JPH0420514B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an echo signal receiving system for an echo telemeter.

An echo telemeter is a sensor (so-called echo sensor) that resonates at a specific frequency, such as a crystal oscillator, at a measurement point of an individual to be detected or an individual to be measured, or at a frequency determined by the event to be measured. When the echo sensor is made to resonate by applying excitation energy (excitation signal) having a frequency equal to or in the vicinity of the resonance frequency to the echo sensor from the outside without contact, the above-mentioned external excitation Utilizing the fact that the echo sensor continues to vibrate at its resonant frequency while attenuating for a while after the energy is cut off, the attenuated vibration (echo signal) is received in a non-contact manner and the detected individual or subject is detected from that frequency. This type of telemeter requires a power supply means such as a battery and an active element in the mobile station (a station equipped with an echo sensor and transmitting detection or measurement data). It is suitable for various fields (industrial telemeters, medical telemeters, etc.) are widely used.

[Problem that the invention seeks to solve]

In the echo telemeter mentioned above, since the duration of the echo signal from the echo sensor is short, it is extremely difficult to detect this echo signal and directly count its frequency due to the high frequency characteristics of the echo signal. How to solve this problem is an important issue in echo telemetry.

The present invention solves the above problems and proposes a new echo signal reception method for improving measurement accuracy.

[Summary of the Invention] The present invention focuses on the fact that an echo sensor resonates with an excitation signal and emits an echo signal when the frequency of the excitation signal becomes approximately equal to the resonant frequency of the echo sensor. The echo signal receiving section is configured in a superheterodyne system, and its local oscillation frequency is swept in accordance with the sweep of the excitation signal, so that the difference between the local oscillation frequency and the frequency of the excitation signal is always constant (including zero). ), the echo signal detection frequency range is made narrow, thereby making it possible to reliably detect the echo signal.

[Embodiments of the invention]

The drawings are all for explaining the embodiments of the present invention; FIG. 1 is a block diagram, FIG. 2 is a diagram explaining the frequency sweep of the excitation signal in the transmitting section, and FIG. 3 is a diagram explaining the frequency sweep of the excitation signal in the receiving section. FIG. 3 is a diagram illustrating frequency relationships of various signals.

First, each part shown in FIG. 1 will be explained.

1 is a collective circuit that generates various signals, and terminal P ₁
~ _P4 outputs various signals using the operations described below.
That is, as shown in FIG. 2A, the clock pulse generator 101 generates a clock pulse with a pulse width t ₁ at a constant period t, and this clock pulse is output to the terminal P ₁ as a transmission/reception switching control signal. becomes.

The clock pulse is also input to a step voltage generator 102. Step voltage generator 10
2 has, for example, a counting function and a digital-to-analog conversion function, counts the clock pulses at their leading edges, and converts the counted value (digital) into a voltage (analog). Due to this action, the voltage of the step voltage generator 102 changes by a constant value every time a clock pulse is input, and this change is repeated every set number of steps to generate a voltage signal E _S (voltage value
es: Hereinafter, regarding various signals, a signal is indicated in uppercase letters, and its value (voltage value, frequency value) is indicated in lowercase letters. ) is generated. This voltage signal E _S
is output to terminal _P2 and becomes the signal to be operated on in the arithmetic processing after receiving the echo signal.

In addition, the voltage signal E _S is the V/F converter 10
3 and is converted into an alternating current signal Fs of frequency s corresponding to the voltage value es. This AC signal Fs is the second
As shown in FIG. It is a repeated signal.

AC signal F _S from the above V/F converter 103
is input to the first mixer 104 and mixed with the local signal F ₁ output from the first local oscillator 106 . The first local oscillator 106 outputs a local signal F ₁ having a relatively high and constant frequency ₁ in the resonant frequency region of the echo sensor 11, and the first mixer 104
A high frequency signal Fc ₁ whose frequency changes stepwise by a constant frequency Δ in the resonant frequency region of
Output to _P3 . The high frequency signal Fc ₁ outputted to this terminal P ₃ becomes a transmission signal (excitation signal of the echo sensor 11), and its frequency c ₁ is c ₁ = ₁ + s (1).

In addition, the high frequency signal from the first mixer 104
Fc ₁ is input to the second mixer 105 and further mixed with the local signal F ₂ from the second local oscillator 107. The second local oscillator 107 outputs a local signal F ₂ with a relatively low constant frequency ₂ , and the second mixer 105 outputs a high frequency signal F 2 with a frequency c ₂ higher than the frequency c ₁ of the high frequency signal Fc ₁ by the frequency ₂ . Output signal Fc ₂ to terminal P ₄ .
This high frequency signal Fc ₂ is also a signal whose frequency changes stepwise, and its frequency c ₂ is c ₂ = ₂ + c ₁ = ₁ + ₂ + s (2). This high frequency signal Fc ₂ is a signal used as a local signal in processing after receiving the echo signal.

Note that the second mixer 105 and the second local oscillator 107 are not required when there is no need to measure the amount of resonance frequency deviation of the echo sensor 11 itself, such as in a telemeter for individual identification, for example. In this case, the high frequency signal Fc ₁ from the first mixer 104 is used as a local signal in processing after receiving the echo signal.

As described above, the clock pulse is applied to the terminal P ₁ of the aggregate circuit 1, the voltage signal Es whose voltage value changes by a constant value is applied to the terminal P ₂ , and the frequency changes by a constant value to the terminals P ₃ and P ₄ . Changing high frequency signal
Fc ₁ and Fc ₂ (c ₁ <c ₂ ) are respectively output.

2 is a transmission amplifier which amplifies the high frequency signal Fc ₁ outputted to the terminal P ₃ of the collective circuit 1 and uses it as an excitation signal for the echo sensor 11.

Reference numeral 3 designates a transmitting/receiving switch, which uses the clock pulse outputted to terminal _P1 of the collective circuit 1 as a control signal, and when the clock pulse is present, the antenna 9 is set to the transmitting side (transmitting amplifier 2 side), and when the clock pulse is not present, the antenna 9 is set to the transmitting side (transmitting amplifier 2 side). At times, the antenna 9 is switched to the receiving side (RF amplifier 4 side).

4 is an RF amplifier that amplifies the received echo signal Fe.

A mixer 5 mixes the echo signal Fe from the RF amplifier 4 and the high frequency signal Fc ₂ outputted to the terminal P ₄ of the collective circuit 1, and outputs a signal Fm having a frequency that is the difference between the two. The frequency of this signal Fm
m is m=|c ₂ −e| = | ₂ +c ₁ −e| ...(3).

6 is an F/V converter which converts the signal Fm output from the mixer 5 into a voltage signal Em.

7 is a data processor, and the above F/V converter 6
Data processing is performed on the voltage signal Em output from the terminal P2 and the voltage signal Es output to the terminal _P2 of the collective circuit 1, and measurement data is generated and output.

In addition, when processing in the data processor 7 is performed in frequency stages, the F/V converter 6 is deleted and the output signal Fm of the mixer 5 and the V/F converter 103 of the collective circuit 1 are output signal of
Fs may be input to the data processor 7.

A display 8 displays or records the measurement data output by the data processor 7.

9 is the antenna on the fixed station side, and the echo sensor 11
emits an excitation signal Fc ₁ or echo sensor 11
receives an echo signal Fe from

10 is an antenna on the mobile station side, and echo sensor 1
1 emits an echo signal Fe, or receives an excitation signal Fc ₁ of the echo sensor 11.

Reference numeral 11 denotes an echo sensor, which is attached to a part to be measured of an object to be measured or to an individual to be detected. This echo sensor 11 is an energy storage type vibration characteristic element, and due to the energy stored in itself during excitation, it continues to vibrate at its resonant frequency e for a while immediately after excitation stops, and this vibration becomes an echo signal Fe.
As the element for this echo sensor 11, a crystal oscillator is optimal because it has a large amount of stored energy (therefore, the emission time of the echo signal Fe is longer than other elements).

In addition, some echo sensors 11 have resonance frequencies e that change according to changes in physical events at the part to be measured (for physical event measurement), and others whose resonance frequencies e do not change depending on environmental conditions. Generally, there is a plurality of them, each having a different resonance frequency e (for individual identification).

In each of the above parts, the antenna 10 and the echo sensor 11 constitute a mobile station, and the others constitute a fixed station.

Next, the operation of the embodiment will be explained. In the following description, it is assumed that the echo sensor 11 is for measuring physical events.

The excitation signal Fc ₁ outputted to the terminal P ₃ of the collective circuit 1 and amplified by the transmission amplifier 2 is generated every time the transmission/reception switch 3 is switched to the transmission amplifier 2 side, that is, as shown in FIG. 2A. It is radiated from the antenna 9 every time the time t ₁ shown in FIG. The frequency of the radiation of the excitation signal Fc ₁ from the antenna 9 increases by Δ due to the action of the collective circuit 1 each time the transmitting/receiving switch 3 is switched. In this way, the excitation signal _Fc1 of the echo sensor 11 is sent out intermittently while sweeping the frequency in steps.

When the frequency c ₁ of the excitation signal Fc ₁ falls within the resonance range of the echo sensor 11, the echo sensor 11 effectively resonates (here, effective means that the echo signal resonates at a level that can be sufficiently identified by the fixed station). ). This is shown in Figure 3, where the excitation signal
The resonant frequency e of the echo sensor ₁₁ is within the range of "c ₁ ±Δc" (within the range indicated by the dashed line) with respect to the frequency c 1 of Fc ₁ , and a crystal oscillator is used as the echo sensor 11. In this case, the above Δc is 2 to 3 KHz.

When the echo sensor 11 resonates effectively, an echo signal Fe is emitted from the echo sensor 11 immediately after the excitation stops, that is, at time _t2 shown in FIG. 2A, and this echo signal Fe is emitted from the antenna 10. Ru. At this time _t2 , the transmit/receive switch 3 is switched to the receiving side and the antenna 9 is connected to the RF amplifier 4, so the antenna 10 is connected to the RF amplifier 4.
The echo signal Fe emitted from the
is input. This mixer 5 performs processing to reduce the frequency e of the echo signal Fe by using the high frequency signal Fc ₂ outputted to the terminal P ₄ of the collective circuit 1 as a local signal. This processing is a so-called superheterodyne reception method processing.

By the way, the frequency e of the echo signal Fe and the excitation signal Fc ₁ when the echo sensor 11 resonates effectively
Let Δe be the frequency difference from the frequency c ₁ of (however,
Let e＞c ₁ . ), from the relationship of equation (3) above, mixer 5
The frequency m of the output signal Fm is m = | ₂ − Δe | ...(4). Here, Δe is less than or equal to the above Δc, and
It is at most 2 to 3KHz, and if we set the above ₂ to 455KHz, which is the frequency used in the most common IF filters, IF detectors, etc.
Since the above Δe is extremely low compared to ₂ , it can be considered that m≒ ₂ ...(5).

The signal output from the mixer 5 as described above
Fm is input to the F/V converter 6 and the frequency
A voltage conversion is performed.

By the way, the frequency m of the signal Fm output from the mixer 5 through the processing by the mixer 5 is
As is clear from the above, regardless of the frequency c ₁ of the excitation signal Fc ₁ when the echo sensor 11 resonates, it is always near the oscillation frequency ₂ of the second local oscillator 107. This is an effect of sweeping the frequency c ₂ of the signal Fc ₂ , which is a local signal to the mixer 5, in accordance with the frequency sweep of the excitation signal Fc ₁ .
The frequency/voltage conversion operation performed by the V converter 6 is performed with high accuracy. To explain this further, if we convert the frequency e of the echo signal Fe directly into a voltage, the frequency e will be 20~
The frequency is approximately 30 MHz (when a crystal resonator is used as an echo sensor), and the F/V converter 6 is required to have ultra-high-speed operating characteristics. However, in the present invention, the frequency m of the signal Fm input to the F/V converter 6 is extremely low compared to the frequency e of the echo signal Fe, and its variation range is less than ±Δc shown in FIG. Since the range is extremely narrow, frequency/voltage conversion in the F/V converter 6 is performed with extremely high precision.

As is clear from equation (4) above, the signal Em output from the F/V converter 6 in the above operation is an excitation signal when the echo sensor 11 resonates effectively.
It includes a voltage component corresponding to the frequency difference Δe between Fc ₁ and the echo signal Fe. For example, when the object to be measured is temperature, this voltage component may indicate a lower digit of the measured temperature, for example, a value below the decimal point. In this case, the excitation signal
Assuming that the sweep step of Fc (Δ shown in FIG. 2) is a frequency corresponding to 1°C in temperature, the voltage signal Es from the step voltage generator 102 that generated the excitation signal _Fc1 is data in units of 1°C. In other words, data of the upper digits of the measured temperature is given.
There is no need to take out the data of the upper digits from the echo signal Fe, which is weak and has a short duration, and is taken out directly from the step voltage generator 102 in this embodiment. That is, the data processor 7 receives the signal Em from the F/V converter 6 and the signal Es from the step voltage generator 102, and the data processor 7 inputs these two signals.
Generate measurement data using Em and Es.

The measurement data output from the data processor 7 is sent to the display 8 and displayed.

Next, an embodiment will be described in which it is not necessary to measure the amount of resonance frequency deviation of the echo sensor 11. This embodiment is implemented, for example, for a telemeter for individual identification.

In an echo telemeter for individual identification, echo sensors 1 each having a different resonance frequency are used for each individual to be identified.
1 is attached, and the resonance frequency e of each is set to the frequency at each step of the high frequency signal (excitation signal output from the transmission amplifier 2) _Fc1 output from the first mixer 104. Further, in the collective circuit 1, the second mixer 105 and the second local oscillator 107 are removed, and the local signal input terminal of the mixer 5 is directly connected to the terminal _P3 . That is, the frequency of the local signal of the mixer 5 becomes the same as the frequency c ₁ of the excitation signal Fc ₁ .

When the excitation signal Fc ₁ is radiated from the antenna 9 in the same manner as in the above embodiment, and the echo sensor 11 effectively resonates with the frequency c ₁ of the excitation signal Fc ₁ at that time, the resonant frequency e is equal to the frequency c 1 of the excitation signal Fc ₁ . frequency c ₁
is equal to Therefore, the frequency m of the signal Fm output from the mixer 5 becomes zero (the output of the mixer 5 becomes a so-called zero beat). This causes the F/V converter 6 to output a specific signal.

By the way, the resonance frequency e of each echo sensor 11
corresponds one-to-one with the frequency _c1 at each step of the excitation signal _Fc1 , and therefore also corresponds one-to-one with the output signal (voltage signal) Es at each step of the step voltage generator 102, which is the base thereof. do. As a result, the data processor 7 operates as a step voltage generator 102 when a specific signal is output from the F/V converter.
Identify the echo sensor 11 from the output signal Es of
Perform individual identification. The identified individual is displayed on the display 8.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the echo signal detection frequency range can be set to a narrow band lower than the resonant frequency of the echo sensor, so that short-duration echo signals can be detected reliably with high precision. Furthermore, since the echo signal detection processing portion (the portion subsequent to the mixer 5) can be constructed from circuit means in the low frequency range, the device configuration can be realized at low cost.

[Brief explanation of drawings]

The drawings are for explaining the embodiments of the present invention, and FIG. 1 is a block diagram, FIG. 2 is a diagram explaining the frequency sweep of the excitation signal in the transmitting section, and FIG. 3 is a diagram showing various signals in the receiving section. It is a figure explaining the frequency relationship of. Main symbols: 1... Collective circuit, 102... Step voltage generator, 104... First mixer, 105...
...Second mixer, 3...Transmission/reception switch, 5...
...Mixer, 11...Echo sensor.

Claims (1)

[Claims] 1. An excitation signal is intermittently sent to an echo sensor while sweeping its frequency in steps, and from the moment the excitation signal is cut off, the echo signal emitted by the echo sensor is received and a physical event is detected. In an echo telemeter designed to measure or identify an individual to be detected, the echo signal receiving section is configured using a superheterodyne method, and the echo signal is supplied to a mixer that mixes the received echo signal and a local oscillation signal. The frequency of the local oscillation signal is changed stepwise in response to the stepwise change in the frequency of the excitation signal so that the difference between the frequency of the excitation signal and the frequency of the local oscillation signal is always constant. echo signal reception method.