JPH0624738Y2 - Correlation flow meter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a correlation flow meter that stops measurement in a flow rate or flow rate measurement using cross-correlation in which the cross-correlation cannot be obtained or in a very low flow rate range.

2. Description of the Related Art A sensor for detecting a turbulence signal of a fluid is arranged at a fixed distance along a flow of a fluid to be measured, a cross-correlation function of a fluid turbulence signal transmitted from each of the sensors is obtained, and the cross-correlation function is calculated. A so-called correlated flow meter for obtaining a flow velocity by obtaining a maximum delay time and dividing the constant distance by the delay time is well known. Thus, in the correlation flowmeter, the measurement accuracy of the delay time determines the flow measurement accuracy, but the delay time can be measured with high accuracy when the peak value of the cross-correlation function is sharp. However, when it is flat, it is difficult to obtain the maximum value, and the accuracy is unavoidable. It is known that the cross-correlation function in the flow velocity measurement has a larger peak value as it shows a larger value, has a sharp exponential curve, and conversely has a flat peak value as it shows a smaller value. Furthermore, when the distance between the sensors is constant, the lower the flow velocity, the lower the peak value, and therefore it is also known that it is a flat exponential function. I can't. However, in normal flow rate measurement, low flow velocity is not measured for a long time, and it is operated in the middle of the flow rate range of the flow meter. The flow rate integrated value in the small flow rate range outside the flow rate range in the state can be ignored. For this reason, the flow rate integration is stopped below the predetermined flow rate, and the error included in the total integrated value is allowed. The predetermined flow rate may be detected by the correlation flow meter itself,
Since it is unstable in the small flow region as described above, a flow velocity detector such as a heat ray system is separately provided, and the flow rate integrating operation of the correlation flow meter is stopped in accordance with the signal from the flow velocity detector.

Problems of Conventional Technology As described above, in the conventional technology, a flow velocity detector separate from the correlation flow velocity detector is arranged in the low flow velocity region, but a large flow rate measurement with a large flow rate, for example, exhaust gas In the case of measurement such as, the turbulence of the flow is large, the noise component makes the reliability of the detection low in the velocity meter that measures locally, and further, a separate flow velocity detector is required for velocity detection. There was a problem.

Means for Solving Problems According to the present invention, the turbulence signal becomes small in the low flow velocity region, and the turbulence signal level is low particularly when there is no flow rate when operation is stopped
Furthermore, when a trigger output of a predetermined level or higher is taken, the output is discontinuous. FIG. 3 (A) is a signal waveform diagram for explaining the operation in the flow rate region of the present invention, and FIG. 3 (B) shows the detection signal in the normal flow, both of which are (a) ) Is a detector output, (b) is a trigger output, Tn is a trigger level, and depending on the adjustment of the trigger level Tn, the trigger output is not output within a predetermined time. The present invention has been made paying attention to this, and counts whether or not the disturbance signal of a predetermined level or more reaches a predetermined number within a predetermined time, and when it does not reach the predetermined number, it is determined that the flow rate is stopped. The flow rate integration is stopped, and the flow rate integration is continued when a predetermined number is exceeded.

Embodiment FIG. 1 is a block diagram showing an embodiment of the present invention, in which 1 is a flow tube, and a fluid to be measured flows in the flow tube 1 in the direction of arrow Q. Reference numeral 2 is an upstream disturbance signal detector, and 3 is a downstream disturbance signal detector. 4 is a disturbance signal detector 2 on the upstream side
The upstream signal conversion in which the disturbance signal detected from the signal is amplified by a predetermined amplification factor and then the binary signal obtained by comparing with the voltage value of the reference level is output as Xt to the upstream input terminal of the insertion calculator 7 It is a vessel. Similarly to the upstream signal converter 4, 5 also outputs the disturbance signal output from the downstream disturbance signal detector 3 to the downstream input terminal of the correlation calculator 7 as a binary signal Yt. 6 is a zero detector, which is 2 of the disturbance signal shown in FIG.
This is a zero flow rate detector that determines the continuity or discontinuity of the binary signal from the value signal and issues an instruction to continue or stop the flow rate integration of the correlation calculator 7.

FIG. 2 is a detailed diagram showing an example of the zero detection circuit. In the figure, 10 is an input terminal to which the binary signal Xt from the upstream signal converter 4 is input, and 11 is emitted by the binary signal. And a voltage Vcc supplied from a power source (not shown) through a resistor R ₁ and a light receiving element for receiving light from the light emitting element. The output of the shift coupler 11 is output by the Schmitt circuit 12. It is shaped and input to the retrigger timer 13 and the AND gate 14. Since the output 17 of the binary counter 15 is at the roll level and the AND gate 14 is opened by the NOT circuit 16 at the initial stage when the turbulence signal of a predetermined level or more is continuously output while the flow rate is flowing, The counter 15 starts counting and the counter output 17 becomes high level when the counting is completed. On the other hand, the retrigger type timer 13 is set by the variable resistance VR _1, but since this set time is set longer than the longest value of the pulse cycle input during operation, the timer 13 is set.
Output remains low due to retriggering, counter 15 is not reset, and counter output 17 therefore remains high. The downstream disturbance signal also has the same circuit configuration as the upstream disturbance signal described above, and the binary signal Yt from the downstream signal converter 5 is input to the downstream signal terminal 20, the photo coupler 21, the Schmitt circuit. It is shaped by 22 and timer 23 and AND gate 2
Enter 4 and. When the binary signal Yt is continuously output, the counter output 27 is at the high level, the NAND circuit 30 is at the low level, and the output circuit 31 outputs the output circuit 31 from the power supply voltage Vcc. Since no current flows through the constituent constant current circuit, transistor, light emitting diode, etc., the light emitting diode does not emit light. Next, regarding the case where a disturbance signal of a low level or higher does not appear within the time set in the timer 13, a pulse at a certain time input to the upstream signal terminal 10 causes First, the AND gate 14 opens and the counter 15 starts counting, but at the same time, the timer 1
3 also works. In this case, since there is no pulse input within the set time of the timer 13, the counter output 17 remains low level, and the AND gate 14 also keeps the open state.
Since the integrated value of is reset, the input side of the disturbance signal on the upstream side of the NAND circuit 30 remains at the low level. Similarly, since the input of the NAND circuit 30 on the downstream disturbance signal side also remains at the low level, the output becomes the high level,
A current is supplied to the light emitting diode of the output circuit to cause the light emitting diode to emit light, which indicates that the turbulent component signal is discontinuously transmitted and the flow rate is stopped.
The stop signal is output from the stop display output terminal and the flow rate value becomes zero.

Effects As described above, according to the present invention, it becomes unnecessary to detect the lower limit value of the correlation flow meter by other flow velocity detecting means other than the conventional upstream and downstream detectors of the turbulence signal. In many cases, the detection means is also unstable in the small flow rate range, and the problem of reduced reliability of the measurement result caused by this is also eliminated.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining an embodiment of the correlation flowmeter according to the present invention, and FIG. 2 is a block diagram showing an embodiment of the zero detector 6 shown in FIG. FIG. 3 is a diagram showing a waveform of signal conversion. 1 ... Flow tube, 2, 3 ... Disturbance signal, 4, 5 ... Signal converter, 6 ... Zero detector, 7 ... Correlation calculator.

Claims (1)

[Scope of utility model registration request] 1. A detection means for detecting a noisy signal contained in a fluid to be measured at two points separated by a constant distance, and a calculation means for obtaining a cross-correlation of signals from these two points. In the correlation flowmeter for determining the flow velocity or flow rate of the fluid to be measured by means of the flow velocity when the integrated value of the detection signals above a certain level detected by the detecting means at at least one of the two locations does not reach the set value within a predetermined time. Alternatively, a correlation flowmeter characterized by setting and displaying the flow rate value at zero.