JP2014002090A - Level gauge and method of controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide a level gauge capable of reducing its size.SOLUTION: A level gauge comprises: transmission pulse generating means for generating a transmission pulse 4 with a first pulse repeat cycle; an input/output part 33 for outputting the transmission pulse 4 to a probe 20 and inputting a reflection pulse 5 from the probe 20; sampling pulse generating means for generating a sampling pulse SP with a second pulse repeat cycle; expansion signal generating means for generating an expansion signal that temporally expands an input/output signal according to a difference between the first and the second pulse repeat cycles, by sampling the input/output signal in the input/output part 33 according to the sampling pulse SP; interface level measuring means for measuring an interface level on the basis of a propagation time of the reflection pulse; and pulse cycle controlling means for controlling a difference between the first and the second pulse repeat cycles on the basis of a repeat cycle of the expansion signal.

Description

  The present invention relates to a level meter for measuring an interface level such as a liquid level or a powder level and a control method thereof, and more specifically, the interface level is determined based on a propagation time until a transmission pulse returns as a reflected pulse from the interface. It relates to improvement of the level meter to measure.

  The liquid level measuring device is a level meter that measures the liquid level based on the propagation time from when the transmission pulse is sent toward the liquid level until the transmission pulse returns as a reflected pulse from the liquid level. It is. Such liquid level measuring devices include a guide pulse type that transmits a pulsed current signal along a conductive guide probe and a radio wave type that transmits a high-frequency pulse from an antenna (for example, Patent Document 1).

  In the liquid level level measuring apparatus of the guide pulse method, if the liquid level exists in the middle of transmission of the transmission pulse input to one end of the guide probe, a reflected pulse is generated at the position of the liquid level. For example, the time interval TK from when the transmission pulse is input to one end of the guide probe until the reflected pulse reaches the one end corresponds to the reciprocation time between one end of the guide probe and the liquid surface. The distance L from one end to the liquid level is obtained by TK × light speed × (1/2).

  Usually, the transmission pulse is generated using a clock signal having a frequency of about several MHz, and the pulse repetition period is about several hundred ns. On the other hand, the time interval TK is very short, and the reciprocation time per 1 mm of the length of the guide probe is about several ps. For this reason, it is difficult to compare the transmitted pulse and reflected pulse as they are on the time axis, and the transmission pulse and reflected pulse are time-extended using a sampling pulse whose pulse repetition interval is slightly different from the transmitted pulse. Processing is performed. That is, the liquid level is measured by comparing the signal waveforms of the transmission pulse and the reflected pulse that have been extended in time.

  The transmission pulse is generated by shaping the clock signal generated in the reference oscillator. On the other hand, the sampling pulse is generated by shaping the clock signal generated in the local oscillator. A constant frequency difference needs to be maintained between the reference oscillator and the local oscillator, but the oscillation frequency of the reference oscillator or the local oscillator varies due to a temperature change or the like. Since the time interval TK is obtained based on the frequency difference between the reference oscillator and the local oscillator, if the frequency difference changes, the measurement accuracy of the liquid level decreases.

JP 2002-535641 A

  Therefore, in the conventional level meter as described above, feedback control of the local oscillator is performed using a PLL (Phase-Locked Loop) circuit so that a constant frequency difference is maintained between the reference oscillator and the local oscillator. . The PLL circuit requires a phase comparator that compares the output signal of the reference oscillator and the output signal of the local oscillator and converts the phase difference into a voltage, and a low-pass filter that removes high-frequency components in the feedback loop. For this reason, there existed a problem that manufacturing cost increased and the mounting area of the circuit board also increased.

  This invention is made | formed in view of the said situation, and aims at providing the level meter which can be reduced in size at low cost. In particular, it is an object of the present invention to provide a level meter capable of maintaining a constant pulse repetition period difference between a transmission pulse and a sampling pulse without increasing the manufacturing cost and the circuit board mounting area. Another object of the present invention is to provide a method for controlling the level meter.

  A level meter according to a first aspect of the present invention is a level meter for measuring an interface level such as a liquid level or a powder level, and includes a transmission pulse generating means for generating a transmission pulse at a first pulse repetition period, and the transmission described above. An input / output unit that outputs a pulse to the measuring element and receives a reflected pulse from the measuring element, sampling pulse generating means for generating a sampling pulse at a second pulse repetition period, and an upper frequency according to the sampling pulse By sampling the input / output signal in the entry output unit, an expansion signal generating means for generating an expansion signal obtained by time-expanding the input / output signal according to the difference between the first and second pulse repetition periods, and the reflection The interface level measuring means for measuring the interface level based on the propagation time of the pulse and the difference between the first and second pulse repetition periods based on the repetition period of the extension signal. Constructed and a that pulse cycle control means.

  In this level meter, the difference in the pulse repetition period is controlled based on the repetition period of the expanded signal obtained by time-expanding the input / output signal according to the difference in the pulse repetition period between the transmission pulse and the sampling pulse. At that time, the sampling pulse is only used for sampling the input / output signal at the input / output terminal, and the expansion signal is used for controlling the difference between the pulse repetition periods. That is, the difference in the pulse repetition period can be controlled without using circuit elements such as a phase comparator or a low-pass filter that compares the phases of the transmission pulse and the sampling pulse. Therefore, the difference in the pulse repetition period between the transmission pulse and the sampling pulse can be kept constant without increasing the manufacturing cost and the circuit board mounting area.

  The level meter according to the second aspect of the present invention is configured such that, in addition to the above configuration, the pulse period control means controls either one of the first and second pulse repetition periods. According to such a configuration, it is possible to prevent the circuit configuration from becoming complicated.

  A level meter according to a third aspect of the present invention includes pulse extraction means for extracting the transmission pulse and the reflected pulse from the expanded signal in addition to the above-described configuration, and the pulse period control means is extracted by the pulse extraction means. A difference between the first and second pulse repetition periods is controlled based on one of the transmission pulse and the reflected pulse.

  According to such a configuration, the pulse repetition period of the transmission pulse or the sampling pulse is automatically adjusted by obtaining the repetition period of the stretched signal by using the transmission pulse or the reflection pulse used for measuring the interface level. Stability can be improved.

  In a level meter according to a fourth aspect of the present invention, in addition to the above-described configuration, the measurement element transmits the transmission pulse input to one end to the other end, and the reflected probe is generated at the position of the interface. It is comprised so that it may consist of.

  According to such a configuration, a guide pulse type level meter capable of maintaining a constant pulse repetition period difference between the transmission pulse and the sampling pulse without increasing the manufacturing cost or the circuit board mounting area. Can be realized.

  A level meter according to a fifth aspect of the present invention includes a detector for detecting the input / output signal in addition to the above-described configuration, and the measuring element transmits the transmission pulse including a high-frequency signal toward the interface. The extension signal generating means is configured to sample the input / output signal after detection.

  According to such a configuration, the radio wave type level meter capable of maintaining a constant pulse repetition period difference between the transmission pulse and the sampling pulse without increasing the manufacturing cost and the mounting area of the circuit board. Can be realized.

  A level meter control method according to a sixth aspect of the present invention is a level meter control method including an input / output unit that outputs a transmission pulse to a measurement element and receives a reflection pulse from the measurement element. A transmission pulse generation step for generating a transmission pulse at a pulse repetition period; a sampling pulse generation step for generating a sampling pulse at a second pulse repetition period; and an input / output signal at the input / output unit according to the sampling pulse , Based on the propagation time of the reflected pulse, and a stretched signal generating step for generating a stretched signal obtained by time-stretching the input / output signal according to the difference between the first and second pulse repetition periods. The difference between the first and second pulse repetition periods is controlled based on the interface level measurement step for measuring the interface level and the repetition period of the extension signal. Constructed and a pulse period control step that.

  According to the present invention, the difference in pulse repetition period can be controlled without using a circuit element such as a phase comparator or a low-pass filter for comparing the phases of the transmission pulse and the sampling pulse. Can be provided at low cost. In particular, it is possible to provide a level meter capable of maintaining a constant pulse repetition period difference between the transmission pulse and the sampling pulse without increasing the manufacturing cost and the circuit board mounting area. Further, according to the present invention, a method for controlling the level meter can be provided.

It is the perspective view which showed one structural example of the level meter by Embodiment 1 of this invention, and the liquid level meter 1 of a guide pulse system is shown. It is sectional drawing which showed an example of the usage condition of the liquid level meter 1 of FIG. 1, and the case where the liquid level meter 1 is attached to the storage tank 2 is shown. FIG. 2 is a block diagram illustrating a configuration example of a liquid level meter 1 in FIG. 1. It is the figure which showed an example of the waveform of the expansion | extension signal of FIG. 3, and the time change of the signal level is shown. FIG. 4 is a diagram showing a comparison of examples of waveforms of a transmission pulse 4, a sampling pulse SP, and an extension signal generated in the liquid level meter 1 of FIG. 3. It is the figure which showed the waveform of the expansion | extension signal produced | generated in the liquid level meter 1 of FIG. It is the block diagram which showed an example of the function structure in CPU39 of FIG. It is the block diagram which showed one structural example of the level meter by Embodiment 2 of this invention, and the electric wave type liquid level meter 1 is shown.

Embodiment 1 FIG.
<Liquid level meter 1>
FIG. 1 is a perspective view showing an example of the configuration of a level meter according to Embodiment 1 of the present invention, in which a guide pulse type liquid level meter 1 is shown. The liquid level meter 1 is a liquid level measuring device that transmits a pulse signal along a rod-shaped guide probe 20, and includes a display unit 11, an operation unit 12, a cable connection unit 13, and a tank mounting unit 14. The main body 10 and the guide probe 20 are included.

  The display unit 11 displays a liquid level measurement result and setting contents. The operation unit 12 is an input unit for inputting measurement conditions and the like. The display unit 11 and the operation unit 12 are provided on the upper surface of the cylindrical main body unit 10.

  The cable connection unit 13 is a connector unit that detachably connects a transmission cable including a power line for supplying power to the main body unit 10 and a signal line for transmitting an output signal indicating a measurement result. The cable connection portion 13 is provided on the peripheral surface of the main body portion 10.

  The tank attaching part 14 is used when attaching the liquid level meter 1 to a storage tank or the like, and is a cylindrical pedestal part having a diameter smaller than that of the main part of the main body part 10, and has a thread. The tank attaching portion 14 is provided at the lower portion of the main body portion 10.

  The guide probe 20 is a measuring element for measuring the liquid level using a pulse signal. If the liquid level exists in the middle of transmitting the pulse signal, a reflected pulse is generated at the position of the liquid level. For example, the guide probe 20 is a linear conductive probe whose upper end is an input / output end and whose lower end is an open end. The guide probe 20 is attached to the main body portion 10 so as to protrude from the lower surface of the tank attachment portion 14.

  The liquid level meter 1 is based on a time interval from when a transmission pulse is input from the main body 10 to the upper end of the guide probe 20 until a reflected pulse due to the liquid level is input from the upper end of the guide probe 20 to the main body 10. And measure the liquid level.

  FIG. 2 is a cross-sectional view showing an example of how the liquid level meter 1 shown in FIG. 1 is used, and shows a case where the liquid level meter 1 is attached to the storage tank 2. The liquid level meter 1 is attached to a through hole provided in the upper plate of the storage tank 2.

  The main body 10 is arranged such that the guide probe 20 intersects the horizontal plane. For example, the main body 10 is arranged such that the guide probe 20 is orthogonal to the liquid level 3 in the storage tank 2. The measurement of the liquid level is performed by obtaining the distance L between the root portion 21 of the guide probe 20 and the liquid level 3 when the tip 22 of the guide probe 20 is below the liquid level.

  The main body 10 generates the transmission pulse 4 at a predetermined pulse repetition period and inputs it to the root portion 21 of the guide probe 20. The transmission pulse 4 is transmitted from the root portion 21 to the tip portion 22 at the speed of light C. If the tip 22 is below the liquid level 3, the reflected pulse 5 is formed from the transmission pulse 4 at the position of the liquid level 3 on the guide probe 20. A part of the transmission pulse 4 is transmitted as it is below the liquid level even after the reflection pulse 5 is formed at the position of the liquid level 3.

  The reflected pulse 5 is formed with a signal intensity corresponding to the difference in dielectric constant between air and liquid, and transmitted to the root portion 21 at the speed of light C. The main body 10 calculates the distance L based on the time interval TK from when the transmission pulse 4 is input to the base 21 to when the reflected pulse 5 due to the liquid level is input from the root 21 to the main body 10. . The distance L can be obtained by L = TK × C × (1/2).

  FIG. 3 is a block diagram showing a configuration example of the liquid level meter 1 of FIG. The liquid level meter 1 includes a display unit 11, an operation unit 12, a tank mounting unit 14, a guide probe 20, a reference oscillator 31, a transmission pulse generation circuit 32, an input / output unit 33, a local oscillator 34, a sampling pulse generation circuit 35, A sampling hold circuit 36, an amplifier 37, an ADC 38, a CPU 39, a DAC 40, and a signal output unit 41 are included.

The reference oscillator 31 is a high-frequency signal generation unit that generates a reference signal for a transmission pulse and outputs the reference signal to the transmission pulse generation circuit 32. For example, a clock signal having a frequency of 19.2 MHz is generated as the reference signal. The transmission pulse generation circuit 32 generates the transmission pulse 4 based on the reference signal and outputs it to the input / output unit 33. Transmission pulse 4 is generated repeatedly at the pulse repetition period PT _1.

Specifically, the reference signal is frequency-divided using a frequency divider (not shown), and the waveform of the frequency-divided signal is shaped to obtain a transmission pulse 4 having a short pulse width. Frequency of the divided signal is 2.4 MHz, pulse repetition period PT ₁ is 416.7Ns.

  The input / output unit 33 is a signal coupling unit that outputs the transmission pulse 4 input from the transmission pulse generation circuit 32 to the guide probe 20 and the sampling hold circuit 36, and receives the reflected pulse 5 from the guide probe 20, Consists of branch terminals. The reflected pulse 5 input from the guide probe 20 to the input / output unit 33 is output to the sampling hold circuit 36.

  The local oscillator 34 is a high-frequency signal generation unit that generates a reference signal for a sampling pulse and outputs the reference signal to the sampling pulse generation circuit 35. For example, a clock signal whose frequency is slightly different from the reference signal is generated as the reference signal. As the local oscillator 34, a VCO (Voltage Controlled Oscillator) capable of adjusting the oscillation frequency according to the voltage level is used.

The sampling pulse generation circuit 35 generates a sampling pulse SP based on the reference signal and outputs it to the sampling hold circuit 36. Sampling pulse SP is generated repeatedly at the pulse repetition period PT _2.

Specifically, the reference signal is frequency-divided using a frequency divider (not shown), and the waveform of the frequency-divided signal is shaped to obtain a sampling pulse SP with a short pulse width. For example, the frequency of the frequency-divided signal is (2.4 MHz-16 Hz), and the pulse repetition period PT ₂ is (416.7 ns + 2.8 ps).

  In general, a pulse signal is a signal output in a relatively short period, and its waveform is arbitrary, and may be rectangular, triangular, or other shapes. The transmission pulse 4 and the sampling pulse SP are signals whose signal level such as current or voltage level rises from zero level and falls in a short time.

  The sampling and holding circuit 36 is a decompressed signal generating unit that generates a decompressed signal obtained by expanding the input / output signal with time and outputs the decompressed signal to the amplifier 37. The expansion signal is generated by sampling the input / output signal in the input / output unit 33 using the sampling pulse SP as a trigger, and holding the sampling value until the input / output signal is newly sampled by the next sampling pulse SP. .

The stretching signal, in accordance with the difference ΔT of the pulse repetition period PT ₁ and PT _2, is stretched in the time axis direction. Elongation rate in the time axis direction, a difference ΔT of the pulse repetition period PT ₁ and PT _2, is defined by the ratio of the one of the pulse repetition period PT ₁ or PT _2. For example, the expansion ratio r in the time axis direction is (transmission pulse frequency) / {(transmission pulse frequency) − (sampling pulse frequency)} = 2.4 MHz / 16 Hz = 150 × 10 ³ .

  The amplifier 37 is an amplifier circuit that amplifies the decompressed signal from the sampling hold circuit 36 and outputs the amplified signal to the ADC 38. The ADC (analog-to-digital converter) 38 is a conversion element that converts an analog signal into a digital signal, converts the expanded signal after amplification into digital data, and outputs the digital data to the CPU 39.

  The CPU 39 controls the display unit 11 and the signal output unit 41 based on the input signal from the operation unit 12, and measures the liquid level by analyzing the waveform of the extension signal. The display unit 11 displays a measurement value of the liquid level and a predetermined determination result based on the measurement value, for example, a determination result of whether or not the liquid level has reached a predetermined level. The signal output unit 41 is an output circuit for generating an output signal indicating a measurement value or a determination result and outputting the output signal to an external device.

The CPU39, as a difference ΔT between the pulse repetition period PT ₂ of the pulse repetition period PT ₁ and the sampling pulse SP transmitted pulse 4 is held constant, to control the pulse repetition period PT _2. Specifically, based on the repetition period PT extension signal, to control the pulse repetition period PT _2, the operation of adjusting the oscillation frequency of the local oscillator 34 is performed. The DAC (digital-analog converter) 40 is a conversion element that converts a digital signal into an analog signal, converts the VCO control signal from the CPU 39 into an analog signal, and outputs the analog signal to the local oscillator 34.

  The liquid level meter 1 generates a stretched signal obtained by time-stretching the input / output signal using the difference ΔT between the pulse repetition periods of the transmission pulse 4 and the sampling pulse SP. The distance L from the root portion 21 of the guide probe 20 to the liquid level 3 is obtained by obtaining the propagation time until the transmission pulse 4 returns as the reflected pulse 5 from the liquid level 3 based on such an extension signal. . The transmission pulse 4 is a signal repeatedly generated at a constant cycle, and the reflection pulse 5 by the liquid surface 3 is also a signal repeatedly generated at the same cycle as the transmission pulse 4.

<Transmission pulse 4 and reflection pulses 5 and 6>
FIG. 4 is a diagram illustrating an example of the waveform of the decompression signal in FIG. 3, in which the signal level changes with time. In the input / output unit 33, the transmission pulse 4, the reflected pulse 5 due to the liquid surface 3, and the reflected pulse 6 due to the root portion 21 are input / output. The transmission pulse 4 is repeatedly input to the input / output unit 33 at a constant pulse repetition period PT ₁ and is output to the guide probe 20 and the sampling hold circuit 36.

The transmission pulse 4 output to the sampling hold circuit 36 has an extremely small signal strength compared to the transmission pulse 4 output to the guide probe 20. On the other hand, the transmission pulse 4 output to the sampling hold circuit 36 has a sufficiently large signal strength compared to the reflection pulses 5 and 6. In this example, such a transmission pulse 4 is observed at times t ₁ and t ₄ . Peak level of the transmitted pulse 4 is a _1.

The tank mounting portion 14 of the guide probe 20 is configured by a coaxial structure called a probe housing. For this reason, the reflected pulse 6 is generated at the outlet of the tank mounting portion 14, that is, near the root portion 21. The reflected pulse 6 by the root portion 21 has the same signal level as that of the transmission pulse 4, and its signal intensity is smaller than that of the transmission pulse 4. In this example, such reflected pulse 6 is observed at time t _2.

When the liquid level 3 exists in the middle of the guide probe 20, the reflected pulse 5 is generated at the position of the liquid level 3. The reflected pulse 5 has a signal level opposite in polarity to that of the transmission pulse 4, and its signal intensity is smaller than that of the reflected pulse 6. If the position of the liquid surface 3 does not change dynamically, the reflected pulse 5 is repeatedly input / output at the input / output unit 33 at the same cycle as the transmission pulse 4. In this example, at time t _3, the peak level is observed reflected pulse 5 in a _2.

The transmission pulse 4 and the reflection pulse 5 in the stretched signal are identified by detecting the peak point from the waveform of the stretched signal and comparing the signal level at the peak point with the threshold values b ₁ and b ₂ . That is, the transmission pulse 4 is detected by comparing the signal level of the peak point with a predetermined threshold b _1. The reflected pulse 5 is detected by comparing the signal level at the peak point with a predetermined threshold value b ₂ having an absolute value smaller than the threshold value b ₁ .

  On the other hand, the reflected pulse 6 can be specified by the peak intensity, the pulse width, and the position on the time axis. For example, the reflected pulse 6 can be identified by estimating the position on the time axis of the reflected pulse 6 with respect to the transmission pulse 4 from the wiring length between the input / output unit 33 and the root portion 21.

  The position on the time axis of the reflection pulse 5 with respect to the transmission pulse 4 and the reflection pulse 6 is constant even if the type of the liquid to be measured is changed.

Therefore, for example, the distance L between the root portion 21 and the liquid surface 3 is obtained from the time interval TK ₁ between the reflected pulse 6 and the reflected pulse 5. This time interval TK ₁ corresponds to the propagation time from when the transmission pulse 4 is output from the root portion 21 to the liquid surface 3 until the reflected pulse 5 is input to the root portion 21, and the time interval between peak points. It is determined by _(t 3 -t _2). The distance L can be obtained by L = TK ₁ × (1 / r) × C × (1/2) using the expansion rate r. Here, the pulse repetition period PT ₁ multiplied by r is sufficiently longer than the time interval TK ₁ , so that the next transmission pulse 4 does not affect the detection of the reflected pulses 5 and 6.

  However, the distance L between the root portion 21 and the liquid surface 3 may be obtained based on the time interval between the transmission pulse 4 and the reflection pulse 5. In this case, the distance L is obtained from the difference between the time interval between the transmission pulse 4 and the reflected pulse 5 and the time length corresponding to the round trip time between the input / output unit 33 and the root unit 21.

Control of the pulse repetition period PT ₂ is performed based on the repetition period PT extension signal. For example, repetition period PT extension signal can be determined by determining the pulse repetition period PT ₁ of the transmitted pulse 4 by utilizing the waveform decompression signal.

  FIG. 5 is a diagram showing a comparison of examples of waveforms of the transmission pulse 4, the sampling pulse SP, and the extension signal generated in the liquid level meter 1 of FIG. (A) in the figure shows the waveform of the transmission pulse 4, (b) shows the waveform of the sampling pulse SP, and (c) shows the waveform of the expanded signal.

The transmission pulse 4 is a triangular wave having a pulse width PW ₁ and is formed for each pulse repetition period PT ₁ . For example, PW ₁ = 500 ps and PT ₁ = 416.7 ns. Sampling pulse SP, the pulse width is short rectangular wave than the transmit pulse 4, it is formed for each pulse repetition period PT _2. The pulse repetition period PT ₂ is PT ₂ = 416.7 ns + 2.8 ps, and the difference ΔT between the transmission pulse 4 and the pulse repetition period PT ₁ is ΔT = 2.8 ps.

The extended signal is formed by sampling such a transmission pulse 4 using a sampling pulse 5. If the transmission pulse 4 is extracted from the expansion signal, the transmission pulse 4 whose waveform is expanded in the time axis direction is obtained as compared with the transmission pulse 4 before expansion. The transmission pulse 4 has a pulse width PW ₂ expanded to 150 × 10 ³ times.

FIG. 6 is a diagram showing a waveform of the extension signal generated in the liquid level meter 1 of FIG. In this figure, the time scale on the horizontal axis is enlarged by 150 × 10 ³ times compared to FIG. Repetition period PT ₃ of the transmission pulse in stretching signal _is a PT 3 = 62.5 ms.

In liquid level gauge 1, by analyzing the waveform of the extension signal, determining the repetition period PT ₃ of the transmitted pulse 4. The repetition period PT _3, since corresponding to the difference ΔT between the pulse repetition period PT ₂ of the pulse repetition period PT ₁ and the sampling pulse SP of the transmitted pulse 4, so repetition period PT ₃ is constant The oscillation frequency of the local oscillator 34 is adjusted.

<CPU 39>
FIG. 7 is a block diagram showing an example of a functional configuration in the CPU 39 of FIG. The CPU 39 includes a pulse extraction unit 110, a liquid level measurement unit 120, and a pulse cycle control unit 130, and generates a liquid level measurement result and a VCO control signal based on the expansion signal.

  The pulse extraction unit 110 includes a peak point detection unit 111, a determination threshold storage unit 112, a peak intensity comparison unit 113, and a pulse determination unit 114, and extracts the transmission pulse 4 and the reflected pulse 5 from the stretched signal.

  The peak point detection unit 111 detects the peak point of the signal intensity based on the waveform of the extension signal, and outputs the detection result to the peak intensity comparison unit 113. By detecting the peak point, the influence of foreign matter and noise attached to the guide probe 20 can be ignored. The determination threshold storage unit 112 holds determination thresholds K1 and K2. The determination threshold value K1 is an intensity threshold value for identifying the transmission pulse 4. The determination threshold value K2 is an intensity threshold value for identifying the reflected pulse 5 by the liquid surface 3, and is smaller than the determination threshold value K1.

  The peak intensity comparison unit 113 compares the signal intensity at the peak point with the determination threshold values K1 and K2, and outputs the comparison result to the pulse determination unit 114. The pulse determination unit 114 determines whether the waveform including the peak point is the transmission pulse 4 or the reflection pulse 5 by the liquid level 3 based on the comparison result of the peak intensity, and the determination result is the liquid level. It outputs to the measurement part 120 and the pulse period control part 130.

  Specifically, a waveform including a peak point whose signal intensity is higher than the determination threshold value K <b> 1 is determined as the transmission pulse 4. Further, the waveform including the peak point whose signal intensity is equal to or lower than the determination threshold value K1 and higher than the determination threshold value K2 is determined as the reflected pulse 5.

The liquid level measuring unit 120 measures the liquid level based on the time interval TK ₂ between the transmission pulse 4 and the reflected pulse 5 extracted from the extension signal, and outputs the measurement result. Specifically, a time interval TK ₂ between the peak point of the transmission pulse 4 and the peak point of the reflected pulse 5 is obtained, and the liquid level is obtained from the time interval TK ₂ and the expansion rate r.

Pulse period control unit 130, based on the repetition period PT ₃ of the transmitted pulse 4 extracted from the stretched signal, generating a VCO control signal for controlling the difference ΔT of the pulse repetition period. Specifically, determine the repetition period of the peak point of the transmission pulse 4 as repetition period PT _3, the repetition period with a predetermined time threshold TH, based on the comparison result, the local oscillator 34 Control the voltage level.

  According to the present embodiment, it is possible to control the difference ΔT in the pulse repetition period without using a PLL circuit. Therefore, the difference ΔT in the pulse repetition period between the transmission pulse 4 and the sampling pulse SP can be kept constant without increasing the manufacturing cost and the circuit board mounting area.

Further, by using the transmission pulse 4 used to measure liquid level by obtaining the repetition period PT ₃ decompression signal, the stability when automatically adjusting the pulse repetition period PT ₂ of the sampling pulse SP Can be improved.

Embodiment 2. FIG.
In the first embodiment, the guide pulse type liquid level meter 1 that transmits a pulse signal along the guide probe 20 has been described. In contrast, in the present embodiment, a case will be described in which the present invention is applied to a radio wave type liquid level measuring device that transmits high-frequency pulses from an antenna.

  FIG. 8 is a block diagram showing an example of the configuration of a level meter according to Embodiment 2 of the present invention, in which a radio wave type liquid level meter 1 is shown. The liquid level meter 1 includes a high frequency generation circuit 50, a transmission pulse generation circuit 51, a gate circuit 52, a directional coupler 53, an antenna 54, a detection circuit 55, a sampling pulse generation circuit 56, a sampling hold circuit 57, an amplifier 58, An ADC 59, a CPU 60, an operation unit 61, a display unit 62, a signal output unit 63, and a DAC 64 are included.

  The configuration of the transmission pulse generation circuit 51, the sampling pulse generation circuit 56, the sampling hold circuit 57, the amplifier 58, the ADC 59, the CPU 60, the operation unit 61, the display unit 62, the signal output unit 63, and the DAC 64 is the liquid level meter 1 shown in FIG. It is the same.

The high frequency generation circuit 50 generates a carrier wave having a predetermined frequency and outputs it to the gate circuit 52. The transmission pulse generation circuit 51 generates a transmission pulse at a predetermined pulse repetition period PT ₁ and outputs it to the gate circuit 52. Based on the transmission pulse, the gate circuit 52 amplitude-modulates the carrier wave in a pulse shape to generate a transmission pulse composed of a high-frequency signal (burst wave) and outputs the transmission pulse to the directional coupler 53. This transmission pulse is a signal output in a relatively short period by amplitude control of the high-frequency signal.

  The directional coupler 53 is an input / output terminal that outputs the transmission pulse input from the gate circuit 52 to the antenna 54 and the detection circuit 55, and receives the reflected pulse from the antenna 54. The antenna 54 is a radiating element that transmits a transmission pulse toward the liquid surface and receives a reflected pulse from the liquid surface.

  The detection circuit 55 detects the input / output signal in the directional coupler 53 and outputs the input / output signal after detection to the sampling hold circuit 57. In the detection circuit 55, an envelope detection is performed on a transmission pulse and a reflection pulse made of a high-frequency signal. The sampling hold circuit 57 generates an expanded signal by sampling the input / output signal after detection based on the sampling pulse.

The CPU 60 measures the liquid level by analyzing the waveform of the extension signal. Further, CPU 60 is so that the difference ΔT between the pulse repetition period PT ₂ of the pulse repetition period PT ₁ and the sampling pulse SP transmitted pulse is kept constant, control the pulse repetition period PT ₂ of the sampling pulse SP To do.

  According to the present embodiment, a radio wave type liquid level capable of maintaining a constant pulse repetition period difference ΔT between a transmission pulse and a sampling pulse without increasing the manufacturing cost and the circuit board mounting area. A level measuring device can be realized.

In the first embodiment, based on the repetition period PT extension signal, an example has been described in the case of controlling the pulse repetition period PT ₂ of the sampling pulse SP, the present invention is limited to such a configuration It is not something. For example, based on the repetition period PT extension signal, and controls the pulse repetition period PT ₁ transmission pulse 4, or be configured so as to control both the pulse repetition period PT ₁ and PT ₂ good.

In the first embodiment, an example is described of a case of obtaining the repetition period PT ₃ peak points of the transmitted pulse 4 extracted from the extended signal as the repetition period PT extension signal, the present invention, the expansion signal The method for obtaining the repetition period PT is not limited to this. For example, the configuration may be such that the repetition period of the reflected pulse 5 extracted from the expansion signal is obtained as the expansion period PT of the expansion signal.

  Moreover, although Embodiment 1 and 2 demonstrated the liquid level meter 1 which measures a liquid level, this invention is applied to the whole level meter which measures interface levels, such as a liquid level and a powder surface. Can do.

  In the first and second embodiments, an example in which the transmission pulse is a pulse wave composed of a triangular wave or a burst wave and the sampling pulse is composed of a rectangular wave whose pulse width is shorter than the transmission pulse has been described. The invention does not limit the configuration of the transmission pulse and sampling pulse. For example, the transmission pulse and the sampling pulse may be pulse waves having the same shape and pulse width. Further, the transmission pulse and the sampling pulse are not limited to a triangular wave, a burst wave, or a rectangular wave, and may be a pulse wave having a shape such as a Gaussian distribution, for example.

DESCRIPTION OF SYMBOLS 1 Liquid level meter 10 Main body part 11 Display part 12 Operation part 13 Cable connection part 14 Tank attachment part 20 Guide probe 21 Root part 22 Tip part 31 Reference oscillator 32 Transmission pulse generation circuit 33 Input / output part 34 Local oscillator 35 Sampling pulse generation Circuit 36 Sampling hold circuit 37 Amplifier 38 ADC
39 CPU
40 DAC
41 Signal Output Unit 111 Peak Point Detection Unit 112 Determination Threshold Storage Unit 113 Peak Intensity Comparison Unit 114 Pulse Discrimination Unit 2 Storage Tank 3 Liquid Level 4 Transmission Pulse 5 Reflection Pulse

Claims (6)

In a level meter that measures the interface level of the liquid surface or powder surface,
Transmission pulse generating means for generating a transmission pulse at a first pulse repetition period;
An input / output unit that outputs the transmission pulse to the measurement element and receives a reflection pulse from the measurement element;
Sampling pulse generating means for generating a sampling pulse at a second pulse repetition period;
By sampling the input / output signal in the input / output unit according to the sampling pulse, an expanded signal is generated by time-expanding the input / output signal according to the difference between the first and second pulse repetition periods. Expansion signal generation means;
An interface level measuring means for measuring the interface level based on a propagation time of the reflected pulse;
A level meter comprising pulse period control means for controlling a difference between the first and second pulse repetition periods based on the repetition period of the expansion signal.   The level meter according to claim 1, wherein the pulse cycle control means controls one of the first and second pulse repetition cycles. Pulse extraction means for extracting the transmission pulse and the reflected pulse from the stretched signal;
The pulse period control means controls the difference between the first and second pulse repetition periods based on one of the transmission pulse and the reflected pulse extracted by the pulse extraction means. The level meter according to 1 or 2.   The measuring element comprises a conductive probe that transmits the transmission pulse input to one end to the other end, and generates the reflected pulse at the position of the interface. Level meter as described in. A detection means for detecting the input / output signal;
The measurement element includes an antenna that transmits the transmission pulse including a high-frequency signal toward the interface and receives the reflection pulse from the interface.
The level meter according to any one of claims 1 to 3, wherein the expansion signal generation means samples the input / output signal after detection. A control method of a level meter including an input / output unit that outputs a transmission pulse to a measurement element and receives a reflection pulse from the measurement element,
A transmission pulse generating step for generating a transmission pulse at a first pulse repetition period;
A sampling pulse generating step for generating a sampling pulse at a second pulse repetition period;
By sampling the input / output signal in the input / output unit according to the sampling pulse, an expanded signal is generated by time-expanding the input / output signal according to the difference between the first and second pulse repetition periods. A decompression signal generation step;
An interface level measuring step for measuring the interface level based on a propagation time of the reflected pulse;
A level meter control method comprising: a pulse period control step for controlling a difference between the first and second pulse repetition periods based on the repetition period of the expansion signal.

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