JP3821102B2 - Flow measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flow rate measuring device that measures a flow rate of gas or the like using ultrasonic waves.
[0002]
[Prior art]
As shown in FIG. 7, a conventional flow measuring device of this type is provided with ultrasonic transducers 2 and 3 in a part of a fluid pipe line 1 in the flow direction, and includes a trigger circuit 4 and a transmission circuit 5. The ultrasonic wave is generated from the vibrator 1 in the flow direction, the ultrasonic wave is received by the vibrator 2, the ultrasonic wave is again generated from the vibrator 1 via the amplifier circuit 6 and the comparison circuit 7, and the repetition means 8 repeats this. Then, the propagation time is measured by the time measuring means 9, and on the contrary, the switching means 10 generates ultrasonic waves against the flow from the vibrator 2 and measures the same repetition time. Was used to calculate the flow rate of the fluid.
[0003]
[Problems to be solved by the invention]
However, in the conventional flow rate measuring device, there is a slight difference in time between when ultrasonic waves are transmitted from the vibrator 1 to the vibrator 2 and when ultrasonic waves are transmitted from the vibrator 2 to the vibrator 1. Due to this time difference, the temperature around the electronic circuit may change, and in the case of intermittent measurement, the temperature changes with time due to heat generated by energization. The signal transmission speed of the circuit changes due to the influence of these temperature changes. Due to the change in the transmission speed, the measurement of the propagation time of the ultrasonic wave causes an error, and the accuracy is lowered.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, the flow rate measuring device of the present invention has the following configuration.
[0005]
In other words, a timer means for measuring a first oscillator and a second oscillator for transmitting receive ultrasound signals provided upstream and downstream of the fluid conduit, between the time of ultrasonic wave propagation between the transducers, the clock means a flow rate calculation means for calculating a flow rate based on the value, the comprising a sampling control means for intermittently driving measured vibrator, and a preliminary measuring means for disabling the meter Hakachi, said sampling control means The actual measurement is performed after the measurement by the preliminary measurement means .
[0007]
The present invention eliminates the influence of temperature and performs flow rate measurement with the above configuration.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In FIG. 1, a first vibrator 13 that transmits ultrasonic waves and a second vibrator 14 that receives ultrasonic waves are arranged in the flow direction in the middle of a fluid conduit 12. Reference numeral 15 denotes a trigger circuit for starting transmission, which transmits an ultrasonic signal from the first vibrator 13 via the transmission circuit 16. The ultrasonic signal is received by the second vibrator 14, filtered and amplified by the amplifier circuit 17, and the amplified signal is compared with the reference signal by the comparison circuit 18, and a signal equal to or higher than the reference signal is detected. The time from the trigger to the comparison is measured by the time measuring means 19 comprising an hour counter.
[0009]
A flow rate value is obtained by a flow rate computing means 20 that multiplies the correction coefficient based on the value of the time measuring means 19. Reference numeral 21 denotes a start circuit for starting measurement. The start circuit 21 selects the upstream preceding measurement means 22 and the downstream preceding measurement means 23. The upstream preceding measurement means 22 first transmits an ultrasonic signal from the vibrator 13 (upstream side) to the vibrator 14 (downstream side) to obtain the propagation time, and then the switching means 24 uses the vibrator 13 and the vibrator 14. Is transmitted from the switching vibrator 14 (downstream side) to the vibrator 13 (upstream side) to determine the propagation time.
[0010]
Next, the operation will be described with reference to FIGS. When the measurement start signal is issued from the start circuit, the upstream preceding measurement means is first selected, the transmission is the first vibrator 13 and the reception is the second vibrator 14. After the trigger circuit 15 timer 19 is reset, a signal is transmitted from the transmission circuit 16 and an ultrasonic signal is generated from the vibrator 13 (upstream side).
[0011]
This ultrasonic wave is received by the second vibrator 14 (downstream side) after the propagation time affected by the speed of sound and the flow velocity, and the signal passes through the amplifier circuit 17 and is judged by the comparison circuit 18. The time T1 from the trigger is measured and the data is stored in the flow rate calculation means 20. Next, the switching means 24 is operated in the start circuit 21, and the transmission is the second vibrator 14 and the reception is the first vibrator 13. That is, an ultrasonic signal is transmitted from the second vibrator 14 to the first vibrator 13, and the propagation time T2 is measured as described above. Next, the downstream leading measurement means 23 is selected by the start circuit 21. First, an ultrasonic signal is transmitted from the second transducer 14 to the first transducer 13, and its propagation time T 3 is measured, and then from the first transducer 13. An ultrasonic signal is transmitted to the second vibrator 14 and its propagation time T4 is measured. The propagation times T1, T2, T3, and T4 are stored in the flow rate calculation means 20, and in the flow rate calculation means 20,
ΔT = (T2 + T3) − (T1 + T4)
Is calculated, and this value is multiplied by a correction coefficient corresponding to the size of the fluid pipe 12 and the flow velocity distribution in the pipe to obtain a flow rate value. Since this series of measurements is completed in a short time on the order of milliseconds, it is safe to assume that the temperature change of the circuit changes linearly at this time. In the calculation of ΔT, the time from the start when the propagation time (T1 + T4) from the first vibrator 13 to the second vibrator 14 is measured, and the propagation time from the second vibrator 14 to the first vibrator 13 ( The time from the start when T2 + T3) is measured is almost the same, and even if there is a temperature change, the average temperature is almost the same.
[0012]
FIG. 3 shows a second embodiment, and shows a case of sampling control in which measurement is performed intermittently. In the sampling control measurement, the voltage is lowered or cut off during the measurement pause, and the voltage is increased at the same time as the measurement is started. The power consumption is lowered and the battery can be driven. The sampling control means 25 performs measurement every time, and when the measurement is started, the operation by the preliminary measurement means 26 is performed. The preliminary measurement means 26 performs measurement by ultrasonic transmission a predetermined number of times from the start of measurement or measurement for a predetermined time, but discards the measurement value during that time. When the preliminary measurement is completed, the actual measurement is performed. The number and time of the preliminary measurement are set in advance according to the magnitude at which the energized power increases and the temperature rapidly increases at the start of measurement.
[0013]
FIG. 4 shows a third embodiment, which is performed in accordance with the above-described sampling control. When the ultrasonic wave transmitted from the first vibrator 13 is received by the second vibrator 14, and the received signal is detected by the amplifier circuit 17 and the comparison circuit 18, the signal is transmitted from the repetition means 27 to the trigger means 15, The transmission circuit 16 is triggered again. The number of repetition means 27 is set by repetition setting means 28. The propagation of the ultrasonic wave is repeated as many times as set by the repeat setting means 28, and when this repetition is completed, the time counting means 19 measures the accumulated time. As shown in FIG. 5, when measurement is started by the sampling control means 25, a trigger is started by the initial measurement means 29 and a predetermined number of initial measurements are performed, and the number of repetition setting means 28 is set by this measurement value. Is done.
[0014]
When the initial measurement flow rate value is large, that is, when the difference in propagation time from upstream to downstream and from downstream to upstream is large, the number of repeated settings is relatively small, but when the flow rate value is small, the above difference in propagation time is small. Therefore, the accuracy cannot be ensured sufficiently, so that the number of repetitions is relatively increased to increase the accumulated propagation time. After the number of repetitions is set by the initial measuring means 29, normal measurement is performed by the actual measuring means 30 to measure the flow rate.
[0015]
FIG. 6 shows a fourth embodiment in which the ultrasonic wave transmitted from the first vibrator 13 is received by the second vibrator 14 and the received signal is detected by the amplifier circuit 17 and the comparison circuit 18 to measure the time. The positive characteristic element circuit 32 and the negative characteristic element circuit 33 are included in the circuit until the time is measured by the means 19, that is, the signal processing circuit 31 from the trigger to the time measurement. The positive characteristic element circuit 32 has a higher transmission speed as the temperature rises, and this tendency is observed in a normal semiconductor element. The negative characteristic element circuit 33 has a transmission speed that decreases as the temperature rises. When the negative characteristic element circuit 33 is configured by a delay circuit including a capacitor C and a resistor R, the time constant of this circuit is the product (C * R). If the capacitor C has a temperature characteristic that increases as the temperature rises, the time constant increases as the temperature rises, so the transmission speed becomes slower. By combining the positive characteristic element circuit 32 and the negative characteristic element circuit 33, the change in transmission speed is canceled out by the influence of temperature, and the influence is reduced.
[0016]
【The invention's effect】
As is apparent from the above description, the flow measurement device of the present invention provides the following effects.
[0017]
And timer means for measuring a first oscillator and a second oscillator for transmitting receive ultrasound signals provided upstream and downstream of the flow body conduit, between the time of ultrasonic wave propagation between the transducers, the value of the clock means with a flow rate calculating means for calculating a flow rate based on the sampling control means for intermittently driving measured vibrator, and a preliminary measuring means for disabling the meter Hakachi, said sampling control means, said preliminary measurement Since the actual measurement is performed after the measurement of the means is completed, the instability immediately after the start of measurement that occurs during sampling measurement can be eliminated, and the measurement error is small.
[Brief description of the drawings]
FIG. 1 is a control block diagram of a flow rate measuring apparatus according to a first embodiment of the present invention. FIG. 2 is a flowchart showing the control of the apparatus. FIG. 3 is a flowchart showing control of a flow rate measuring apparatus according to a second embodiment of the present invention. FIG. 4 is a control block diagram of a flow rate measuring apparatus according to a third embodiment of the present invention. FIG. 5 is a flowchart showing control of the apparatus. FIG. 6 is a flow chart of the flow rate measuring apparatus according to the fourth embodiment of the present invention. Control block diagram [Fig. 7] Control block diagram of a conventional flow rate measuring device [Explanation of symbols]
12 Fluid line 13 First vibrator 14 Second vibrator 19 Time measuring means 20 Flow rate calculating means 21 External setting means 22 Upstream preceding measuring means 23 Downstream preceding measuring means 24 Switching means 25 Sampling control means 26 Preliminary measuring means 27 Repeating means 28 Repeat setting means 29 Initial measurement means 30 Actual measurement means 31 Signal processing circuit 32 Positive characteristic element circuit 33 Negative characteristic element circuit

Claims (2)

And timer means for measuring a first oscillator and a second oscillator for transmitting receive ultrasound signals provided upstream and downstream of the fluid conduit, between the time of ultrasonic wave propagation between the transducers, the value of the clock means with a flow rate calculating means for calculating a flow rate, and sampling control means for intermittently driving measure the oscillator, and a preliminary measuring means for disabling the meter Hakachi based on the sampling control means, said A flow rate measuring device that performs actual measurement after the measurement by the preliminary measuring means . The flow measurement device according to claim 1, wherein the preliminary measurement means invalidates the measurement value a predetermined number of times or a predetermined time from the start of measurement by the sampling control means .

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