JPH08271321A - Ultrasonic liquid level measurement method - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain an ultrasonic liquid level measurement method that can reliably and stably measure the liquid level even when the liquid level suddenly increases or decreases, or even when the liquid level is within the low level range. . With respect to a liquid in a horizontal pipe, an ultrasonic pulse emitted from a lower side to an upper side outside the pipe receives a reflected ultrasonic pulse obtained by reflecting on a liquid surface of the liquid, In an ultrasonic liquid level measuring method for measuring the liquid level of the liquid based on the time required to receive the reflected ultrasonic pulse, after a dead zone for a predetermined time has elapsed from the transmission time of the ultrasonic pulse. The liquid level is measured based on the time between the plurality of reflected ultrasonic pulses received.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic liquid level measuring method for measuring the liquid level of a liquid in a horizontal pipe such as a steam generator.

[0002]

2. Description of the Related Art In order to measure the liquid level of a liquid flowing in a pipe such as a steam generator, an ultrasonic measuring technique by a pulse reflection method is usually used. An ultrasonic sensor that transmits and receives an ultrasonic pulse for measurement is fixed to a substantially lowermost surface of a horizontal pipe with its transmitting / receiving portion facing upward. Therefore, the ultrasonic pulse is transmitted from the reception / transmission unit of the ultrasonic sensor upward with the liquid level (this pulse is referred to as a reference transmission ultrasonic pulse). The reference transmission ultrasonic pulse is reflected by the liquid surface and then received as a reflected ultrasonic pulse by the transmitting / receiving unit of the ultrasonic sensor.

The time required from the transmission of the reference transmission ultrasonic pulse to the reception of the reflected ultrasonic pulse is
It corresponds to the distance and velocity of propagation of ultrasonic waves in a liquid. Since the medium is fixed under normal measurement conditions, the propagation velocity is known and hardly changes. Therefore, the time required for reception is a measured amount according to the propagation distance. Therefore, the liquid level in the tube is measured by measuring the time required for reception and converting the time into a distance.

Conventionally, the liquid level in the tube has been measured by the following method. First, the transmission time of the reference transmission ultrasonic pulse transmitted from the reception / transmission unit of the ultrasonic sensor upward with the liquid level is stored in the arithmetic unit as the reference time. Next, the reception time of the first reflected ultrasonic pulse in the reflected ultrasonic pulse train reflected by the liquid surface and received by the transmitting / receiving section of the ultrasonic sensor is stored in the arithmetic unit. The arithmetic unit calculates the time difference between the reference time and the reception time as the time required for reception.

The reflected ultrasonic pulse received at the very beginning is usually one that has been reflected once on the liquid surface. Therefore, the distance traveled by the ultrasonic pulse corresponds to about twice the distance from the transmitting / receiving portion of the ultrasonic sensor to the liquid surface. In consideration of this, the liquid level of the liquid in the tube is measured by the method of converting the distance according to the time difference calculated by the arithmetic device.

In the conventional method, the reflected ultrasonic pulse received second is not limited to the reflected ultrasonic pulse first received as described above (one that has been reflected once on the liquid surface). The liquid level of the liquid in the tube can be measured in the same manner by using (the one that has been reflected twice on the liquid surface). In any case, even if the liquid level in the tube increases or decreases with time, if the same (always first if the first) reflected ultrasonic pulse is always received and the time difference (time required for reception) is calculated. Since this time difference increases and decreases following the increase and decrease of the liquid level, it is possible to measure the liquid level at each time.

[0007]

However, the liquid level in the pipe may suddenly increase or decrease. At this time, the liquid surface becomes wavy. Also, there is little liquid in the pipe,
The liquid level may be in the low level range. In the above cases, the reception state of reflected ultrasonic pulses becomes very unstable, and it becomes difficult to always receive the same reflected ultrasonic pulse. Therefore, it may happen that the reflected ultrasonic pulse that is different for each reception is received and the time difference is calculated.

For example, when the liquid level is measured by using the reflected ultrasonic pulse received first (those that have been reflected on the liquid surface once) for calculating the time difference, And not the first reflected ultrasonic pulse, but the second (three reflections from the liquid surface) or the third (three reflections from the liquid surface) reflected ultrasonic pulse. Suppose At this time, a long time difference is measured as compared with the case where the first reflected ultrasonic pulse is received. Therefore, the liquid level obtained by converting the distance based on the measured time difference becomes higher than the actual liquid level in the tube, resulting in erroneous display.

The present invention has been made in view of the above problems, and can reliably and stably measure the liquid level even when the liquid level sharply increases or decreases, or even when the liquid level is within the low liquid level range. The purpose is to obtain an ultrasonic liquid level measurement method.

[0010]

In order to achieve the above object, in the invention described in claim 1 of the present application, an ultrasonic wave is transmitted to a liquid in a lateral pipe from below the pipe outside to above. An ultrasonic liquid level measurement for receiving a reflected ultrasonic pulse obtained by reflecting a pulse on the liquid surface of the liquid, and measuring the liquid level of the liquid based on the time required for receiving the reflected ultrasonic pulse. In the method, the liquid level is measured based on the time between the plurality of reflected ultrasonic pulses that are received after a dead zone has passed for a predetermined time from the transmission time of the ultrasonic pulse. The present invention provides an ultrasonic liquid level measuring method.

[0011]

Since the present invention is constructed as described above, it has the following effects. With respect to the liquid in the horizontal pipe, the reflected ultrasonic pulse obtained by reflecting the ultrasonic pulse emitted from the outside of the pipe upward from the outside of the pipe is reflected once on the liquid surface. There are a large number of first reflected ultrasonic pulses obtained as a result, second reflected ultrasonic pulses obtained by reflecting twice on the liquid surface, and third reflected ultrasonic pulses obtained by reflecting three times on the liquid surface.

However, in the present invention, the reflected ultrasonic pulse received within the dead zone over a predetermined time from the time when the ultrasonic pulse is transmitted is not recognized as the reflected ultrasonic pulse from the liquid surface, and It is not a target when measuring position. Therefore, only the reflected ultrasonic pulse received after passing through the dead zone is recognized as the reflected ultrasonic pulse from the liquid surface, and is targeted when measuring the liquid level.

First, for a plurality of pulses recognized as such reflected ultrasonic pulses, the time required to receive each reflected ultrasonic pulse is detected. The time required for this reception represents the time from the transmission time of the reference transmission ultrasonic pulse to the reception time of each reflected ultrasonic pulse. Since the plurality of pulses recognized as reflected ultrasonic pulses have different numbers of reflections on the liquid surface, different reception times are detected according to the number of reflections. Then
The time between the plurality of reflected ultrasonic pulses is detected, and distance conversion is performed based on this time to measure the liquid level.

As described above, according to the present invention, unlike the conventional method, the distance conversion is not performed based on the time itself from the transmission time of the reference transmission ultrasonic pulse to the reception time of the reflected ultrasonic pulse. The relative time of the time required for each reception of the reflected ultrasonic pulse is detected, and distance conversion is performed based on this relative time. Therefore, in the method of the present invention,
It is not necessary to know the time required to receive the reflected ultrasonic pulse received after the dead zone has passed and the property of the reflected ultrasonic pulse (how many times it was reflected on the liquid surface).

Therefore, as in the case where the liquid level suddenly increases or decreases, or when the liquid level is within the low liquid level range, the time required to receive the reflected ultrasonic pulse and the nature of the reflected ultrasonic pulse ( Even if it is difficult to know how many times the liquid level has reflected, it is possible to reliably and stably measure the liquid level.

[0016]

The present invention will be described in more detail with reference to the following examples. 1 to 3 show an example of an ultrasonic liquid level measuring device and a liquid in a horizontal pipe to be measured, for explaining an example of the ultrasonic liquid level measuring method according to the present invention. The schematic diagram (a) and an example (b) of an ultrasonic pulse train to be measured are shown.

FIG. 1 (a) shows a cross section of a horizontal pipe 4 such as a steam generator. Usually, a metal material such as a cast material is used for the horizontal piping 4 such as a steam generator, and the outer peripheral surface thereof is covered with a heat insulating material 5. Inside the pipe 4, the water 6 is flowing at an appropriate water level, and the ultrasonic sensor 1 which transmits and receives an ultrasonic pulse for measuring the water level has its receiving and transmitting section directed upward, It is fixed to the substantially lowermost surface of the horizontal pipe 4.

The ultrasonic sensor 1 is fixed to the pipe 4 by using a jig such as a belt. In order to block air from the contact surface between the pipe 4 and the transmitting / receiving surface of the ultrasonic sensor 1, it is preferable to interpose an oil or fat or silicon-based contact medium. The material of the contact medium is selected to be suitable for the temperature inside the pipe 4 or the environment. Here, the transmission frequency of the ultrasonic sensor 1 is selected according to the material of the pipe 4. In addition, the cross-sectional area of the transmitting / receiving portion of the ultrasonic sensor 1 is set to a size that matches the inclination of the pipe 4 and the pipe diameter. In the above apparatus, the limit of measurable water temperature is the durable temperature of the ultrasonic sensor.

From the transmitting / receiving part of the ultrasonic sensor 1, the water surface 6
An ultrasonic pulse is emitted upward with a being present (this pulse is referred to as a reference transmission ultrasonic pulse). The reference transmission ultrasonic pulse is reflected by the water surface 6a in the pipe 4 and then received as a reflected ultrasonic pulse by the transmitting / receiving unit of the ultrasonic sensor 1. Here, the reflected ultrasonic pulse has a height equal to or higher than a certain threshold.

The received signal is sent to the arithmetic unit 3 via the signal cable 2. In this arithmetic unit 3, the time-axis linearity of the measurement system is calibrated in advance, and the transmission signal and the reception signal from the ultrasonic sensor 1 are analyzed and calculated to detect the water level in the pipe 4 ( Details will be described later). The oscilloscope 7 or the like may be used to check the reception / transmission status of the transmission signal and the reception signal from the ultrasonic sensor 1.

With the above structure, one reference transmission ultrasonic pulse A transmitted from the ultrasonic sensor 1 is reflected / transmitted on the boundary surface between the pipe 4 and the water 6 or the water surface 6a to repeat various routes. Traced and received as a reflected ultrasonic pulse train by the transmitting / receiving unit of the ultrasonic sensor 1 (B, C1,
C2, ...). Here, FIG. 1B shows an example in which the oscilloscope 7 confirms the reception / transmission status of the transmission signal and the reception signal from the ultrasonic sensor 1. FIG.
The horizontal axis of (b) is the time axis, and the reference transmission ultrasonic pulse A
Represents the relative time when the origination time of is used as the reference (time zero). The vertical axis represents the intensity (voltage) of the pulse signal.

When the reference transmission ultrasonic pulse A is transmitted from the ultrasonic sensor 1, the pulse first propagates through the pipe wall of the pipe 4 and reaches the boundary surface between the pipe 4 and the water 6. On this boundary surface, a part of the reference transmission ultrasonic pulse A is reflected and another part is transmitted. The transmitted pulse propagates in water and reaches the water surface 6a (boundary surface between water 6 and air). The pulse reflected once on the water surface 6a propagates in the water in the opposite direction to the previous direction and reaches the boundary surface between the pipe 4 and the water 6 again.
At this boundary, a part of the pulse is reflected and the other part is transmitted. The reflected pulse here returns to the water surface 6a again as a twice-reflected ultrasonic pulse.

On the other hand, the transmission pulse of the single reflection pulse transmitted through the boundary between the pipe 4 and the water 6 propagates through the pipe wall portion of the pipe 4 and is received by the ultrasonic sensor 1 as the first reflected ultrasonic pulse C1. To be done. In this way, the time at which the first reflected ultrasonic pulse C1 obtained by reflecting the reference transmitted ultrasonic pulse A once on the water surface 6a reaches the ultrasonic sensor 1 is T1.
Similarly, the time at which the second reflected ultrasonic pulse C2 obtained by reflecting twice on the water surface 6a reaches the ultrasonic sensor 1 is T2.

Further, although not shown in FIG. 1 (b),
The number of reflections on the water surface 6a is 1 in the order of the third reflected ultrasonic pulse (C3) obtained by reflecting the water surface 6a three times and the fourth reflected ultrasonic pulse (C4) obtained by reflecting the water surface 6a four times. The reflected ultrasonic pulses, which are many times, appear one after another over time after the second reflected ultrasonic pulse C2. This state is shown in FIG. 2 as an example when the water level is lower than that in FIG. In FIG. 2B, the third reflected ultrasonic pulse C3
The time when T reaches the ultrasonic sensor 1 is T3, and the time when the fourth reflected ultrasonic pulse C4 obtained by being reflected four times on the water surface 6a reaches the ultrasonic sensor 1 is T4.

By the way, in FIG. 1B, there is a pulse train that appears shortly after the transmission time of the reference transmission ultrasonic pulse A. This is a pipe portion reflected ultrasonic pulse train B observed one after another due to multiple reflection in the pipe wall portion of the pipe 4, and the reflected ultrasonic pulse (C1,
C2, ...), that is, a noise pulse train irrelevant to the water level measurement. Therefore, in the present embodiment, the time TG from the transmission time of the reference transmission ultrasonic pulse A, which is set according to the time when the signal intensity of the pipe reflected ultrasonic pulse train B is almost attenuated.
The dead zone is defined as the time period over which the pulse is received, and the pulse received by the ultrasonic sensor 1 within this dead zone (time TG) is not recognized as a reflected ultrasonic pulse.

For example, as shown in FIG. 1 (a), if the water level in the pipe 4 is high to some extent, as shown in FIG. 1 (b), after the reflected ultrasonic pulse train B for the pipe portion is almost attenuated, That is, the first reflected ultrasonic pulse C1 is first observed after the dead zone time TG has elapsed. Then, the second reflected ultrasonic pulse C2, the third reflected ultrasonic pulse (C3), etc. are then observed. Therefore, the first reflected ultrasonic pulse C1, the second reflected ultrasonic pulse C2, the third reflected ultrasonic pulse (C
3) and the like are all recognized as pulses reflected on the water surface.

However, as shown in FIG. 2 (a), when the water level in the pipe 4 becomes low, as shown in FIG. 2 (b), the pipe portion reflected ultrasonic pulse train B finishes being attenuated. It is possible that the first reflected ultrasonic pulse C1 appears before. Then, after the dead zone time TG has passed, what is first observed is the second reflected ultrasonic pulse C2, and then the third reflected ultrasonic pulse C3, the fourth reflected ultrasonic pulse C4, etc. are observed.

In this way, the first reflected ultrasonic pulse C1 that has entered the dead zone time TG is not recognized as a reflected pulse from the water surface 6a. In this case, the second reflected ultrasonic pulse C2, the third reflected ultrasonic pulse C3, the fourth reflected ultrasonic pulse C4, etc. are recognized as the pulses reflected on the water surface.

In the liquid level measuring method of this embodiment, first, a reference transmission ultrasonic pulse A transmitted from the ultrasonic sensor 1 is sent to the arithmetic unit 3 via the signal cable 2 to start measuring the water level. It The measurement is the ultrasonic pulse B reflected from the pipe.
Then, the multiple reflections of the first reflected ultrasonic pulse C1, the second reflected ultrasonic pulse C2, the third reflected ultrasonic pulse C3, etc. reflected from the water surface 6 in the pipe 4 are sequentially received. These received signals are sent to the arithmetic unit 3 via the signal cable 2.

The arithmetic unit 3 recognizes only the received pulses observed after the dead zone time TG has passed, as reflected pulses from the water surface 6a, that is, reflected ultrasonic pulses, and these reflected ultrasonic pulses are detected by the ultrasonic sensor 1. Detect the time to reach. For example, in the case shown in FIG. 1B, the first reflected ultrasonic pulse C1, the second reflected ultrasonic pulse C2, etc. are recognized as reflected ultrasonic pulses, and the respective times T
1, time T2, etc. are detected.

Next, in the arithmetic unit 3, the dead zone time TG
After the passage of, the reflected ultrasonic pulse observed first,
The difference between the arrival times of the next reflected ultrasonic pulse and the reflected ultrasonic pulse is calculated. For example, in the case of FIG. 1B, the first reflected ultrasonic pulse C1 and the second reflected ultrasonic pulse C2
And the time difference δT12 between time T1 and time T2 are calculated.

This time difference δT12 corresponds to the time required for the ultrasonic pulse to propagate the difference between the paths of the two reflected ultrasonic pulses. In the case of the above example, since the time difference δT12 is calculated using two reflected ultrasonic pulses adjacent to each other over time, the ultrasonic pulse propagates over a distance corresponding to the water level including the wall thickness of the pipe 4. This means that the time required for is approximately half the time difference δT12. In this way, distance conversion can be performed based on the time difference δT12, and the water level in the pipe 4 is detected.

As another example, in the case of FIG. 3 (b), the second reflected ultrasonic pulse C2, the third reflected ultrasonic pulse C3, etc. are recognized as reflected ultrasonic pulses, and their respective times T2. , Time T3, etc. are detected. Then
Second reflected ultrasonic pulse C2 and third reflected ultrasonic pulse C
3, the difference between arrival times, that is, the time difference δT23 between time T2 and time T3 is calculated. Therefore, similar to the above,
The distance conversion can be performed based on the time difference δT23, and the water level in the pipe 4 is detected.

That is, in the liquid level measuring method of the present embodiment, whether the pulse observed by the ultrasonic sensor 1 is always a reflected ultrasonic pulse obtained by reflection from the water surface 6a (significance). First, make a judgment. Then, the arrival times of the two pulses recognized as the reflected ultrasonic pulses are detected, and the difference between the arrival times is calculated. Then, distance conversion is performed based on the obtained time difference, and the water level in the pipe is detected.

Therefore, even if the water level in the pipe 4 changes with time, even if the water level falls within the low water level range, the time difference calculated by the arithmetic unit 3 using the above method increases or decreases in accordance with the increase or decrease of the water level. Therefore, it is possible to stably measure the water level at each time. Also, like the conventional method,
There is no need to always receive the same reflected ultrasonic pulse, which facilitates measurement.

By the way, as shown in FIG. 1, even if the water level in the pipe 4 does not fall within the low water level range as shown in FIG. The water surface 6a may swell due to a change or the like.
According to the ripple of the water surface 6a, the portion on the water surface 6a where the ultrasonic pulse is reflected locally changes. Even in such a case, the above method according to the present invention causes no problem, and the water surface 6a
It is possible to stably measure the water level following the vertical change of

That is, two pulses recognized as reflected ultrasonic pulses at a certain moment (Nth measurement) change to the next moment (N
In the (+ 1st measurement), it is assumed that the dead zone time TG has fallen within the range due to the decrease in the water surface 6a. At this time, the pulse that has entered the range of the dead zone time TG is not recognized as a reflected ultrasonic pulse. However, by again determining the significance of the observed pulse, the earliest reflected ultrasonic pulse observed after the dead zone time TG and the arrival time of the next pulse are measured again, If distance conversion is performed by calculating these time differences, the water level at the next moment (N + 1th measurement) is measured.

Further, when the water level in the pipe 4 is in an extremely low water level region that cannot be measured, the dead zone time TG
Since a plurality of reflected ultrasonic pulses enter the inside, stable reflected ultrasonic pulses (second, third ...) Can not be obtained. In this case, the method according to the present invention has an advantage that the arithmetic unit of the measurement system automatically suspends the measurement and the water level display on the assumption that the reliability of the water level measurement value is low.

Here, in the above embodiment, the dead zone time TG
After passing, the distance conversion is performed by the arrival time difference between the reflected ultrasonic pulse received first and the reflected ultrasonic pulse received next, but the present invention is not limited to this. For example, in the case of FIG. 3B, the dead zone time T
After G has passed, the difference δT34 (= T4−) between the arrival times of the second reflected ultrasonic pulse C3 observed second and the fourth reflected ultrasonic pulse C4 observed next (third).
Even if T3) is calculated, based on the time difference, similarly,
The distance is converted and the water level in the pipe 4 is detected.

After passing the dead zone time TG, the second reflected ultrasonic pulse C2 received first and the third reflected ultrasonic pulse C3 received next (second).
Alternatively, a method of calculating the time using a total of three pulses of the fourth reflected ultrasonic pulse C4 received next (third) and converting the distance may be used. In this way, when measuring the water level based on the time between a plurality of reflected ultrasonic pulses received after the dead zone time TG has elapsed, the accuracy of measuring the water level is improved as the number of pulses used increases. Needless to say.

In the above embodiment, the dead zone time TG is
Although it is assumed that the setting is made according to the time when the signal intensity of the reflected ultrasonic pulse train B for the pipe portion is almost attenuated, a threshold value is set for the signal intensity of the reflected ultrasonic pulse train B for the pipe portion, and the signal of the reflected ultrasonic pulse train B for the pipe portion is It may be set according to the time it takes for the intensity to decay to a threshold value or less.

[0042]

As described above, according to the ultrasonic liquid level measuring method of the present invention, when the liquid level suddenly increases or decreases, or when the liquid level is within the low liquid level range, the reflection Even if it is difficult to grasp the property of the reflected ultrasonic pulse (how many times it was reflected on the liquid surface) along with the time required to receive the ultrasonic pulse, it is possible to reliably and stably measure the liquid level.

[Brief description of drawings]

FIG. 1A is a cross-sectional view showing an apparatus and a liquid in a horizontal pipe to be measured, for explaining an embodiment of an ultrasonic liquid level measuring method according to the present invention. (B) is a schematic diagram showing an example of an ultrasonic pulse train to be measured.

2 is a cross-sectional view (a) showing the liquid in the apparatus and the horizontal pipe to be measured when the liquid level is smaller than that in FIG.
It is the schematic (b) which shows an example of the ultrasonic pulse train to be measured.

FIG. 3 is a cross-sectional view (a) showing the liquid in the apparatus and the horizontal pipe to be measured when the liquid level is within the low liquid level range.
FIG. 3B is a schematic diagram (b) showing an example of an ultrasonic pulse train to be measured.

[Explanation of symbols]

 1: Ultrasonic sensor 2: Signal cable 3: Arithmetic device 4: Horizontal piping 5: Heat insulating material 6: Liquid 7: Oscilloscope

Claims (1)

[Claims] 1. A reflected ultrasonic pulse, which is obtained by reflecting an ultrasonic pulse emitted from a lower part of the pipe to a upper part of the liquid in a horizontal pipe and reflecting the liquid pulse on the liquid surface of the liquid. Then, in the ultrasonic liquid level measuring method for measuring the liquid level of the liquid based on the time required to receive the reflected ultrasonic pulse, the dead zone over a predetermined time from the transmission time of the ultrasonic pulse is passed. The ultrasonic liquid level measuring method, characterized in that the liquid level is measured based on a time between the plurality of reflected ultrasonic pulses received after.