JPS62187272A - Pulse radar - Google Patents

Abstract

PURPOSE:To measure correct time even if there is a noise by slicing a signal obtained by detecting the envelope of a received signal above a constant amplitude value, and differentiating the slice signal and finding a zero-cross point. CONSTITUTION:Reflected light which is radiated from a transmission part 10 through an antenna 13 and received by an object of measurement is received by an antenna 1. This received signal is amplified 3, detected by an envelope detector 4, and then sliced above the constant amplitude value by a comparator 5 and an analog switch 6. Consequently, a slice signal 106 existing after the noise is removed is differentiated by a differentiating circuit 7 to obtain a signal 107 whose middle point crosses zero. The signal is waveform-shaped 8 into a pulse signal 108, which is inputted to a counter 9, so that a time interval between the middle point of the transmitted wave envelope and the zero- cross point is counted in the form of the number of input clocks from a clock oscillator 11. Then, the distance of the body to be measured is computed by an arithmetic display part 12 from the counted number of clocks and displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pulse radar that measures distance using pulse waves.

[Conventional technology]

Measurements using pulse radar emit a pulse modulated wave with a rectangular envelope, and measure the distance from the reception time until the reflected wave from the target object is received.

Note that the pulse radar may use not only radio waves but also ultrasonic waves, but the principles are the same.

[Means to be solved by the invention]

In a pulse radar, a transmitted wave repeatedly emits a waveform including several waves of constant amplitude, as shown in FIG. The received wave is received with a delay of the time it takes to propagate twice the distance to the target object. The waveform at this time does not have a rectangular envelope line as shown in the figure, but a mountain-shaped waveform with gentle rises and falls.

Conventionally, when measuring distance, the rise time t0 of the transmitted wave,
The time difference between the rise and the rise of the received wave is taken, but in order to distinguish the received wave from noise, this time difference t was determined by assuming that the received wave arrived when it exceeded a certain threshold level m. . However, since the rise of the received wave is gentle, waveforms below level m are ignored, resulting in an error of ΔL. If the level m is lowered, the error will be reduced, but there is a risk that noise will be mistaken for a signal.

SUMMARY OF THE INVENTION An object of the present invention is to provide a pulse radar that eliminates the above-mentioned drawbacks and can accurately measure time even in the presence of noise.

[Means for solving problems]

The pulse radar of the present invention includes means for slicing a signal obtained by envelope detection of a received wave at a predetermined amplitude value or more.

means for differentiating the slice signal to find a zero crossing point;
The apparatus includes means for determining the time interval between the midpoint of the transmitted wave envelope waveform and the zero crossing point.

[Effect]

In the present invention, the time measurement point is the midpoint of both the transmitted wave and the received wave. The received wave is sliced into a waveform with a level higher than that which can be sufficiently distinguished from noise, and the midpoint is determined by differentiating the sliced waveform and finding the zero crossing point. From the waveform of the received wave, the differential zero crossing point indicates the midpoint. Since the noise is removed, the noise is not differentiated.

The time can be determined correctly even at the rising edge of the transmitted wave, but from the relationship of the received wave, if the midpoint is used as the reference point,
This will accurately measure the time difference between received waves.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic block diagram of a pulse radar using radio waves. Figure 2 shows the waveforms of each part.

Radio waves are emitted from the transmitter 10 via the antenna 13, and the antenna 1 receives reflected waves from the object to be measured. The antennas 1 and 13 may be a common antenna. Although the received signal 101 of the antenna l contains noise, the noise P away from the radio wave frequency is removed by the tank circuit 2. However, noise Q at the frequency of the radio wave or a nearby frequency is mixed in as is. Next, the signal 103 amplified by the amplifier 3 is detected by the envelope line detector 4, and then the waveform having the amplitude level E or higher is sliced. This slicing is performed by a comparator 5° analog switch 6. The detected signal 104 includes not only the envelope of the signal S but also noise Q, although the amplitude is small as shown. Therefore, the comparator 5 sends a gate signal 105 to the analog switch 6 to make the signal conductive only when the signal is at level E or higher. As a result, a signal 106 from which noise Q has been removed is obtained.

Since the signal 106 reaches its maximum value exactly at the midpoint of the received signal S, when it is differentiated by the next differentiating circuit 7, the signal 107
As in, the midpoint crosses zero. Next, the waveform shaping circuit 8 shapes the pulse signal 108 so that the midpoint falls. The waveform shaping may be performed using, for example, an operational amplifier that outputs "1" when the input signal is positive. The signal 108 is input to the reset terminal of the counter 9, and is reset at the falling edge.

A pulse signal 109 that falls at the midpoint of the waveform of the transmitter 10 is input to the log counter 9 at the cent terminal, and when a transmission wave is generated, the counter 9 is set at the midpoint of the transmission wave, and the signal 109 due to the reception wave is set. The time until the clock is reset is counted by the number of high-power clocks from the Cronk oscillator 11. The calculation/display unit 12 calculates the distance to the object to be measured from the counted number of clocks and displays the distance.

If the frequency is low, the midpoint of the transmitted wave is determined when the number of pulses in the rectangular pulse train is known, so the number of pulses is 1.
/2 can be calculated by counting.

If the frequency is high, it may be determined from the midpoint of the modulated wave.

In the above description, the conditions for selecting level E for slicing are not strict. In the conventional method, the time point when level E is reached is used as the time reference, but in the present invention, this is simply for noise removal.

The above embodiment is a case where radio waves are used, but in the case of ultrasonic waves, a similar circuit configuration may be used if a resonant vibrator is used instead of the antenna.

〔Effect of the invention〕

As described in detail above, in the present invention, noise contained in a signal obtained by envelope detection of a received wave is removed by setting a certain level and slicing the signal. Even if the transmitted wave is a pulse train of constant amplitude with a rectangular envelope, the received wave's envelope will have a mountain-shaped center at the center due to the propagation characteristics, so if you differentiate and find the zero crossing point, the zero crossing point will be the midpoint. It becomes like this.

This determination of the midpoint is accurate because it is determined regardless of the rising state of the received wave, and the distance between the midpoint of the transmitted wave and the lid can be determined without error.

As described above, the pulse radar of the present invention can perform distance measurement without causing errors in measurement values due to noise contained in the received signal and the rising state of the waveform.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of an embodiment of the present invention, FIG. 2 is a signal waveform diagram of each part of the block diagram, and FIG. 3 is a diagram for explaining conventional distance measurement. 1.13 - antenna, 4 - envelope detector, 5 - comparator, 6 - analog switch, 7 - differentiator circuit, 8 -
Waveform shaping circuit, 9--counter, 10- transmitter.

Claims (1)

[Scope of Claims] A pulse radar that measures distance based on the reception time of reflected waves includes means for slicing a signal obtained by envelope detection of a received wave at a constant amplitude value or more, and differentiating the slice signal to find a zero crossing point. and means for determining the time interval between the midpoint of the transmitted wave envelope waveform and the zero crossing point.