JPH0961472A - Phase difference measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a phase difference measuring apparatus having small circuit scale and improving the measuring accuracy. SOLUTION: The phase difference measuring apparatus simultaneously fetches a pair of first and second signals having different phases, converts the fetched signals to digital signals, and measures the phase difference of the signals. The apparatus has a selector 3a for alternately selecting a pair of signals, a sample and hold circuit 1a for fetching the output of the selector, an A-D converter 4a for converting the output of the circuit 1a to a digital signal, and a phase difference calculating circuit 5a for calculating the phase of the first signal corresponding to the sampling time of the second signal based on the two sampling results of the first signal of the outputs of the converter to obtain the phase difference from the phase of the second signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase difference measuring device, and more particularly to a phase difference measuring device having a small circuit scale and improved measuring accuracy.

[0002]

2. Description of the Related Art A phase difference measuring device measures, for example, a phase difference between a pair of sinusoidal signals having the same frequency but different phases.

FIG. 5 is a block diagram showing an example of such a conventional phase difference measuring apparatus. In FIG. 5, 1 and 2 are sample-and-hold circuits (hereinafter referred to as S & H circuits), 3 is a selection circuit such as a multiplexer, 4 is an A / D converter, and 5 is a phase difference calculation circuit. Also, 10
0 and 101 are a pair of sinusoidal signals having the same frequency but different phases, and 102 is a phase difference signal.

The sine wave signals 100 and 101 are input to the S & H circuits 1 and 2, respectively, and the outputs of the S & H circuits 1 and 2 are connected to the selection circuit 3, respectively. The output of the selection circuit 3 is connected to the A / D converter 4, the output of the A / D converter 4 is connected to the phase difference calculation circuit 5, and the phase difference calculation circuit 5 outputs the phase difference signal 102.

The operation of the conventional example shown in FIG. 5 will be described. The sine wave signals 100 and 101 are the S & H circuits 1 and 2
Are simultaneously sampled and the results are held. A
The / D converter 4 sequentially selects the held data by the selection circuit 3 and converts it into digital signals.

The phase difference calculation circuit 5 calculates the phase difference between the sine wave signals 100 and 101 based on the two digital signals sampled from the A / D converter 4 at the same time, and outputs the phase difference signal 102.

[0007]

However, in the conventional example shown in FIG. 5, a plurality of S & H circuits are required to sample the sine wave signals 100 and 101 at the same time, which not only increases the circuit scale but also increases the size of each S & H. Errors occur due to variations in circuit characteristics. Therefore, an object of the present invention is to realize a phase difference measuring device having a small circuit scale and improved measurement accuracy.

[0008]

In order to achieve such an object, the present invention provides a first signal and a second signal having different phases.
In the phase difference measuring device that simultaneously captures a pair of signals of the above signals and converts the captured signals into a digital signal and measures the phase difference between them, a selection circuit that alternately selects the pair of signals and the output of this selection circuit. Sample-and-hold circuit that captures
A / D that converts the output of the hold circuit into a digital signal
A phase of the first signal corresponding to the sampling time of the second signal is calculated based on two sampling results of the first signal of the converter and the output of the A / D converter, And a phase difference calculating circuit for obtaining a phase difference from the phase of the second signal.

[0009]

A pair of sine wave signals are alternately sampled at equal intervals, and based on two sampling results of the first sine wave signal, a first sine wave corresponding to a sampling time of the second sine wave signal. By calculating the phase of the signal and obtaining the phase difference from the phase of the second sine wave signal, one S & H circuit is sufficient.

[0010]

The present invention will be described in detail below with reference to the drawings.
FIG. 1 is a configuration block diagram showing an embodiment of a phase difference measuring apparatus according to the present invention. In FIG. 1, 1a is an S & H circuit,
3a is a selection circuit, 4a is an A / D converter, and 5a is a phase difference calculation circuit. Further, 100a and 101a are sine wave signals, 102a is a phase difference signal, and 103 is a digital signal.

The sine wave signals 100a and 101a are input to the selection circuit 3a, and the output of the selection circuit 3a is S &.
It is connected to the H circuit 1a. The output of the S & H circuit 1a is A /
The digital signal 103, which is connected to the D converter 4a and is the output of the A / D converter 4a, is connected to the phase difference calculation circuit 5a, and the phase difference calculation circuit 5a outputs the phase difference signal 102a.

FIG. 2 is a block diagram showing a concrete example of the phase difference calculation circuit 5a shown in FIG. In FIG. 2, 6,
7, 9 and 10 are memories, 8 and 11 are phase shifters for advancing a 90 ° phase, and 12 is an arithmetic circuit.
5, 106, 107, 108 and 109 are arithmetic circuits 12
Is a signal input to.

The digital signal 103 is input to the memories 6 and 7, and the signal 104 output from the memory 6 is connected to the phase shifter 8, the memory 9 and the arithmetic circuit 12. Phase shifter 8
The signal 105 that is the output of the
Connected to.

The signals 106 and 107 output from the memories 9 and 10 are connected to the arithmetic circuit 12.

On the other hand, the signal 108 output from the memory 7 is connected to the phase shifter 11 and the arithmetic circuit 12, and the signal 109 output from the phase shifter 11 is connected to the arithmetic circuit 12. The arithmetic circuit 12 also outputs the phase difference signal 102a.

The operation of the embodiment shown in FIGS. 1 and 2 will be described with reference to FIG. FIG. 3 is a characteristic curve diagram showing the relationship between the sampling time and the phase of the sine wave signals 100a and 101a.

The sine wave signal 100a is a reference signal, and the sine wave signal 101a is a signal whose phase is advanced by "φ".
The phases of the sine wave signals 100a and 101a are "
When α ”and“ β ”are set, α = ωt (1) and β = ωt + φ (2).

However, "ω" is the sine wave signals 100a and 1
The angular velocity of 01a and "t" are time. Also, in Fig. 3 "
It is assumed that "a" and "b" correspond to the sine wave signals 100a and 101a.

First, as the first step, the selection circuit 3a selects the sine wave signal 100a at the timing of the sampling time "t ₁ " in FIG. 3, and the S & H circuit 1a samples and holds the sine wave signal 100a. That is, FIG.
The data for the middle "C" points will be captured.

The held signal is converted into a digital signal 103 by the A / D converter 4a and stored in the memory 6. The signal 104 output from the memory 6 is further output to the memory 9
Stored in. And the phase at the point of "C" is shown in Fig. 3.
Because it is "alpha _1" from the signal 1 which is the output of the memory 9
06 is expressed as S ₁₀₆ = A · sin ωt ₁ = A · sin α ₁ (3). However, "A" is the amplitude of the sine wave signal 100a.

On the other hand, the output of the memory 6 is 90 ° by the phase shifter 8.
Since the phase is advanced and stored in the memory 10, the signal 106 which is the output of the memory 10 is expressed as S ₁₀₇ = A · sin (ωt ₁ +90) = A · cos ωt ₁ = A · cos α ₁ (4) It

As the second step, the selection circuit 3a selects the sine wave signal 101a at the timing of the sampling time "t ₂ " in FIG. 3, and the S & H circuit 1a selects this sine wave signal 1a.
01a is sampled and held. That is, in FIG.
The data of the point "D" will be captured.

This held signal is converted into a digital signal 103 by the A / D converter 4a and stored in the memory 7. Further, since the phase at the point "d" is "β ₂ " from FIG. 3, the signal 108 which is the output of the memory 7 is as follows: S ₁₀₈ = B · sin (ωt ₂ + φ) = B · sin β ₂ (5) expressed. However, "B" is the amplitude of the sine wave signal 101a.

On the other hand, the output of the memory 7 is 90 by the phase shifter 11.
Since the phase is advanced, the signal 109 is expressed as S ₁₀₉ = B · sin {(ωt ₂ + φ) +90} = B · cos (ωt ₂ + φ) = A · cos β ₂ (6).

As the third step, the selection circuit 3a again selects the sine wave signal 100a at the timing of the sampling time "t ₃ " in FIG. 3, and the S & H circuit 1a samples and holds the sine wave signal 100a. That is, FIG.
The data of the middle "e" point will be captured.

The held signal is converted into a digital signal 103 by the A / D converter 4a and stored in the memory 6. Further, since the phase at the point of "e" is "α ₃ " from FIG. 3, the signal 104 which is the output of the memory 6 is expressed as S ₁₀₄ = A · sinωt ₃ = A · sin α ₃ (7) .

On the other hand, the output of the memory 6 is 90 ° by the phase shifter 8.
Since the phase is advanced, the signal 105 is expressed as S ₁₀₅ = A · sin (ωt ₃ +90) = A · cos ωt ₃ = A · cos α ₃ (8).

Therefore, the signals 104 to 109 are input to the arithmetic circuit 12 by the above first to third steps. However, the sampling time “t ₂ ” has a relationship of t ₂ = (t ₁ + t ₃ ) / 2 (9).

Further, in FIG. 3, "H" is the phase difference at the sampling time "t ₂ ", which is represented by "β ₂ -α ₂ ". Substituting this value officially described below, tanθ = (1-cos2θ) / sin2θ tan (β 2 -α 2) = {1-cos2 (β 2 -α 2)} / sin2 (β 2 -α 2) (10)

From the relation of the equation (9), α ₂ = (α ₁ + α ₃ ) / 2 (11), and when substituted into the equation (10), tan (β ₂ −α ₂ ) = [1-cos { 2β ₂ − (α ₁ + α ₃ )}] / sin {2β ₂ − (α ₁ + α ₃ )} (12).

Further, the signals 104 to 109 are changed to "a" to "".
The following “g” to “n” are defined as f ”: g = A ² · sin (α ₁ + α ₃ ) = A ² (sinα ₁ · cosα ₃ + cosα ₁ · sinα ₃ ) = b · c + a · d (13)

[0032] ^{h = A 2 · cos (α} 1 + α 3) = A 2 (cosα 1 · cosα 3 -sinα 1 · sinα 3) = b · d-a · c (14)

I = B ² · sin ₂ β ₂ = B ² · ₂ sin β ₂ · cos β ₂ = 2 · e · f (15)

[0034] _{^{j = B 2 · cos2β 2 =}} B 2 · (cos 2 β 2 -sin 2 β 2) = f 2 -e 2 (16)

K = A ² · B ² · sin {2β ₂ − (α ₁ + α ₃ )} = A ² · B ² · {sin 2β ₂ · cos (α ₁ + α ₃ ) −cos 2β ₂ · sin (α ₁ + α ^{_{3)} = A 2 · cos}} (α 1 + α 3) · B 2 · sin2β 2 -A 2 · sin (α 1 + α 3) · B 2 · cos2β 2 = h · i-g · j (17)

L = A ² · B ² · cos {2β ₂ − (α ₁ + α ₃ )} = A ² · B ² · {cos 2β ₂ · cos (α ₁ + α ₃ ) −sin 2β ₂ · sin (α ₁ + α ₃ )} = A ² · cos (α ₁ + α ₃ ) · B ² · cos ₂ β ₂ −A ² · sin (α ₁ + α ₃ ) · B ² · sin ₂ β ₂ = h · j + g · i (18)

M = A ² = (A · sin α ₃ ) ² + (A · cos α ₃ ) ² = a ² + b ² (19)

N = B ² = (B · sin β ₂ ) ² + (B · cos β ₂ ) ² = e ² + f ² (20)

Here, by rewriting the equation (10) using the above "a" to "n", tan (β ₂ -α ₂ ) = A ² · B ² · {1-cos ₂ (β ₂ -α _2). )} / A ² · B ² · sin ² (β ₂ −α ₂ ) = (m · n−1) / k (21).

Therefore, the phase difference "β ₂ -α ₂ " between the sine wave signal 100a and the sine wave signal 101a is φ = tan ^-1 {(m · n-1) / k} (22).

That is, using the signals 104 to 109, the equation (1
The phase difference signal 102a can be obtained by calculating 3) to 20 and further calculating the formula (22).

As a result, the sine wave signals 100a and 101
a is alternately sampled at equal intervals to obtain a sine wave signal 100
a sinusoidal signal 1 based on the two sampling results of a
Sine wave signal 100 corresponding to the sampling time of 01a
By calculating the phase of a and obtaining the phase difference from the phase of the sine wave signal 101a, one S & H circuit is sufficient, the circuit scale is reduced, and errors due to variations in the characteristics of the S & H circuit are eliminated. Measurement accuracy is improved.

FIG. 4 is a configuration block diagram showing an application example in which the phase difference measuring device according to the present invention is used in a Coriolis mass flowmeter.

Here, the Coriolis mass flowmeter is a device for vibrating the pipe through which the fluid to be measured vibrates and detecting the Coriolis force generated at this time to measure the mass flow rate of the fluid to be measured.

In FIG. 4, reference numerals 1a, 3a, 4a and 5a are the same as those in FIG. 1, 13 is a tube through which the fluid to be measured flows, 14 and 15 are vibration detectors, 16 is a frequency measuring circuit, and 17 is A temperature measuring circuit, 18 is a mass flow rate calculating circuit.

The vibration of the tube 13 is detected by the vibration detectors 14 and 15 and input to the selection circuit 3a.
The output of the selection circuit 3a is connected to the S & H circuit 1a,
The output of the H circuit 1a is connected to the A / D converter 4a.

The output of the A / D converter 4a is connected to the phase difference calculation circuit 5a, and the output of the phase difference calculation circuit 5a is connected to the mass flow rate calculation circuit 18. In addition, the frequency measuring circuit 16
The output of the temperature measuring circuit 17 is also connected to the mass flow rate calculating circuit 18. Further, the mass flow rate calculation circuit 18 outputs a mass flow rate signal 110.

Now, the operation of the application example shown in FIG. 4 will be described. The tube 13 is vibrated in a specific vibration mode by a vibrator not shown. Further, the fluid to be measured flows through the tube 13 in the directions indicated by "a" and "b" in FIG. 4 to generate Coriolis force, and vibration in a vibration mode different from the vibration is generated.

When the vibration detectors 14 and 15 detect the vibrations at the two points of the upstream and downstream of the tube 13, the vibrations detected at the two points have a phase difference depending on the mass flow rate of the fluid to be measured.

Therefore, the phase difference measuring device according to the present invention detects this phase difference, the frequency measuring circuit 16 measures the vibration frequency of the tube 13, and the temperature measuring circuit 17 measures the temperature of the fluid to be measured flowing through the tube 13. The mass flow rate can be determined by measuring

That is, the mass flow rate is "Q" and the phase difference is "
If φ ”, the temperature of the fluid to be measured is“ T ”, the vibration frequency of the tube 13 is“ F ”, and the correction coefficient is“ K ”, then Q = K · tan φ · T / F (23)

Here, the phase difference measuring device according to the present invention can output the phase difference in the form of "tan φ" as shown in the equation (21), so that it can be effectively used in the Coriolis mass flowmeter.

In FIGS. 1 and 2, the sine wave signal 100a is a reference signal and the sine wave signal 101a is "
Although the sine wave signal 100a is treated as a signal whose phase is advanced by φ ″, the sine wave signal 100a may be a signal whose phase is advanced by “φ” and the sine wave signal 101a may be used as a reference signal.

[0054]

As is apparent from the above description,
The present invention has the following effects. The two sine wave signals are alternately sampled at equal intervals, the phase corresponding to the sampling time of the second sine wave signal is calculated based on the two sampling results of the first sine wave signal, and the second sine wave signal is calculated.
By finding the phase difference from the phase of the sine wave signal of
A phase difference measuring device having a small circuit scale and improved measurement accuracy can be realized.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of a phase difference measuring apparatus according to the present invention.

FIG. 2 is a configuration block diagram showing a specific example of a phase difference calculation circuit.

FIG. 3 is a characteristic curve diagram showing the relationship between sampling time and phase.

FIG. 4 is a configuration block diagram showing an application example in which the phase difference measuring device is used in a Coriolis mass flowmeter.

FIG. 5 is a configuration block diagram showing an example of a conventional phase difference measuring device.

[Explanation of symbols]

1,1a, 2 Sample and hold circuit 3,3a selection circuit 4,4a A / D converter 5,5a Phase difference calculation circuit 6,7,9,10 Memory 8,11 Phase shifter 12 Calculation circuit 13 Tube 14, 15 Vibration detector 16 Frequency measurement circuit 17 Temperature measurement circuit 18 Mass flow rate calculation circuit 100, 100a, 101, 101a Sine wave signal 102, 102a Phase difference signal 103 Digital signal 104, 105, 106, 107, 108, 109 signal 110 Mass flow signal

Claims (1)

[Claims] 1. A phase difference measuring apparatus for simultaneously capturing a pair of signals of a first signal and a second signal having different phases, converting the captured signals into a digital signal, and measuring the phase difference between them. A selection circuit that alternately selects signals, a sample-and-hold circuit that captures the output of this selection circuit, an A / D converter that converts the output of this sample-and-hold circuit into a digital signal, and this A / D converter Based on the two sampling results of the first signal among the outputs of the D converter, the phase of the first signal corresponding to the sampling time of the second signal is calculated to obtain the phase of the second signal. And a phase difference calculating circuit for obtaining the phase difference of the phase difference measuring device.