JP4512247B2

JP4512247B2 - Ultrasonic level gauge

Info

Publication number: JP4512247B2
Application number: JP2000279243A
Authority: JP
Inventors: 森本博文
Original assignee: Nippon Ceramic Co Ltd
Current assignee: Nippon Ceramic Co Ltd
Priority date: 2000-09-14
Filing date: 2000-09-14
Publication date: 2010-07-28
Anticipated expiration: 2020-09-14
Also published as: JP2002090210A

Description

【０００１】
【発明の属する技術分野】
本発明は、パルス状の超音波信号を送出し、送出された超音波信号の液面での反射信号を受信して、液面までの距離を算出する超音波液面計に関する。
【０００２】
【従来の技術】
従来の超音波液面計はパルス状の超音波信号を送出し、送出された超音波信号の液面での反射信号を受信して、反射してくる時間のみに注目し、液面までの距離を算出している。
【０００３】
【発明が解決しようとする課題】
従来の超音波液面計では液面の測定のみで、水等の不純物層を検出することができなかった。しかし不純物がたまるとタンク内の液体を供給して利用している機器に不純物が回り悪影響を与えるため、定期的にドレインで水等の不純物を抜いてやる必要があるが、その時期を知らせる手段が無く、求められていた。
【０００４】
本発明は、上記した実情に鑑みてなされたものであり、タンク内に水等の不純物がたまったことを知らせることができる超音波液面計を提供することを課題とする。
【０００５】
【課題を解決するための手段】
上記課題を解決するために、請求項１の発明は、パルス状の超音波信号である送信信号を液面に向けて送信し、当該送信信号の反射信号を受信するまでの時間により前記液面までの距離を計測する超音波液面計であって、さらに、受信した信号のパルス幅を受信パルス幅として検出する受信パルス幅検出手段と、検出された受信パルス幅を所定の不純物検出パルス幅と比較して不純物層を検出する不純物検出手段と、を備える。
また、請求項２の発明は、請求項１に記載の超音波液面計であって、前記不純物検出手段が、液体中の不純物層を検出すべき前記液面までの所定距離である不純物検出距離を記憶する距離記憶手段と、不純物層がない状態における前記液面までの距離が前記不純物検出距離であるときの受信パルス幅を前記不純物検出パルス幅として記憶するパルス幅記憶手段と、計測された液面までの距離が前記不純物検出距離とほぼ等しい場合に、前記検出された受信パルス幅と前記不純物検出パルス幅との差が所定以上ある場合に不純物層があると判定するパルス幅比較手段と、を備える。
【０００６】
【発明の実施の形態】
以下に、本発明に係わる超音波液面計の実施形態について、図に基づいて詳細に説明する。
【０００７】
図１は、本発明の一実施形態に係わる超音波液面計の装置構成を表した図であり、図２は本発明を具体的に説明するために、タンク内の測定液体を灯油とし、タンク内にたまった不純物を水とした場合の超音波信号波形を模擬的に図示したものである。
【０００８】
図１で、タンク底面に不純物が溜まっていない時、本発明の受信パルス幅記憶手段及び不純物検出手段に相当するＣＰＵ５より出力された超音波送出タイミング信号は、送信回路２へと送られ、送信回路２は一定のパルス幅で超音波振動子１を駆動する為の駆動信号を出力する。この信号はタンク１０２の底面に貼り付けられた超音波振動子１により超音波振動に変換されタンク１０２の底面より液体１０３中へ放出される。そして液面１０１により反射され、反射波は超音波振動子１により受信され、受信された超音波振動は超音波振動子１により電気信号に変換され、受信回路３により、増幅、検波され、この信号がコンパレータ４の閾値を超えた信号の幅と等しい幅のパルスがコンパレータ４より、ＣＰＵ５に入力される。ＣＰＵ５は超音波送出から、コンパレータ４のパルス出力が入力されるまでの時間と、パルスの幅の時間を計測することにより、まずタンク底面から液面までの距離を算出することができ、次にＣＰＵ５はこのときの距離とパルスの幅をそれぞれ不純物検出距離、および不純物検出パルス幅として記憶しておく。次に、タンク１０２の底に水等の不純物がたまってきた場合、超音波振動子１から送出された超音波信号はまず水等の不純物１０４の層を通過し当然密度の違う測定液体１０３との境界で一部が反射し一部が測定液体１０３中へ通過する。このとき不純物１０４の層は測定液体１０３の層に比較して非常に薄い層である為、反射した超音波は短時間でタンク１０２の底面より再び反射して境界面１０５に達し、このとき反射しないで通過した一部の超音波は最初に通過した超音波に少し遅れて重なり、測定液体１０３の液面１０１へ達する。測定液体１０３の液面１０１に達した超音波は液体と空気の密度の差でほとんど反射して再び不純物１０４との境界面１０５に達する。ここでもまた反射する成分と通過する成分に分かれ、反射した成分は通過してタンク１０２の底で再び反射した２次反射成分より少し時間が早く重なり、液面１０１へと向かっていく。このようなことをくりかえし、１次反射、２次反射、３次反射となるにつれて超音波パルスの幅も広がっていく。また、当然不純物の層が厚くなれば、超音波パルスの幅の広がりも厚さに比例して大きくなっていく。
そこで、その後の液面１０１までの距離の計測時には、ＣＰＵ５は、常にその距離の計測結果を記憶していた不純物検出距離と比較し、両者がほぼ等しいと判定された場合、具体的にはそれら距離の差が所定の閾値内である場合には、さらに以下の判定を行う。すなわち、受信パルスの幅を検出し、記憶していた不純物パルス幅とを比較し、その差が設定した閾値を超えたとき、不純物層があると判定し、警報出力６によりドレインを抜くべき旨の警報を出力させる。
【０００９】
具体例として、タンク１０２内の液体１０３を灯油、タンク１０２内に溜まる不純物１０４を水とし、灯油のタンク１０２の底から液面１０１までの距離が１０ｃｍ、不純物１０４の水が１ｃｍ溜まったとき上記超音波送出波形がどのように変化するか図２に基づき説明する。このとき灯油内の音速は１３００ｍ／ｓｅｃ、水内の音速は１５５０ｍ／ｓｅｃとし、超音波受信パルスの幅は、５０μｓｅｃとする。
【００１０】
不純物水が溜まっていない時、タンク１０２底面の超音波振動子１から発信される超音波パルス送出から約１５４μｓｅｃ後にパルス幅５０μｓｅｃで灯油液面１０１からの液面１次反射波２０１が得られる。液面１次反射波２０１は再度タンク１０２底面で反射して底面１次反射波２０２となり、その後灯油液面１０１で再度反射してタンク１０２底面へ向かう液面２次反射波２０２が観測されることとなる。図２（ａ）を参照。本出願が注目するのは、このときの液面１次反射波２０１のパルスの幅５０μｓｅｃをＣＰＵ５は記憶しておくことにある。
この状態で不純物である水がタンク１０２底面に１ｃｍ溜まると、タンク１０２底面の超音波振動子１から送出された超音波信号の１部は、最初に水と灯油の境界面１０５でタンク１０２底面方向へ反射し、次にタンク１０２底面で再度反射し、再度境界面１０５方向へ向かい、そこでまた反射して再度タンク１０２底面方向へ向かうという事象を繰り返す成分と、境界面１０５を反射せずに直進通過して灯油液面方向に向かう通過成分２０５に分かれるが、境界面１０５で反射してタンク１０２底面方向へ向かう成分は、タンク１０２底面での反射後に再度境界面１０５方向へ向かい、ここでまた境界面１０５を直進通過する成分とタンク１０２底面方向へ反射する成分へと分かれるが、灯油液面１０１方向へ向かう通過成分であろうが、タンク１０２底面と境界面１０５の間で反射を繰り返す成分であろうが、何れの反射成分も境界面反射の都度、反射せずに直進する成分の２０％の音圧成分となることから、無視できるほど微弱な信号となり、本出願の注目する計測に影響を及ぼさないものとなる。結果、境界面１０５を直進通過した成分２０５はさきほど境界面１０５で反射しないで直進通過し灯油液面１０１方向へ向かった直進通過成分２０３より１３μｓｅｃ遅れて灯油液面で反射し、その後タンク１０２底面方向へ向かう液面１次反射波２０５となり、境界面１０５を反射することなくタンク１０２底面方向へ直進通過し、タンク１０２底面の超音波振動子１にて液面１次反射波２０３との比較で幅の広がった合成波２０８として受信される。この２０８の信号幅が不純物のないときの信号幅に比較して広くなっていることを検出することで水を検出することができる。
以上が、液面１次反射波２０３および液面１次反射波２０５のみを用いて計測する場合の説明であり、本出願が最も注目する範囲である。
以下はタンク１０２底面における１次反射より後に起こる事象ついての補足説明である。
灯油液面１０１で反射した液面１次反射波２０３の１部はタンク１０２底面の超音波振動子１で受信される前に水と灯油の境界面１０５で再度灯油液面１０１方向に境界面１次反射波２０６として反射される。その一方、境界面１０５で反射せずタンク１０２底面へ向かい、タンク１０２底面で再度反射して底面１次反射波２０４となる成分よりも、境界面１次反射波２０６は１３μｓｅｃ早く灯油液面１０１方向に向かい、灯油液面１０１で反射され液面２次反射波２０６となりタンク１０２底面方向へ向かい、再度水と灯油の境界面１０５で直進通過成分と反射成分に分かれる。この時、灯油と水の境界面１０５で灯油液面１０１方向へ反射する境界面２次反射波は微弱なものとなり、無視することができる。一方、境界面１０５で反射せずにタンク１０２底面方向へ向かう液面２次反射波２０６は、液面２次反射波２０４よりも１３μｓｅｃ早くタンク１０２底面の超音波振動子１にて計測される。同様に、液面１次反射波２０５のうち境界面１０５で反射せずにタンク１０２底面へ向かい、タンク底面で再度反射して境界面１０５へ向かい、境界面１０５を反射することなく直進通過して灯油液面１０１へ向かう成分は、灯油液面１０１で反射され再度境界面１０５方向へ向かい、境界面１０５で反射する成分と反射せずに、境界面１０５を直進通過し、タンク１０２底面へ向かう成分へ分かれるが、このとき境界面１０５を直進通過する成分は、液面２次反射波２０４が境界面１０５を通過してタンク１０２底面の超音波振動子１が受信するときも１３μｓｅｃ遅れてタンク１０２底面の超音波振動子１に到達する液面２次反射波２０７となり、信号幅７６μｓｅｃの合成波２０９となる。
【００１１】
上記よりＣＰＵ５は超音波送出から１次反射受信までの時間１５１μｓｅｃを、不純物水の影響で３μｓｅｃ早くなるが、ほぼ正確に測定することが出来、受信したパルス幅２０１と２０８を比較し１３μｓｅｃ以上の差が発生したとき警報出力６が警報を出力するよう設定しておけば、不純物水が１ｃｍ以上存在することを検知することが出来る。また今回は１次反射の比較を示したが２次反射２０２、２０９の比較でも可能である。又図３に実際の測定波形を示す。
以上、この実施の形態では、予め不純物層の無い状態における受信パルス幅を不純物パルス幅として記憶し、不純物検出距離において、受信パルス幅と不純物パルス幅とを比較して不純物層を検出するものとしたが、この発明はこれに限られず、例えば、不純物層検出の精度がさほど要求されない場合には、予め設定されている送信パルス幅を不純物パルス幅として用いてもよい。その場合には不純物検出距離以外の距離においても不純物層の検出が行える。
【００１２】
【発明の効果】
請求項１および請求項２に記載の超音波液面計は、液面までの距離を計測するだけでなく、不純物の存在も検知することが出来、タンクの液体を利用する機器へ不純物が入り機器に重大なダメージを与えるのを回避することができるようになる。
また、請求項２に記載の超音波液面計は、不純物検出パルス幅を記憶する時の液面までの距離を同時に不純物検出距離として記憶し、ほぼ同じ距離の条件での受信パルス幅を比較することで、距離による超音波信号の減衰によるパルス幅の変動をキャンセルし、より正確に不純物層の厚さを測定することができる
【図面の簡単な説明】
【図１】本発明の実施形態に係わる超音波液面計の装置構成図である。
【図２】本発明の実施形態に係わる超音波液面計での超音波受信信号の模擬図である。
【図３】本発明の実施形態に係わる超音波液面計での超音波受信信号の測定波形を示す図である。
【符号の説明】
１超音波振動子
２送信回路
３受信回路
４コンパレータ
５ＣＰＵ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic liquid level gauge that transmits a pulsed ultrasonic signal, receives a reflection signal of the transmitted ultrasonic signal on the liquid level, and calculates a distance to the liquid level.
[0002]
[Prior art]
A conventional ultrasonic liquid level gauge sends a pulsed ultrasonic signal, receives a reflected signal at the liquid level of the transmitted ultrasonic signal, pays attention only to the reflected time, and reaches the liquid level. The distance is calculated.
[0003]
[Problems to be solved by the invention]
Conventional ultrasonic liquid level gauges cannot detect an impurity layer such as water only by measuring the liquid level. However, if impurities accumulate, the impurities in the tank that are used by supplying the liquid in the tank will be adversely affected, so it is necessary to drain water and other impurities regularly at the drain. There was no need.
[0004]
This invention is made | formed in view of the above-mentioned actual condition, and makes it a subject to provide the ultrasonic level gauge which can notify that impurities, such as water, accumulated in the tank.
[0005]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 is characterized in that a transmission signal which is a pulsed ultrasonic signal is transmitted toward the liquid surface, and the liquid surface is measured depending on a time until a reflection signal of the transmission signal is received. An ultrasonic liquid level gauge for measuring the distance to the received pulse width detecting means for detecting the pulse width of the received signal as a received pulse width, and the detected received pulse width as a predetermined impurity detection pulse width. And an impurity detection means for detecting the impurity layer.
The invention according to claim 2 is the ultrasonic liquid level meter according to claim 1, wherein the impurity detection means is a predetermined distance to the liquid level where the impurity layer in the liquid is to be detected. A distance storage means for storing the distance, a pulse width storage means for storing a reception pulse width when the distance to the liquid surface in the state where there is no impurity layer is the impurity detection distance, as the impurity detection pulse width, and Pulse width comparing means for determining that there is an impurity layer when the difference between the detected reception pulse width and the impurity detection pulse width is greater than or equal to a predetermined distance when the distance to the liquid surface is substantially equal to the impurity detection distance And comprising.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of an ultrasonic liquid level gauge according to the present invention will be described in detail with reference to the drawings.
[0007]
FIG. 1 is a diagram showing an apparatus configuration of an ultrasonic liquid level gauge according to an embodiment of the present invention, and FIG. 2 is a kerosene measurement liquid in a tank for specifically explaining the present invention. FIG. 2 schematically illustrates an ultrasonic signal waveform when water is used as impurities accumulated in a tank.
[0008]
In FIG. 1, when no impurities are accumulated on the bottom surface of the tank, the ultrasonic wave transmission timing signal output from the CPU 5 corresponding to the reception pulse width storage means and the impurity detection means of the present invention is sent to the transmission circuit 2 for transmission. The circuit 2 outputs a drive signal for driving the ultrasonic transducer 1 with a constant pulse width. This signal is converted into ultrasonic vibration by the ultrasonic vibrator 1 attached to the bottom surface of the tank 102, and emitted from the bottom surface of the tank 102 into the liquid 103. Then, it is reflected by the liquid surface 101, the reflected wave is received by the ultrasonic vibrator 1, the received ultrasonic vibration is converted into an electric signal by the ultrasonic vibrator 1, amplified and detected by the receiving circuit 3, A pulse having a width equal to the width of the signal whose signal exceeds the threshold value of the comparator 4 is input from the comparator 4 to the CPU 5. The CPU 5 can first calculate the distance from the tank bottom surface to the liquid surface by measuring the time from the ultrasonic transmission until the pulse output of the comparator 4 is input and the time of the pulse width. The CPU 5 stores the distance and the pulse width at this time as the impurity detection distance and the impurity detection pulse width, respectively. Next, when impurities such as water accumulate on the bottom of the tank 102, the ultrasonic signal sent from the ultrasonic transducer 1 first passes through the layer of impurities 104 such as water and naturally has a different density from the measuring liquid 103. A part of the light is reflected at the boundary and a part of the light passes through the measurement liquid 103. At this time, since the layer of the impurity 104 is very thin compared to the layer of the measurement liquid 103, the reflected ultrasonic wave is reflected again from the bottom surface of the tank 102 in a short time and reaches the boundary surface 105. Some of the ultrasonic waves that have passed without being overlapped with the first ultrasonic wave that has passed through a little later, and reach the liquid surface 101 of the measurement liquid 103. The ultrasonic wave reaching the liquid surface 101 of the measurement liquid 103 is almost reflected by the difference in density between the liquid and air and reaches the boundary surface 105 with the impurity 104 again. Again, the component is divided into a component to be reflected and a component to be transmitted. The reflected component passes through the secondary reflection component reflected again at the bottom of the tank 102 and overlaps with the time slightly before moving toward the liquid surface 101. This is repeated, and the width of the ultrasonic pulse increases as primary reflection, secondary reflection, and tertiary reflection occur. Naturally, as the impurity layer becomes thicker, the width of the ultrasonic pulse increases in proportion to the thickness.
Therefore, when measuring the distance to the liquid level 101 thereafter, the CPU 5 always compares the result of measuring the distance with the impurity detection distance, and if both are determined to be substantially equal, When the difference in distance is within a predetermined threshold, the following determination is further performed. That is, the width of the received pulse is detected, compared with the stored impurity pulse width, and when the difference exceeds a set threshold value, it is determined that there is an impurity layer, and the drain should be pulled out by the alarm output 6 Alarm is output.
[0009]
As a specific example, when the liquid 103 in the tank 102 is kerosene, the impurity 104 accumulated in the tank 102 is water, the distance from the bottom of the tank 102 of kerosene to the liquid level 101 is 10 cm, and the water of the impurity 104 is accumulated 1 cm. How the ultrasonic transmission waveform changes will be described with reference to FIG. At this time, the speed of sound in kerosene is 1300 m / sec, the speed of sound in water is 1550 m / sec, and the width of the ultrasonic reception pulse is 50 μsec.
[0010]
When the water impurities are not accumulated, the liquid level primary reflected wave 201 from kerosene liquid surface 101 is that obtained by pulse width 50μsec after approximately 154μsec from ultrasonic pulses transmitted is transmitted from the ultrasonic transducer 1 of the tank 102 bottom . The liquid surface primary reflected wave 201 is reflected again on the bottom surface of the tank 102 to become the bottom surface primary reflected wave 202, and then the liquid surface secondary reflected wave 202 is reflected again on the kerosene liquid surface 101 and directed toward the bottom surface of the tank 102. It will be. See FIG. 2 (a). The present application is noted that the pulse width 50μsec of the liquid level first order reflection wave 201 at this time CPU5 is to store.
When water accumulates 1cm in tank 102 the bottom, which is an impurity in this state, a portion of the ultrasonic signal transmitted from the ultrasonic transducer 1 of the tank 102 bottom, the tank 102 bottom first in the boundary surface 105 of the water and kerosene And then re-reflecting at the bottom surface of the tank 102 and again toward the boundary surface 105, where it is reflected again and again toward the bottom surface of the tank 102 , and without reflecting the boundary surface 105. A component that passes straight and travels toward the kerosene liquid level is divided into components 205, but the component reflected by the boundary surface 105 and directed toward the bottom surface of the tank 102 is directed again toward the boundary surface 105 after being reflected from the bottom surface of the tank 102. Moreover, although it is divided into a component that passes straight through the boundary surface 105 and a component that reflects toward the bottom surface of the tank 102, it may be a component that passes toward the kerosene liquid surface 101, As will be component repeatedly reflected between the tank 102 bottom surface and the boundary surface 105, one of the reflected components also each of the boundary surface reflection, since it is 20% of the sound pressure component of the components to be straight without being reflected, ignoring weak signals enough to the do Ri, and shall not affect the measurement of interest of the present application. Results, the boundary surface 105 straight passes ingredients 205 straight passes to a delay 13μsec than straight passage component 203 toward the kerosene liquid surface 101 direction not just reflected at the boundary surface 105 is reflected by the kerosene liquid surface, then the tank 102 bottom The liquid surface primary reflected wave 205 is directed toward the direction, passes straightly toward the bottom surface of the tank 102 without reflecting the boundary surface 105, and is compared with the liquid surface primary reflected wave 203 by the ultrasonic transducer 1 on the bottom surface of the tank 102. Is received as a combined wave 208 having a wider width . Water can be detected by detecting that the signal width of 208 is wider than the signal width when there is no impurity.
The above is an explanation of measurement using only the liquid surface primary reflected wave 203 and the liquid surface primary reflected wave 205, and is the most noticeable range of the present application.
The following is a supplementary explanation of an event that occurs after the primary reflection at the bottom surface of the tank 102.
A portion of the liquid surface primary reflected wave 203 reflected by the kerosene liquid surface 101 is again a boundary surface in the direction of the kerosene liquid surface 101 at the boundary surface 105 between water and kerosene before being received by the ultrasonic vibrator 1 on the bottom surface of the tank 102. Ru is reflected as a primary reflected wave 206. On the other hand, the boundary primary reflected wave 206 is 13 μsec earlier than the component that does not reflect at the boundary surface 105 but travels toward the bottom surface of the tank 102 and is reflected again at the bottom surface of the tank 102 and becomes the bottom surface primary reflected wave 204. have unsuitable direction, toward the to-liquid surface secondary reflection wave 206 becomes tank 102 bottom direction reflected by kerosene liquid surface 101, split into reflected component and the rectilinear passage components at the interface 105 of the water again and kerosene. In this case, the interface secondary reflection wave reflected to the kerosene liquid surface 101 direction at the boundary surface 105 of the kerosene and the water becomes as weak, can be ignored. On the other hand, the liquid surface secondary reflected wave 206 directed toward the bottom surface of the tank 102 without being reflected by the boundary surface 105 is measured by the ultrasonic transducer 1 on the bottom surface of the tank 102 13 μsec earlier than the liquid surface secondary reflected wave 204. . Similarly, the liquid surface primary reflected wave 205 is not reflected by the boundary surface 105 but is directed to the bottom surface of the tank 102, is reflected again by the tank bottom surface and is directed to the boundary surface 105, and passes straight without reflecting the boundary surface 105. The component directed toward the kerosene liquid surface 101 is reflected by the kerosene liquid surface 101 and travels again toward the boundary surface 105, and does not reflect the component reflected by the boundary surface 105, but passes straight through the boundary surface 105 to the bottom surface of the tank 102. At this time, the component that passes straight through the boundary surface 105 is delayed by 13 μsec when the liquid surface secondary reflected wave 204 passes through the boundary surface 105 and is received by the ultrasonic transducer 1 at the bottom of the tank 102. The liquid surface secondary reflected wave 207 reaches the ultrasonic transducer 1 on the bottom surface of the tank 102 and becomes a combined wave 209 having a signal width of 76 μsec.
[0011]
From the above, the CPU 5 can measure the time 151 μsec from the ultrasonic transmission to the primary reflection reception 3 μsec faster due to the influence of the impurity water, but it can be measured almost accurately. If the alarm output 6 is set to output an alarm when a difference occurs, the presence of 1 cm or more of impurity water can be detected. In addition, the comparison of the primary reflection is shown this time, but the comparison of the secondary reflections 202 and 209 is also possible. FIG. 3 shows an actual measurement waveform.
As described above, in this embodiment, the reception pulse width in the absence of the impurity layer is stored in advance as the impurity pulse width, and the impurity layer is detected by comparing the reception pulse width with the impurity pulse width at the impurity detection distance. However, the present invention is not limited to this. For example, when the accuracy of the impurity layer detection is not so required, a preset transmission pulse width may be used as the impurity pulse width. In that case, the impurity layer can be detected at a distance other than the impurity detection distance.
[0012]
【The invention's effect】
The ultrasonic liquid level meter according to claim 1 and 2 can not only measure the distance to the liquid level but also detect the presence of impurities, and impurities enter the equipment using the liquid in the tank. It will be possible to avoid serious damage to the equipment.
The ultrasonic liquid level meter according to claim 2 stores the distance to the liquid level when storing the impurity detection pulse width as an impurity detection distance at the same time, and compares the received pulse widths under substantially the same distance conditions. By doing so, the fluctuation of the pulse width due to the attenuation of the ultrasonic signal due to the distance can be canceled, and the thickness of the impurity layer can be measured more accurately [Brief description of the drawings]
FIG. 1 is an apparatus configuration diagram of an ultrasonic liquid level gauge according to an embodiment of the present invention.
FIG. 2 is a simulation diagram of an ultrasonic reception signal in the ultrasonic liquid level meter according to the embodiment of the present invention.
FIG. 3 is a diagram showing a measurement waveform of an ultrasonic reception signal in the ultrasonic liquid level gauge according to the embodiment of the present invention.
[Explanation of symbols]
1 Ultrasonic vibrator 2 Transmission circuit 3 Reception circuit 4 Comparator 5 CPU

Claims

In an ultrasonic liquid level meter that transmits a transmission signal that is a pulsed ultrasonic signal toward the liquid surface and measures the distance to the liquid surface according to the time until the reflected signal of the transmission signal is received,
A reception pulse width detection means for detecting the pulse width of the received signal as a reception pulse width;
Impurity detection means for detecting the impurity layer by comparing the detected reception pulse width with a predetermined impurity detection pulse width;
An ultrasonic liquid level gauge comprising:

The ultrasonic liquid level meter according to claim 1,
The impurity detection means is
A distance storage means for storing an impurity detection distance which is a predetermined distance to the liquid surface where the impurity layer in the liquid is to be detected;
Pulse width storage means for storing, as the impurity detection pulse width, a reception pulse width when the distance to the liquid surface in the state where there is no impurity layer is the impurity detection distance;
When the measured distance to the liquid level is substantially equal to the impurity detection distance, the pulse width for determining that there is an impurity layer when the difference between the detected reception pulse width and the impurity detection pulse width is greater than or equal to a predetermined value A comparison means;
An ultrasonic liquid level gauge comprising: