JP4362890B2 - Flow measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flow rate measuring device that measures the flow rate of a fluid such as a gas.
[0002]
[Prior art]
A conventional flow measuring device of this type is disclosed in JP-A-10-318811. That is, as shown in FIG. 6, the signal propagation time is measured by the propagation time difference detection means 3 at the time of flow rate measurement from the reception means 2 connected by the flow velocity detection means 1, and compared with the stored value of the propagation time storage means 4, and stored. When the measurement by the receiving means is longer than the value, it is detected that a different medium is mixed and a warning is displayed.
[0003]
[Problems to be solved by the invention]
However, in the above conventional flow rate measuring device, although it can be detected that a different medium is mixed, the flow rate cannot be accurately measured in the mixed state, and it is a problem to maintain the flow rate accuracy in a state where the gas component changes. It was.
[0004]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a transmitter / receiver that transmits / receives ultrasonic waves in a fluid, a repetitive unit that transmits again after receiving ultrasonic waves, transmission from upstream to downstream of a flow, or transmission from downstream to upstream. Measuring means for measuring the accumulated time during repetition, flow rate calculating means for calculating the flow rate based on the ultrasonic propagation time, and frequency setting means for changing the number of repetition means according to the signal level of the receiver The flow rate is measured with high accuracy by changing the number of repetitions according to the ultrasonic wave reception sensitivity.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a transmitter / receiver for transmitting / receiving ultrasonic waves in a fluid, a repetitive means for retransmitting after receiving ultrasonic waves, and an accumulated time during the repetition of upstream to downstream transmission or downstream to upstream transmission. And a number setting means for changing the number of repetition means according to the signal level of the receiver.
[0006]
Also, automatic gain means for changing the signal amplification degree according to the reception level of the receiver, and the number of repetitions are changed according to the value of the automatic gain means.
[0007]
In addition, a transmitter / receiver that transmits / receives ultrasonic waves in the fluid, a repeating unit that transmits again through the delay unit after receiving the ultrasonic waves, a number setting unit that changes the number of repeating units, and a flow from upstream to downstream The time measuring means for measuring the accumulated time during the repetition of transmission or transmission from downstream to upstream, the flow rate calculating means for calculating the flow rate based on the ultrasonic propagation time, and the number setting means are changed according to the propagation time.
[0008]
In addition, a transmitter / receiver that transmits / receives ultrasonic waves in the fluid, a repetitive unit that transmits again through the delay unit after receiving the ultrasonic waves, and a repetition of transmission from upstream to downstream of the flow or transmission from downstream to upstream A time measuring means for measuring the accumulated time and a flow rate calculating means for calculating a flow rate based on the ultrasonic propagation time are provided, and the delay time is changed according to the propagation time.
[0009]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0010]
Example 1
In FIG. 1, transmitters / receivers 5 and 6 for transmitting / receiving ultrasonic waves in a fluid are provided upstream and downstream of a flow path 7, respectively, and the propagation time of transmission from upstream to downstream or transmission from downstream to upstream is measured. The ultrasonic propagation time is obtained as a result of the measurement circuit 8, and the flow rate is calculated by the flow rate calculation means 9. In the measurement circuit 8, switching means 10 for switching between transmission and reception of the transceivers 5 and 6, an amplification means 11 for amplifying the received signal, a comparison means 12 for comparing the signal of the amplification means 11 with a reference voltage, There is a repetition means 14 for transmitting from the transmission means 13 again by the signal of the comparison means 12. The magnitude of the received signal is also detected by the reception detection means 15, and the number setting means 16 for setting the number of repetitions of the repetition means 14 can be changed according to the magnitude. The time from the start by the start means 17 to the end of the predetermined number of repetitions is measured by the time measuring means 18 and the flow rate calculating means 9 calculates the flow rate.
[0011]
Next, the operation will be described. The timer of the time measuring means 18 is reset by the signal of the start means 17 and an ultrasonic drive signal is sent from the transmission means 13 of the measuring circuit 8 and the ultrasonic waves are transmitted from the transceivers 5 to 6 via the switching means 10, that is, in the flow. The ultrasonic wave transmitted along the channel 7 and propagated in the flow path 7 reaches the transmitter / receiver 6 after being increased by the flow velocity. The signal in the transmitter / receiver 6 is amplified by the amplifying means 11 and further sent to the comparing means 12 to detect reception of ultrasonic waves. When it is detected that the ultrasonic wave is received, the signal is sent again to the transmission unit by the repeating unit 14, and the ultrasonic wave is transmitted from the transceiver 5 to the transmitter 6 again.
[0012]
Thereafter, when the number of repetitions set by the number setting unit 16 is transmitted, the transmission is stopped and the time is measured by the time measuring unit 18. The propagation time of the ultrasonic wave is very small, and the difference in the ultrasonic wave propagation time due to the flow is further reduced, so that it is necessary to accurately measure the time difference of about nanosecond per time. If the number of repetitions is increased, integration is performed, so that not only the time accuracy is improved, but even a signal including noise is measured many times, so that variation is averaged and S / N is improved. Since the S / N can be large when the received signal is relatively large as shown in FIG. 2A, the accuracy can be sufficiently obtained even if the number of repetitions is relatively small. Reduce power consumption by reducing measurement time. Further, when the received signal is small and the S / N is bad as in the case B of FIG. 2, the number of repetitions is set to be large so as to compensate for the decrease in S / N by improving the accuracy by averaging.
[0013]
In this way, the time for repeating the transmission time of the ultrasonic waves from the transceivers 5 to 6 is measured by the time measuring means 17 and stored as the forward propagation time. Next, the switching means 14 is switched to transmit ultrasonic waves against the flow from the transmitter / receiver 6 to 5, and the transmission time from the transmitter / receiver 6 to 5 is stored as the backward propagation time in the same manner as described above. The flow rate calculation means 9 calculates the flow rate from the time difference between the time and the forward propagation time, and the flow rate coefficient calculated in advance according to the cross-sectional area of the flow path 7 and the flow state.
[0014]
In the actual calculation, the flow rate is calculated based on the reciprocal difference of the propagation time so that the influence of the sound speed is theoretically eliminated, and a microcomputer is used for this calculation. The level of the received signal varies depending on manufacturing variations of the transceivers 5 and 6, aging, or the nature of the fluid. In any case, the level of the received signal can be dealt with by detecting the level of the received signal.
[0015]
(Example 2)
FIG. 3 shows the second embodiment, in which the size of the amplifying means 11 is compared by the comparing means 12, the amplification level of the amplifying means 11 is changed by the automatic gain means 19 according to the level of the received signal, and the signal level after amplification. Is to be controlled to a predetermined size. That is, when the amplified signal is small, the comparison means 12 detects the signal and the automatic gain means 19 sets the amplification degree to be large. Conversely, when the amplified signal is small, the amplification degree is set to be small.
[0016]
Therefore, the magnitude of the input level of the received signal can be known from the amplification value. Since the S / N ratio of the signal is often determined by the received signal level, the flow rate accuracy can be kept constant by changing the setting value of the number-of-repetition setting unit 16 according to the amplification degree. Since the received signal level is high when the amplification level is small, the accuracy can be maintained even if the number of repetitions is reduced. When the amplification level is large, the S / N ratio is small, so the number of repetitions is increased and the accuracy is kept high by averaging. . The automatic gain means 19 can be constituted by a microcomputer in software, or can be integrated with the amplification means as an IC.
[0017]
(Example 3)
FIG. 4 shows the third embodiment, in which the number setting means 16 is changed according to the value of the time measuring means 18. The 18 values of the time measuring means indicate the propagation time of the ultrasonic wave, and the value varies depending on the sound speed of the fluid, that is, the type and temperature of the fluid. The longer the sound wave stays in the fluid, the greater the influence of the change in propagation time due to the fluid flow velocity, so the accuracy of detecting the flow velocity increases.
[0018]
Accordingly, since the detection accuracy increases as the propagation time per time increases, the number of repetitions may be set small. Conversely, when the speed of sound is high and the propagation time per time is short, the detection accuracy decreases, so the number of repetitions needs to be increased. In the end, if the total measurement time is repeated, the accuracy can be kept constant.
[0019]
(Example 4)
FIG. 5 shows the fourth embodiment, in which a delay means 20 is provided in the middle of repetition, and the next transmission is performed after a predetermined time delay after the reception is detected. This prevents reflection between 5 and 6 and overlapping with a signal to be transmitted next time. Since the delay time needs to be set in consideration of not only a single reflection but also a signal of five reflections, the influence of reflection can be reduced by changing the delay time according to the propagation time.
[0020]
In this embodiment, the time measuring means 18 determines the propagation time, the optimum delay time at that time is calculated, and the delay means 20 sets it. Since the value of the time measuring means 18 is a value including the delay time in the propagation time of the ultrasonic wave, the actual propagation time is calculated by subtracting the delay time from the value of the time measuring means 18. As the delay means 20, a timer or a microcomputer composed of an oscillator and a counter can be used.
[0021]
【The invention's effect】
As is apparent from the above description, the flow measurement device of the present invention provides the following effects.
[0022]
(1) Transmitter / receiver that transmits / receives ultrasonic waves in the fluid, repetitive means that transmits again after receiving ultrasonic waves, and measures the accumulated time during the repetition of transmission from upstream to downstream or transmission from downstream to upstream Time measuring means, flow rate calculating means for calculating the flow rate based on the ultrasonic propagation time, and frequency setting means for changing the number of repetition means according to the signal level of the receiver, Since an appropriate number of repetitions can be set, even if the sensitivity change of the transmitter / receiver occurs, while maintaining high flow rate accuracy, unnecessary measurement can be prevented and power consumption can be reduced, and the battery can be operated for a long time.
[0023]
(2) Since the number of repetitions is changed according to the automatic gain means for changing the signal amplification degree according to the reception level of the receiver and the value of the automatic gain means, an appropriate number of repetitions can be set with a simple configuration.
[0024]
(3) A transmitter / receiver that transmits / receives ultrasonic waves in the fluid, a repeating unit that transmits the ultrasonic waves again after receiving the ultrasonic waves, a number setting unit that changes the number of repeating units, and from upstream to downstream of the flow Since the time measuring means for measuring the accumulated time during the transmission of the transmission or the transmission from the downstream to the upstream, the flow rate calculating means for calculating the flow rate based on the ultrasonic propagation time, and the number setting means are changed by the propagation time, the gas Even when the quality is changed, the number of repetitions corresponding to the detection accuracy can be set and high flow accuracy can be maintained.
[0025]
(4) Transmitter / receiver that transmits / receives ultrasonic waves in the fluid, repetitive means that transmits again via the delay means after receiving the ultrasonic waves, and repeats transmission from upstream to downstream of the flow or transmission from downstream to upstream It is equipped with a time measuring means that measures the accumulated time and a flow rate calculation means that calculates the flow rate based on the ultrasonic propagation time, and the delay time is changed according to the propagation time, so the optimum delay is always maintained even if the fluid properties change The time can be set, and a decrease in detection accuracy due to reflection of the ultrasonic signal can be prevented.
[Brief description of the drawings]
FIG. 1 is a block diagram of a flow rate measuring device according to a first embodiment of the present invention. FIG. 2 is a received signal waveform diagram of the same device. FIG. 3 is a block diagram of a flow rate measuring device according to a second embodiment of the present invention. FIG. 5 is a block diagram of a flow rate measuring apparatus according to a fourth embodiment of the present invention. FIG. 6 is a block diagram of a conventional flow rate measuring apparatus.
5 Transmitter / Receiver 6 Transmitter / Receiver 9 Flow rate calculating means 14 Repeating means 16 Count setting means 18 Timekeeping means 19 Automatic gain means 20 Delay means

Claims (2)

A transmitter / receiver that transmits ultrasonic waves from the upstream side to the downstream side of the fluid flow or from the downstream side to the upstream side, and receives the transmitted ultrasonic waves ;
Repeating means for transmitting ultrasonic waves again using the transceiver after receiving ultrasonic waves,
According to the signal level of the receiver and a number setting means for setting the transmission count by said repeating means,
The number-of-times setting means sets the number of times of transmission by the repetition means as the signal level of the receiver decreases . A transmitter / receiver that transmits ultrasonic waves from the upstream side to the downstream side of the fluid flow or from the downstream side to the upstream side, and receives the transmitted ultrasonic waves;
Repeating means for transmitting ultrasonic waves again using the transceiver after receiving ultrasonic waves,
Automatic gain means for varying the signal amplification degree according to the reception level of the receiver;
A number of times setting means for setting the number of transmissions by the repetition means according to the signal amplification degree by the automatic gain means,
The number of times setting means sets the number of times of transmission by the repetition means as the signal amplification degree by the automatic gain means increases .

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