Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Reexamination Certificate
2001-11-16
2003-11-11
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
Reexamination Certificate
active
06644129
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a flow rate measurement apparatus for measuring a flow rate of fluid, such as gas or the like.
BACKGROUND ART
There are many known methods for measuring the flow rate of fluids, such as gases, liquids, etc. Especially, reliable flow velocity/flow rate measurement apparatuses which utilize ultrasonic waves have been remarkably developed thanks to progress in techniques of electronics. The flow velocity/flow rate measurement apparatuses which utilize ultrasonic waves can be employed in various application fields, such as a meter for fuel gas, an industrial measurement device, a blood-flow meter for medical use, measurement of flow velocity in the ocean or atmosphere, etc. Such flow velocity/flow rate measurement apparatuses can directly utilize ultrasonic waves in some cases, and in other cases, can be utilized as a detecting section of a measurement apparatus which operates based on other measurement principles and which indirectly utilize ultrasonic waves.
As shown in
FIG. 21
, a conventional ultrasonic flow-velocity meter includes: an ultrasonic transmitting transducer
2
which is placed in a measurement path
1
through which fluid flows; a transmission circuit
3
for driving the ultrasonic transmitting transducer
2
; a controller
5
for simultaneously transmitting a vibration start signal from the transmission circuit
3
and for starting a timer
4
; an ultrasonic receiving transducer
6
which is placed upstream or downstream of the ultrasonic transducer
2
and which receives ultrasonic waves emitted by the ultrasonic transducer
2
; an amplifier
7
for amplifying a received signal from the ultrasonic receiving transducer
6
; and a comparator
9
for comparing the signal output from the amplifier
7
and a reference signal output from a reference signal generating section
8
and for stopping the timer
4
when the relationship of the magnitudes between these signals is inverted. This conventional ultrasonic flow-velocity meter is structured such that the flow velocity of the measured fluid is measured based on a time measured by the timer
4
.
In the above ultrasonic flow-velocity meter, in response to a start signal from the controller
5
, the transmission circuit
3
outputs a pulse during a predetermined time so as to drive the ultrasonic transducer
2
. An ultrasonic wave emitted by the ultrasonic transducer
2
propagates through the measured fluid and is then received by the ultrasonic receiving transducer
6
after a lapse of time t. This received signal is compared with a reference signal by the comparator
9
. When the relationship in voltage between the received signal and the reference signal is inverted, a stop signal is transmitted to the timer
4
. In response to this stop signal, the timer
4
stops. The flow velocity v of the measured fluid is calculated by assigning an output value, obtained for time t, in expression (1):
V=
(
L
/(
t−a
))
−c
(1)
where L denotes the effective distance along a flowing direction between the ultrasonic wave transmitter and the ultrasonic wave receiver, c denotes a sonic velocity, v denotes a flow velocity of the measured fluid, a denotes a delay time from when the signal is received to when the output of the comparator
9
is inverted. A direction from the ultrasonic transducer to the ultrasonic receiving transducer is referred to as the positive direction.
Alternatively, the ultrasonic transducer
2
and the ultrasonic receiving transducer
6
are switched, and a propagation time t
1
from upstream to downstream and a propagation time t
2
from downstream to upstream are measured so as to obtain a flow velocity v based on expression (2):
v=L
/2(1
/t
1
−1
/t
2
)+a (2)
According to this method, the velocity of a flowing fluid can be measured independent from influences caused by a change in sonic velocity due to changes in temperature. Thus, this method has been widely used in measurement of flow velocity, flow rate, distance, etc.
Not only flow velocity/flow rate measurement apparatuses which utilize ultrasonic waves but also general flow velocity/flow rate measurement apparatuses that use many sensors, such as a flow rate sensor, a resistance sensor, a temperature sensor, a voltage sensor, etc. These sensors, which transmit electric signals, are influenced by external conditions such that the sensitivity thereof is changed in some cases. Thus, a flow rate measurement apparatus used in a meter for fuel gas or the like is required to measure even a very small change in flow rate, e.g., 3 liters/hour. In order to correctly detect such a very small change, a measurement apparatus must be structured such that it can perform zero-point correction for measurements.
In view of the above, a technique disclosed in Japanese Laid-Open Publication No. 8-271307 is a gas flow-rate meter which determines, at a predetermined time interval, whether or not performing zero-point correction is appropriate and performs zero-point correction based on such a determination. This is regarded as a very useful technique in the field of gas equipment.
However, when the above conventional structure is applied to a flow rate measurement apparatus for fuel gas such as propane gas, the flow rate of fluid widely varies in a flow path; for example, change in flow rate is very small in some cases, but change in flow rate is several ten-thousand liters per hour in other cases. Accordingly, the input waveform of a received signal widely varies according to the flow velocity. Thus, it is difficult to measure the flow rate without adjusting reception sensitivity.
In general, a sensor which transmits an electric signal is influenced by external conditions such that the sensitivity thereof may be changed. Thus, a flow rate measurement apparatus used in a meter for fuel gas or the like is required to measure even a very small change in flow rate, e.g., 3 liters/hour. In order to correctly detect various magnitudes of change over such a wide range of a very small change to several ten-thousand liters per hour, a measurement apparatus must be structured such that reception conditions for measurement (gain or the like) are adjusted at a predetermined time interval. In such a case, in equipment where a flow of fluid is never interrupted, it is impossible to close a flow path, such that a correction cannot be performed.
In view of the problems involved in the above conventional example, an objective of the present invention is to provide a structure having a plurality of flow paths, wherein the gain of a circuit which receives and amplifies a signal from a sensor is corrected and adjusted in a flow path in which flow rate measurement is not being performed, and the flow path in which the gains of the sensor and the circuit have been adjusted is opened for use in the flow rate measurement.
According to a method for performing zero-point correction, it is determined at a predetermined time interval whether or not it is necessary to perform zero-point correction, and when necessary, the zero-point correction is performed. Thus, in equipment where a flow of fluid is never interrupted, it is impossible to close a flow path, such that the zero-point correction cannot be performed.
In view of the problems involved in the above conventional example, another objective of the present invention is to provide a structure having a plurality of flow paths wherein the zero-point correction is performed in a flow path in which flow rate measurement is not being performed, and the flow path in which the zero-point correction has been completed is opened for use in the flow rate measurement.
DISCLOSURE OF INVENTION
The present invention is very useful when it is applied to a meter for fuel gas such as propane gas or city gas. This is because a flow rate measurement apparatus for fuel gas is required to detect a change in the flow rate, e.g., 3 liters/hour. The present invention is useful in that a correct flow rate can be measured by correcting the gains of various
Nakabayashi Yuji
Shiba Fumikazu
Lefkowitz Edward
Matsushita Electric Co., Ltd.
Snell & Wilmer LLP
Thompson Jewel V.
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