JPS58205817A - Ultrasonic respiration current meter - Google Patents

Abstract

PURPOSE:To enable the measurement of a flow velocity in a stable manner without being affected by the turbulence of gas, by detecting the amplitude of an ultrasonic wave reception signal in each measurement of the flow velocity, and by controlling the gain of an AGC circuit according to the amplitude. CONSTITUTION:An ultrasonic wave emitted from each oscillator reaches each oscillator opposite to the former, and is transduced into an electric signal, which is amplified by reception circuits 7 and 8. The outputs of the reception circuits 7 and 8 are input to AGC circuits 9 and 10 and a peak hold circuit 11. The peak hold circuit 11 controls the gain of the AGC circuits 9 and 10 according to the amplitude of the ultrasonic wave reception signal. Consequently, the ultrasonic signal transmitted and received from a driving pulse is amplified by the AGC circuits 9 and 10 having an appropriate gain.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a pneumotachograph using ultrasound.

[Technical background of the invention and its problems]

Traditionally, medical pneumoflowmeters include differential pressure type (a resistive object such as a thin tube or orifice is placed in the flow path and the flow rate is determined from the pressure difference between the two ends), hot wire type (a hot wire type placed in the flow path) One-impeller type (a turbine is placed in the flow path and the flow velocity is determined from the number of revolutions) has a long lifespan. However, these measurement methods require that there are structures inside the flow path that may become obstacles or create resistance, that the measured values may change due to the effects of temperature, humidity, gas composition, etc. It is difficult to measure respiratory flow rate continuously for a long period of time due to the complicated nature of the method. Therefore, as a method to solve the above-mentioned problems, a respiratory flow rate needle using the difference in propagation time of ultrasonic waves was devised. According to this method, the propagation time (TI) of ultrasonic waves and the propagation time difference (Δ
t) is measured, and the flow velocity (■) is determined based on the following formula.

However, in this method, the received ultrasonic signal is attenuated due to gas turbulence in the flow path when the flow velocity is high or when the flow velocity changes rapidly. Therefore, measurement of propagation time and time difference becomes unstable, making it difficult to measure flow velocity values.

[Purpose of the invention]

The object of the present invention is to improve the above-mentioned conventional drawbacks and to provide an apparatus for stably measuring flow velocity using an ultrasonic propagation time difference method.

[Summary of the invention]

In order to achieve this objective, the present invention detects the amplitude of the ultrasonic reception signal for each flow velocity measurement, and according to the amplitude,
A means for stably receiving the signal by controlling the amplitude of the received signal was added to the conventional ultrasonic pneumotachograph.

(Example of the invention) The present invention will be explained in detail below.

FIG. 1 shows a block diagram of the respiratory flow rate needle of the present invention. The operation of the device is recommended using the output clock of clock 1) as a reference clock, which is 100 MHz in this embodiment. The timing pulse generation circuit 2 is driven by a clock (g) and generates all pulses that control the operation of the device. As shown in FIG. 2, the flow velocity value is measured using lQmsa, which is output by a peak hold pulse.

It is done every time. Also, along with the output of this peak hold pulse, 5 pulses are output at 1μ intervals for 1 m5ecflj
The timing pulse generation circuit 2 outputs multiple driving pulses that are generated at J intervals of 5@. This pulse drives the driving circuit 3, 4 and the ultrasonic transducers (5) (c) 5, 6. The ultrasonic waves emitted from the transducers (6), (B) 5 and 6 are transmitted to the opposing transducers (C) and (6) 6.
It propagates towards ゜5. Along the way, the υ propagation speed changes depending on the direction in which the gas flows. In this example, since the gas is flowing in the direction of the arrow, the oscillator @-5 and the oscillator @-6
The speed of ultrasound waves traveling in the opposite direction is delayed. Opposing vibrator■.

The ultrasonic waves arriving at @5.6 are converted into electrical signals and amplified by the receiving circuit @7.8. This receiving circuit prisoner @7.
The input number 8 is the same as shown in FIG. Receiving circuit prisoner 0
The outputs of 7 and 8 are input to AGC circuits 9 and 10 and a peak hold circuit 11. The k:'-p ho/L/do circuit 11 is driven by the peak hold pulse and receives and transmits nine ultrasonic signals and amplitudes using the first five drive pulses. Transmission and reception of ultrasonic signals using each of the five drive pulses is shown in FIG.

The time between the initialization pulse output next to the five drive pulses and the fourth waveform of the ultrasonic signal received by the receiving circuit (8) 7 is defined as the ultrasonic propagation time T, and The ultrasonic signal received at (B) is 9
The time with the fourth waveform is taken as the ultrasonic propagation time difference T. Now, the output signal of the peak hold circuit 11 is added as a gain and control signal to the AGC circuit (5) (b) 9.10. Therefore, the ultrasonic signals transmitted and received by the next five drive pulses are amplified by the AGO circuit (B) 9.10 having an appropriate gain. Next, this amplified electrical signal is sent to the waveform circuit) (B) 12.1
After being converted into a pulse in step 3 (Figure 3), the pulse extraction time w
Only the fourth pulse is extracted at I(5)(B) 14 and 15, and this pulse (Fig. 3) is sent to the T counter 16 which measures the ultrasonic propagation time, and the ΔT counter 17 which measures the ultrasonic propagation time difference. , which is further input to a flip-flop 18 which determines the direction of flow.

As mentioned above, the T counter 16 starts counting by the initializing pulse output from the timing generating circuit 2, stops p counting by the output pulse from the pulse extracting circuit 14, and then the T counter 16 starts counting. p
The frequency is 10 MHz in this case. Also, the ΔT counter 17 first receives an initialization pulse! After 771-1, the pulse extraction circuit (A) @14.15 starts counting with the pulse that arrived first, stops counting with the pulse that arrives later, and measures ΔT, but the clock for this time measurement is based on the clock (6 ). Similarly, the direction discrimination flip-flop 18 is first cleared by an initializing pulse and then set by pulses from the pulse extraction circuits (A) and (B) 14 and 15.
It is reset and its state is determined by the pulse that arrives later.

After this operation is repeated three more times, the timing pulse generation circuit 2 applies the data collection pulse (FIG. 3) to the interrupt controller 19, and the microprocessor 20 receives the output from the interrupt controller 19. T counter 16, ΔT counter 17 .
Read the contents of the direction determination flip-flop 18, store the data in the ROM/RAM 22, and then
1) The APU 23 performs numerical calculations based on the formula, and outputs the results via the D/A 24. Therefore D
/A output) The flow velocity value sampled every 10 m5ec is output.

〔Effect of the invention〕

As described above, according to the present invention, each time the flow velocity value is sampled, the amplitude of the received ultrasonic signal that reflects the state of the gas is first detected, and the gain of the AGC circuit is controlled based on the result. Therefore, the ultrasonic signal can be processed stably and at an appropriate amplitude, so it has the advantage of being able to measure flow velocity stably without being affected by gas turbulence caused by high flow velocity measurements or sudden changes in flow velocity. be.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG.
The figure is a time chart for explaining the operation of the embodiment. 3.4... Drive circuit, 5.6... Ultrasonic transducer, 7.8... Receiving circuit, 11... Peak hold circuit, 9.10... AGC (b) path,
16...T counter, 17...ΔT counter, 18... Direction determination flip-flop.

Claims (1)

[Claims] A transducer attached to the flow path, a transmitter/receiver circuit that drives the transducer and receives the ultrasonic signal, means for measuring the magnitude of the received ultrasonic signal, and is controlled by the output of the above means. An ultrasonic respiratory current meter that includes a circuit that changes the gain and measures the propagation time or propagation time difference of ultrasonic waves in the output to determine the flow velocity.