JP2969255B2 - Ultrasonic level sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Industrial application] Ultrasonic level sensor that emits ultrasonic waves and detects and controls the distance based on the reflected wave from the detected object, improves the short distance detection, realizes accurate distance measurement, and wide detection range It is about the contents to do.

[0002]

2. Description of the Related Art In general, in an ultrasonic level sensor, reverberation generated after an ultrasonic wave is emitted is caused by mechanical vibration that continues for a long time in a transmission / reception type sensor. If the reverberation time is longer than the reflection time of the ultrasonic wave, that is, if the detection target is at a short distance from the ultrasonic level sensor, the detection of the detection target is physically impossible. For this reason, a non-detection time period in which no reception signal is detected for a certain period of time after the emission of ultrasonic waves is set, but short-range detection is impossible. In the case of a transmission / reception type sensor, a drive circuit for emitting ultrasonic waves and a reception circuit for receiving sound waves must be taken out from the same sensor terminal. In the case of the measurement, the voltage of the drive circuit had to be increased as shown in FIG. 2, and an element having a large withstand voltage was required, causing problems such as power loss and heat generation.
Also, the resistor R1 requires a large resistance value, and large amplification cannot be expected due to noise.

[0003]

SUMMARY OF THE INVENTION A method for detecting a short distance by switching a distance measurement by a reflected wave of an ultrasonic wave at a short distance and a long distance every cycle of a reflected wave, and a method for accurately detecting a distance. , Which realizes a wide detection range.

[0004]

A short distance and a long distance are switched every cycle of a reflected wave. At a short distance, the pulse emission width is reduced to reduce the detection sensitivity, and at a long distance, a pulse emission is performed. Although the width is increased and the detection sensitivity is increased,
The error of the distance to the detection object is short distance, reflection at long distance
Different by changing the width of the wave and the detection sensitivity,
Because it may increase the distance between to create a data table of the relationship between the width of the reflection wave, the detection distance to the detection object near
Distance measurement range and long-distance measurement range
Each time a short distance measurement is performed,
Select the measurement value according to the reflection width at the
When the measurement is fixed, the measurement is based on the width of the reflected wave during short-range measurement.
The value is selected, and a short-range or long-range measurement switching command is issued.
The measurement distance was corrected by the short distance / long distance switching unit .

[0005]

The present invention eliminates the difficulty of short-range detection due to reverberation and wraparound waves, and eliminates physical errors caused by differences in the intensity of sound waves depending on the reflection distance and the detected object, thereby providing accurate detection. Achieves distance measurement and a wide detection range.

[0006]

FIG. 1 is a block diagram showing an embodiment of the present invention. A CPU 1 controls the entire ultrasonic level sensor. Reference numeral 2 denotes a drive circuit, which supplies a drive signal to the transducer 4. A power supply circuit 3 is a power supply unit for the entire ultrasonic level sensor. Reference numeral 17 denotes a measuring distance adjusting switch which determines a control range. In the embodiment, a dip switch is used.
A button 18 is pressed when the measurement distance measurement mode or the like is determined. Reference numeral 5 denotes a sensor receiving unit that receives the ultrasonic wave transmitted from the transducer 4 and is amplified by the first-stage amplifier 6. Reference numeral 7 denotes a detection unit that converts the AC signal amplified by the first-stage amplification unit 6 into a DC signal. The detection unit 7 detects the AC signal, and the amplified signal is further amplified by the amplification unit 8. Reference numeral 10 denotes a short-distance / long-distance switching unit in which a switching command for short-distance measurement and long-distance measurement is issued from the port a of the CPU 1, which varies the gain of the amplification unit 8 and the detection level of the comparison unit 9. In addition, the width of the emitted wave is varied in the drive circuit 2 for a short distance and a long distance. The rise time of the peak value of the reflected wave is measured from the comparison unit 9 to the A / D input of the CPU 1,
Measure the width of the reflected wave at the interrupt input. 11 is CPU
1 to 4 to 20 mA output.

FIG. 3 is a diagram showing the wiring of the transmitting section, the sensor receiving section, and the first-stage amplifier section incorporated in the driving circuit section of the present invention. The principle of operation is as follows. 1
Reference numerals 2 and 13 denote transmission units which are driven alternately according to the firing frequency by a signal from the CPU. 15 and 16 are FETs and CP
By the gate signal from U, ON when receiving, O when firing
It becomes FF. A signal is sent from the FET to the first-stage amplifier 14 through the resistor R2. In FIG.
13, the same performance can be obtained with half the driving voltage in FIG. Therefore, an element with a high withstand voltage is not required. Since the FETs 15 and 16 have a cut-off at the time of transmission and a low impedance AC at the time of reception, even if R is 0 ohm to the receiving circuit, there is no problem. can get.

FIG. 4 shows the signal waveform of each part of the block diagram of FIG. 1 when the detected object is far, and FIG. 5 shows the signal waveform when the detected object is close. A short-range and long-range emission signal alternates between short-range and long-range emission signals, reducing the pulse emission width and weakening the detection sensitivity, and increasing the pulse emission width at long-range distances. Increase sensitivity and repeat. "b" indicates the amplified reception signal at point "b" in FIG. 1, and the broken line indicates that the wraparound wave is cut on the circuit and the program. In addition, the detection level of the comparison unit 9 detects the presence of an object at a short distance or a long distance, and c measures the width of the reflected wave at the interrupt input at point c in FIG. 1. If the detection width is large, the reflected wave becomes large. If the distance measurement time can be measured accurately and the detection width is small, it means that the reflected wave is small and the accurate distance measurement time cannot be obtained. In this case, some correction is required. d is a switching waveform of the short distance measurement and the long distance measurement in FIG. 1 and shows the switching of the gain from the port a.

FIGS. 6 to 8 are flowcharts showing a microprogram for distance measurement. FIG. 6 shows a main program in which initial settings are made in step 101 and
In step 2, an ultrasonic emission program is set up, distance calculation is performed in step 103, and the process returns to step 101.

In FIG. 6, the firing program of step 102 is as shown in FIG. If the ultrasonic emission time is long, the sensitivity is high, and the ultrasonic emission time is short, the sensitivity is low, the long distance measurement is performed with high sensitivity, the short distance measurement is performed with low sensitivity. Step 107
, High-sensitivity time emission is performed, and distance measurement is prohibited in step 108 when the detection distance is within 80 cm. In step 105, low-sensitivity time firing is performed, and in step 106, the detection distance is 4
Distance measurement is prohibited within 0 cm. In other words, this implementation
In the example, the range of low sensitivity measurement is more than 40cm and less than 80cm
And the high-sensitivity measurement is in a range exceeding 80 cm. still
If the detection distance is less than 40 cm, it cannot be detected in the dead zone.

[0011] The error of the distance to the detection object is a short distance,
At long distances, it may be different and larger depending on the reflected wave width and detection sensitivity, so it is necessary to create a data table of the relationship between distance and reflected wave width and make corrections. Is the step 103 in FIG. 6, specifically as shown in FIG.

[0012] In FIG. 8, in the case of long distance measurement, high sensitivity measurement, in the case of short distance measurement, but calculates the actual distance by the low sensitivity measurement, firstly the distance detected first object 90
A description will be given of the case where the position is at the position of cm. Step 1
When the high sensitivity measurement is performed in step 09, the distance is calculated in step 113 using the high sensitivity reflection width. In step 114, if the distance is larger than 90 cm based on the low sensitivity distance, in step 115, the actual distance = the distance based on the high sensitivity reflection width. The result of the calculation is stored in the memory RAM . If the distance is smaller than 90 cm on the basis of the low sensitivity distance in step 114, the distance is not measured. Therefore, the distance of the detection object is 90 cm
When the position is
The result is assured.

Next, the distance to the detection object exceeds 40 cm
The case where the distance is within 80 cm will be described. Step 10
If high sensitivity measurement is not performed in step 9, distance calculation is performed using the low sensitivity reflection width in step 110, and step 111 is performed.
In greater than 8 0 cm with respect to the low sensitivity range kuna ku, 4
If it is larger than 0 cm , the actual distance =
The result of the distance calculation based on the low-sensitivity reflection width is stored in the memory RAM . In step 111, 80 based on the low sensitivity distance
If not greater than cm, so that the distance measuring are not.
Therefore, the distance to the detection object is over 40 cm and within 80 cm
Distance calculation by low sensitivity reflection width is accurate
Results. As mentioned above, low sensitivity and high sensitivity
Accordingly, only accurate calculation results are stored in the memory RAM.
As a result, more accurate measurement than before can be performed.

As described above, short-distance and long-distance switching are performed for each cycle of the reflected wave, the pulse emission width is reduced in short-distance measurement, the detection sensitivity is weakened, and the pulse emission width is increased in long-distance measurement. By increasing the detection sensitivity, creating a data table of the relationship between the measurement distance and the width of the reflected wave, and performing correction, an accurate distance measurement can be obtained according to the type of the detected object. became.

[0015]

According to the present invention, it is impossible to measure a wide range from a short distance to a long distance due to a wraparound wave. However, an accurate distance measurement according to the type of the detected object can be obtained. Since the drive is operated by the two transmission units, a high-withstand-voltage element is not required, and a marketable element can be used, thereby reducing the cost. As a result, the receiving circuit section and the driving section can be separated from each other, so that the driving circuit can be resistant to noise.

[Brief description of the drawings]

FIG. 1 is a block diagram of the present invention.

FIG. 2 is a diagram showing wiring of a transmitting unit, a sensor receiving unit, and a first-stage amplifying unit incorporated in a conventional driving circuit unit.

FIG. 3 is a diagram showing wirings of a transmitting unit, a sensor receiving unit, and a first stage amplifying unit incorporated in a drive circuit unit of the present invention.

FIG. 4 is a signal waveform of each part of the block diagram of the present invention when a detected object is far away.

FIG. 5 is a signal waveform of each part in the block diagram of the present invention when a detected object is close;

FIG. 6 is a flowchart showing a microprogram for distance measurement.
Chart.

FIG. 7 is a flowchart showing a microprogram for distance measurement.
Chart.

FIG. 8 is a flowchart showing a microprogram for distance measurement.
Chart.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CPU 2 Drive circuit 3 Power supply circuit 4 Transmitter / receiver 5 Sensor receiver 6 First stage amplifier 7 Detector 8 Amplifier 9 Comparison unit 10 Near / far distance switching unit 11 Current output unit 12 Transmitting unit 13 Transmitting unit 14 First stage amplification unit 15 FET 16 FET 17 Measurement distance adjustment switch 18 button

────────────────────────────────────────────────── ─── Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01S 3/80-3/86 G01S 5/18-5/30 G01S 7/52-7/64 G01S 15 / 00-15/96 G01B 17/00 G01F 23/28

Claims (2)

(57) [Claims] An ultrasonic wave transmitter / receiver, a driving circuit unit for driving the ultrasonic wave transmitter / receiver, a sensor receiving unit for receiving an ultrasonic wave received from a detection object of the ultrasonic wave, and a signal of the sensor receiving unit Amplifying unit, a detecting unit for detecting the ultrasonic reception wave, an amplifying unit for amplifying a signal of the detecting unit, a comparing unit for comparing the signal of the amplifying unit, and a long-distance measurement by a reflected wave In an ultrasonic level sensor having means for measuring short distances alternately in one cycle and measuring the distance by the reflected wave , each time a long distance measurement and a short distance measurement are performed,
Measured value by the width of the reflected wave and the short distance at the long distance measurement
The measured value based on the width of the reflected wave at the time of separation measurement is used as the detection distance.
Selection is made according to the command, and a short-range or long-range measurement switching command is issued.
An ultrasonic level sensor having means for correcting a measurement distance by a short distance / long distance switching unit. 2. Two transmitting units driven alternately in accordance with a firing frequency by a signal from a CPU, two transistors driven by a gate signal from the CPU, and a first stage amplifying unit through a resistor from the transistor. The ultrasonic level sensor according to claim 1, wherein a signal is transmitted.