JPS5946512A - Ultrasonic wave flowmeter - Google Patents

Abstract

PURPOSE:To operate VCOs in a correct region all the time and to expand a measuring range, by combining an operating point detecting means for the VCOs and a variable frequency dividing device. CONSTITUTION:A control voltage, which is supplied to VCOs 1a and 1b, is converted from the analog value to the digital value by a means 23, which detects the operating points of the VCOs 1a and 1b. The result is supplied to a control means 20, which changes the frequency dividing ratio of a variable frequency dividing device 17'. When the means 20 detects the fact that the operating point of the VCO 1a or 1b is deviated from the correct region, a preset command signal P is generated. Then, the digital value, which is imparted to a preset input terminal 24 of the variable frequency dividing device 17' from a decoder 20a, is preset, and the frequency dividing ratio of the frequency dividing device 17' is variably controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic flowmeter, and more particularly, it is an object of the present invention to provide an ultrasonic flowmeter that does not require adjustment during installation or even when the properties of the fluid change.

Various methods have been proposed for ultrasonic flowmeters, but they can be broadly classified into sing-around methods and methods using phase lock-loose.

<Disadvantages of the sing-around method> As is well-known, the sing-around method propagates ultrasonic waves from one to the other and from the other between a pair of ultrasonic transusers that are installed diagonally opposite to the flow path. This method oscillates at a period equal to time and determines the flow velocity of the fluid to be measured from the difference in the oscillation frequency.

This system has the disadvantage that if a piece of dirt or foxtail that blocks the ultrasonic waves passes between a pair of ultrasonic transducers, the sing-around oscillation will stop, making measurement impossible.

The sing-around oscillation frequency f is as follows: C: velocity of sound in the fluid, ■=flow velocity of the fluid to be measured, D: diameter of the two channels, θ: angle of incidence of the ultrasonic wave with respect to the channel.

Here, C = 1450 m/sec, v = 1 tn/sec,
When D = 50 and θ-22°, the difference between the sing-around oscillation frequency when the ultrasonic wave is propagated in the forward direction of the flow and the sing-around oscillation frequency when the ultrasonic wave is propagated in the opposite direction. Δf becomes Δf−0, 1.4 Hz. In order to set the resolution of flow velocity measurement to 1 m/sec, a measurement time of about 14 seconds or more is required to obtain the frequency difference Δf. Therefore, it also has the disadvantage of poor response.

The single-around method has the drawbacks mentioned above, so a method using a phase-locked loop% type % <Conventional technology using a phase-locked loop> Figure 1 shows a conventional ultrasonic flowmeter using a phase-locked loop show. Figure 1. a, Ibi are voltage controlled oscillators (hereinafter referred to as vCO)
). The outputs of vCOla and lb are selectively supplied to the synchronization circuit 2 by the switch SWI. The synchronization circuit 2 intermittently outputs an oscillation signal at regular time intervals in synchronization with the oscillation signal of vCO1a or 1dlb. The oscillation signal of VCOla or 1b taken out from the synchronous circuit 2 is supplied to the input terminal 4 of the ultrasonic propagation path 3. Ultrasonic propagation path 3
Originally, it is thought that should refer only to the part that propagates in the fluid to be measured flowing through the flow path 5, but in this case, the excitation amplifier 6, the switching circuit 7, and the part that is diagonally opposed to the flow path 5 The pair of ultrasonic transducers 8 and 9 and the amplifier 11 that amplifies the received signal are collectively referred to as an ultrasonic propagation path. Therefore, 4 is the input terminal of this ultrasonic propagation path 3, and 13 is the output terminal of the ultrasonic propagation path 3.

The switching circuit 7 performs a switching operation so that the ultrasonic transducers 8 and 9 are operated alternately as a wave transmitter and a wave receiver. This switching allows the ultrasonic waves to move in the fluid flow direction (
The state of propagation is switched between a forward direction and a reverse direction with respect to the direction of arrow 12).

This switching control is performed by a control signal from measurement control means 14, which will be described later.

The ultrasonic waves propagating through the fluid to be measured and received by one or the other ultrasonic transducer 8 or 9 are transmitted to an amplifier 11.
The signal is amplified and sent to the output terminal 13. A reception timing detection circuit 15 is connected to the output terminal 13, and detects when the reception signal reaches a predetermined level to define the reception timing.

This reception timing signal is supplied to one input terminal 16a of the time difference voltage conversion circuit 16.

The other input terminal 16b of the time difference voltage conversion circuit 16 is supplied with a frequency-divided signal obtained by dividing the oscillation signal of VCOla or 1b by 1/N from the frequency divider 17. This frequency divider 17 can be constituted by a counter, for example, and starts frequency dividing operation in synchronization with the rising edge of the synchronous output signal of the synchronous circuit 2. vc
If the oscillation frequencies of o, ta and 1b are fa and fb,
The frequency-divided output signal Sf is output after time N/f a or N/fb.

The time from when the oscillation signal of VCOla or 1b is applied to the input terminal 4 of the ultrasonic propagation path 3 until the signal is output to the output terminal 13 is as follows. Therefore, the time differences ΔTa and ΔTb between the two signals supplied to the time difference voltage conversion circuit 16 are as follows.

The time difference voltage conversion circuit 16 converts this time difference ΔTa.

ΔT+) is generated, and this voltage is alternately supplied to the sample and hold circuits 18a and 18b through the switch SW2.
8b is the sample hold 1 ~ voltage and pressure integration circuit 19
a, ], 9b, and the integral output gives V
Controls the oscillation frequency of COla, ], b.

The switches SW+ and SW2 are switched by the control circuit 20 in conjunction with the switching operation of the switching circuit 7. The oscillation frequencies fa and fl of VCOla and 1b) are such that the time differences ΔTa and ΔTb between the frequency-divided output signal Sf output from the frequency divider 17 and the signal passed through the ultrasonic propagation path 3 are predetermined values, for example, zero. controlled as follows. Therefore, if VCOla is connected to the circuit when, for example, ultrasonic waves propagate in the forward direction with respect to the flow direction 12, its oscillation frequency fa will be (N is the frequency division number of the frequency divider 17). . Further, assuming that VCOlb is connected to the circuit when the ultrasonic wave propagates in the opposite direction to the flow direction 12, its oscillation frequency fb increases.

These oscillation frequencies fa and fb are determined by the sample and hold circuit 18.
a, 18b and integration circuits 19a, 19b, and the flow velocity V is obtained from the difference between the frequencies fa and fb.

The oscillation signals of VCOla and Ib are input to the counter 2], and the difference between them can be determined by alternately counting up and down the frequency of VC01,a and 1-b in the counter 21. From the value, the flow velocity V is determined by the calculator 22.

Instead of the counter 21, a cross-modulation circuit that extracts the beats of fa and fb may be used.

<Conventional disadvantages> According to the conventional ultrasonic flowmeter shown in Fig. 1, the propagation time of the ultrasonic signal passing through the ultrasonic propagation path 3 is determined by the flow path length and the ultrasonic wave, as can be seen from the second equation. It changes depending on the incident angle θ of the sound wave and the sound velocity V in the fluid. Therefore, the propagation time of the ultrasonic waves in the ultrasonic propagation path 3 differs greatly between ultrasonic flowmeters with different diameters.

On the other hand, the control range of VCOla and lb is limited,
Generally speaking, when the center frequency is fO, it is about 10-10% of the center frequency fo. If the propagation time of the ultrasonic propagation path 3 differs greatly depending on the ultrasonic flow meter due to differences in diameter or properties of the fluid, the frequency division ratio of the frequency divider 17 is adjusted to 1/N, and each ultrasonic flow rate is VCOla, lb for each total
must be adjusted so that it operates in the appropriate range. Therefore, conventionally, the division ratio of the frequency divider 17 is set for each ultrasonic flowmeter when it is installed, so that C01a and C01b operate in appropriate ranges. VCO center frequency value fO
It is given in free.

On the other hand, if the temperature of the fluid changes significantly during flow rate measurement,
Alternatively, when the properties of the fluid change, the sound speed V changes significantly. Therefore, in such a case as well, there is a risk that VCOla and lb may deviate from the control range and become unmeasurable.

<Objective of the Invention> The present invention aims to provide an ultrasonic flowmeter having a function of automatically adjusting the frequency division ratio of the frequency divider 17 so that the VCO always operates at a proper operating point.

<Summary of the Invention> In this invention, a means for detecting the operation of the VCO is provided, the frequency divider is a presettable variable frequency divider, and the VCO
The frequency division ratio of the variable frequency divider is automatically set so that the operating point of O is within a proper range.

Therefore, according to this invention, even when the propagation time of the ultrasonic wave changes significantly due to changes in the properties of the fluid during installation, the frequency division ratio of the frequency divider is automatically adjusted to the appropriate frequency division ratio. It is automatically controlled to reach the target. Therefore, measurement operation can be started without any adjustment at the same time as installation. Another advantage is that flow rate measurement can be maintained even if the properties of the fluid change during measurement.

<Embodiment of the Invention> FIG. 2 shows an embodiment of the invention. In FIG. 2, parts corresponding to those in FIG.
Means 23 are provided for detecting the operating point of CO], b. This operating point detection means 23 can be configured by, for example, an AD converter. For example, v
The analog control voltage supplied to co:ta and 1b is AD
The AD conversion value is supplied to the frequency division ratio control means 20 that changes the frequency division ratio of the variable frequency divider 5-17', and the frequency division ratio control means 20 changes the frequency division ratio of the variable frequency divider 17'. Performs control to change. This frequency division ratio control means 20 converts the operating point detection signal of the operating point detection means 23 into a frequency division number N of the variable frequency divider 17'.
and a means 2b for detecting, in the operating point detection means 23, that the operating point of VCOla or 1b deviates from the appropriate range.

When this detection means 20b detects that the operating point of VCOla or 1b is out of the appropriate range, it outputs a preset command signal P, and this preset command signal P is used to input the preset input terminal 24 of the variable branching unit 171. The digital value from the given decoder 20a is preset, and the frequency division ratio of the frequency divider 17' is changed and controlled.

The operating point detection means 23 (d) may have a function of detecting whether the control voltage output from the integrating circuits 19a and 19b is within the operating range of VCOla and VCOlb, or deviated from the upper limit side or the lower limit side. The simplest example is shown in FIG.

In the example shown in FIG. 3, it is determined whether the control voltages output from the integrating circuits 19a and 19b are within the operating range of VCOla and 1b, and whether the operating range has deviated from the upper limit side or the lower limit side, and the judgment result is This shows a case in which the data is configured to be converted into a digital code.

The operating point detection means 23 can be constructed by two voltage comparators 26, 27 and two comparison voltage sources 28, 29, and the non-inverting input terminals of the two voltage comparators 26 and 27. The inverting input terminals are commonly connected, and this common connection point is connected to the integrating circuits 19a and 19b via the switch 31.
The voltage E1 of the comparison voltage source 28 is applied to the non-inverting input terminal of the voltage comparator 27, and the voltage sources 28 and 29 are connected to the inverting input terminal of the voltage comparator 26 alternately. The sum of the voltages E1 and E2 is the voltage E I +E
Give 2.

According to this configuration, in the region where the control voltage EC supplied through the switch 31 is EC)E1+E2, the output terminal 3
The output of 2.33 is H and L logic. Also, EC is E s
In the region of 10 E 2 > E c > E 1, output terminal 3
2゜33 output is L, L logic, EC is E1
) E In the region of c, the output beams of output terminals 32 and 33,
This becomes H logic. Therefore, EC is E I+E 2>E c>
By setting the values of voltages E1 and E2 of voltage sources 28 and 29 so that the region of E1 corresponds to the proper operating region of VCOla, 1b, when LEc is in the region of F++E+)Ec>F,+, In other words, the output of the output terminals 32 and 33 is L.
In the case of logic, the code is converted by the decoder 20a so that the frequency division ratio of the frequency divider 1710 becomes 1/N, and the frequency division ratio of the variable frequency divider 171 is preset. Also, when in the region of EC)E1+E2, the frequency division ratio of the frequency divider 1710 is set to, for example, 1/(N+1.), and when in the region of Ec(El), the frequency division ratio of the frequency divider 171 is set to, for example, 1/(N-1.). If the frequency division ratio of the frequency divider 17' is preset so that the frequency division ratio of the frequency divider 171 is changed, VCOla and 1b can always be operated in an appropriate range.The decoder 20a has a counter function. By having the operating point detecting means 23, for example, each time the operating point deviates to the upper limit side, the number of times is counted, and the frequency dividing ratio is set to the counted value... I can do that.

With this configuration, the measurement range can be expanded infinitely.

<Another embodiment of the invention> FIG. 4 shows another embodiment of the invention. In this example vC
O is one, and this one VCOI is configured to be used alternately in both the state in which ultrasonic waves propagate in the forward direction of the flow and the state in which the ultrasonic waves propagate in the opposite direction to the flow. Indicates the case where

In this case, a case is shown in which a measurement control means 34 constituted by a microcomputer is used as means for measuring the oscillation frequency of the VCO1. This measurement control means 34 measures the oscillation frequency of the VCOI when the ultrasonic wave propagates in the forward direction and the reverse direction with respect to the flow, calculates the difference between the oscillation frequencies, and calculates the error v from the difference in frequency. It also includes the calculation means for the calculation. Furthermore, it also includes frequency division ratio control means 20 that detects when the operating point of the VCOJ deviates from the appropriate range and changes the frequency division ratio of the variable frequency divider 17'.

Even in the case of this configuration, an operating point detecting means 23 constituted by an AD converter is provided as means for detecting the operating point of the VCOL, and the operating point detecting means 23 detects the operating point of the VCOL. The detection output of 23 is supplied to the measurement control means 34. In the measurement control means 34, V
It detects that the operating point of COL deviates from the proper range and the direction in which it deviates, and controls the frequency division ratio of variable frequency divider 17' to be changed.

By operating the frequency division ratio of the frequency divider 171 so as to automatically change the setting each time the operating point of the VCOL deviates from the proper range, it is possible to always maintain the proper operating range as explained in FIG. The VCOI can be operated with

Note that when the number of VCOIs is one as shown in FIG. 4, unlike the case of FIG. 3, there is no possibility that the VCOIs will interfere with each other. Therefore, there is an advantage that measurement accuracy can be improved in a low flow rate measurement region.

1. When two VCOIs, a and VC'O]b, are provided in one device as shown in Fig. 1 or Fig. 2, the oscillation frequencies of these two vcos:ta and 1b are The later they get, the closer they get to each other. For this reason, a mutual attraction phenomenon of oscillation frequencies occurs, and this attraction phenomenon generates a dead zone in a low flow velocity region. This dead zone may reduce measurement accuracy in low-flow areas, but if one VCOL is used alternately as shown in Figure 4,
There is no risk of this pull-in phenomenon occurring, and even in the low flow velocity region, highly accurate flow velocity or flow rate measurement can be performed even in the case of a flowmeter with a small diameter.

Still in FIG. 4, numeral 35 indicates an abnormality detection circuit.

This abnormality detection circuit 35 monitors the time difference between the rising edge of the signal taken out from the synchronization circuit 2 and supplied to the ultrasonic propagation path 3 and the reception timing signal output from the reception timing detection circuit 15, When this time difference reaches a predetermined value or more, it is determined that the ultrasonic propagation path 3 is abnormal, and based on this determination result, the sampling of the sample and hold circuit 18 is interrupted, and the output voltage of the time difference voltage conversion circuit 16 at the time of the abnormality is changed. It is configured so that it is not imported.

By providing the abnormality detection circuit 35 in this manner, even if the propagation of the ultrasonic wave is temporarily interrupted due to millet or dust passing through the flow path 5, the oscillation frequency of the VCOL will not change greatly, and measurement errors will be reduced. can be prevented from occurring.

<Effects of the Invention> As explained above, according to the present invention, the means 23 for detecting the operating point of vCO and the presettable variable frequency divider 1
7' in combination, the VCO can always be operated in an appropriate operating range.

Therefore, there is no need to adjust the frequency division ratio of the frequency divider 171 at the time of installation, and the installation work can be completed without adjustment. In addition, even if the properties of the fluid change during actual use and the propagation time of high waves changes significantly, this change is detected and the frequency division ratio of the variable frequency divider 17' is controlled so that the VCO operates in an appropriate range. Therefore, it is possible to provide an ultrasonic flowmeter that does not become impossible to measure due to a change in the properties of the fluid and has a wide measurement range, and its effects are significant in practical use.

In the above description, the means 23 for detecting the operating point of vCO
The control voltage supplied to vCO from the integrating circuit is A,
Although a case has been described in which an AD converter that performs D conversion is used, as another example, it is also possible to measure the oscillation frequency of the vCO and detect the operating point of the vCO from the oscillation frequency.

[Brief explanation of the drawing]

FIG. 1 is a block diagram for explaining a conventional ultrasonic flowmeter, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3 is a connection diagram showing a specific example of the main parts of the present invention. FIG. 4 is a block diagram showing another embodiment of the invention. 1, 1-a, 1b: Voltage controlled oscillator, 2:
Synchronous circuit, 3: Ultrasonic propagation path, 5: Flow path, 8, 9: Ultrasonic transducer, 15: Receiving timing detection circuit,
16: Time difference voltage conversion circuit, 17I: Variable frequency divider, 20
: Frequency division ratio control means, 22: Calculation means for determining flow velocity, 23
: Operating point detection means.

Claims (1)

[Claims] (IIA: a voltage-controlled oscillator whose oscillation frequency is controlled by a voltage; B: a synchronous circuit that extracts the oscillation signal of this voltage-controlled oscillator at regular intervals; C1: oscillation extracted by this synchronous circuit) A signal is selectively given to one and the other of a pair of ultrasonic transducers installed diagonally opposite to the flow path, and ultrasonic waves are propagated in the forward and reverse directions relative to the flow of the fluid to be measured. a sound wave propagation path; D. a reception timing detection circuit for detecting the ultrasonic waves passing through this ultrasonic wave propagation path; A variable frequency divider that divides the oscillation signal of the controlled oscillator; and F, converts it into a voltage signal proportional to the time difference between the divided output extracted from the variable frequency divider and the detection signal of the reception timing detection circuit. G. a time difference voltage conversion circuit that controls the oscillation frequency of the voltage controlled oscillator so that the time difference reaches a predetermined value; a calculation means for determining the flow velocity from the oscillation frequency of the voltage controlled oscillator in a state where the ultrasonic wave is propagated; (2) operating point detection means for detecting the operating point of the voltage controlled oscillator; An ultrasonic flowmeter comprising frequency division ratio control means for controlling the frequency division ratio of the variable frequency divider so that the operating point falls within a predetermined range.