Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Reexamination Certificate
2002-03-29
2004-09-28
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
Reexamination Certificate
active
06796189
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a flowmeter for measuring the flow rate of liquid or air. The present invention relates to means for measuring a flow rate value in an accurate manner even when there is a variation in pressure or temperature.
BACKGROUND ART
Conventionally, such a type of flowmeter is known, for example, in Japanese Laid-Open Publication No. 9-15006. As shown in
FIG. 64
, the flowmeter includes: a sampling program
2
for reading a measurement value, at an interval having a predetermined first sampling time, from an analog flow sensor
1
that measures the flow rate of gas; a consumed gas amount calculation program
3
for calculating the flow rate of consumed gas at a predetermined time; a mean value calculation program
4
for calculating the mean value of measurement values, which are read from the analog flow sensor at the first sampling time, at an interval of a second sampling time within a predetermined time period; a pressure variation frequency estimation program
5
for estimating the frequency of a pressure variation based on an output of the flow sensor; and a RAM
6
which functions as a memory. Herein, reference numeral
7
a
denotes a CPU for executing the programs, and reference numeral
7
b
denotes a ROM for storing the programs. In such a structure, a measurement process is performed such that the predetermined measurement time is equal to or longer than a single cycle of the vibration frequency of a pump or is a multiple of the cycle. Averaging is performed to suppress variation in the flow rate.
As another conventional example, the invention disclosed in Japanese Laid-Open Publication No. 10-197303 is known. As shown in
FIG. 65
, the flowmeter includes: flow rate detection means
8
for detecting the flow rate; frequency detection means
9
for detecting the frequency of a variation of a flow; and measurement time set means
10
for setting the measurement time for flow rate detection to about a multiple of one cycle of the variation frequency. Herein, reference numeral
11
denotes flow rate calculation means;
12
denotes measurement start means;
13
denotes signal processing means; and
14
denotes a flow rate. With this structure, the flow rate is measured in accordance with the frequency of a variation waveform, whereby a correct flow rate measurement is achieved within a short time period.
As still another conventional example, the invention disclosed in Japanese Laid-Open Publication No. 11-44563 is known. As shown in
FIG. 66
, the flowmeter includes: flow rate detection means
15
for detecting the flow rate; variation detection means
16
for detecting a variation waveform of the flow rate of fluid; pulse measurement means
17
for starting the measurement of the flow rate detection means when an alternating component of the variation waveform is in the vicinity of zero; and flow rate calculation means
18
for processing a signal from the flow rate detection means. Herein, reference numeral
19
denotes a signal processing circuit;
20
denotes a time measurement circuit;
21
denotes a trigger circuit;
22
denotes a transmission circuit;
23
denotes a comparison circuit;
24
denotes an amplification circuit;
25
denotes a switch;
26
denotes a measurement start signal circuit; and
27
denotes start-up means;
28
denotes a flow path. In this structure, the flow rate near the average of the variation waveforms is measured, whereby a correct flow rate measurement is achieved within a short time period.
As yet another conventional example, the invention disclosed in Japanese Laid-Open Publication No. 8-271313 is known. As shown in
FIG. 67
, whether or not a flow rate value has been detected in flow sensor measurement (
29
) is confirmed (
30
). Until a flow rate is confirmed to have been detected, the process does not proceed, and the measurement with the flow sensor is continued. Once a flow rate is found, it is determined whether or not the flow rate Q is equal to or higher than a predetermined value (
31
). When the flow rate Q is equal to or higher than the predetermined value, it is further determined whether or not the pressure variation surpasses a predetermined value Cf (
32
). When the pressure variation does not surpass a predetermined value Cf, measurement
34
is performed with a piezoelectric film sensor of a fluidic flowmeter. When the pressure variation surpasses a predetermined value Cf, it is confirmed if the pressure variation surpasses a second predetermined value (
33
). When the pressure variation surpasses the second predetermined value, the measurement (
34
) is performed with the piezoelectric film sensor of the fluidic flowmeter. When the pressure variation does not surpass the second predetermined value, the measurement (
29
) is performed with the flow sensor.
As shown in
FIG. 68
, ultrasonic wave transducers
51
and
52
are provided in a flow rate measurement section
50
so as to oppose the direction of a flow. A control section
53
starts a timer
54
, and simultaneously, outputs a transmission signal to a driver circuit
55
. An ultrasonic wave is transmitted from the ultrasonic wave transducer
51
which received an output of the driver circuit
55
. The ultrasonic wave is received by the ultrasonic wave transducer
52
. A reception detection circuit
56
which received an output of the ultrasonic wave transducer
52
detects the ultrasonic wave and stops the timer
54
. By such an operation, a time (t
1
) spent from a time when an ultrasonic wave is transmitted from the ultrasonic wave transducer
51
to a time when the wave is detected by the ultrasonic wave transducer
52
is measured. Next, a switching circuit
58
is operated based on a signal from the control section
53
, such that the driver circuit
55
and the ultrasonic wave transducer
52
are connected, and the reception detection circuit
56
and the ultrasonic wave transducer
51
are connected. Under this state, transmission and reception of an ultrasonic wave is performed again to measure a time (t
2
) spent from a time when an ultrasonic wave is transmitted from the ultrasonic wave transducer
52
to a time when the wave is detected by the ultrasonic wave transducer
51
. Based on the two propagation times (t
1
) and (t
2
), a calculation section
57
calculates the flow rate from a difference between inverse numbers of the propagation times.
As a conventional example of this type of flowmeter, the invention disclosed in Japanese Laid-Open Publication No. 6-269528 is known.
However, in the first of the above conventional inventions, the gas flow rate is measured by using a mean value. Therefore, measurement over a long time period is necessary in order to obtain a reliable mean value, and hence such flow rate measurement cannot be performed within a very short space of time. In the second of the above conventional inventions, measurement cannot deal with a variation in frequency. In the third and fourth conventional inventions, the method for measuring the flow rate must be changed according to the presence/absence of a pressure variation, and it is necessary to provide two means, pressure measurement means and flow rate measurement means. In the first to forth inventions, when any abnormality occurs, measurement either cannot be performed, or can be performed but with decreased accuracy.
Still further, in the above conventional structures, when receiving a signal, if noise which is in synchronization with the measurement frequency or transmission frequency of an ultrasonic wave is present, the noise is superposed on the signal always at the same phase when the propagation time is the same. The noise is counted as a measurement error, and accordingly, correct measurement cannot be performed. Moreover, when the propagation time is varied due to a variation in temperature or the like, the phase at which noise is superposed is varied, and accordingly, a measurement error is varied. As a result, a correction value cannot be stabilized. Furthermore, since the measurement resolution is determined based on th
Abe Shuji
Adachi Akihisa
Eguchi Osamu
Fujii Yuji
Hashimoto Masahiko
Lefkowitz Edward
Mack Corey D.
Snell & Wilmer LLP
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