JPS59173715A - Correlation type flow velocity meter - Google Patents

Abstract

PURPOSE:To measure a velocity of flow by a mutual correlation without dropping the accuracy by installing three or more sensors responding to a fluid physical quantity at different intervals in a duct line, and selecting freely a combination of an optimum interval to a velocity of flow. CONSTITUTION:Three pieces, etc. of sensors 3, 4 and 7 responding to a fluid physical quantity are installed at different intervals L1, L2 and L3 in a duct line 1. Also, correlation function operators 5a, 5b and 5c which connect the sensors such as 3 and 4, 4 and 7, 3 and 7, etc. are provided. Accordingly, a combination of the sensors whose interval is optimum in accordance with a velocity of flow is selected, and by a delay time based on a correlation function whose similarity and resolution are good, a velocity of flow can be measured without dropping the accuracy.

Description

[Detailed Description of the Invention] (Technical Field) The flow rate of fluids mainly transported through pipes, such as gases, liquids, and two-phase flows in which solid particles such as pulverized coal are mixed into these fluids, is The following description of the development results that advantageously improve the measurement accuracy regardless of the flow velocity when measuring by the cross-correlation method 1 is in the field of technology related to fluid metering.

(Prior art and its problems) Focusing on the fluctuation of a certain physical quantity, such as capacitance, in a fluid flowing through a pipe, the distance is varied along the pipe as shown in Figure 1(a)2. Transmission delay τ of the above fluctuation between points. Obtained by the total reciprocal correlation method, the flow velocity between them ■ =
L/τ. is a well-known method in correlation type anemometers.

In FIG. 1(a), 1 is a pipe through which fluid flows, 2 is a fluid, 3.4 is a sensor installed at a distance along the pipe, and 5 is a signal U of the two sensors; u2
and 6 is the obtained delay time τ. This is a calculation unit that converts the flow velocity V into the flow velocity V.

The sensors 3 and 4 vary depending on which fluctuation of the physical quantity of the fluid is to be focused on, but in addition to the above-mentioned capacitance, well-known examples include detectors for temperature, radiation, and ultrasonic waves. .

FIG. 1(b) shows the state of the signals at the sensors 3 and 4. For example, a minute change (fluctuation) in the capacitance of the sensor 3
It was ahead on the side, and a little later there was also hail on the sensor 4 side. This is an example of actually measuring the capacitance of solid-gas two-phase flow of pulverized coal.

FIG. 1(0) shows their cross-correlation function, and the delay time τ at which l reaches its peak value. is the transmission delay of fluctuation between two points that separate the distance, and the cross-correlation function is expressed by the following equation (1
) can be calculated.

Peak value τ. differentiates yj(τ) with respect to τ, and since it is transformed to zero, specifically, the differential signal of u2 and u
The cross-correlation of optical signals of o is often determined.

Now, in FIG. 1, the identity of both signals U□ and u2 is less likely to be preserved as the distance between them increases and as the flow velocity V decreases, that is, as the difference in space and time increases.

For example, Fig. 2(a), Φ) shows the relationship corresponding to 1', (C1) in Fig. 1 when the flow velocity V is about i, and the waveform of 2(τ) collapses to the cross-correlation function. It has become extremely difficult to determine the peak value.

Also, if the flow velocity ■ is very large and the distance is too small, the signal similarity is very good, but the delay time τ.

If the length is too short, its resolution will be poor, and the accuracy of flow rate measurement will be extremely poor.

From the above, it can be seen that the selection of the distance is extremely important in the measurement method using the correlation method, and must be selected appropriately depending on the flow condition.

(Objective of the Invention) It is an object of the present invention to provide a particularly advantageous solution to the above-mentioned problems in the conventional correlation type current meter as described below.

(Structure of the Invention) That is, the present invention provides a sensor that responds to a physical quantity of fluid in a pipe by three sensors along the direction of fluid flow in the pipe.
This is a correlation-type current meter that is installed at different intervals at different locations, selects an optimal combination of distances between sensors according to the flow velocity of the fluid, applies a cross-correlation method, and calculates the flow velocity. .

Now in Figure 3, the distance between the sensors 314 is 5 cIrL and 1.
(This shows a comparison of the cross-correlation functions of the unloaded pulverized coal flow when the flow is 1 m long.) When the flow velocity is large (14 to 15/S), the flow velocity is When the distance is small (7 to 8), the shorter the distance as shown in the figure (0>), the more stable the cross-correlation function can be obtained, and the delay time τ can be measured with high accuracy.

The figure (b) shows stable cross-correlation for both distances of 5c7n and 10cIn when the flow velocity V is 10 to l 1 m/s.・It shows that a function is obtained.

Therefore, if there is a large variation in the flow velocity (2) of the object to be measured, by selecting an appropriate distance according to the flow velocity, it is possible to measure the flow velocity with high precision over a wide range.

FIG. 4 shows an embodiment of the present invention based on the configuration of a new measurement system based on the results of the above experiments.

That is, in addition to the sensors 3 and 4 of the conventional configuration, a sensor 7 is further added on the downstream side. At that time, for the distance L0 between sensors 3 and 4, the distance between sensors 4 and 7, 'i 2 L
Therefore, the distance L8 between the sensors 3 and 7 is preferably about 3Lτ.

Here, the interaction function calculators 5a, 5b and 5C are U□ and u2. The cross-correlation function of ua and u8 and U□ and u8 is 0. 0. Calculate 0.

12 28 18 In the figure, 8 denotes arithmetic units 5a', pb and 5C, respectively.
This is a logic circuit that receives signals DA, 21 τOI "28-1", :P and "111'" to determine the flow velocity V.

Various methods can be used to determine the flow velocity V, but the simplest method is shown in FIG. .

τ. , τ0 respectively satisfy the following formula (3) % formula % (3) (i.e., only when within their respective upper and lower limits)
Then, v, (i=1.2.3) is determined by the following equation (4). Then, the average value is determined only from this effective V4 ('i=1.2.8), and the normal V=< is determined by the following equation (5).

In addition to this method, it is of course possible to employ the following logic circuit.

■ Method of selecting only the correct shape of correlation function '121 '2111 ``121 ■ Method of adopting majority logic of τ0.τ., τ0゜■ Da0.(τ and 0., j (偕), da0 .(τ0°) is above the lower limit.Also, Fig. 4 shows an example of using eight sensors 3, 4, and 7, but it is also possible to use four or more sensors, using exactly the same logic as above. It can be determined with a higher flow velocity than the true flow velocity v2.

In this invention, as described above, the distances between the sensors are made different and the sensors are installed at three or more locations, and the flow velocity is determined by selecting the optimal combination of the distances between the sensors depending on the magnitude of the flow velocity. , the flow rate can always be accurately measured even if the flow rate changes greatly.

[Brief explanation of the drawing]

Figures 1 (a), (b), (0) are sensor layout diagrams, waveform diagrams of signals from each sensor, and graphs of cross-correlation functions, showing the procedure for measuring flow velocity using the correlation method. a) and (b) are graphs of signal waveforms and cross-correlation functions from each sensor when the distance between the sensors is inappropriate; FIG. 4 is a detailed explanatory diagram of the present invention, and FIG. 5 is a flowchart showing the logic for determining the flow velocity. 8.4.7...Sensor Ll, L2. ' L8... Distance between sensors.

Claims (1)

[Claims] L Sensors that respond to the physical quantity of the fluid in the pipeline are installed at three or more locations along the direction of fluid flow in the pipeline at different intervals, and the optimal distance between the sensors is determined according to the flow rate of the fluid. A correlation-type current meter characterized by selecting a combination of distances and applying a cross-correlation method to determine the flow velocity.