second signal generation section3B, the second removal section5B, and the measurement section7of the measuring device1according to Embodiment 6. An electrical configuration of the measurement section7according to Embodiment 9 is the same as the electrical configuration illustrated inFIG. 5A. The detector19is a two-channel detector. However, the measurement section7has a different configuration from the configuration illustrated inFIG. 5B. The following mainly describes differences of Embodiment 9 from Embodiment 6 (FIGS. 21 to 24) and from Embodiment 5 (FIGS. 19A-19B and 20).

FIG. 30is a functional block diagram illustrating the measurement section7. The measurement section7includes a second difference calculating section71(second difference calculating means), a storage section18(storage means), a third ratio calculating section55(third ratio calculating means), and a correction section57(correction means) in addition to the configuration of the measurement section7illustrated inFIG. 23.

The processor17functions as the phase difference calculating section61, the delay difference calculating section63, the second ratio calculating section65, the second difference calculating section71, the third ratio calculating section55, and the correction section57through execution of a computer program stored in the storage section18.

The following describes operation of the measuring device1in the first mode with reference toFIGS. 21, 29A, and 30. Operation of the signal source8, the first signal generation section3, and the first removal section5is the same as the operation of the signal source8, the first signal generation section3, and the first removal section5in the first mode according to Embodiment 5.

The second signal generation section3B outputs the second source signal x2(t) in which the first physical quantity p1is maintained constant and the second physical quantity p2is changed in a stepwise manner. The second summing section11B of the second removal section5B sums the harmonic signal hB[n] and the second source signal x2(t) to output the second summed signal y2(t). Having the harmonic signal hB[n] added thereto, the second summed signal y2(t) is a signal from which a corresponding harmonic has been removed. The measurement section7inputs the second summed signal y2(t) and outputs the second measurement signal z2(t) from which the harmonic has been removed. In Embodiment 9, the second measurement signal z2(t) from which the harmonic has been removed is referred to as a second measurement signal z2a(t). It should be noted that as in Embodiment 5, the first measurement signal z1(t) from which the harmonic has been removed is referred to as the first measurement signal z1a(t).

Based on the first measurement signal z1a(t) and the second measurement signal z2a(t), the second ratio calculating section65calculates the value r of the ratio of the second physical quantity p2to the first physical quantity p1for each second physical quantity p2. That is, the phase difference calculating section61calculates a phase difference Δθ between the fundamental in the first measurement signal z1a(t) and the fundamental in the second measurement signal z2a(t) for each second physical quantity p2. The delay difference calculating section63calculates a delay time difference Δτ between the first measurement signal z1a(t) and the second measurement signal z2a(t). The second ratio calculating section65calculates the value r of the ratio in accordance with the equation (2) using the phase difference Δθ and the delay time difference Δτ based on the first measurement signal z1a(t) and the second measurement signal z2a(t) for each second physical quantity p2, and stores the value r of the ratio in the storage section18. The value r of the ratio includes a reduced non-linearity error, and therefore the accuracy thereof is high. Through the above, the first mode has been described.

The following describes operation of the measuring device1in the second mode. Operation of the signal source8, the first signal generation section3, and the second signal generation section3B is the same as the operation of the signal source8, the first signal generation section3, and the second signal generation section3B in the first mode. Operation of the first removal section5is the same as the operation of the first removal section5in the second mode according to Embodiment 5.

The harmonic generation section9B [n] of the second removal section5B does not generate the harmonic signal hB [n]. Accordingly, the second summing section11B outputs the second source signal x2(t) as the second summed signal y2(t) without summing the harmonic signal hB[n] and the second source signal x2(t). Having no harmonic signal hB [n] added thereto, the second summed signal y2(t) is a signal from which none of the harmonics has been removed. The measurement section7inputs the second summed signal y2(t) and outputs the second measurement signal z2(t) from which none of the harmonics has been removed. In Embodiment 9, the second measurement signal z2(t) from which none of the harmonics has been removed is referred to as a second measurement signal z2b(t). It should be noted that as in Embodiment5, the first measurement signal z1(t) from which none of the harmonics has been removed is referred to as a first measurement signal z1b(t).

Based on the first measurement signal z1b(t) and the second measurement signal z2b(t), the second ratio calculating section65calculates the value r of the ratio of the second physical quantity p2to the first physical quantity p1for each second physical quantity p2. That is, the phase difference calculating section61calculates a phase difference Δθ between the fundamental in the first measurement signal z1b(t) and the fundamental in the second measurement signal z2b(t) for each second physical quantity p2. The delay difference calculating section63calculates a delay time difference Δτ between the first measurement signal z1b(t) and the second measurement signal z2b(t). The second ratio calculating section65calculates the value r of the ratio in accordance with the equation (2) using the phase difference Δθ and the delay time difference Δτ based on the first measurement signal z1b(t) and the second measurement signal z2b(t) for each second physical quantity p2, and stores the value r of the ratio in the storage section18. The value r of the ratio includes a non-linearity error that is not reduced. Through the above, the second mode has been described.

The second difference calculating section71acquires from the storage section18the value r of the ratio calculated in the first mode and the value r of the ratio calculated in the second mode for each second physical quantity p2. Subsequently, the second difference calculating section71calculates a difference Δr between the value r of the ratio calculated in the first mode and the value r of the ratio calculated in the second mode for each second physical quantity p2. The storage section18stores therein the difference Δr in association with the value r of the ratio calculated in the second mode for each second physical quantity p2.

As a result, a table associating the value r of the ratio calculated in the second mode with the difference Δr (hereinafter, referred to as an “error table”) is created. The difference Δr represents the non-linearity error, and therefore the error table is a table associating the value r of the ratio calculated in the second mode with the non-linearity error. Preferably, the second physical quantity p2is changed finely in a sufficiently large number of steps so that data in the error table is sufficiently continuous and sufficiently precise.

Since the error table is prepared, an analog signal p3indicating a third physical quantity p3and an analog signal p4indicating a fourth physical quantity p4can be input into the measurement section7as in Embodiment 5. Therefore, as in Embodiment 5, the third ratio calculating section55calculates a value R (=p4/p3) of a ratio of the fourth physical quantity p4to the third physical quantity p3. The correction section57corrects the value R of the ratio calculated by the third ratio calculating section55based on the error table, that is, based on the difference Δr stored in the storage section18to calculate a value Rc of the ratio including a reduced non-linearity error. In a case where a drift in the non-linearity error is negligible, the error table may be prepared at any timing as in Embodiment 5.

The following describes a measuring device1according to a variation of Embodiment 9 with reference toFIG. 29B.FIG. 29Bis a block diagram illustrating the measuring device1according to the variation. The measuring device1includes a first signal source8and a second signal source8B instead of the signal source8of the measuring device1illustrated inFIG. 29A. The first signal source8is included in the first signal generation section3, and the second signal source8B is included in the second signal generation section3B. According to the variation, in each of the first and second modes, the first signal source8generates and outputs the first source signal x1(t) in which the first physical quantity p1is maintained constant and the second physical quantity p2is changed in a stepwise manner, and the second signal source8B generates and outputs the second source signal x2(t) in which the first physical quantity p1is maintained constant and the second physical quantity p2is changed in a stepwise manner.

According to Embodiment 9 (hereinafter, including the variation thereof), as described above with reference toFIGS. 29A-29B and 30, it is possible to easily determine the value r of the ratio including a non-linearity error reduced through harmonic removal and the value r of the ratio including a non-linearity error that is not reduced. Therefore, the error table for achieving utilization in multipoint calibration can be easily prepared. In addition to the above, Embodiment 9 also achieves the same effects as Embodiment 5.

The measuring device1according to Embodiment 8 described with reference toFIGS. 26 and 28may have the non-linearity error reduction mode and the non-linearity error measurement mode. As described with reference toFIGS. 26 and 28, the measuring device1in the non-linearity error reduction mode is utilized in simultaneous calibration. The measuring device1in the non-linearity error measurement mode operates in the same manner as the measuring device1according to Embodiment 9 and is utilized in multipoint calibration.

The following describes a measuring device1according to Embodiment 10 of the present invention with reference toFIGS. 13 and 31. As illustrated inFIG. 13, the measuring device1according to Embodiment 10 has the same configuration as the configuration of the measuring device1according to Embodiment 2. However, the measuring device1according to Embodiment 10 includes a measurement section7illustrated inFIG. 31instead of the measurement section7of the measuring device1according to Embodiment 2. The measuring device1according to Embodiment 10 is utilized in simultaneous calibration.

FIG. 31is a block diagram illustrating the measurement section7of the measuring device1according to Embodiment 10. As illustrated inFIG. 31, a detector19of the measurement section7includes an isolation amplifier100and an ADC19a. The isolation amplifier100is an amplifier in which an input section and an output section of the isolation amplifier100are isolated from each other. The isolation amplifier100amplifies the first summed signal y1(t) and outputs the first summed signal y1(t) to the ADC19aas an amplified signal110. The ADC19aconverts the amplified signal110, which is an analog signal, to a digital signal and outputs the digital signal as the first measurement signal z1(t). Other than the above, operation of the measuring device1is the same as that of Embodiment 2, and therefore description thereof is omitted.

The measuring device1according to Embodiment 10 can for example be applied to an isolation input type digital voltmeter in which an isolation amplifier is located upstream of an AD converter. Generally, non-linearity of the isolation amplifier is higher than non-linearity of the AD converter. It is therefore difficult to perform measurement with high linearity using a general insulation input type digital voltmeter. However, the use of the measuring device1according to Embodiment 10 can for example allow an insulation input type digital voltmeter having a linearity of 10 ppm to be achieved. In addition to the above, the measuring device1according to Embodiment 10 also achieves the same effects as the measuring device1according to Embodiment 2.

The following describes a measuring device1according to Embodiment 11 of the present invention with reference toFIGS. 13 and 32. As illustrated inFIG. 13, the measuring device1according to Embodiment 11 has the same configuration as the configuration of the measuring device1according to Embodiment 2. However, the measuring device1according to Embodiment 11 includes a measurement section7illustrated inFIG. 32instead of the measurement section7of the measuring device1according to Embodiment 2. The measuring device1according to Embodiment 11 is utilized in simultaneous calibration.

FIG. 32is a block diagram illustrating the measurement section7of the measuring device1according to Embodiment 11. As illustrated inFIG. 32, a detector19of the measurement section7includes a compressor101, an ADC19a, and an expander102. The compressor101compresses the amplitude of the first summed signal y1(t) and outputs the first summed signal y1(t) as an amplitude-compressed signal111to the ADC19a. The compressor101is for example an amplitude compression circuit such as a logarithmic amplifier. The ADC19aconverts the amplitude-compressed signal111, which is an analog signal, to a digital signal and outputs the digital signal to the expander102as an amplitude-compressed signal112. The expander102expands the amplitude of the amplitude-compressed signal112and outputs the amplitude-compressed signal112as the first measurement signal z1(t). The expander102is for example a digital expansion operation device. Other than the above, operation of the measuring device1is the same as that of Embodiment 2, and therefore description thereof is omitted.

The measuring device1according to Embodiment 11 can for example be applied to a compressed amplitude input type digital voltmeter. In the compressed amplitude input type digital voltmeter, an amplitude compression circuit is located upstream of an AD converter, and a digital expansion operation device is located downstream of the AD converter. Generally, a compression function of the amplitude compression circuit drifts depending on temperature and elapsed time, and therefore it is difficult to accurately expand an amplitude-compressed signal with the amplitude compression circuit. Therefore, a digital signal expanded by the digital expansion operation device typically exhibits higher non-linearity than a digital signal output by the AD converter. The compressed amplitude input type digital voltmeter is therefore rarely used in general quantitative voltage measurement. That is, the compressed amplitude input type digital voltmeter has limited applicability and is for example used in ultrasonic diagnostic equipment for dynamic range expansion.

However, the use of the measuring device1according to Embodiment 11 can for example allow a compressed amplitude input type digital voltmeter having a linearity of 100 ppm to be achieved. As a result, the use of the measuring device1enables voltage measurement with a wide dynamic range in a wider range of applications than that requiring quantification. In addition to the above, the measuring device1according to Embodiment 11 also achieves the same effects as the measuring device1according to Embodiment 2.

The following describes the present invention in detail using an example. However, the present invention is not limited to the following example.

EXAMPLE

In the present example, the measuring device1according to Embodiment 8 described with reference toFIGS. 26 and 28was used to experiment with utilization in simultaneous calibration. The frequency f of the fundamentals in the first source signal x1(t) and the second source signal x2(t) was set to 307.2 Hz. The ADC97was a 24 bit delta-sigma (ΔΣ type) analog-digital converter (PEX-320724, product of Interface Corporation). A reduction of a non-linearity error in the ADC97was confirmed in the present example.

First, conditions in the present example will be described. The FG91(WF1947, product of NF CORPORATION) generated a square wave at 12.288 MHz as the base clock clk0. The base clock clk0was input into the FPGA94(DE0, product of Terasic Inc.). The FPGA94generated the clocks clk1 and clk2 at 153.6 Hz(=f/2) by dividing the base clock clk0by 80,000. The FPGA94also generated the clock clk3at 307.2 Hz (=f) by dividing the base clock clk0by 40,000. The clock clk1was used for driving the switch82a. The clock clk2was used for driving the switch82b. The clock clk3 was used for driving the switch85and the switch86.

The FPGA94generated the sampling clock clk4at 614.4 kHz by dividing the base clock clk0by 20. The sampling clock clk4was common among both the channels of the ADC97. The non-linearity error and signal bandwidth of the ADC97were 24 ppm and 614.4 kHz, respectively, which are typical values.

The SG93included three nickel-metal-hydride rechargeable batteries (Eneloop 1.3 V, product of SANYO Electric Co., Ltd.) and a six resistor divider. The SG93maintained the direct current voltage p1 at approximately 3.9 V. The SG93changed the direct current voltage p2in a range of from 0 V to 3.6 V in six steps at equal intervals. The reference voltage pr was 0 V. The direct current voltage p1and the direct current voltage p2 generated by the SG93were measured using a ratiometer provided in the DVM95(6581, product of ADC CORPORATION). The DVM95had an accuracy of 1 microvolt, which was equal to an error of approximately 0.3 ppm in ratio measurement.

The SB96generated the first source signal x1(t) and the second source signal x2(t) through the switches82a,82b,85, and86(MAX4527, product of Maxim). The harmonic electric signal h[1] and the harmonic electric signal hB[1] at 614.4 Hz (=20 were input into the SB96from the FG92(WF1948, product of NF CORPORATION). Each of the harmonic electric signal h[1] and the harmonic electric signal hB[1] was a sine wave. Through the first summing section11, the SB96summed the first source signal x1(t) and the harmonic electric signal h[1] to generate the first summed signal y1(t). Through the second summing section11B, the SB96summed the second source signal x2(t) and the harmonic electric signal hB [1] to generate the second summed signal y2(t). The resistance elements R1a, R1b, R2a, R2b, and R6each had a resistance value of 100 kΩ The resistance element R3aand R3beach had a resistance value of 10 kΩ.

The ADC97measured the first summed signal y1(t) and the second summed signal y2(t). The ADC97accumulated digital data for 2.5 seconds and determined mean data for random noise reduction. Prior to the measurement, two input terminals of the ADC97were grounded, a reference signal including offset of an operational amplifier and switching noise was obtained, and the offset of the operational amplifier and the switching noise were removed by subtraction.

The following describes calculation of a voltage ratio rt by time averaging with reference toFIGS. 33A-33E.FIG. 33Ais a waveform diagram illustrating the first measurement signal z1(t) from which none of the harmonics has been removed.FIG. 33Bis a waveform diagram illustrating the second measurement signal z2(t) from which none of the harmonics has been removed. In order to remove switching noise and a transition time effect, an average voltage value was calculated in each of regions V11to V28represented by shaded areas. The average voltage values in the respective regions V11to V28are indicated by the same reference signs as those of the regions. For example, the average voltage value in the region V11is indicated by the reference sign V11. The voltage ratio rt was calculated in accordance with an equation (3).

The voltage ratio rt was recorded in the PC98and compared with a measurement value determined by the DVM95. Thus, the non-linearity error in the ADC97was calculated.

The following describes calculation of the voltage ratio r based on the phase with reference toFIGS. 34A-34B.FIG. 34Ais a waveform diagram illustrating the first measurement signal z1(t) from which the second-order harmonic has been removed.FIG. 34Bis a waveform diagram illustrating the second measurement signal z2(t) from which the second-order harmonic has been removed. The PC98performed zero replacement in each of regions m represented by shaded areas to remove remaining switching noise. Subsequently, the PC98calculated the fundamental (frequency f) and the second-order harmonic (frequency2f) in each of the first measurement signal z1(t) and the second measurement signal z2(t) through Fourier transform of each of the first measurement signal z1(t) and the second measurement signal z2(t).

The PC98calculated and displayed on a display the phase and the amplitude of the second-order harmonic in each of the first measurement signal z1(t) and the second measurement signal z2(t). In the present example, an operator manually controlled the FG92while monitoring the phase and the amplitude of the second-order harmonic and thus adjusted the amplitude and the phase of the harmonic electric signal h[1] and the harmonic electric signal hB[1] such that the amplitude of the second-order harmonic was less than 0.1. The PC98then calculated the voltage ratio r in accordance with the equation (2). The voltage ratio r was recorded in the PC98and compared with a measurement value determined by the DVM95. Thus, the non-linearity error in the ADC97was calculated. An effect of the harmonic removal was evaluated through comparison between the non-linearity error in the voltage ratio r and the non-linearity error in the voltage ratio rt.

The following describes the effect of the harmonic removal with reference toFIG. 35.FIG. 35is a diagram illustrating the non-linearity error. The horizontal axis represents voltage ratio based on the measurement values determined by the DVM95, and the vertical axis represents non-linearity error. Points Et represent the non-linearity error in the voltage ratio rt, and points Ec represent the non-linearity error in the voltage ratio r. Through comparison between points Et and points Ec, it was confirmed that the removal of the second-order harmonic reduced the non-linearity error by approximately 70%. The non-linearity error in the voltage ratio r was reduced to as low as approximately 2 ppm or less.

A curve NE10represents a result obtained by approximating the non-linearity of the ADC97before the harmonic removal with a sixth-order polynomial function G(r). The curve NE10agrees with the experimental result of the voltage ratio rt. A curve NE20 was obtained by approximating the non-linearity of the ADC97with the curve NE10. The curve NE20represents a result of simulation for the non-linearity error in the case where the second-order harmonic is removed. The curve NE20agrees with the experimental result of the voltage ratio r. A curve NE30represents a result of simulation for the non-linearity error when the second-order harmonic, the third-order harmonic, and the fifth-order harmonic are removed. The curve NE30was obtained by approximating the non-linearity of the ADC97with the curve NE10. The non-linearity error was reduced to less than 1 ppm.

The following describes switching operation in the signal generation circuit81with reference toFIGS. 28 and 33A-33E.

The switch82awill be described. When the clock clk1is at a high level, a signal input to the terminal j1is output from the terminal j2, and a signal input to the terminal j3is output from the terminal j4. When the clock clk1is at a low level, a signal input to the terminal j1is output from the terminal j4, and a signal input to the terminal j3is output from the terminal j2.

In the case of the switch82b, the clock clk1is replaced with the clock clk2in the description of the switch82a. In the case of each of the switches85and86, the clock clk1is replaced with the clock clk3in the description of the switch82a.

FIG. 33Aillustrates the first measurement signal z1(t) from which none of the harmonics has been removed. Accordingly, this first measurement signal z1(t) has the same waveform as the waveform of the first source signal x1(t). The following description therefore deems the waveform of the first measurement signal z1(t) as the waveform of the first source signal x1(t). Likewise, the following description deems the waveform of the second measurement signal z2(t) inFIG. 33Bas the waveform of the second source signal x2(t).

FIG. 33Cis a waveform diagram illustrating the clk1that is supplied to the switch82a.FIG. 33Dis a waveform diagram illustrating the clock clk2that is supplied to the switch82b.FIG. 33Eis a waveform diagram illustrating the clock clk3that is supplied to the switches85and86.

During an interval from time t0to time t1, the clock clk1is at a high level, the clock clk2is at a low level, and the clock clk3is at a low level. Accordingly, the first source signal x1(t) has a level of the direct current voltage p1, and the second source signal x2(t) has a level of the direct current voltage p2.

During an interval from time t1to time t2, the clock clk1is at the high level, the clock clk2is at the low level, and the clock clk3is at a high level. Accordingly, the first source signal x1(t) and the second source signal x2(t) have the level of the reference voltage pr.

During an interval from time t2to time t3, the clock clk1is at a low level, the clock clk2is at the low level, and the clock clk3is at the high level. Accordingly, the first source signal x1(t) and the second source signal x2(t) have the level of the reference voltage pr.

During an interval from time t3to time t4, the clock clk1is at the low level, the clock clk2is at the low level, and the clock clk3is at the low level. Accordingly, the first source signal x1(t) has the level of the direct current voltage p2, and the second source signal x2(t) has the level of the direct current voltage p1.

As described above, the signal generation circuit81generates the staircase first source signal x1(t) and the staircase second source signal x2(t) through the switching operation.

Through the above, embodiments of the present invention have been described with reference to the drawings. However, the present invention is not limited to the above-described embodiments and can be practiced in various ways within the scope without departing from the essence of the present invention (for example, as described below in sections (1)-(8)). The drawings schematically illustrate elements of configuration in order to facilitate understanding and properties of elements of configuration illustrated in the drawings, such as thickness, length, and number thereof, may differ from actual properties thereof in order to facilitate preparation of the drawings. Furthermore, properties of elements of configuration described in the above embodiments, such as shapes and dimensions, are merely examples and are not intended as specific limitations. Various alterations may be made so long as there is no substantial deviation from the effects of the present invention.

(1) In Embodiments 1 to 11 (FIGS. 1 to 32), which order of harmonic is to be removed can be determined as appropriate, and the number N of harmonics to be removed can be determined as appropriate. Removing only a low-order harmonic can reduce the non-linearity error. However, further removing higher-order harmonics can further reduce the non-linearity error.

(2) In Embodiments 1 to 11 (FIGS. 1 to 32), each measuring device1may be produced as one product, or the measuring device1excluding the measurement section7may be produced as one product. In the latter case, an existing or commercially available measuring device is used as the measurement section7.

(3) In Embodiments 2, 10, and 11 (FIGS. 13, 31, and 32), the first summer11ais provided in one stage. Alternatively, a plurality of stages of summers may be provided to sum the first source signal x1(t) and the harmonic electric signal ha[n]. For example, a first-stage summer sums the harmonic electric signals ha[1] to ha[N] to generate a summed signal including the harmonic electric signals ha[1] to ha[N], and a second-stage summer sums the thus generated summed signal and the first source signal x1(t) to generate the first summed signal y1(t).

(4) In Embodiments 2, 10, and 11 (FIGS. 13, 31, and 32), the oscillator9a[n] generates the harmonic electric signal ha[n] of a sine wave. Alternatively, the oscillator9a[n] may generate the harmonic electric signal ha[n] of any other waveform. For example, the oscillator9a[n] may generate the harmonic electric signal ha[n] of a square wave or the harmonic electric signal ha[n] of a triangle wave. In Embodiment 3 (FIG. 14), the harmonic generation section9b[n] generates the harmonic optical signal hb[n] of a square wave. Alternatively, the harmonic generation section9b[n] may generate the harmonic optical signal hb[n] of any other waveform. For example, the harmonic generation section9b[n] may generate the harmonic optical signal hb[n] of a triangle wave.

(5) The measuring device1according to Embodiment 3 (FIG. 14) may be applied to a spectrometry instrument with an array detector, which is referred to as a multi-channel spectrograph or polychromator. In the case of quantitative determination (chemometrics) performed based on spectroscopic measurement result, it is an important factor that measurement data is highly precise. The present invention can therefore be applied to spectroscopic measurement in such a case.

(6) In Embodiments 4 and 7 (FIGS. 18 and 25), a low-pass filter may be provided instead of the first bandpass filter4or in addition to the first bandpass filter4. In Embodiment 7, a low-pass filter may be provided instead of the second bandpass filter4B or in addition to the second bandpass filter4B. The low-pass filter is an analog filter for attenuating a harmonic. The low-pass filter may be additionally used in order to remove high-order harmonics (for example, frequency-decupled or higher harmonics) in Embodiments 1 to 11. For example, the low-pass filter is located upstream or downstream of the first summing section11, upstream or downstream of the first summer11a, upstream or downstream of the first summer11b, or upstream or downstream of the second summing section11B.

(7) In a case where the measuring device1according to Embodiment 4, 5, 6, 7, or 9 (FIG. 18, 19A-19B, 21, 25, or29A-29B) is applied to voltage measurement, the configuration of the measurement section7may be the same as the configuration of the measurement section7according to Embodiment 10 (FIG. 31) or the configuration of the measurement section7according to Embodiment 11 (FIG. 32). In Embodiment 8 (FIG. 26), the isolation amplifier100illustrated inFIG. 31may be disposed upstream of the ADC97. Alternatively, in Embodiment 8, the compressor101illustrated inFIG. 32may be disposed upstream of the ADC97, and the expander102illustrated inFIG. 32may be disposed downstream of the ADC97.

(8) In Embodiments 1 to 11 and the example, the measuring device1is applied to voltage measurement or optical measurement. However, scope of application of the present invention is not limited thereto. For example, the measuring device1according to Embodiment 1, 4, 5, 6, 7, or 9 (FIG. 1, 18, 19A-19B, 21, 25, or29A-29B) may be applied to current measurement, acoustic measurement, or vibration measurement.

In the case where the measuring device1is applied to current measurement, for example, each of the first physical quantity p1to the fourth physical quantity p4and the reference physical quantity pr is an electric current, and each of the first source signal x1(t), the second source signal x2(t), the harmonic signal h[n], the harmonic signal hB[n], the first summed signal y1(t), the second summed signal y2(t), the first measurement signal z1(t), and the second measurement signal z2(t) is an electric signal.

In the case where the measuring device1is applied to acoustic measurement, for example, each of the first physical quantity p1to the fourth physical quantity p4and the reference physical quantity pr is an acoustic pressure, and each of the first source signal x1(t), the second source signal x2(t), the harmonic signal h[n], the harmonic signal hB[n], the first summed signal y1(t), and the second summed signal y2(t) is an acoustic wave. Each of the first measurement signal z1(t) and the second measurement signal z2(t) is an electric signal.

In the case where the measuring device1is applied to vibration measurement, for example, each of the first physical quantity p1to the fourth physical quantity p4and the reference physical quantity pr is an elastic wave displacement, and each of the first source signal x1(t), the second source signal x2(t), the harmonic signal h[n], the harmonic signal hB[n], the first summed signal y1(t), and the second summed signal y2(t) is an elastic wave. Each of the first measurement signal z1(t) and the second measurement signal z2(t) is an electric signal.

INDUSTRIAL APPLICABILITY

The present invention is applicable to the field of measuring devices for measuring physical quantities.

REFERENCE SIGNS LIST