JPH0347559B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an echo signal detection method for an echo telemeter.

An echo telemeter is a sensor that resonates at a specific frequency, such as a crystal oscillator, at the measurement point of an individual to be detected or an individual to be measured, or a sensor that resonates at a frequency determined by the event to be measured. Excitation energy (excitation signal) with a frequency equal to or near the resonant frequency
When the sensor is caused to resonate by being applied from the outside without contact, the sensor continues to vibrate at the resonant frequency while attenuating for a while even after the excitation energy from the outside is cut off. This type of telemeter uses a mobile station (equipped with a sensor, which transmits detection or measurement data There is no need for a power supply means such as a battery or an oscillation circuit that requires an active element in the fixed station (the station that radiates the excitation energy and receives and analyzes the echo signal) and the mobile station. It is widely used in various fields (industrial telemeters, medical telemeters, etc.) because it allows for non-contact.

In this echo type telemeter, since the echo signal is generally a weak signal, it is possible to distinguish between signals other than the echo signal such as noise and the regular echo signal.
That is, improving the S/N ratio for echo signals is an important issue, and the present invention solves this issue,
The present invention provides an echo signal detection method that can dramatically improve the S/N ratio.

That is, in order to solve the above-mentioned problem, the present invention makes it a condition for detecting an echo signal that the signal obtained by comparing the excitation signal of the sensor with the received signal from the sensor is within a set range. .

Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 are block diagrams showing first and second embodiments of the present invention, and FIG. 3 is a time chart illustrating the first and second embodiments.

Each component shown in FIGS. 1 and 2 will be explained below.

A pulse generator 1 generates a pulse signal having a constant pulse width at a constant period. In this embodiment, a clock oscillator that generates a signal serving as a time reference for the entire system is used in this part.

A counter 2 counts the pulses output from the pulse generator 1 and outputs a count output signal for each count. In the embodiment, a binary counter is used.

3 is a digital-to-analog converter (hereinafter referred to as D/analog converter)
A converter) converts the output (digital value) of the counter 2 into a voltage (analog value) at a level corresponding to the output.

4 is a voltage-frequency converter (hereinafter referred to as a V/F converter), which converts the voltage signal output from the D/A converter 3 into a signal with a frequency corresponding to the voltage level of the signal.

A transmitter 5 superimposes the frequency signal output from the V/F converter 4 on a carrier wave to generate radio waves.

Reference numeral 6 denotes a transmit/receive switch, which uses the pulse output from the pulse generator 1 as a control input, connects the output of the transmitter TX to an antenna 7 (described later) when the pulse is present, and connects the output of the transmitter TX to the antenna 7 when the pulse is not present. Connect 7 to receiver RX.

An antenna 7 emits an excitation signal (excitation energy) that excites a sensor 16, which will be described later, and receives an echo signal from the sensor 16.

A receiver 8 demodulates the radio waves received through the antenna 7 and outputs a frequency signal, and also outputs a reception level signal corresponding to the strength of the received radio waves.

Reference numeral 9 denotes a level detector, which generates an output signal when the received level signal output from the receiver 8 is equal to or higher than a set level.

Reference numeral 10 denotes a frequency-voltage converter (hereinafter referred to as an F/V converter), which converts the frequency signal output from the receiver 8 into a voltage signal at a level corresponding to the frequency of the signal. This F/V converter 10 exists only in the second embodiment (FIG. 2);
It is composed of a PLL circuit.

11 is a comparator, the first embodiment (Fig. 1)
Then, the frequency signal output by the V/F converter 4 and the frequency signal output by the receiver 8 are compared, and when the difference is within a set frequency range, an output signal is generated. Furthermore, in the second embodiment (FIG. 2), the D/A converter 3
The voltage signal output by the F/V converter 10 is compared with the voltage signal output by the F/V converter 10, and an output signal is generated when the difference is within a set level range.

12 is an AND gate, which indicates that there is an output signal of the comparator 11, that no pulse is output from the pulse generator 1, that is, that the system is in reception mode, and that there is an output signal of the level detector 9. When the three conditions are met, a write pulse (in the case of the first embodiment) or a hold pulse (in the case of the second embodiment) is output.

Reference numeral 13 denotes a memory, which stores the frequency of the signal being output by the receiver RX when the write pulse is output from the AND gate 12. This memory 13 is present only in the first embodiment (FIG. 1).

Reference numeral 14 denotes a sample and hold circuit, which holds the voltage signal output from the F/V converter when a hold pulse is output from the AND gate 12. This sample and hold circuit 14 exists only in the second embodiment (FIG. 2). Further, this sample-and-hold circuit 14 falls within the scope of a memory because it stores the input voltage (output voltage of the F/V converter 10) when a hold pulse is input.

15 is a display device that receives information stored in the memory 13 (first embodiment) or sample hold circuit 14 (second embodiment), analyzes the information, and displays measurement data or identification of the detected individual. Display data etc.

Reference numeral 16 denotes a sensor, which is attached to an individual to be detected or an individual to be measured. Echo telemeters use sensors with vibration characteristics, but because they emit echo signals, they store a lot of energy.
A crystal resonator is most suitable as the sensor. Depending on the selection of the cutting angle from the crystal, these crystal units are either temperature-sensitive (resonant frequency changes with changes in temperature) or pressure-sensitive (resonance frequency changes with applied pressure changes). It is possible to obtain products with various characteristics, such as those whose resonance frequency is not affected by environmental changes (temperature changes, etc.).

An antenna 17 receives an excitation signal from the sensor 16 and radiates an echo signal generated by the sensor 16. Note that when the fixed station and the mobile station are coupled by electromagnetic induction, the antennas 7 and 17 are replaced with coupling coils.

Next, the operation of the embodiment will be explained with reference to FIG.

FIG. 3 shows signal forms (waveforms) at points A to N shown in FIGS. 1 and 2.

The pulse generator 1 outputs a pulse signal of a constant period to a point A as shown in FIG. 3A. This pulse signal is counted by the counter 2, and a count output (digital value) for each count is output at point B as shown in Figure 3B.
Output.

The counter 2 is set in various ways depending on the object to be measured or detected, but in the following explanation it is assumed that the maximum count value is "5" (expressed in binary from "0000" to "0100"). explain. Incidentally, in reality, for example, if you want to cover the range of -50℃ to +150℃ in temperature measurement, you will need about 200 counts, and if you want to identify 1000 individuals, you will need 1000 counts.
Requires counting.

When the maximum count value of the counter 2 is set to "5" as described above, the counter 2 outputs the count value from "0000" to "0100" (however, the counter 2 outputs the count value from "0000" to "0100". ),
The circuit is operated so that the counter 2 is reset to "0000" by inputting a pulse signal corresponding to "0101".

The counting output output by counter 2 is D/A
The signals are input to the converter 3, converted into voltage signals _e1 to _e5 at levels corresponding to the respective count values "0000" to "0100" as shown in FIG. 3C, and outputted to point C. The range of change of this voltage signal is assumed to be the same over the entire area. That is, the voltage at n counts (n≦5)
en is en=e ₁ +(n-1)Δe. However, Δe is the level width that changes with one count,
e ₁ is the voltage at count value “0000”.

The voltage signals e ₁ to _{e 5} whose levels change stepwise, generated as described above, are input to the V/F converter 4, and as shown in FIG. 3D, the respective voltage levels e ₁ to e It is converted into frequency signals ₁ to ₅ corresponding to ₅ and output to point D. The range of change of this period number signal is assumed to be the same over the entire area. That is, the frequency n of the frequency signal at the voltage en is n= ₁ +(n-1)Δ. However, Δ is the frequency change range with respect to the change range Δe of the voltage signal, and ₁ is the frequency of the frequency signal at voltage e ₁ .

For example, if an LC cut crystal resonator with a resonance frequency of around 28MHZ is used as a sensor to measure temperature changes in the range of -50℃ to +150℃, the resonance frequency of the sensor will be within the above temperature change range.
Varies in the range of 28.15MHz to 28.35MHz. That is, the sensitivity is 1000Hz/°C. If we try to cover the total range of change in the number of cycles, 2000KHz, in 200 steps, the range of change in frequency Δ for each step is 1KHz.
becomes. In the present invention, since the frequency of the sensor 16 is determined on the receiving side, there is no need to adjust the frequency change range Δ of the excitation signal to the accuracy of the measured temperature.
Measurements can be made with a maximum accuracy of 0.001°C with the above 1KHz variation range.

The above frequency signals ₁ to ₅ outputted to point D are transmitted by the transmitter 5 at a frequency close to the resonant frequency of the sensor 16.
When the pulse signal is converted into an excitation signal of F ₁ to _{F 5} and outputted from the pulse generator 1 by the transmission/reception changeover switch 6, the excitation signal is supplied to the antenna 7 for the duration of the pulse width. That is, the third
As shown in Figure E, the frequency from the antenna 7 is
An excitation signal that changes stepwise like F ₁ to F ₅ is intermittently emitted.

The excitation signals of frequencies F ₁ to _{F 5} radiated as described above are sequentially supplied to the sensor 16 via the antenna 17 .

The sensor 16 resonates at maximum amplitude due to the arrival of an excitation signal with a frequency closest to the resonant frequency Fx of the sensor 16 at that time. FIG. 3F shows this situation, and in this example, the resonant frequency of the sensor 16 is
An example is shown where Fx is closest to frequency _F3 .

While the excitation signal is interrupted, an echo signal, that is, a damped signal vibrating at the resonant frequency Fx, is radiated from the sensor 16 via the antenna 17.

While the excitation signal is interrupted, the transmit/receive switch 6 is switched to the receiver 8 side, and the above frequency is
The Fx echo signal is outputted to point G as shown in FIG. 3G via the antenna 7 and the transmission/reception changeover switch 6.

The echo signal output at point G is input to the receiver 8 and demodulated, and at point I, an attenuated signal with a frequency x as shown in FIG. Level signal proportional to received level
er ₁ to er ₃ are output respectively.

The level signals er ₁ to _{er 3} outputted to the H point are input to the level detector 9 and compared with the threshold level eh ₁ . Here, when the level signals er ₁ to er ₃ are at a level higher than the threshold level eh ₁ ,
The level detector 9 outputs a pulse signal at point J, as shown in FIG. 3J.

In the first embodiment (FIG. 1), the attenuated signal of frequency x output to the point I is input to the memory 13. Further, the attenuation signal and the frequency signal output from the V/F converter 4 to point D are transferred to the comparator 1.
1, and the frequencies of the respective signals are compared with each other. In the example shown in FIG.
Then, the absolute values of ₂ −x, ₃ −x, and ₄ −x are calculated, and when the absolute value of the difference frequency is within the set frequency range, the comparator 11 outputs a signal at point L as shown in FIG. Outputs a pulse signal. In this case, frequency ₃
is closest to the frequency x, so | ₃ −x| is the minimum, and if only this minimum value | ₃ −x| is within the frequency range set above, when the frequency of the signal at point D is ₃ The pulse signal is output to point L during the reception time period (time period when no pulse signal is sent to point A).

Further, in the second embodiment (Fig. 2), the attenuation signal of frequency x outputted to the point I is inputted to the F/V converter 10, converted to a voltage signal corresponding to the frequency x, and the attenuation signal of the frequency x outputted to the point level as shown in Figure 3 K.
A voltage signal ex is output, and the voltage signal ex is input to the sample and hold circuit 14. Further, the voltage signal ex and the voltage signal output from the D/A converter 3 to point C are input to a comparator 11, and the levels of the respective signals are compared with each other. Third
In the example shown in the figure, the comparator 11 calculates e ₂ -ex, e ₃ -ex, and e ₄ -ex, and when the level difference is within the set level range, that is, within ±eh _{2, the comparator 11 calculates e 2 -ex, e 3} -ex, and e 4 -ex. A pulse signal as shown in FIG. 3L is output to point L. In this case, level e ₃ is closest to level ex, so the difference level e ₃ −ex (absolute value) is the minimum, and only this minimum level e ₃ −ex is within the above set level range ±eh ₂ Then, the above pulse signal is output to point L in the reception time period when the level of the voltage signal at point C is _e3 .

The AND gate 12 receives as input the pulse signal outputted to the L point, the opposite logic of the pulse signal outputted to the A point, and the pulse signal outputted to the J point. At this point, a pulse signal is output to point M as shown in FIG. 3M. In the example shown in FIG. 3, the pulse signal is output during the reception time period when the counter 2 counts "0010". In the first embodiment (FIG. 1), this pulse signal at point M becomes a write pulse for the memory 13, and the frequency of the attenuation signal output at point I when the pulse signal is output is stored in the memory 13. , that is, x is stored. Also,
In the second embodiment (FIG. 2), the pulse signal at point M becomes the hold pulse of the sample and hold circuit 14, and the sample and hold circuit 13 detects the voltage output at point K when the pulse signal is output. Maintain the level of the signal, i.e. ex.

When the above operations are completed, N
Information stored or held by the memory 13 (in the case of the first embodiment) or the sample-and-hold circuit 14 (in the case of the second embodiment) is sent to the point, and these pieces of information are transmitted to the display 15. The data is analyzed and measurement data, individual identification data, etc. are created.
It is displayed on the display 15.

As explained above in detail, in the present invention, the transmitted signal (excitation signal) and the received signal (echo signal) are compared, and if the difference is within the set range, the received signal is determined by the transmitted signal. Therefore, only genuine echo signals can be reliably received. Thus, the present invention provides an echo signal detection method with extremely good S/N characteristics. In some cases, the effect is extremely significant.

[Brief explanation of drawings]

1 and 2 are block diagrams showing the first and second embodiments of the present invention, respectively, and FIG. 3 is a time chart showing the operation of the embodiments. (Main symbols), 1...Pulse generator, 2...Counter, 3...D/A converter, 4...V/F converter, 10...F/V converter, 11...Comparison vessel, 1
2...and gate, 13...memory, 14...
...sample hold circuit, 16...sensor.

Claims (1)

[Claims] 1. An excitation signal whose frequency changes stepwise is intermittently sent to a sensor with vibration characteristics, and an echo signal emitted by the sensor is received from the moment the excitation signal is cut off. In an echo telemeter that measures a physical event or identifies a detected individual, the received signal is compared with the excitation signal, and if the difference is within the set range, the received signal is detected. An echo signal detection method for an echo telemeter that determines that the echo signal is a legitimate echo signal. 2. An echo signal detection method for an echo telemeter according to claim 1, wherein the received signal and the excitation signal are compared when each signal is a frequency signal. 3. An echo signal detection method for an echo telemeter according to claim 1, wherein the received signal and the excitation signal are compared when each signal is a voltage signal.