JPS5836290B2 - Karman vortex flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Karman vortex flow meter that measures the flow rate of fluid using Karman vortices.

When a columnar object is inserted into a fluid, vortices are generated alternately on both sides of the object, which flow downstream in the form of a vortex train.

This vortex is called a Karman vortex. This is already a well-known phenomenon.

A vortex generating device for a flowmeter using this Karman vortex and a vortex detection method are described in detail in Japanese Patent Publication No. 51-13428.

For example, when a Karman vortex flow meter is used to measure the amount of intake air in an automobile engine, and a system is constructed in which a digital computer controls the engine based on this amount of intake air,
The digital computer needs to take in the intake air amount information as a digital quantity.

As for this method. The Karman vortex generated in proportion to the amount of intake air is extracted as a frequency proportional to the vortex. It is conceivable to convert this frequency into a voltage using a frequency-to-voltage conversion circuit, and further convert this voltage into a digital quantity using an analog-to-digital converter.

What is the intake air amount of the engine? It changes about 30 times depending on the engine rotation and the magnitude of the load, and the accuracy needs to be about 3 factors.

Therefore, when the intake air amount is converted into a digital amount, the value Vi is 50 to 1500.

The maximum voltage when converting the Karman vortex frequency to voltage is IO
If it is V. The power of this voltage is 6.7 mV.

Therefore, according to the method described in Section L, it is difficult to maintain the accuracy of Section L in terms of resolution of voltages due to problems such as circuit adjustment and noise.

In order to eliminate problems such as those listed in L, the present invention measures this frequency total sampling L in synchronization with the frequency listed in L, the number of pulses during this sampling time, and its width using a counter, and calculates the number of pulses and its width. A calculation device calculates the frequency based on the data. The object of the present invention is to provide a Karman vortex flowmeter that obtains the above-mentioned accuracy by calculating the amount of intake air.

An embodiment of the present invention shown in the drawings will be described below.

FIG. 1 is a configuration diagram showing one embodiment of the present invention, 1 is an arrow indicating the direction of flow of fluid (for example, air), 2 is an outer box of a vortex generator, 21 is a vortex generator, 22 is generated (-1 of the vortex
It is one.

3 is a vortex detection device, 31 is an ultrasonic transmitter, and 32Vi is an ultrasonic receiver.

The vortex detection device 3 drives an ultrasonic transmitter 31 using an oscillation circuit (not shown) built into the device to generate ultrasonic waves.

This ultrasonic wave receives frequency modulation every time a vortex is generated by the vortex 22 or the like, and reaches the ultrasonic receiver 32 .

The vortex detection device 3 detects the frequency-modulated ultrasonic waves with the ultrasonic receiver 32, and detects the change in the ultrasonic frequency as described in 7.
It is demodulated by a built-in FM signal demodulator (not shown) and output as a pulse train.

4 is an oscillator that outputs a pulse with a higher frequency than the frequency of the L pulse train; 6 is a D flip-flop whose trigger input is the output of the vortex detection device 3; and whose preset input is the output of the timer 5.

The output of the D flip-flop 6 is . 1: r regardless of the trigger input mentioned above.
It becomes HJ level. When the L reset input is at the rLJ level and the L reset input changes from "L" to the rHJ level. It becomes "L" level.

Reference numeral 5 denotes a timer that outputs an rHJ level signal to the above-mentioned preset input for a certain period of time (for example, 50 msec) in response to a trigger signal output from the arithmetic unit 10.

Reference numeral 7 denotes a pulse number counter that counts the pulse train output from the vortex detection device 3, and counts only when the count value is reset to zero by the arithmetic unit 10 and the output of the D flip-flop 6 reaches the rHJ level [6].

8 is a pulse width counter that counts the pulses output from the oscillator 4, and counts only when the count value is reset to zero by the arithmetic unit 10 and the output of the D flip-flop 6 falls to the "H"level; When it overflows,
Outputs an "L" level carry signal.

9 inputs the output of the D flip-flop 6 and the L carry signal, and the output of the D flip-flop 6 is rLJ.
This is an AND circuit that outputs an interrupt signal to the arithmetic unit 10 when the carry signal reaches level E or when the E carry signal is output.

The computing device 10 is . For example, it consists of something like a microprocessor. When the interrupt signal h is input, the count values of the pulse number counter 7 and pulse width counter 8 are input, and then the counters 7 and 8 are reset. Next, a trigger signal is output to the timer 5, and then the flow rate of the fluid is calculated based on the values of the counters 7 and 8.

Next, the operation of the embodiment shown in FIG. 1 will be described with reference to the timing chart shown in FIG.

a is the signal of the above-mentioned pulse train outputted by the vortex detection device 3, b is the output signal of the timer 5, C is the output signal of the D flip-flop 6, the pulse outputted by the CL oscillator 4, and the efl calculation device 10 is used to output the pulse number counter 7 and the pulse Width counter 8
The time at 1 when 9 takes in the count value of 9 and outputs a trigger signal to timer 5, f! I'i indicates the time during which the arithmetic unit 10 calculates the flow rate of the fluid.

At time 11t1, the output signal b of timer 5 is "
If the signal a of the pulse train output from the vortex detection device 3 changes from the rLJ level to the rHJ level, the output signal C of the D flip-flop 6 becomes the "L" level.

When the output signal cy of the D-flip flop 6 becomes cy>E "LJ level, the pulse number counter 7 and the pulse width counter 8 stop the counting operation L.t" AND circuit 9
generates an interrupt signal.

The arithmetic unit 10 detects this interrupt signal. The count values of the pulse number counter 7 and the pulse width counter 8 are taken in, the counters 7 and 8 are then reset, and then a trigger signal is output to the timer 5 at time t2.

The output of timer 5 becomes rHJ level. Since the preset input of D-flip flop 6 is at rHJ level,
The output of D-flip flop 6 becomes u rHJ level,
The pulse number counter 7 and the pulse width counter 8 start counting operations.

Arithmetic device 10ili. At time t2, calculation of the flow rate of the fluid starts, and at time 131, the counting is completed.

Timer 5 is. Time t2 Time △t3 (for example, 50
msec), at time t4K, the output is set to rLJ level.

Thereafter, when the pulse train output from the vortex detection device 3 changes from the rLJ level to the rHJ level at time t5, the pulse number counter 7 and the pulse width counter 8 stop counting operations, and the AND circuit 9 generates an interrupt signal. The arithmetic device 10 repeats the same operation as described above.

Here, the time △t1 from time t1 to t2t is 100μ
sec (the arithmetic unit 10 is composed of an N-MOS microprocessor, and its clock frequency is 2MH2)
degree). On the other hand, since the frequency of the Karman vortex is approximately several KH2, the pulse train a during the time Δt1
pulses are not input to the pulse number counter 7.

Therefore, the pulse number counter 7tj does not miscount the pulse train a.

In the past, time △t1 is almost constant time, so time △
The number of output pulses from the oscillator 4 that is not counted by the pulse width counter 8 during t1 is a substantially constant value.

Therefore, by adding this value to the count value of the pulse width counter 8. The value by which the pulse width counter 8 counts the pulses output from the oscillator 4 between time t1 and time t2 can be accurately determined.

Next, a method in which the arithmetic unit 10 calculates the flow rate from the counts of the pulse number counter 7 and the pulse width counter 8 will be described.

Here, if the frequency of the Karman vortex generated by the vortex generator 21 is fK (Hz), and the pulse constant per flow rate for one Karman vortex is C (7/pulse), then the flow rate ■ is V- C-fK(7) ・・・・・・・・・・・・
...River... (]).

1, the count value of the pulse number counter 7 is N, the count value of the pulse width counter 8 is T, and the frequency of the oscillator 40 is fs. (H2
), the arithmetic unit 10 can calculate the flow rate from the count values of the pulse number counter 7 and the pulse width counter 8 using equation (3).

Here, pulse number counter 7 and pulse width counter 8
is counted in synchronization with the pulse train output from the vortex detection device 3, so the frequency fK of the Karman vortex can be accurately determined.

Since the sampling time of this frequency fK is fixed by the timer 5 and is almost constant, the count value of the pulse width counter 8 is also almost constant regardless of the magnitude of the frequency fK, and the frequency fK does not change at any frequency. is also determined with a certain degree of accuracy.

The accuracy of the flow rate calculated by the arithmetic unit 10K is:
The flow rate is almost constant regardless of the magnitude of the flow rate, and by setting the frequency f3 of the oscillator 4, all the necessary flow rate accuracy can be obtained.

In the embodiment shown in FIG. 1, when the flow rate is close to zero, Karman vortices are hardly generated. becomes.

In this case, the pulse width counter 8Vi overflows (generates a carry signal) after a predetermined time, so that the AND circuit 9 generates an interrupt signal and the arithmetic unit 10 calculates the flow rate.

Therefore, even though the flow rate is zero, there is no possibility that the flow rate calculation result of the calculation device 10 will not be zero K.

In the past, at such low air flow rates, it was impossible to count the pulse width in synchronization with the Karman vortex frequency, but for example, in the case of engine control, such low air flow rates were out of the practical range. It's not a problem.

In the embodiment shown in FIG. 1, the counters 7 and 8 perform a counting operation only when the output of the u, D flipflop 6 is at the 25ErHJ level. The arithmetic unit 10 takes in the counted values of the counters 7 and 8 every time the interrupt signal KL, , f: is input so that the counters 7 and 8 always perform counting operations, and the calculation unit 10 takes in the counted values of the counters 7 and 8 when the previous interrupt signal was input. The values counted by the counters 7 and 8 between the previous and current interrupt signals may be determined from the difference between the counts of the counters 7 and 9.

Alternatively, the output signal of the timer 5 may be generated within the arithmetic unit 10.

As is clear from the above explanation, according to the present invention, the frequency of the Karman vortex is counted at approximately constant time in synchronization with the generation of the Karman vortex. Since the flow rate is calculated from the counted value, it is possible to always obtain a certain level of accuracy, and since the voltage level to be handled is on the order of several volts, which is higher than the voltage level handled by the frequency-to-voltage conversion described above, the noise resistance is improved. can be increased.

In addition, since the arithmetic unit can directly take in the frequency information of the Karman vortex as a digital quantity, it is possible to realize an optimal control method for the digital computer.

[Brief explanation of drawings]

FIG. 1 is a structural diagram showing one embodiment of the present invention. FIG. 2 is a timing chart showing the operation of this embodiment. 2... Outer box of vortex generator, 21... Vortex generator, 3... Vortex detection device, 4... Oscillator. 5... Timer 6... D flip-flop, 7... Pulse number counter, 8...
...Pulse width counter, 10... Arithmetic device.

Claims (1)

[Claims] 1. A Karman vortex generator provided in the fluid, a vortex detector that generates a pulse train in response to the vortex frequency generated by the vortex generator, and a first counter that counts the pulse train. An oscillator that generates a reference frequency, a second counter that counts the output of this oscillator, and a timer that creates a fixed time. An arithmetic unit that calculates the flow rate of the fluid L based on the count values of the first and second counters h starts the timer L in synchronization with the pulse train L, and the predetermined period of time has elapsed from the time of activation. E to count until the first pulse of the next pulse train
Let the values of the first and second counters be N and T, respectively.
and L, and when the output frequency of the h oscillator is F8,
A Karman vortex flowmeter characterized in that a value corresponding to the product of N and Fs and the ratio of T is calculated by an L calculation device, and an E flow rate is determined from the calculated value.