JPS58135478A - Ultrasonic speedometer - Google Patents

Abstract

PURPOSE:To measure the speed of an object travelling at >=90km/H speed, by switching the oscillating frequency of a speedometer using a Doppler effect within a working band of a receiver/transmitter. CONSTITUTION:The oscillating frequency of an oscillator 8 is changed in 3 steps by a switching operation of a switch 9. The oscillator 8 is usually oscillated with an intermediate frequency WO i.e., the switch 9 is fixed at a position of resistance RX=RO. Under such conditions, the speed V can be measured for a travelling object 4 regardless of its travelling direction as long as the speed of the object 4 is <=90km/H. However, the switch 9 is previously switched so as to obtain resistance RX=RL in case the approach of the object 4 can be expected. As a result, the oscillating frequency of the oscillator 8 is changed to omegaL, and the reflected wave of the object 4 is changed to a higher level by DELTAomega from omegaL. Thus the variable range is increased up to omegaH from omegaL, and as a result the measurable maximum value is increased up to a double (180km/H) from 90km/H.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speedometer that utilizes the Doppler effect of ultrasonic waves.

A speedometer that utilizes the Doppler effect of ultrasonic waves is based on the fact that the frequency of the reflected waves of ultrasonic waves emitted from a single oscillator from a moving object changes according to the speed of the moving object, as is well known. That kind of relationship means that the frequency of the transmitted wave is ω0. If the speed of the moving object is V, the frequency ωr of the two reflected waves is expressed by the following equation.

ωr=(1+-1L)ω0・・・・・・・・・・・・
・・・・・・・・・・・・・(1) P However, 0 is the propagation speed of the ultrasonic wave.

Therefore, the frequency of the reflected wave shifts by 2vω010 depending on the speed of the moving object. If we express this as Δω, when a moving object approaches the speedometer.

ω[=ω0+Δω ・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・C) When moving away, ωr=ω0−Δω ・・・・・・・・・・・・・−
・・・・・・・・・・・・・・・・・・(8) From this, the velocity V of the moving object can be found by calculating Δω.

FIG. 1 is the simplest configuration diagram of this type of speedometer. In this figure, 2 is a transmitter consisting of an ultrasonic transducer, 3
is also a receiver. Oscillator 10 oscillation output is sent to transmitter 2
1C converts it into an ultrasonic wave and radiates it into space, but at the same time it is supplied as a local oscillation signal to the mixer 5. The reflected wave from the moving object 4 is converted into an electric signal by the transfer device 5, and then only the difference frequency component (M) is extracted by the mixer 5. Furthermore, the value of Δω is measured using the frequency measuring device 6.

The speed V of the moving object 4 obtained from the result is displayed on the display 7. However, in this 3 P case, it is impossible to know whether Δω has shifted to the (+) side or to the (-) side due to the nature of the mixer.

will be determined. FIG. 2 shows the bandwidth of the ultrasonic transducer. FIG. 2 shows the frequency characteristics of the transducer for the transmitter, and shows the relationship between the frequency of the input electric signal and the output level of the output ultrasonic wave. The transducer for the receiver has similar characteristics in terms of receiving sensitivity.

Since the level rapidly decreases when the frequency ω is above ωH or below ωL, the bandwidth is (ωH - ωL). Since the frequency ω of the oscillator 1 is selected to be the center value of ωH and ωL, when the moving object 4 approaches, ωr shifts by Δω from ω0 to the ωH side. Conversely, when moving away, ωr shifts by Lω towards the ωL side.

The maximum value Δωmax that can be shifted is 1ωH−ωL Δωmax = ωH−ω0=ω0−ωL−, 2 rivers (4)
becomes.

In reality, the bandwidth of an ultrasonic transducer is so narrow that it does not pose a problem, but it is manufactured especially for a wide band, and is about ω0±15%.

In this case, the maximum measurable value of the velocity V of the moving object is (1)
According to the formula, it is approximately 901H. (Go to 0=33.

Therefore, measurements cannot be made for speeds exceeding 901 $H.

The present invention has been made in view of the drawbacks of the prior art, and is capable of measuring the speed of an object moving at 9.90 km/h or more by switching one oscillation frequency within the operating band of the transducer. We provide an ultrasonic speed meter that can

An embodiment of the present invention will be described below based on the drawings. Third
In the figure, the oscillation frequency of an oscillator 8 can be changed in three stages by changing the resistance value by switching a switch 9. The details of the oscillator 8 consist of an astable multivibrator using an operational amplifier as shown in FIG. The oscillation period T is well known.

Since T = 201Rxtn (1+"")2 P, T can be set to any value by setting Rx to RH, Ro, or RL.

Now, operate the changeover switch 9... Assume that the oscillation frequency when Rx = R1 is ωLK in Fig. 2, and Rx = R.
If o, then h0. Same (assuming that ωH occurs when Rx==RH).

Oscillator 8Fi usually ω. Let it oscillate. That is.

Fix the switch 9 at the Rx=Ro position.0 In this state, for the reasons already mentioned, if the speed of the moving object is less than 90 kg+/H, the moving direction (approaching/departing)
The velocity V can be measured regardless of. but,
If it is predicted that the moving object 4 will clearly approach, change the switch 9 in advance so that Rx-IJ, and the oscillation frequency of the first oscillator 8 changes to ωLK, and the reflected wave from the moving object 4 changes. is shifted higher than ωL by Δω, and the range in which it can be shifted is expanded from ωm to ωH. That is.

Δω=ωH−ωL, and the amount of deviation that can be measured is (6
It is twice the maximum value at 1'. This means that if it is predicted in advance that the moving object 4 will approach, the maximum measurable value of the velocity V can be doubled from the conventional 90 km/H.
Similarly, if the moving object 4 is expected to move away, the 9 oscillation frequency can be increased by setting the switch 9 to Rx=RH in advance. ωH, and the separation speed of the object can be measured up to a maximum of 180 kll/11.

As described above, according to the present invention, by appropriately switching the oscillation frequency of the 9 oscillators within the operating band of the transducer of the transducer, Doppler type ultrasonic speed can easily measure a wider range of speed than conventional measurable speeds. We can provide a meter.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional Doppler ultrasonic velocity meter.
Figure 2 is a frequency characteristic diagram of the ultrasonic transducer. FIG. 3 is a circuit configuration diagram of an ultrasonic velocity meter showing an embodiment of the present invention, and FIG. 4 is a circuit configuration diagram of an oscillator 7 P in FIG. 3. 2: Transmitter, 3: Receiver, 4: Moving object. 8... Oscillator. Applicant Hitachi Thermal Appliances Co., Ltd. Japanese Patent Publication No. 1983-35478 (3) Fig. 1 Fig. 2yA ff1

Claims (1)

[Claims] In a speedometer that measures the speed of a moving object using the Doppler effect using a pair of ultrasonic transmitting and receiving transducers, the frequency of the signal from the oscillator that excites the transmitting transducer (Q) is set by the transmitting and receiving transducer (2) ( 8) An ultrasonic velocity meter characterized in that switching is made as appropriate within the operating band.