Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Reexamination Certificate
2000-08-11
2003-05-27
Williams, Hezron (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
C073S861280, C073S861290
Reexamination Certificate
active
06568281
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultrasonic-wave propagation-time measuring method, a gas-pressure measuring method, a gas-flow-rate measuring method, and a gas sensor.
2. Description of the Related Art
Techniques for measuring sound velocity on the basis of propagation time of ultrasonic waves have been proposed in, for example, Japanese Patent Publication (kokoku) No. 5-72527 and Japanese Patent Application Laid-Open No. 60-502171.
In these techniques, an ultrasonic element is caused to transmit an ultrasonic wave (transmission wave) and receive its reflection wave (reception wave); and sound velocity is measured on the basis of the propagation time between transmission of the transmission wave and reception of the reception wave.
In a well-known method of measuring propagation time; more particularly, with regard to detecting the reception signal, a threshold level (reference value) of a comparator is fixed, and the reception wave itself or an integrated value of the reception wave is compared with the fixed threshold level.
However, ultrasonic reception waves sometimes attenuate due to pressure or other causes. In such a case, since the conventional techniques use a fixed value for the threshold level of the comparator, a measured propagation time includes an error stemming from attenuation of the reception wave.
Thus, in some cases a sound velocity calculated from the propagation time becomes inaccurate. Therefore, a gas concentration sensor which detects gas concentration on the basis of sound velocity encounters difficulty in accurately detecting gas concentration.
SUMMARY OF THE INVENTION
The present invention has been achieved in order to solve the above problems, and an object of the invention is to provide an ultrasonic-wave propagation-time measuring method which enables accurate determination of propagation time, a gas-pressure measuring method, a gas-flow-rate measuring method, and a gas sensor.
The above objectives of the invention are achieved by providing:
(1) An ultrasonic-wave propagation-time measuring method in which an ultrasonic wave is transmitted by use of an ultrasonic element, a reflection wave of the transmission wave is received as a reception wave by use of the same ultrasonic element or a different ultrasonic element, and a period of time between transmission of the ultrasonic wave and reception of the reception wave is measured as a propagation time, the method being characterized by comprising: a reference-value setting step of integrating a reception wave or a portion thereof in order to obtain an integral value, and setting a reference value on the basis of the integrated value; and a time measurement step performed when a propagation time is to be measured and comprising integrating a reception wave or a portion thereof in order to obtain an integral value, and measuring, as an arrival time of the reception wave, a point in time when the integral value attains the reference value.
In the present invention, an ultrasonic reception wave or a portion thereof is integrated in order to obtain an integral value, and a reference value (a threshold level) is set on the basis of the integrated value. At the time of actual measurement of propagation time, a reception wave or a portion thereof is integrated in order to obtain an integral value, and a point in time when the integral value attains the reference value is measured as an arrival time of the reception wave.
That is, ultrasonic reception waves sometimes attenuate due to the surrounding atmosphere (e.g., atmospheric pressure). In such a case, when a fixed reference value is used as in the conventional techniques, the time at which an integral value of a reception wave attains the reference value varies depending on the surrounding atmosphere, so that accurate measurement of propagation time becomes impossible. Therefore, in the present invention, the reference value is adjustably set on the basis of an actual integral value.
Accordingly, when the integral value of a reception wave decreases due to attenuation of the reception wave, the reference value (which is set on the basis of the integral value) also decreases. Therefore, at the time of actual measurement, the point in time when the integral value of a reception wave attains the (lowered) reference value represents an accurate arrival time. In other words, in the present invention, the reference value itself can be adjusted in consideration of pressure and other factors which influential propagation time. Therefore, even when a reception wave is attenuated due to pressure or other causes during actual measurement, the propagation time between transmission of the transmission wave and reception of the reception wave does not change, so that accurate measurement of propagation time can be effected at all times.
(2) The ultrasonic-wave propagation-time measuring method as described in (1), which further comprises integrating the reception wave or a portion thereof in the reference-value setting step, and setting a predetermined integral value obtained during a period between the start of integration and the time when a maximum integral value is obtained as the reference value.
In embodiment (2), a reference value which is optimal for measurement of propagation time can be set freely within the range in which the integral value of the reception wave varies. For example, in order to set the reference value, a peak integral value (voltage value) which is held using a peak-hold circuit is divided by use of a resistance-voltage-division circuit.
(3) The ultrasonic-wave propagation-time measuring method as described in (2), which further comprises setting the reference value to half the maximum integral value.
In embodiment (3) above, a value corresponding to half the maximum integral value (a center point of the range of variation of the integral value) is used as the reference value. Since the reference value corresponds to the center of the range of variation of the integral value, measurement of propagation time is hardly affected by noise and other causes, and failure to judge arrival time accurately can be avoided. Therefore, the present invention is practically useful.
(4) The ultrasonic-wave propagation-time measuring method as described in (1), which comprises representing the integral value in the form of a voltage valve in the reference-value setting step, and setting a ratio of the reference value to a maximum integral value on the basis of a maximum voltage value, which represents the maximum integral value.
In embodiment (4) above, for example, a peak integral value (maximum voltage value) which is held by use of a peak-hold circuit is reduced at a predetermined ratio by use of a voltage amplifying circuit in order to set the reference value.
(5) An ultrasonic-wave propagation-time measuring method in which an ultrasonic wave is transmitted by use of an ultrasonic element, a reflection wave of the transmission wave is received as a reception wave by use of the same ultrasonic element or a different ultrasonic element, and a period of time between transmission of the ultrasonic wave and reception of the reception wave is measured as a propagation time, the method being characterized by comprising: a reference-value setting step of integrating a reception wave or a portion thereof in order to obtain an integral value, and setting a reference value on the basis of the integrated value; and a time measurement step performed when a propagation time is to be measured and measuring, as an arrival time of the reception wave, a point in time when the level of a reception wave attains the reference value.
In embodiment (5), an ultrasonic reception wave or a portion thereof is integrated in order to obtain an integral value, and a reference value is set on the basis of the integrated value. At the time of actual measurement of propagation time, the point in time when the level of a reception wave attains the reference value is measured as an arrival time of the reception wave.
As describ
Banno Keigo
Ishida Noboru
Ishikawa Hideki
Oshima Takafumi
Sato Yoshikuni
Martir Lilybett
NGK Spark Plug Co. Ltd.
Sughrue & Mion, PLLC
Williams Hezron
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