JPH0436405Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to the improvement of an ultrasonic propagation time detection circuit device suitable for use in, for example, an ultrasonic flowmeter. )
This will be explained using an example of an ultrasonic flowmeter known as a method.

[Prior art and its problems]

The ultrasonic propagation time detection circuit device using the TLL method is disclosed in detail in Fuji Jiho, Vol. 48, No. 2, pages 29 to 38, published by the applicant in 1975. FIG. 1 is a block diagram showing the principle of an ultrasonic propagation time detection circuit using the TLL method published in the Fuji Jiho. In the figure, 1 is a receiving circuit, 2 is a counter, 3 is a time difference detection circuit, 4 is a voltage controlled oscillator (VCO), and 5
1 is a synchronization generating circuit, 6 is a transmitting circuit, and 8a and 8b are each a vibrator.

Next, the circuit operation will be explained. The transmitting side transducer 8a driven by the transmitting circuit 6 sends out ultrasonic pulses into the measurement medium. The receiving side transducer 8b receives the ultrasonic pulse and sends the received output to the receiving circuit 1. On the other hand, the synchronization generating circuit 5 generates a start pulse in synchronization with the pulse output from the oscillator 4 to start the transmitting circuit 6 and also starts the counter 2.

The counter 2 is configured to send a count end signal to the time difference detection circuit 3 after counting N pulses with a repetition frequency from the oscillator 4. N is an appropriately chosen integer.

The time difference detection circuit 3 receives a timing signal from the receiving circuit 1 when the ultrasonic pulse has finished propagating through the measurement medium from the transmitting side transducer 8a to the receiving side transducer 8b, and receives a pulse with a repetition frequency from the counter 2. A counting operation end signal indicating that N counts have been completed is given. Then, the time difference detection circuit 3 converts the time difference between the timing signal (propagation end signal) sent out from the receiving circuit 1 and the counting operation end signal sent out from the counter 2 into a voltage value proportional to this, and this voltage value is The repetition frequency of the oscillator 4 is controlled to a predetermined value, for example approximately zero. That is, the time difference detection circuit 3 equivalently compares the time t required for propagation and the time N/ required for counting, and controls the oscillator 4 so that the time difference (t-N/) becomes a predetermined value, for example, zero. Control repetition frequency. As a result, the relationship t=N/ is established, and when this is transformed, it becomes =N/t, so the output frequency of the oscillator 4 is used to extract the value N times the reciprocal of the propagation time of the ultrasonic pulse, 1/t. I can do it.

Next, the receiving side vibrator 8b is set as a transmitting side vibrator,
Using the transmitting-side transducer 8a as the receiving-side transducer, an ultrasonic pulse is propagated in the measurement medium in the opposite direction, and the same operation is performed to determine the output frequency of the oscillator 4.

The two output frequency values from the oscillator 4 obtained in this way are used to determine the flow rate related to the ultrasonic propagation direction of the measurement medium, which is the principle of the TLL type ultrasonic flowmeter. Since the details are not directly related to the present invention, further explanation will be omitted (if you want to know the details, please refer to
101569, JP-A-54-149669, etc.).

Figure 2 is a block diagram showing a TLL type ultrasonic flowmeter including a conventional ultrasonic propagation time detection circuit device.
FIG. 2A is a circuit diagram showing details of the time difference detection circuit 3 in FIG. 2.

In these figures, the same elements as in FIG. 1 are given the same reference numerals. In addition, 7 is a timing generation circuit, S _1a and S _1b are sampling contacts, S _2a , S _2b , S _4a and S _4b are switching contacts, and S ₃ is a synchronization start contact.

The timing generation circuit 7 is made up of, for example, four flip-flops (FF) connected in cascade.
Timing pulse A is generated from the Q output of the FF in the second stage, and timing pulse B is generated from the Q output of the FF in the second stage.
The timing pulse C is output from the Q output of the third stage FF.
Timing pulses D are each taken out from the Q output of the final stage FF.

FIG. 3 is a timing chart of various signals in the circuits of FIGS. 2 and 2A.

An outline of the circuit operation will be explained with reference to FIGS. 2 and 3.

In FIG. 2, switching contacts S _4a , S _4b and switching contact S ₂ are at the solid line position when timing pulse D is L (low), and when timing pulse D is H
(high), it is assumed to be at the broken line position. However,
Now, timing pulses A to D are all L (low)
At timing t ₁ , the synchronization generation circuit 5
causes the transmission circuit 6 to send out a transmission pulse I and closes the start contact _S3 .

Therefore, ultrasonic pulses are sent out from the transmitting side transducer 8a and received by the receiving side transducer 8b. As a result, the receiving circuit 1 generates a received wave output RO at timing t ₂ and sends it to the time difference detection circuit 3 . On the other hand, the counter 2 counts N output pulses from the oscillator 4a, and when the count is finished, the count end signal C, which had been set to H (high) at a timing a while before, is changed to L, and the time difference detection circuit 3 to notify the end of the count.

Please refer to FIG. 2A, which is a circuit diagram showing details of the time difference detection circuit 3. The NAND gate changes its output level to L according to the received wave output L received at timing _t2 , and turns off the transistor T _r . Therefore, the current I that had been flowing from the constant current source through the transistor T _r flows into the capacitor C _p through the diode D _i , and the voltage across the capacitor C _p gradually increases.

Next, the NAND gate, at timing t ₃ ,
When it is detected that the count end signal C changes from H to L due to the end of counting, the output is changed to H and the transistor T _r is turned on. Therefore, current I flows through transistor T _r and capacitor C _p
Charging stops and lamp output d occurs. The magnitude ΔR of this lamp output is determined by the time difference (t- This is an output corresponding to N/).

Next, during a period (sampling period) t ₄ in which timing pulses A and D are L and timing pulses B and C are H (sampling period), the sampling contact S _1a closes, and the oscillator 4a oscillates so that the magnitude of the lamp output ΔR becomes zero. Control frequency ₁ .

Next, when timing pulse D becomes H (high),
Switching contacts S _4a , S _4b and switching contact S ₂ are switched from the solid line position to the dashed line position. Then, at timing _t5 when the timing pulse D changes from L to H, the synchronization generating circuit 5 sends out a transmission pulse I,
Then, the start contact _S3 is closed, and the switch SW shown in FIG. 2A is also closed momentarily to discharge the capacitor _Cp .

As a result, the receiving side transducer 8b now becomes the receiving side, the oscillating side transducer 8a becomes the receiving side, and the propagation direction of the ultrasonic pulse is reversed. Thereafter, in the same manner, the sampling contact S _1b is closed in the next sampling period t ₅ and the oscillation frequency ₂ of the oscillator 4b is controlled so that the magnitude of the lamp output becomes zero.
In this way, the oscillation frequency of the oscillators 4a and 4b
The difference Δ between ₁ and ₂ is detected by the frequency difference detection circuit 9,
Then, a calculation circuit (not shown) calculates the flow rate from the difference Δ between the two frequencies according to a well-known calculation formula.

The outline of the operation of a flowmeter including a conventional ultrasonic propagation time detection circuit device has been described above. The problem here is
The sampling periods _t4 , _t5 , etc. are selected at fixed timings determined by the combination of each logical value of timings A to D, and the received wave output from the receiving circuit 1 and the count end signal from the counter 2 are In connection with the fact that there is no direct interlocking relationship,
This is because an error occurs in the measured value of flow rate.

This problem will be specifically explained below with reference to FIG.

In FIG. 4, α represents the lamp output waveform during the first measurement, and β represents the lamp output waveform during the second measurement.

The lamp output waveform (the voltage waveform generated across the capacitor C _p in FIG. 2A) should originally maintain its highest level M, but in reality, the leakage current in the diode D _i in FIG. 2A, The level decreases over time due to other circumstances.
In FIG. 4, it is exaggerated in order to clearly show how it decreases.

When the first lamp output waveform α reaches its highest level M and the second lamp output waveform β
When they reach the same highest level M (in reality, the highest level is usually different for the first and second time, but here it is assumed to be the same for the sake of clarity), the fixed Assume that there is a time difference of ΔT when looking at the sampling time t _s with a timing phase of . Then, at sampling time t _s , the first lamp output waveform α is sampled at a level that is lower than the highest level M by ΔL ₂ , whereas the second lamp output waveform β is sampled at a level that is lower than the highest level M by ΔL ₁ . sampled at the specified level.

As is clear from FIG. 4, since ΔL ₁ = /ΔL ₂ , originally the same size M should be sampled for α and β, but (M−ΔL ₂ ) and (M−
Different sizes of ΔL ₁ ) will be sampled, and this will affect the measurement frequency as an error.

[Purpose of invention]

The present invention was made in order to solve the problems of the prior art as described above, and the purpose of the present invention is to solve the problems caused by the fact that the sampling point of the output of the time difference detection circuit has a fixed timing phase. An object of the present invention is to provide an ultrasonic propagation time detection circuit device that can eliminate measurement errors caused by the ultrasonic propagation time detection circuit device.

[Key points of the idea]

The key point of the present invention is that the sampling point of the output of the time difference detection circuit is not determined based on a fixed timing phase, but is determined based on the point in time when the lamp output waveform reaches the highest level. If the time point at which the value reaches the highest level fluctuates (as in α and β in FIG. 4), the difference is determined based on the time point at which the fluctuation occurs.

[Example of idea]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 5 is a block diagram showing a first embodiment of the present invention. The embodiment shown in the figure is essentially different from the conventional circuit shown in FIG. Sampling contact S _1a or S _1b is set after a certain period of time ΔT _s (the certain period of time ΔT _s may be zero) based on the timing t ₃ of lamp output 2 in the figure.
The point is that sampling is performed by closing the .

That is, the sampling time setting circuit 10 is
As shown in FIG. 5A, the ΔT _s delay circuit 11 receives the count end signal from the counter 2 and transmits an output signal after a certain period of time ΔT _s (this certain period of time ΔT _s may be zero), and this ΔT _s A monostable multivibrator (MMV) that receives the output signal of the delay circuit 11 and generates a sampling pulse with a predetermined time width.
For example, it is composed of 12. The output signal of the monostable multivibrator 12, that is, the output signal E of the sampling time setting circuit 10, is guided to AND circuits A1 and A2. AND circuit A
A negation signal of the sampling pulse D and a sampling pulse D are introduced to the other input terminals of the input terminals 1 and A2, respectively. The negation signal can be formed by inverting the sampling pulse D, for example by an inverter, or can be taken from the output of the final flip-flop of the timing generation circuit 7.

Therefore, the sampling contacts S _1a and S _1b are selected by the sampling pulse D and its negative signal, and the sampling time setting circuit 10
The ON time of the selected sampling contacts S _1a and S _1b is determined by the occurrence of the output signal E of .

FIG. 6 shows the relationship between the lamp output waveform and the sampling time point when the present invention is implemented. That is, as seen in the figure, when the present invention is implemented, the first lamp output waveform α reaches the highest level M
Timing tα after a certain period of time ΔT _s after reaching .
is taken as the sampling time, and thereafter a predetermined time determined by the monostable multivibrator 12 is taken as the sampling period, and the timing is also a certain period of time ΔT _s after the second lamp output waveform β reaches the highest level M. Since tβ is taken as the sampling time and a predetermined time thereafter similarly determined by the monostable multivibrator 12 is taken as the sampling period, the amount of decrease in α from the highest level M, ΔL ₂ , and the amount of decrease in β, ΔL ₁ , are equal. , so it will be observed that no measurement error occurs.

FIG. 7 is a block diagram of a second embodiment of the present invention. The difference between the second embodiment and the first embodiment is that a delay circuit 13 is provided at the subsequent stage of the counter 2 to delay the output signal of the counter 2, that is, the count end signal C, by a predetermined time τ. is led to the sampling time setting circuit 10.

The idea of providing the delay circuit 13 after the counter 2 is also disclosed in the Fuji Times mentioned at the beginning. In this case, sampling time setting circuit 1
The delay time ΔT _s ′ of the delay circuit 11 constituting 0 is set so that ΔT _s ′=ΔT _s +τ.

FIG. 8 is a block diagram of a third embodiment of the present invention. The third embodiment differs from the first embodiment in that the output signal LO of the receiving circuit 1 is guided to the sampling time setting circuit 10. Therefore, in this case, the delay time ΔT _s ″ of the delay circuit 10 constituting the sampling time setting circuit 10 is not shorter than the time difference detected by the time difference detection circuit 3, which is empirically predicted. It is set as follows.

In addition, in the embodiment shown in FIG. 5, the delay time ΔT _s
When is set to zero, the delay circuit 11 in FIG. 5A can be omitted.

[Effect of idea]

As explained above, according to the present invention, in an ultrasonic propagation time detection circuit device, it is possible to eliminate the measurement error that conventionally occurs due to the fact that the sampling point of the output of the time difference detection circuit has a fixed timing phase. There is an advantage.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the principle of an ultrasonic propagation time detection circuit using the TLL method, Fig. 2 is a block diagram showing a TLL method ultrasonic flowmeter including a conventional ultrasonic propagation time detection circuit device, and Fig. 2A is a block diagram showing the principle of an ultrasonic propagation time detection circuit using the TLL method. FIG. 2 is a block diagram showing details of the time difference detection circuit 3, FIG. 3 is a timing chart of various signals in FIG. 2, FIG. 4 is a lamp output waveform diagram for explaining problems in the prior art, and FIG. The figure is a block diagram showing the first embodiment of the present invention, Figure 5A is a block diagram showing an example of the configuration of its main parts, and Figure 6 is the relationship between the lamp output waveform and the sampling time when the present invention is implemented. Explanatory diagram showing 7th
8 and 8 show the second and third embodiments of the present invention.
FIG. 2 is a block diagram of an embodiment. Explanation of symbols, 1... Receiving circuit, 2... Counter, 3... Time difference detection circuit, 4... Voltage controlled oscillator (VCO), 5... Synchronization generation circuit, 6... Transmission circuit, 7... Timing generation Circuit, 8a, 8b...
Oscillator, 9... Frequency difference detection circuit, 10... Sampling time setting circuit, 11... Delay circuit, 12
...Monostable multivibrator, A1, A2...
AND circuit.

Claims (1)

[Claims for Utility Model Registration] When the counter counts the oscillation output of the oscillator until it reaches a set value, a counting operation end signal outputted from the counter causes a transmitting circuit driven in synchronization with the counter to A propagation end signal output from the receiving circuit when the ultrasonic wave emitted from the sonic transducer propagates through the measurement medium and reaches the ultrasonic transducer on the receiving circuit side is input, and the counting operation end signal is inputted. and converting the time difference between the propagation end signal into a voltage signal proportional to this, sampling the voltage signal, and controlling the oscillation frequency of the oscillator so that this sample value (voltage value) becomes a predetermined value,
The circuit device for detecting the propagation time of the ultrasonic wave from the oscillation frequency of the oscillator, further comprising means for determining the timing of sampling the voltage signal based on the counting end time of the counter or the propagation end time of the ultrasonic wave. An ultrasonic propagation time detection circuit device characterized by: