JPH0682059B2 - Correlation type flow meter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a correlation type flow meter which detects flow information on an upstream side and a downstream side of a flow path and measures a flow rate from a cross-correlation value thereof. Is.

"Prior Art" Conventionally known correlation type flowmeters include those described in Japanese Utility Model Laid-Open No. Sho 60-21925 and Japanese Utility Model Laid-Open No. 60-25920. These flowmeters have a plurality of detection signals corresponding to the change in the flow at a plurality of points spaced in the flow direction.
For example, a sensor that outputs the propagation characteristics of ultrasonic waves or the capacitance of a fluid is provided, and the "turbulence of the flow" generated in the fluid is detected by each sensor from the correlation of the measurement data of these sensors. It is possible to know the flow rate of the fluid by calculating the time difference.

FIG. 2 is a diagram showing an example of the conventional correlation type flow meter using an ultrasonic sensor as a sensor. In the figure, reference numeral 1 is a pipe for measuring the flow rate, and the pipe 1 is provided with an upstream side sensor 2 and a downstream side sensor 3 at intervals in the flow direction. The upstream-side sensor 2 and the downstream-side sensor 3 have the same configuration, and an ultrasonic transmitter (hereinafter, simply referred to as “transmitter”) arranged on the outer periphery of the pipe 1.
2a, 3a, and an ultrasonic receiver (hereinafter, referred to as an ultrasonic receiver that is disposed at a position facing the transmitters 2a, 3a with the pipe 1 in between, and receives an ultrasonic signal transmitted from the transmitters 2a, 3a. It is simply referred to as a "receiver") 2b, 3b.

An ultrasonic source 4 is connected to the transmitters 2a and 3a of the sensors 2 and 3, respectively, and by driving the ultrasonic source 4, the transmitters 2a and 3a are connected.
From the ultrasonic wave is transmitted toward each receiver 2b, 3b, this ultrasonic wave is received by each receiver 2b, 3b across the duct,
Here, it is converted into an electric signal.

Further, signal processors 5a and 5b are connected to the receivers 2b and 3b, respectively. These signal processors 5a, 5b include respective receivers 2b,
When an electric signal is input from 3b and the flow of the fluid flowing in the pipe 1 is disturbed and this input signal is modulated, the disturbed signal is A / D converted from the signal processors 5a and 5b. The state is output to the correlator 6. Then, the correlator 6 performs a cross-correlation operation on the flow turbulence signals input from the signal processors 5a and 5b, and uses the time delay τ of the flow turbulence signals between the two sensors 2 and 3 as a measurement result. Output.

Next, the method of calculating the time difference will be described more specifically, taking the correlation type flowmeter having such a configuration as an example. Since each sensor is arranged at a certain interval in the direction of fluid flow, the timing at which these sensors detect flow turbulence is a time proportional to the flow velocity and the interval between the upstream and downstream sensors. There is a delay τ. Further, the measurement data of each of the upstream side and downstream side sensors can be expressed as a function of the time series data as given by the following equation at the stage of being input to the correlator 6.

f (t) = X ₁ , X ₂ , ..., X _n ……… (1) g (t) = Y ₁ , Y ₂ , ……, Y _n ……… (2) (t = n × Δt , Δt is the sampling period of A / D conversion), and these functions f (t) and g (t) have substantially the same waveform with a phase difference corresponding to the time delay τ (strictly speaking, for fluid and The waveform changes slightly depending on the flow path. Therefore, a cross-correlation with the time delay τ as a variable is established between these f (t) and g (t).

Therefore, an expression obtained by integrating the product of the function f (t) and g (t-τ) over a certain interval [0, T] at time t When τm is maximized (when the phase difference between both functions is eliminated), τm is obtained, and this is the measured value of the time delay τ at which the turbulence of the flow between the sensors is detected. Actually, τm = m × Δ when the value R (τ) given by the following equation takes the maximum value
It suffices to use t as an actual measurement value of the time delay τ (see FIG. 3).

When the distance between the upstream side sensor and the downstream side sensor is L, the flow velocity V of the fluid in this section is given by V = L / τm (5), and the flow velocity in the flow passage is Assuming that the flow path cross-sectional area is S, assuming that the flow path is substantially uniform, the flow rate Q of the fluid in the section can be calculated by the following equation: Q = V · S (6)

“Problems to be Solved by the Invention” In the conventional correlation type flowmeter, the flow rate of the fluid is calculated from the sum of products of signal values from a plurality of sensors within a certain section. Therefore, the number of data to be handled and the amount of data are enormous. That is, the larger the number of data (data in the interval [0, T] in the previous equation) required for the correlation calculation, the more statistically averaged and the more accurate the calculation can be performed. Therefore, the number of data more than a certain amount is required. On the other hand, since the resolution of the time delay τ is equal to the sampling period Δt, the sampling period Δt is also determined as a period shorter than a certain amount. It is determined. Since the cross-correlation calculation is performed over the entire captured data, the amount of data to be calculated becomes enormous. Therefore, in order to measure the flow rate in real time, a large number of numerical calculation processors capable of instantaneously calculating a huge amount of data are used, resulting in complication of the device in terms of both software and hardware and an increase in cost. There was a point. Further, noise or the like may be mixed in the data, and due to the influence of the noise or the like, the cross-correlation value may not show an accurate peak value, that is, a time delay τ. As an example, if a large noise having the same phase is mixed in the f (t) and g (t), the calculation result of the cross-correlation of these signals becomes as shown in FIG. 4, and accordingly, the time delay τ = 0. The calculation result is output.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a correlation type flow meter capable of performing high-speed arithmetic processing of flow rate measurement and eliminating the influence of noise and the like.

[Means for Solving Problems] In order to solve the above problems, the present invention provides a cross-correlation calculation of detection signals of a plurality of sensors arranged at intervals in the flow direction of a fluid channel. From the value, the correlation type flow meter for measuring the flow rate of the fluid is provided with control calculation means for limiting the calculation range of the cross correlation calculation based on the change amount corresponding to the change of the flow. Is.

[Operation] In the present invention, since the calculation range of the cross-correlation calculation is limited by the control calculation means based on the amount of change corresponding to the change in the flow, the data to be calculated without impairing the calculation accuracy used for the calculation of the cross-correlation. The number and amount of data can be reduced.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram in which the present invention is applied to an ultrasonic correlation flowmeter, and reference numeral 10 in the drawing is piping for measuring the flow rate.

An upstream sensor 11 is provided on the upstream side (left side in the figure) of the outer periphery of the pipe 10 and the downstream side (right side in the figure) thereof.
Is provided with a downstream sensor 12 at a distance from the upstream sensor 11 in the pipe axis direction. These upstream sensors
11 and the downstream sensor 12 have the same configuration, and the transmitters 11a and 12a arranged on the outer periphery of the pipe 10 and the pipe
It is composed of receivers 11b and 12b which are arranged at positions opposite to the transmitters 11a and 12a with the 10 in between and which receive the ultrasonic signals transmitted from the transmitters 11a and 12a.

An ultrasonic source 13 is connected to the transmitters 11a and 12a of the sensors 11 and 12, respectively. By driving the ultrasonic source 13, ultrasonic waves are transmitted from the transmitters 11a and 12a toward the receivers 11b and 12b, respectively, and the ultrasonic waves traverse the pipelines and the receivers 11b and 12b.
Is received by and converted into an electrical signal.

Further, demodulators 14a and 14b are connected to the receivers 11b and 12b, respectively. These demodulators 14a and 14b include receivers 11b and 12b, respectively.
When the electrical signal from the input signal is input and the flow of the fluid flowing in the pipe 14 is disturbed, and this input signal is modulated, the disturbed signal is output from the demodulators 14a and 14b.

The flow turbulence signals output from the demodulators 14a and 14b are input to the signal recorders 15a and 15b. This signal recorder
15a, 15b, the input signals from the demodulators 14a, 14b are A / D converted and temporarily stored in a built-in memory, and further these stored digital signals are used as disturbance signal data D ₁ and D _2. It is output to the correlator 17. Further, the signal recorders 15a and 15b are provided with memory controllers 16a and 16b for controlling respective functions of the memory.

The correlator 17 performs a cross-correlation calculation of the flow turbulence signal data D ₁ and D ₂ input from the signal recorders 15a and 15b to obtain a time delay τ of the flow turbulence between the both sensors 11 and 12. The measurement result data S ₁ is output to the control calculator 18. The control arithmetic unit 18, the flow rate calculated according to a constant result data S ₁ of from correlator 17, and outputs it as the flow rate data S _2, detection amount corresponding to this the flow rate data S ₂ to a change in the flow And has a function of limiting the calculation range of the cross-correlation calculation performed by the correlator 17 based on this.

That is, the control calculator 18 refers to the past flow rate data S ₂ stored therein, that is, the change amount corresponding to the change in the flow, and predicts the time delay of the flow turbulence between the two sensors 11 and 12. Calculate the value τ ′. The method of calculating the predicted value τ ′ is arbitrary, and one example is a method of setting the average value of the past flow rate data S ₂ stored in the control calculator 18 as the predicted value τ ′. Here, the past flow rate data S necessary for calculating the expected value τ ′ of the time delay is
₂ is preferably the flow rate data S ₂ calculated in the previous time or the time before the last time so as not to impair the real-time property. Then, a predetermined width Δ is provided before and after the expected value τ ′ of the time delay.
The control signals C ₁ , C ₂ , C ₃ are output to the correlator 17 and the memory controllers 16a, 16b, respectively, so that the cross-correlation calculation is performed only within the range of the time delay τ '± Δτ with τ. Here, the setting range of the predetermined width Δτ is appropriately determined in consideration of the fluctuation range of the fluid flow rate and the like.

The calculation procedure of the control calculator 18 described above will be described more specifically. If the time when the upstream sensor 11 receives the disturbance is 0 seconds, it is considered that the downstream sensor 12 receives the disturbance within the range of τ ′ ± Δτ seconds.
The data between 0 and τ'-Δτ seconds obtained from 12 are unnecessary. Therefore, the start point of the disturbance signal data D ₂ output from the signal recorder 15b to the correlator 17 is set to τ′−Δτ seconds, the previous data is truncated, and the measured value of the time delay obtained by the correlator 17 is obtained. By adding τ′−Δτ to, the correct time delay τ can be obtained. From the above, the control signals C ₁ , C ₂ , C ₃ may be set in the time delay range τ ′ ± Δτ.

When the fluid is circulated in the pipe 10 in which the correlation type flowmeter having the above-described configuration is installed, the flow disturbance occurs in the fluid, and the upstream side sensor 11 and the downstream side sensor 12 are provided in the section. When this turbulence passes through, each sensor 11,
The ultrasonic waves received by the twelve receivers 11b and 12b are modulated. Then, by each demodulator 14a, 14b, a disturbance signal is extracted from the modulated reception signal, and the disturbance signal is
A / D conversion is performed by the signal recorders 15a and 15b, and the signal recorder 15
It is temporarily stored in the memory inside a and 15b.

At the same time, the control calculator 18 causes the expected value of the time delay τ ′
Is calculated, and the control signals C ₂ and C ₃ are output to the memory controllers 16a and 16b based on the predicted value τ ′. Therefore,
The memory controller 16a, 16b, in the disturbance signal stored in the memory in the signal recorder 15a, 15b, only the data corresponding to the time delay τ '± Δτ is the disturbance signal data D ₁ ,
Limit the output of these memories to output as D ₂ . Then, the disturbance signal data D ₁ and D ₂ output from the signal recorders 15a and 15b in this manner are input to the correlator 17.

Further, the correlator 17 performs the cross-correlation calculation of the input data D ₁ and D ₂ , and the time delay τ′−Δτ is added to the calculated value of the time delay obtained by this calculation, so that the time An actual measurement value τ of delay is obtained, and this actual measurement value τ is input to the control calculator 18. Then, the control calculator 18 performs a calculation for obtaining the flow rate, which is output to the outside as the flow rate data S ₂ .

Therefore, in the correlation type flow meter of the present embodiment, the range τ ′ ± of the predicted value of the time delay is referred to with reference to the past flow rate data S ₂ stored in the control calculator 18, that is, the change amount corresponding to the change in the flow. Δτ is set, and the disturbance signal data D ₁ and D ₂ output from the signal recorders 15a and 15b based on this expected value range.
The range is limited and the calculated value of the time delay obtained by the correlator 17 is corrected. Therefore, the number of data to be calculated by the correlator 17 is reduced and the number of product sums of data to be performed by the correlator 17 is significantly reduced without impairing the accuracy of the cross-correlation calculation. Is possible. In particular, in this embodiment, the memory controller 7a,
Since the output range of the memory in the signal recorders 15a and 15b is directly limited via 16b, the range of the data D ₁ and D ₂ is limited, so that the data D ₁ and D ₂ in the correlator 17 are limited. Since it is not necessary to transfer and rewrite data by software, higher speed data processing becomes possible. In addition, by limiting the range of data D ₁ and D ₂ , the risk of noise and other signals that may cause errors is extremely reduced, so the effects of noise, etc. on the measured flow rate data S ₂ are eliminated as much as possible. can do.

“Modified Embodiment of the Invention” (a) In the above embodiment, the past flow rate data S ₂ is used as the change amount corresponding to the change in the flow which is the basis for calculating the expected value τ ′ of the time delay. The amount of change is not limited to this. As an example, another ultrasonic sensor is arranged in the pipe 10, and the flow rate data is obtained from the signal obtained from this sensor by a method different from the present embodiment, such as a propagation time difference method, and this is used in response to the change in the flow. The expected value τ ′ of the time delay may be calculated as the change amount. In addition, the upstream sensor
Provided with a flow rate measuring means such as a pressure gauge upstream of 12, after giving a time delay by a timer or the like considering the distance between the flow rate measuring means and the upstream side sensor 12 and the signal processing time before and after the correlator 17, The flow rate data from the flow rate measuring means is used by the correlator 17
It is also possible to calculate the expected value of the time delay τ ′ by inputting the value into the equation (3) and using this as the amount of change corresponding to the change in the flow.

(B) In the above-mentioned embodiment, two pipes are provided on the upstream side and the downstream side of the pipe 10.
Although the sensors 11 and 12 are arranged at the positions, similar sensors may be arranged at a larger number of positions to obtain the correlation value between them.

(C) The sensors 11 and 12 for detecting the flow state are not limited to the ultrasonic type as in the above embodiment, but may be capacitance type or electromagnetic type sensors.

"Effect of the Invention" As described in detail above, according to the present invention, the calculation range of the cross-correlation calculation is limited by the control calculation means based on the change amount corresponding to the change of the flow such as the flow rate data. Since the number of pieces of data to be subjected to the correlation calculation can be reduced without degrading the accuracy of the correlation calculation, the number of times the sum of products of the data in the correlation calculation can be significantly reduced, and therefore, the high-speed calculation processing of the flow rate measurement can be performed. Further, by limiting the range of the cross-correlation calculation, the risk that a signal that causes an error such as noise is mixed becomes extremely small, so that the influence of noise or the like on the measured flow rate data can be eliminated as much as possible.

[Brief description of drawings]

FIG. 1 is a side sectional view and a block diagram of a pipe showing a correlation type flow meter which is an embodiment of the present invention, and FIG. 2 is a side sectional view and a block diagram of a pipe showing a conventional correlation type flow meter. FIG. 4 is a diagram showing the relationship between the time delay of flow turbulence and the calculation result of cross-correlation, and FIG. 4 is a diagram showing the relationship between the time delay when noise is mixed and the calculation result of cross-correlation. 10 ... Piping, 11 ... Upstream sensor (sensor), 12 ... Downstream sensor (sensor), 18 ... Control calculator (control calculator).

Claims (1)

[Claims] 1. A sensor for outputting a detection signal corresponding to a change in flow is arranged at a plurality of locations spaced from each other in a flow direction of a fluid, and a cross-correlation calculation of detection signals of these respective sensors is provided. In the correlation type flow meter which measures the flow rate of the fluid from the value, control calculation means for limiting the calculation range of the cross-correlation calculation based on the detected amount corresponding to the change in the flow is provided. Correlation type flow meter.