JPS638430B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a phase difference detection method for measuring a phase difference between two signals.

[Prior art]

Conventionally, there are various measurement systems that obtain a target physical quantity by measuring the phase difference between two signals from a detector. For example, in a mass flowmeter that applies the Coriolis force, the phase difference between two detected signals is proportional to the mass flow rate. An example of a conventional method for detecting this phase difference is shown in the time charts of FIG. 1A to D. When two detection signals e ₁ and e ₂ having a phase difference of Δt as shown in _FIG . e ₄ is generated (Figure 1 B). These comparison outputs e ₃ and e ₄ are set as Exclusive−
Using an OR gate or the like, an output with a pulse width proportional to the phase difference as shown in Figure 1C is obtained. Another method, as shown in Figure 1D, uses a timing circuit to start charging a capacitor etc. at the rising edge of signal _e3 , stop charging at the rising edge of _e4 , and then start charging again at the falling edge of _e3 . Start the death charge. In this method, the capacitor charge voltage is proportional to the phase difference. The signal e ₅ or e ₆ obtained as described above is smoothed by an integrating circuit or the like, and becomes a DC voltage proportional to the phase difference (ie, mass flow rate).

In the case of a phase difference detection device using the above principle, the following problem occurs when in-phase noise is superimposed on two signals. That is, since the timing of comparison in the two-signal comparator is shifted by the phase difference, common-mode noises are not canceled and appear as errors in the phase difference output. As a result, a problem arises in that the stability of the phase difference output deteriorates the resolution.

[Purpose of the invention]

The present invention has been made to solve the above problems, and an object of the present invention is to provide a phase difference detection device that generates a phase difference output with excellent stability and resolution even if there is common-mode noise in the input signal. It is said that

[Summary of the invention]

The present invention compares two input signals with threshold values in two comparators respectively;
By integrating a constant time value corresponding to the time difference between the rising or falling edges of the two comparison outputs, and using this integrated output as the threshold value of one of the comparators, the comparison can be performed at the same point in time. This is the realization of a phase difference detection device.

〔Example〕

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 2 is a block diagram showing an embodiment of a phase difference detection device according to the present invention. Reference numeral 1 designates a mass flowmeter that utilizes the Coriolis force, 2 a tube through which fluid flows, and 3 and 4 strain detection elements such as piezoelectric elements for detecting strain in the tube 2. 5 is a phase difference detection device for determining the phase difference between the output signals e ₁₁ and e ₁₂ from the distortion detection elements 3 and ₄ ;
amplifiers 8 and 9 for amplifying e ₁₂ ; comparison means for comparing the outputs e ₁₃ and e ₁₄ from these amplifiers 6 and 7 with respective threshold values (voltages); 1;
0 is the output e ₁₅ , e ₁₆ from these comparison means 8 and 9
A time difference measuring means 11 generates a pulse width waveform whose pulse width corresponds to the time difference between rises between the two and whose rising order corresponds to its polarity _. An integrating circuit whose integral output e _OUT becomes the threshold voltage of the comparing means 8, and 12 is an output terminal to which the output e _OUT from the integrating circuit 11 is applied. The threshold value of the comparison means 9 is set to a common level.

FIG. 3 is a time chart for explaining the operation of the phase difference detection device configured as described above. In the mass flowmeter 1, when fluid flows through the self-oscillating tube 2, the strain detection elements 3 and 4 generate signals e ₁₁ and e ₁₂ that are shifted from each other by a phase proportional to the mass flow rate. These signals e ₁₁ and e ₁₂ are sent to amplifiers 6 and 7, respectively.
When the outputs e ₁₃ and e ₁₄ (Fig. 3 A) are applied to comparators 8 and ₉ , respectively, after being amplified by At point ₂ , outputs e ₁₅ and e ₁₆ rise, respectively. In response to this, the time difference measuring circuit 10
The output e ₁₇ generates a pulse width output with a time width Δt ₁ =t ₂ -t ₁ (FIG. 3C). This pulse width output e ₁₇ is integrated by the integrating circuit 11 and becomes a new threshold value e _OUT1 of the integrator 8 (FIG. 3D).
If the phase difference (time difference) of the signals e ₁₃ and e ₁₄ remains unchanged, the comparators 8 and 9 will rise at the same time t ₃ and the output e ₁₇ will not generate a pulse width, so the output e _OUT of the integrating circuit 11 will be e _OUT1 remains unchanged. Next, when the phase difference between the signals e ₁₃ and e ₁₄ becomes smaller, the signal e ₁₅
rises with a delay at time _t5 , and the signal
e ₁₇ generates a pulse width output with negative polarity and pulse width Δt ₂ . As a result, the integrating circuit 11 integrates in a decreasing direction to obtain a new equilibrium value e _OUT2 . As mentioned above,
If there is a phase difference between the outputs from the comparators 8 and 9, the integrating circuit 11 changes the threshold voltage of the comparator 8 in a direction to cancel this difference, and balance is reached when the phase difference disappears. The signals e ₁₁ and e ₁₂ are amplified by amplifiers 6 and 7, respectively, and then compared using the linear portions of their waveforms, so that the balanced output e _OUT is proportional to the phase difference. Furthermore, since the waveforms are compared at the same time in the balanced state, common mode noise can be canceled. In actual experimental results, approximately
When reading a phase difference of 1 μs, the conventional method
The common mode noise error that was 60nsec is reduced to 3nsec with this device.
It decreased to

In the above embodiment, only the rising edge of the comparator output is used, but the time difference between the falling edges may also be used.

Further, in the above embodiment, the common level is used as the threshold voltage of the second comparing means 9, but the invention is not limited to this, and a bias output of, for example, 1 to 5 V can be generated using an appropriate fixed voltage. is also possible.

In addition, although the above example shows the case of a mass flow meter that uses Coriolis force, it is not limited to this and can be applied to many other cases where it is necessary to measure the phase difference (time difference) between two signals. .

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a phase difference detection device with a simple configuration that can generate a phase difference output with excellent stability and resolution even if common-mode noise is present in the input signal.

[Brief explanation of the drawing]

FIG. 1 is a time chart for explaining a conventional phase difference detection device, FIG. 2 is a configuration block diagram showing an embodiment of the phase difference detection device according to the present invention, and FIG.
The figure is a time chart for explaining the operation of the apparatus shown in FIG. 5... Phase difference detection device, 8... First comparing means, 9... Second comparing stage, 11... Integrating circuit,
e ₁₃ ...first signal, e ₁₄ ...second signal, e _OUT ...
...first threshold voltage, Δt ₁ , Δt ₂ ...
…Time lag.

Claims (1)

[Claims] 1. A first comparing means for inputting a first signal and comparing it with a first threshold value; and a second comparing means for inputting a second signal and comparing it with a second threshold value. , and an integrating circuit that integrates a constant time value corresponding to the time difference between rising or falling comparison outputs from the two comparing means, and the output of this integrating circuit is used as the first threshold value. A phase detection device characterized by: