Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Reexamination Certificate
2002-02-01
2004-08-31
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
Reexamination Certificate
active
06782761
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultrasonic flow meter that measures the flow volume of a liquid flowing through a pipe using ultrasonic waves.
2. Description of the Related Art
An ultrasonic flow meter is known in the prior art that uses ultrasonic waves to function as a flow meter that measures the flow volume of a liquid flowing through a pipe.
This ultrasonic flow meter provides two measuring units having a transducer at an interval in the lengthwise direction on a measuring pipe through which liquid flows. Ultrasonic waves are emitted from one of the transducers which are then received by the other transducer. Alternatively, ultrasonic waves are emitted from the other transducer and then received by the first transducer. The flow rate of the liquid in the measuring pipe is determined from the difference in propagation times of these ultrasonic waves, and flow volume is then measured from this flow rate.
However, if this ultrasonic flow meter is subjected to vibrations from the outside between the respective measuring units, measurement error occurring resulting in fluctuations in characteristics of the measurement data and causing problems that the flow volume cannot be measured accurately.
In addition, since the acoustic velocity, namely the velocity of the ultrasonic waves, changes according to the temperature of the liquid, it is necessary to measure flow volume using a conversion value corresponding to the temperature of the liquid. However, if ultrasonic waves emitted from the transducer are influenced by factors other than the temperature of the liquid, such as the outside ambient temperature, although the flow volume was corrected by converting according to the temperature of the liquid, there is the problem that the acoustic velocity is changed due to slight changes in temperature and the flow volume cannot be measured accurately.
The following provides a detailed explanation of changes in the acoustic velocity caused by changes in the temperature of the liquid using the drawings.
FIG. 9
is a graph showing the relationship between the temperature (° C.) of water (liquid) and the acoustic velocity (m/s). In addition,
FIG. 10A
is a graph showing the change in a reference flow volume for each passage of time T in the case of a water temperature of 20° C., while
FIG. 10B
is a graph showing the output of the transducers relative to the reference flow volume of FIG.
10
A. In addition,
FIG. 11A
is a graph showing the change in a reference flow volume for each passage of time T in the case of a water temperature of 29° C., while
FIG. 11B
is a graph showing the output of the transducers relative to the reference flow volume of FIG.
11
A.
Furthermore, the units of flow volume Q and the reference flow volume shown in
FIGS. 10A and 11A
indicate flow volume per minute (mL/min), and the reference flow volume indicates the flow volume flowing through the measuring pipe of the ultrasonic flow meter obtained with a calibrated flow meter.
Conversion values of flow volume relative to the output of the transducers are obtained from the graphs shown in
FIGS. 9 through 11B
.
It is generally known that the acoustic velocity of ultrasonic waves output from the transducers changes considerably according to the temperature of the liquid, and can be represented in the graph showing the relationship between temperature and the acoustic velocity of FIG.
9
. According to the graph shown in
FIG. 9
, the acoustic velocity can be seen to increase the higher the temperature of the liquid.
In consideration of this change in the acoustic velocity due to temperature, as shown in the graph of
FIG. 10A
, water at a temperature of 20° C. is allowed to flow in two stages of 1000 mL and 500 mL per minute from time 0 through the measuring pipe of the ultrasonic flow meter using the reference flow meter. For the flow volume of the former first stage, the water is allowed to flow for time interval T
1
, and for the flow volume of the latter second stage, water is allowed to flow for time interval T
2
so as to be continued from the first stage.
Whereupon, as shown in
FIG. 10B
, although the output of ultrasonic waves outputted from the transducers at the ambient temperature of 24° C. remained nearly level prior to time 0 before the water flows (see A), it can be seen to decrease suddenly by displacement D
1
(see B) corresponding to the start of water flow (time 0). When the flow volume of the water changes from 1000 mL/min to 500 mL/min (see C), the output can be seen to only change slightly by displacement D
2
.
As shown in the drawings, the difference in the output between displacement D
1
and displacement D
2
is such that D
1
□□D
2
, and the change in the output due to the temperature change of the difference of 4° C. between the ambient temperature and the water temperature can be understood to be larger than the change in the output during the change in flow volume.
Next, an explanation is provided of the graphs in the case of allowing water at a water temperature of 29° C. to flow as shown in
FIG. 11
in comparison with the graph of FIG.
10
. As shown in
FIG. 11A
, water at a temperature of 29° C. is allowed to flow in two stages at 1000 mL/min and 500 mL/min starting at time 0 through the measuring pipe of the ultrasonic flow meter using the reference flow meter. For the flow volume of the former first stage, the water is allowed to flow for time interval T
3
, and for the flow volume of the latter second stage, the water is allowed to flow for time interval T
4
so as to be continued from the first stage.
Whereupon, as shown in the graph of
FIG. 11B
, although the output of ultrasonic waves output from the transducers at an ambient temperature of 24° C. was at the same position and remained nearly level (see E) at the stage of time 0 before the water flowed in the same manner as
FIG. 10A
, it can be seen increase suddenly by displacement D
3
(see F) corresponding to the start of the flow of water (time 0). When the flow volume of water changes from 1000 mL/min to 500 mL/min (see G), the output can be seen to only change slightly by displacement D
4
.
As indicated in the drawings, the difference in output between displacement D
3
and displacement D
4
is such that D
3
□□D
4
, and the change in the output caused by a temperature change of the difference of 5° C. between the ambient temperature and water temperature can be seen to be larger than the change in the output for the change in flow volume.
In this manner, in the ultrasonic flow meter, changes in flow volume are captured in an output region that is much smaller than the change in the output of the transducers resulting from a change in the liquid temperature. It can also be understood that the greater the difference between ambient temperature and liquid temperature, the larger the change in the output of the transducers.
Thus, if the liquid temperature is influenced even minimally by the external ambient temperature, the output of the transducer changes considerably, and measurement of flow volume at an extremely small displacement for this output of the transducers has a high potential to invite measurement error.
In this manner, in the conventional ultrasonic flow meter, there were cases in which it was difficult to accurately measure flow volume depending on the ambient temperature.
SUMMARY OF THE INVENTION
In consideration of the above circumstances, the object of the present invention is to provide an ultrasonic flow meter that is able to minimize effects caused by external vibrations, and accurately measure flow volume without being affected by outside temperature.
In order to achieve the above object, the present invention provides an ultrasonic flow meter comprising: a measuring pipe through which a liquid flows, and two measuring units provided on the measuring pipe at an interval in its lengthwise direction and which measures flow volume by determining the flow rate of the liquid from the difference in propagation times
Hasunuma Masahiro
Imai Hiroshi
Kolisch & Hartwell, P.C.
Lefkowitz Edward
Mack Corey D.
Surpass Industry Co. Ltd.
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