JP2004309424A - Microwave level switch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately determine either of transmission or block of a microwave, without complicating a gain regulation circuit, even when an echo sounder transmitter is distant from an echo sounder receiver. <P>SOLUTION: This microwave level switch is provided with the microwave echo sounder transmitter for emitting an oscillation signal from a microwave oscillator as a microwave from an antenna, an antenna for receiving the microwave from the microwave echo sounder transmitter, a Doppler module having an oscillation circuit, and for outputting a signal brought into a prescribed frequency difference with respect to a frequency of the microwave received by the antenna, a logarithmic amplifier module provided with a logarithmic amplifier for logarithm-compressing and amplifying a signal output from the Doppler module, and a switching means for comparing a level of an output signal voltage of the logarithmic amplifier module with that of a set voltage, for determining the either of the transmission or block of the microwave, based on a comparison result, and for controlling start-up of an output drive circuit , based on a determination result therein. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
According to the present invention, a microwave transmitter and a microwave receiver are arranged to face each other, and the level of an object to be detected is detected by blocking or transmitting microwaves from the microwave transmitter to the microwave receiver. Regarding the wave level switch.
[0002]
[Prior art]
FIG. 6 shows a conventional microwave level switch, for example. FIG. 6 is a block diagram showing the microwave level switch. In FIG. 1, a transmitter 10 includes a microwave oscillator 11 and a transmitter antenna 12, and an oscillation output from the microwave oscillator 11 is output from the transmitter antenna 12. The receiver 20 includes a receiver antenna 21, a detection circuit 80, a variable gain amplifier 81, a gain setting circuit 82, a level determination circuit 83, and an output drive circuit 50.
[0003]
In the microwave level switch having such a configuration, first, the microwave output from the transmitter 10 is received by the receiver antenna 21 of the receiver 20 and detected by the detection diode in the detection circuit 80. The detected detection signal is amplified by a variable gain amplifier 81 and then input to a level determination circuit 83 where it is compared with a predetermined value.
[0004]
Here, when there is no object to be detected between the transmitter 10 and the receiver 20, the microwave from the transmitter 10 is received by the receiver 20 without being interrupted. The reception power becomes larger than a predetermined value. On the other hand, when an object to be detected exists between the transmitter 10 and the receiver 20, the microwave from the transmitter 10 is cut off and the reception power of the detection signal is reduced. Becomes smaller than a predetermined value. Therefore, for example, by arranging the transmitter 10 and the receiver 20 to face each other at a predetermined height of the storage container, the stored amount (level) of the detected object can be detected. Then, the result is output to the output drive circuit 50 to drive the display device and the like.
[0005]
[Problems to be solved by the invention]
However, in the conventional microwave level switch, since the magnitude of the received power at the receiver 20 decreases in inverse proportion to the square of the distance from the transmitter 10, if the usable distance range is increased, The reception power range to be determined is widened, and it is necessary to adjust the gain of the variable gain amplifier 81 over a wide range. Further, when the received power of the microwave decreases, the detection output signal sharply decreases due to the square detection characteristics of the detection diode in the detection circuit 80. Therefore, the gain adjustment range of the variable gain amplifier 81 must be further expanded.
[0006]
For example, if the operating distance is 0.3 m to 30 m, and if the output of the transmitter 10 is constant, the received power at 30 m is about 0.0001 times (−40 dB) as compared with 0.3 m. Become. Accordingly, when the reception power becomes about 0.0001 times (-40 dB), the detection output signal becomes a very small voltage of about 0.0000001 times (-80 dB) due to the square detection characteristics. As a result, the gain adjustment range of the variable gain amplifier 81 needs to be at least 80 dB, but in order to realize such a wide range, a plurality of stages of amplifiers must be used so that the gain can be adjusted in each amplification stage. And the circuit becomes complicated.
[0007]
Further, when the received power is reduced to a certain extent, the detection output signal becomes buried in the noise level, and thus cannot be used in such a low received power environment.
[0008]
The present invention has been made in view of such a situation, and even if the distance between the transmitter and the receiver is large, without complicating the gain adjustment circuit, it is possible to transmit or block the microwave. It is an object of the present invention to provide a microwave level switch capable of accurately determining whether or not the microwave level is high.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a microwave transmitter and a microwave receiver opposed to each other, and shields or transmits microwaves from the microwave transmitter to the microwave receiver. In a microwave level switch that detects the level of a detection object,
A microwave transmitter that emits an oscillation signal from a microwave oscillator as a microwave from an antenna,
An antenna for receiving microwaves from the microwave transmitter;
A Doppler module that has an oscillation circuit and outputs a signal having a frequency that is a predetermined frequency difference between the frequency of the received microwave received by the antenna and
A log amplifier module including a logarithmic amplifier that logarithmically compresses and amplifies a signal output by the Doppler module,
Switch means for comparing the magnitude of the output signal voltage of the log amplifier module with the set voltage, determining one of transmission and blocking of the microwave based on the comparison result, and controlling the activation of the output drive circuit based on the determination result. A microwave level switch is provided.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of a microwave level switch according to the present invention will be described with reference to the drawings.
[0011]
(1st Embodiment)
FIG. 1 is a block diagram showing a configuration of the first exemplary embodiment of the present invention. As shown in the figure, the microwave level switch is configured by arranging a transmitter 10 and a receiver 20 to face each other. The transmitter 10 includes a microwave oscillator 11 and a transmitter antenna 12, and an oscillation output from the microwave oscillator 11 is emitted from the transmitter antenna 12. The receiver 20 includes a receiver antenna 21, a Doppler module 22, a log amplifier module 30, a level comparison circuit 40, a determination level setting circuit 41, and an output drive circuit 50. Here, the Doppler module 22, the log amplifier module 30, the level comparison circuit 40 as the switch means, and the judgment level setting circuit 41 constitute a main part of the microwave level switch.
[0012]
The Doppler module 22 also incorporates an oscillation output signal from an oscillation circuit incorporated therein and a received microwave emitted from the transmitter 10 and received by the receiver antenna 21 in the Doppler module 22. The signal is mixed by a mixing circuit, and functions to output a signal having a difference frequency between the frequency of the oscillation output signal and the frequency of the received microwave (hereinafter, referred to as “intermediate frequency signal”). This intermediate frequency signal is provided to a filter circuit of the log amplifier module 30 described later, and unnecessary frequency band components are cut.
[0013]
As shown in FIG. 2, the log amplifier module 30 includes filter circuits 31, 33, and 34 for preventing noise from entering from outside, and a log amplifier circuit 32. The output signal line and the power supply line of the log amplifier module 30 can be antennas for external radio waves. Therefore, the inflow of the high-frequency voltage from the output signal line or the power supply line is prevented by the filter circuits 33 and 34. Further, the log amplifier module 30 is entirely housed in a shield case such as a metal case and is electromagnetically and electrostatically shielded.
[0014]
In the log amplifier module 30, the intermediate frequency signal output from the Doppler module 30 is taken into the filter circuit 31, and an unnecessary frequency band component is cut. Further, the log amplifier module 30 functions to logarithmically amplify the signal obtained by cutting the unnecessary component by the log amplifier circuit 32 and output the logarithmically amplified log amplifier output signal through the reduced-pass filter circuit 33.
[0015]
The level comparison circuit 40 functions to compare the comparison voltage set by the determination level setting circuit 41 with the log amplifier output signal voltage from the log amplifier module 30. The output drive circuit 50 such as a relay is driven based on the comparison result. The value of the comparison voltage that can be set by the determination level setting circuit 41 can be easily changed by a variable resistor or the like built in the determination level setting circuit 41.
[0016]
Next, the operation will be described. First, a microwave is output from the transmitter antenna 12 of the transmitter 10. Here, the oscillation frequency of the microwave oscillator 11 of the transmitter 10 is set in advance so as to be a predetermined frequency difference from the oscillation frequency of the oscillation circuit in the Doppler module 22 of the receiver 20.
[0017]
Then, the receiver 20 receives the microwave from the transmitter 10 via the receiver antenna 21. The Doppler module 22 heterodyne-detects the received microwave using the oscillation circuit and the mixing circuit in the Doppler module 22, and obtains an intermediate frequency signal from the output of the mixing circuit.
[0018]
Since the magnitude of the intermediate frequency signal is proportional to the power of the microwave received by the receiving antenna 21, it does not become extremely small in a region where the received power is small as compared with the method of directly detecting the received microwave by the detection circuit. . As a result, even smaller received power can be handled without being buried in noise, so that microwave reception determination can be made more sensitive.
[0019]
Also, since the log amplifier circuit 32 logarithmically amplifies the intermediate frequency signal, the magnitude of the output signal voltage of the log amplifier circuit 32 is obtained by amplifying the magnitude of the intermediate frequency signal while logarithmically compressing it. . Therefore, the range from a very small level to a large level of the intermediate frequency signal can be handled by the output voltage of the log amplifier circuit 32. Therefore, the minimum reception power required to determine whether the microwave is transmitted or blocked between the transmitter 10 and the receiver 20 can be reduced, and the operation sensitivity as a level switch is improved.
[0020]
Further, the level comparison circuit 40 compares the magnitude of the comparison voltage set by the decision level setting circuit 41 with the output signal voltage from the log amplifier module 30, and based on the result of the comparison, determines whether the microwave is transmitted or cut off. Function as switch means for controlling the activation of the output drive circuit 50 based on the result of the judgment. Therefore, the area in which the output drive circuit 50 can operate is a wide range from a very small level to a large level of the intermediate frequency signal, and the determination level setting circuit 41 can be realized with a small circuit scale. Also, in actual use, the gain setting is complicated because the gain is adjusted in each stage by using a plurality of stages of amplifiers in the related art, whereas the gain setting is simple and easy in the present invention.
[0021]
(Second embodiment)
FIG. 3 is a block diagram showing a second embodiment of the present invention. In the second embodiment, instead of the level comparison circuit 40 and the determination level setting circuit 41 of the first embodiment, an A / D converter 60, a microcomputer 61 having a function as a switch, a setting circuit 62, and a display The circuit 68 is provided. Here, the A / D converter 60, the microcomputer 61, and the setting circuit 62 constitute a microcomputer wave level switch together with the Doppler module 22 and the log amplifier module. Hereinafter, only the changed part of the second embodiment will be described.
[0022]
An output signal from the log amplifier module 30 is given to the A / D converter 60, and a digital conversion output of the A / D converter 60 is connected to one input port of the microcomputer 61. The setting circuit 62 is connected to another input port of the microcomputer 61. An output drive circuit 50 and a display circuit 63 are connected to an output port of the microcomputer 61.
[0023]
The A / D converter 60 functions to convert an analog output signal from the log amplifier module 30 into a digital signal and input the digital output signal to one input port of the microcomputer 61. The setting circuit 62 has an up switch and a down switch, and when these switches are depressed, functions to input a change in the value of the log amplifier comparison determination data described later to another input port of the microcomputer 61. .
[0024]
The microcomputer 61 includes an EEPROM (non-volatile memory) for storing log amplifier comparison determination data. When the up switch or the down switch is pressed, the microcomputer 61 has a function of incrementing or decrementing the value of the log amplifier comparison determination data stored in the EEPROM and displaying the value on the display circuit 63, respectively. Further, the microcomputer 61 functions to compare the value of the log amplifier comparison determination data with the output value of the log amplifier module 30. The output drive circuit 50 is started in accordance with the result of the comparison operation. At this time, the microcomputer 61 functions as a switch for switching between transmission and blocking of the microwave.
[0025]
Next, the operation will be described with reference to the flowchart shown in FIG. First, when the power of the microwave level switch is turned on, the microcomputer 61 reads the value of the log amplifier comparison determination data stored in the EEPROM and displays the value on the display circuit 63. Next, the up switch or the down switch of the setting circuit 62 is depressed, and the microcomputer 61 changes the value of the log amplifier comparison determination data stored in the EEPROM according to the content defined by the depressed setting switch. The process (step S11) is executed. When one of these switches is pressed, the value of the log amp comparison determination data stored in the EEPROM is incremented. On the other hand, when the down switch is pressed, the value of the log amplifier comparison determination data stored in the EEPROM is decremented.
[0026]
Next, the microcomputer 61 causes the display circuit 63 to display the value of the log amp comparison determination data thus incremented or decremented, stores the value in the EEPROM (step S12), and terminates the switch pressing process. I do.
[0027]
Next, the output drive processing of the output drive circuit 50 will be described with reference to the flowchart of FIG. This output drive process is usually invoked and processed at very short time intervals. When the microcomputer 61 detects the output drive processing request, it starts the output drive processing and inputs the output signal of the log amplifier module 30 via the A / D converter 60. At this time, the log amplifier output signal voltage is A / D converted by the A / D converter 60, and is taken into the microcomputer 61 (step S21). Next, the microcomputer 61 compares the value of the log amplifier output value captured in this way with the value of the log amplifier comparison determination data stored in the EEPROM (step S22). Then, according to the magnitude comparison result, it is determined whether the microwave is transmitted or cut off, and the output drive circuit 50 such as a relay is drive-controlled (step S23).
[0028]
In the above description, an example in which the drive circuit 50 is operated immediately based on the result of the magnitude comparison in the output drive processing has been described. However, the log amplifier output value changes the value of the log amplifier comparison determination data for a certain period of time or a certain number of times. The drive circuit 50 may be operated with a delay by changing the drive state of the output drive circuit 50 for the first time when the drive circuit 50 exceeds the threshold or continuously lowers. As a result, the instantaneous change of the output drive circuit 50 can be suppressed, so that the drive control of the drive circuit 50 can be performed accurately and stably.
[0029]
As described above, the present invention does not use the mixing circuit constituting the Doppler module 22 as the original Doppler module as described in each embodiment, but uses the frequency of the microwave from the transmitter 10 and the receiver. The frequency difference from the oscillation frequency of the Doppler module 22 is obtained, that is, the heterodyne detection is performed by the mixing circuit of the Doppler module 22, and the intermediate frequency signal is obtained. Only the intermediate frequency signal is reduced in proportion, and the gain adjustment range of the amplifier can be narrowed as compared with the conventional one.
[0030]
In addition, a logarithmic amplifier is used for a circuit for amplifying the intermediate frequency signal or a circuit for amplifying a signal obtained by detecting the intermediate frequency signal, and the magnitude of the output of the logarithmic amplifier is determined by a voltage comparator. Thus, there is an effect that the determination of either the transmission or the blocking of the microwave can be handled without any problem even if the reception power range is sufficiently increased without having the gain adjustment mechanism of the amplifier.
[0031]
Furthermore, by performing heterodyne detection, if the reception power of the microwave decreases, the intermediate frequency signal only decreases in proportion to it, so the minimum reception power required to determine either transmission or cutoff Is reduced, and the operation sensitivity as a level switch can be improved.
[0032]
【The invention's effect】
As described above, according to the present invention, even if the distance between the transmitter and the receiver is large, it is possible to accurately determine whether to transmit or block the microwave without complicating the gain adjustment circuit. A microwave level switch that can be performed is obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a microwave level switch according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing details of a log amplifier module in FIG. 1;
FIG. 3 is a block diagram illustrating a microwave level switch according to a second embodiment of the present invention.
FIG. 4 is a flowchart showing a procedure for setting log amplifier comparison data by a setting circuit in FIG. 3;
FIG. 5 is a flowchart showing an operation flow of the output drive circuit in FIG. 3;
FIG. 6 is a block diagram showing a conventional microwave level switch.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Transmitter 11 Microwave oscillator 12 Transmitter antenna 20 Receiver 21 Receiver antenna 22 Doppler module 30 Log amplifier module 31, 33, 34 Filter circuit 32 Log amplifier circuit 40 Level comparison circuit (switch means)
41 judgment level setting circuit 50 output drive circuit 61 microcomputer (switch means)
62 Setting circuit

Claims (3)

In a microwave level switch in which a microwave transmitter and a microwave receiver are arranged opposite to each other and the level of an object to be detected is detected by blocking or transmitting microwaves from the microwave transmitter to the microwave receiver. ,
A microwave transmitter that emits an oscillation signal from a microwave oscillator as a microwave from an antenna,
An antenna for receiving microwaves from the microwave transmitter;
A Doppler module that has an oscillation circuit and outputs a signal having a frequency that is a predetermined frequency difference between the frequency of the received microwave received by the antenna and
A log amplifier module including a logarithmic amplifier that logarithmically compresses and amplifies a signal output by the Doppler module,
Switch means for comparing the magnitude of the output signal voltage of the log amplifier module with the set voltage, determining one of transmission and blocking of the microwave based on the comparison result, and controlling the activation of the output drive circuit based on the determination result. A microwave level switch, comprising: The microwave level switch according to claim 1, wherein the log amplifier module is housed in a shield case. 3. The microwave level switch according to claim 1, wherein a filter circuit for preventing noise intrusion is connected in the middle of a line connecting the log amplifier module and an external circuit.

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