JPS6016594B2 - Ultrasonic time width measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention provides an ultrasonic distance measuring device, an ultrasonic position measuring device,
The present invention relates to an ultrasonic time width measuring device, such as an ultrasonic flowmeter, that measures the time width from transmitting an ultrasonic pulse to receiving the ultrasonic pulse.

For example, in an ultrasonic level meter, an ultrasonic pulse oscillator 12 is driven by a timing pulse from a timing circuit 11 as shown in FIG. It is excited and an ultrasonic pulse Ps is transmitted as shown in FIG. 2A.

This pulse is reflected by a wall surface, etc., and is transmitted to the transducer 14.
is received as a pulse Pr, and from this the transmission/reception switching circuit 1
3, and is amplified by an amplifier 15 and sent to the time width conversion circuit 1.
6. The time width conversion circuit 16 converts the ultrasonic pulse P
After the transmission of wave s, the output voltage increases linearly as shown in FIG. 2B, and upon reception of the reflected pulse Pr, the increase is stopped and maintained at that voltage. Therefore, a voltage with an amplitude E corresponding to the time width T from transmission to reception is output. This output voltage is sampled in the sample holding circuit 17 after receiving the reflected wave Pr and before the next transmission pulse Ps as shown in FIG. 2C, and the resulting voltage is held in the circuit 17. This holding voltage is indicated or transmitted to an indicator. In the sample holding circuit 17, as shown in FIG. 3, the output from the time width voltage conversion circuit 16 is supplied to the inverting input terminal of an amplifier 18, and the output is passed through a series circuit of resistors 19 and 21 to an amplifier 22 for an integrating circuit. is supplied to the inverting input terminal of

A capacitor 23 is connected between the input and output terminals of this amplifier 22, and its output terminal is feedback-connected to the non-inverting input terminal of the amplifier 18. The connection point of resistors 19 and 21 is switch 24
connected to a common potential point through. An amplifier 22 and a capacitor 23 constitute an integrating circuit 25. A time point t at which this input signal, that is, the output of the time width conversion circuit 16 is sampled.
The switch 24 is turned off at S, and the output of the integration circuit 25 and the output E of the time width voltage conversion circuit 16 at this time are compared, and a positive or negative output is sent to the output side of the amplifier 18 depending on the magnitude. is generated, which is integrated by the integrating circuit 25,
It operates so that this integrated output approaches the input voltage E. The switch 24 is turned off only when sampling the input voltage E, and then turned on. Therefore, the output voltage of the integrating circuit 25 is maintained. In this case, the switch 24 is turned off every time there is a reflected wave so that the output does not change significantly even if the switch 24 is operated by mistaking the noise for the reflected wave Pr.
The time constant of the integrating circuit 25 is selected to be relatively large so that the reflected wave is received multiple times, that is, E, is compared multiple times with the output of the integrating circuit 25 so that they match, and this is caused by noise. switch 24 is turned off once;
Even if a significantly different output from the time-width voltage conversion circuit 16 is applied to the sample holding circuit 17 before reaching the actual measurement level, the output of the circuit 17 is prevented from changing significantly.

In such conventional devices, when the reflected wave is not received for a long time, the switch 24 remains on.
However, it is difficult to set the connection point between the resistors 19 and 21 to zero potential using the switch 24, and the amplifier 1
Since there is an offset voltage at 8, a small voltage is applied to the integrating circuit 25, and this is gradually integrated, causing the output to drift.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ultrasonic time width measuring device that can hold measured values even if there is no received wave for a long time.

First, the principle of this invention will be explained.

That is, as shown in FIG. 4, the ultrasonic oscillator 12 is driven by a trigger pulse from the timing generation circuit 11, which drives the transducer 13a to emit an ultrasonic pulse.
The reflected wave is received by the receiver 13b and amplified and detected by the receiving circuit 27. That is, the ultrasonic oscillator is driven by the trigger pulse shown in FIG. 5A, and the transmitting pulse Ps is transmitted from the transducer 13a.The counter 28 is reset by the trigger pulse, and at the same time, the flip-flop 29 is set. As shown in FIG. 5C, the output of the flip-flop 29 becomes high level, thereby opening the gate 31, and the clock pulse from the terminal 32 of the gate 31 is supplied to the counter 28 and counted. When the reflected pulse Pr is received as shown in FIG. will be stopped.

Furthermore, when the output of the flip-flop 29 becomes low level, the latch pulse generation circuit 33 is driven, and from this the fifth
A latch pulse as shown in FIG. D is obtained, and the counted contents of the counter 28 are latched by the latch circuit 34'. The output of this latch circuit 34 is sent to a DA converter 35.
The signal is converted into an analog signal at the step E, and an output as shown in FIG. 5E is obtained. According to such a configuration, a constant clock is counted by the counter 28 from the time the pulse is transmitted to the time the pulse is received, and therefore, the counter 28 obtains a count value corresponding to the time width from the time the pulse is transmitted to the time the pulse is received. , this is latched by the latch circuit 34, further converted into an analog signal and output.

Therefore, even if the reflected wave is not received for a long time for some reason, the contents of the counter 28 will not be transferred to the latch circuit 34, and the contents of the latch circuit 34 will be a digital signal. , are held unchanged, and therefore the output of the DA converter 35 also does not change, that is, there is no output drift. If a so-called integration type converter that multiplies the reference voltage by the input digital number is used as the digital-to-analog converter 35, temperature compensation can be performed by changing the reference voltage depending on the ambient temperature.

If an edge trigger type latch circuit is used as the latch circuit 34, the latch pulse generating circuit 33 may be omitted and the output of the flip-flop 29 may be supplied to the input terminal of the latch circuit 34. The accuracy of measurement can be improved by using a clock at the clock terminal 32 with a precise period, but it is also possible to use a voltage-controlled oscillator as the clock oscillator and to change the control voltage depending on the ambient temperature to compensate for the temperature. be. In the above, counter 2
8 was operated to count from 0 every time a pulse was transmitted. For example, when measuring the depth of a liquid level, the count value at the deepest point corresponding to the highest level is shown in Figure 6.
Settings are made in the setting circuit 36 as shown by assigning the same reference numerals to parts corresponding to those shown in the figure, and prior to transmitting the pulse, the counter 28 is preset to the setting value of the setting circuit 36, and the gate 31 is opened. At the same time, a signal from terminal 32 is applied.

It is sufficient to subtract the value of the counter 28 from its set value for each check pulse, that is, to count down. Although the transmitter and the receiver are shown separately in FIGS. 4 and 6, they may be used in combination as shown in FIG.

In this way, according to the configurations of FIGS. 4 and 6, complete holding without output drift can be performed. However, when these time width measurement devices receive noise instead of reflected waves, the influence directly appears.

That is, for example, as shown in Fig. 7, even if the output is curve 37 when the correct reflected wave is received and should be operated, if the latching operation is performed due to noise before the reflected wave is received. That is, if the noise is made into a reflected wave, the level of the curve 38 is significantly lower than the level of the curve 37, and this appears as the directly assisted measurement output. From this point of view, the present invention provides an ultrasonic time width measurement device that has no output drift and is not easily affected by noise. After counting, the count value is latched into a latch circuit, but without converting the latched value directly into an analog signal, the output of the up-down counter and the content of the latch circuit are compared, and if the value is larger, The contents of the up-down counter are corrected so that the contents of the up-down counter match the contents of the latch circuit by counting up or down the up-down counter with a clock slower than the clock that counts the counter depending on whether the up-down counter is small or not.

The speed of correction is made slower than the period of transmission and reception of ultrasonic pulses, and is set to such a speed that correction can only be achieved by receiving waves at least a plurality of times. Check out the contents of that up/down counter. convert it into a digital signal. For example, as shown in FIG. 8, the counter 28 counts clocks from the terminal 32 using the configuration shown in FIG. 4 or 6. The contents of counter 28 are latched into latch circuit 34 in the same manner as described above. In the present invention, the contents of the latch circuit 34 are supplied to a comparator 41 and an up/down counter 42.
The contents of If the content of the latch circuit 34 is greater than the content of the up/down counter 42, an output is generated at the terminal 43, if it is smaller, an output is generated at the terminal 44, and if they match, an output is generated at the terminal 45. The output from the terminal 43 puts the up/down counter 42 into an up-counting state, and the output from the terminal 44 puts it into a down-counting state. The inverted signal of the output of the terminal 45 is applied to the gate 46, and the gate 46 is also provided with information from the terminal 47 indicating that the flip-flop 29 shown in FIG. A clock slower than 32 clocks is combined. Therefore, latch circuit 3
When the content latched at 4 is greater than the content of the up/down counter 42, the gate 46 opens and the up/down counter 42 counts up the second clock from the terminal 48 until the content is close to the content of the latch circuit 34. It works like crazy.

Conversely, if the content of the latch circuit 34 is small, the up/down counter 42 counts down to approach the content of the latch circuit. If both contents are equal, no clock is supplied to the up/down counter 42, and the previous contents are held. Therefore, the up/down counter 42
When the contents of the latch circuit 34 become equal to the contents of the latch circuit 34, that state is held, and this is converted into an analog signal by the DA converter 35. By the way, the clock supplied to the terminal 48 is the first clock of the terminal 32.

Therefore, even if the latch circuit 34 is latched due to miscellaneous temperatures and the difference between the contents of the up-down counter 42 and the contents of the up-down counter 42 becomes large, the up-down counter based on that single latch will The correction effect on 42 is slight, and the clock at terminal 48 is selected so that the contents of up/down counter 42 match the contents of up/down counter 42 only after the contents of latch circuit 34 have been rewritten at least multiple times. Therefore, even if the latch circuit 34 is latched due to noise, the output will not change significantly, and generally a correct received wave will be obtained next time, so malfunctions due to noise will be slight. Since the contents of the up-down counter 42 are slow to follow the latch circuit 34 in this way, it takes a considerable amount of time for the contents of the up-down counter 42 to reach the correct measured value in the initial state.

Therefore, in order to avoid this, for example, as shown in FIG. 8, a clock generator 49 that generates a relatively fast clock is provided.
This world power is directly supplied to the terminal 48 through the changeover switch 51, and the output of the clock generator 49 is supplied to the frequency dividing circuit 52.
The divided output is supplied to the terminal 48 through the switch 51, and when the power switch is turned on, that is, when this device starts operating, the switch 51 is
connects terminal 48 directly to clock pulse generator 49;
A distant clock can be supplied to the gate 46, and after a certain period of time, the switch 51 is switched to the frequency divider circuit 52 side so that a slow clock can be supplied to the gate 46. Even in the analog sample holding circuit shown in FIG. 3, tracking performance is poor in the initial stage of operation. Therefore, in order to quickly track this, for example, the time constant of the integrating circuit 25 must be changed, or in other words, the capacitor 23 must be changed to one with a smaller capacitance. Therefore, it is difficult to perform such switching without contact, but in the present invention, it can be easily performed by digital processing.

Incidentally, in order to correct the up/down counter 42 by a certain amount with one reflected pulse, for example, a latch circuit 34 is used.
Each time the gate 46 is latched, a pulse of a fixed width of a fixed time is generated after the latch, thereby opening the gate 46. In the above, the present invention is applied to an ultrasonic level meter, but it is not limited to an ultrasonic level meter, but can also be applied to, for example, an ultrasonic distance device, a position measuring device, or even a format that receives a transmitted pulse and sends out a response pulse as a reflected pulse. In addition to reflected pulses, various types of ultrasonic waves can be used to measure time, such as ultrasonic flowmeters that emit oblique ultrasonic waves toward a flow path and receive them on the opposite side to measure the flow velocity. The present invention can be applied to a device for measuring width.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an ultrasonic level meter, Fig. 2 is a waveform diagram for explaining its operation, Fig. 3 is a connection diagram showing a conventional sample holding circuit, and Fig. 4 is a supersonic level meter according to the present invention. A block diagram showing an ultrasonic level meter applied to a time width measurement circuit of a sonic level meter, FIG. 5 is a waveform diagram for explaining its operation, and FIG. 6 is a block diagram showing a modification of FIG. 4. FIG. 7 is a curve diagram for explaining the influence of noise on the output in FIGS. 4 and 6, and FIG. 8 is a diagram showing an example of an ultrasonic time width measuring device according to the present invention. This is a diagram. 24: counter, 32: clock input terminal, 34: latch circuit, 35: DA converter, 42: up/down counter, 43: comparator, 48: second clock input terminal. Figure 1 Figure 2 Figure 3 Figure 7 Figure 4 Figure 5 Figure 6 Figure 8

Claims (1)

[Claims] 1 Set or preset before transmitting the transmit pulse,
A counter that counts the first clock from the transmission of the transmission pulse to the reception of the reflected pulse; a latch circuit in which the contents of the counter are transferred each time the pulse is transmitted; an up-down counter into which a predetermined count is loaded; a comparator that compares the contents of the latch circuit with the contents of the up-down counter; and a comparator that compares the contents of the latch circuit with the contents of the up-down counter; During the time until the next pulse transmission, the second clock, which is slower than the first clock,
a correction means for counting up or down using a clock so that the up-down counter approaches the content of the latch circuit; a DA converter that converts the content of the up-down counter into an analog signal; and a DA converter that converts the content of the up-down counter into an analog signal; A time width measuring device using ultrasonic waves, comprising a stopping means for stopping the operation of the correcting means when the content of the circuit matches the content of the circuit.