JPH0421808B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic Doppler flowmeter that measures fluid flow rate by detecting Doppler shift frequency.

In conventional ultrasonic Doppler flowmeters, a comparator is generally provided within the signal processing means to discriminate between the Doppler shift frequency and the noise signal. At that time, the signal that should serve as the reference value of the comparator was set to a fixed value by dividing positive and negative constant voltages using voltage dividing resistors.

Therefore, if the received signal changes significantly and the input signal of the comparator changes accordingly, the noise wave component cannot be effectively removed or a counting error occurs.

In other words, if the input signal becomes significantly larger than the reference value, the noise superimposed on the input signal will also be counted, resulting in a positive error; if the input signal becomes significantly smaller, the signal will fall below the reference value. Each of them was hidden and undetected, resulting in a negative error.

In addition to the above-mentioned causes, such counting errors also occur due to deterioration of the characteristics of the transmitter/receiver and changes over time in the gain of the high/low frequency amplifier.

The present invention has been made to eliminate the drawbacks of the conventional devices described above, and an object thereof is to provide a highly accurate ultrasonic Doppler flowmeter that is stable against fluctuations in received signals due to the various causes described above. do.

A feature of the present invention for achieving this object is a comparison means (1) that compares a reflected signal of a Doppler shift frequency component from a fluid with a reference signal (to be described later) and outputs a signal proportional to the Doppler shift frequency. In addition to providing a "comparator" (hereinafter referred to as a "comparator"),
By setting the reference signal according to the polarity of the comparator output and the signal magnitude of the reflected signal, the comparator for detecting the Doppler shift frequency is provided with a hysteresis function according to the magnitude of the reflected signal. It's somewhere.

An embodiment of the present invention will be described below with reference to the drawings. Figure 1 shows its overall configuration.

The electrical signal from the transmitter 102 is sent to the transmitter 104
The ultrasonic wave is converted into an ultrasonic wave and sent as a transmission wave toward the fluid to be measured. The ultrasonic waves reflected by the scatterer 106 in the fluid reach the receiver 10 together with the transmitted waves.
Only the signal containing the Doppler shift frequency is extracted through a high frequency amplifier 202 and an envelope detector 204. After noise components such as detection noise are removed from this signal by a filter 206 , it is amplified by a low frequency amplifier 208 and becomes an input signal to a zerox cross comparator 302 .

This input signal is divided into a signal directly input to the comparator 302 and a signal input to the full-wave rectifier 304. The full-wave rectified signal is further shaped by an average value detector 306 into a signal proportional to the magnitude of the reflected signal of the Doppler shift frequency component, and is input to a hysteresis controller 308 . This hysteresis controller 308 sets a reference value to be applied to the other input terminal (+) of the comparator 302.
02 output polarity, and the average value detector 30
By setting the reference value according to the magnitude of 6, the comparator 302 is provided with a hysteresis function.

Since the output of the comparator 302 is proportional to the Doppler shift frequency, the flow rate of the fluid to be measured is calculated according to the output signal of the comparator 302. That is, the Doppler shift frequency from the comparator 302 is converted into a DC voltage by the frequency/voltage converter 402. Since this DC voltage is proportional to the flow velocity, the cross-sectional area correction unit 404 performs a calculation to calculate the product of the flow velocity and the cross-sectional area to obtain the flow rate output 5.

Next, the waveforms from each point a to f in Figure 1 are shown in Figure 2 a.
- f respectively.

FIG. 2a shows the received signal waveform including the Doppler shift frequency amplified by the high frequency amplifier 202.
Before being input to the comparator 302, the signal is detected and becomes the Doppler shift signal waveform shown in FIG. The waveforms c and d in the figure are the output waveforms of the full-wave rectifier 304 and the average value detector 306, respectively, and are shaped into signals proportional to the magnitude of the Doppler shift signal. Figure e shows the reference signal e that is the output of the hysteresis controller 308. This reference signal e is combined with the output f of the comparator 302 shown in the figure f and the average value detector 3.
Based on the output d of 06, the polarity of the output f is set to a value having the magnitude of the output d. Therefore, the comparator 302 compares the reference value e with the Doppler shift signal b, and generates the output f in the figure during a period in which the Doppler shift signal b exceeds the reference signal e. This output f is input to the hysteresis controller 308 to form a hysteresis loop as described above, while this output f becomes a signal proportional to the Doppler shift frequency.

When the Doppler shift signal becomes small in this way, the magnitude of the reference signal e also becomes small and the hysteresis becomes small, so that no counting error occurs. Furthermore, when the input signal becomes large, the hysteresis also becomes large, and noise superimposed near zero can be effectively removed.

As described above, according to the present invention, the hysteresis of the comparator with hysteresis always follows the magnitude of the input signal, so that changes in the concentration of scatterers, deterioration of the characteristics of the transmitter and receiver, and the change in the gain of the high and low frequency amplifier over time Even if the input signal strength changes significantly due to changes in the acoustic coupling between the conduit wall and the detector, the ratio of the input signal to the hysteresis is always the same, ensuring high accuracy and stability. This has the effect of being able to count Doppler shift frequencies.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the overall configuration of an embodiment of the present invention, and FIG. 2 is a diagram showing signal waveforms at each point in FIG. 1. 102... Transmitter, 104... Transmitter, 106
...Scatterer, etc., 108...Receiver, 202...High frequency amplifier, 204...Envelope detector, 206...
... Filter, 208 ... Low frequency amplifier, 302
. . . Zero cross comparator, 304 . . . Full wave rectifier, 306 .

Claims (1)

[Scope of Claims] 1. A transmitting means for transmitting ultrasonic waves of a constant frequency to a fluid to be measured flowing through a flow path, and an ultrasonic wave receiving means for receiving reflected waves including a Doppler shift frequency by the fluid and transmitted waves from the transmitting means. sound wave receiving means; envelope detection means for envelope-detecting the output of the receiving means and extracting a reflected signal of the Doppler shift frequency component; comparing the reflected signal from the means with a reference signal to be described later; a comparison means for outputting a signal proportional to the shift frequency; a means for outputting a signal proportional to the magnitude of the reflected signal; and a polarity outputted by the comparison means, the magnitude of the reflected signal hysteresis control means for outputting a signal having a value proportional to the reference signal as the reference signal; and means for calculating the flow rate of the fluid to be measured in accordance with the signal proportional to the Doppler shift frequency from the comparison means. Ultrasonic Doppler flowmeter featuring