JPS63311133A - Quartz-crystal temperature sensor - Google Patents

Abstract

PURPOSE:To make it possible to take out a low frequency output signal in a short time, by providing filters so as to pass the frequency component in a specified band among resonant frequency components from crystal oscillators and a mixer. CONSTITUTION:The output of an oscillating frequency from a temperature sensing crystal oscillator 1 passes through a filter 2, where resonant frequency components outside a specified band are removed. The filter 2 comprises a bandpass filter having a narrow bandpass width with a central frequency as the center. A constant temperature type crystal oscillator 3 is housed in a constant temperature oven and provided in the deep place in the sea like the temperature sensitive crystal oscillator 1. The oscillator 3 comprises a quartz resonator, a temperature sensor, a heater, a temperature-change suppressing circuit and the like. The crystal oscillator 3 outputs resonant frequencies so that the temperature of the inner quartz resonator is approximately constant. The output from the oscillator 3 passes a through a filter 4, where the resonant frequency components outside a specified band are removed. The difference in frequencies of the output signals from both filters 2 and 4 is outputted from a mixer 5. High frequency components are removed in a low-pass filter 6. Thus a low frequency output signal is taken out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a crystal temperature sensor mainly used for deep sea temperature measurement such as a submarine seismic measurement system.

[Prior art]

In a submarine seismic measurement system, a temperature sensor is required to measure the temperature of seawater in the deep sea along with a seismometer. The temperature in the deep sea is approximately 2°C, and the range of temperature fluctuation is smaller than that in the shallow sea. For example, in the deep sea at a depth of 2500 m, the temperature fluctuation range is approximately 0.
There is only a 2°C fluctuation. Therefore, in order to measure this, a temperature sensor having a resolution of approximately 0.01° C. to 0.001° C. is required, and a crystal temperature sensor is used as a temperature sensor that satisfies this requirement. A crystal temperature sensor generally includes an oscillator consisting of a crystal resonator as a temperature sensing element and an attached electric circuit.

In addition, in the submarine seismic measurement system, the signals handled are from seismometers, and the frequency is 2 to 20) 1z
extremely low. In order to efficiently transmit such signals simultaneously from multiple observation points to multiple channels, a frequency modulation division multiplexing method (FM-FI1M method) is adopted for signal transmission, and the upper limit of the transmission frequency is determined by the loss of the transmission path. It is set to about 300K)lz, taking into account the above factors.

Therefore, temperature sensors for deep sea use, such as submarine seismic measurement systems, are required to have high resolution characteristics and low frequency output signals.

There are three types of conventional crystal temperature sensors, and these three types will be briefly explained below.

The first is L, which has good linearity between resonance frequency and temperature coefficient.
This is a format in which the resonant frequency (4 to 28 MHz) of a high frequency crystal resonator such as a C-cut or AC-cut crystal resonator is directly extracted as an output signal. The second method is to divide the output frequency from a high-frequency crystal oscillator to extract a low-frequency output signal. The third is a temperature-sensitive crystal oscillator that uses a crystal oscillator whose resonant frequency changes almost linearly with temperature changes, and a crystal oscillator that uses a crystal oscillator whose resonant frequency changes extremely little with temperature changes compared to the crystal oscillator. This type uses a reference crystal oscillator using a vibrator and a mixer, and uses the mixer to extract the frequency difference between the oscillation frequencies of the two crystal oscillators (Japanese Patent Laid-Open No. 59-32834).

[Problem that the invention seeks to solve]

However, each of the above three types of systems has the following drawbacks.

In the first method, it is easy to increase the measurement resolution, but it has the disadvantage that the signal cannot be transmitted on land because a low frequency output signal cannot be extracted.

In the second method, the frequency change caused by temperature change is also reduced by the frequency division factor. For example, in order to obtain the same resolution as the first method, the measurement time is reduced by the frequency division factor. The disadvantage is that it only increases.

In the third method, the output of the temperature-sensitive crystal oscillator contains noise components and has poor temperature-frequency stability, so the temperature-frequency stability of the output frequency taken out from the mixer deteriorates, making it difficult to accurately The disadvantage is that temperature may not be detected. Another disadvantage is that the output frequency fluctuates due to the influence of harmonics generated when the low frequency component output from the mixer is amplified, resulting in poor temperature frequency characteristics and the inability to perform accurate temperature detection.

The present invention has been made in view of the above circumstances, and is an improvement on the third method described above, in which a filter is used to pass frequency components in a predetermined band among the resonance frequency components from each crystal oscillator and mixer. An object of the present invention is to provide a crystal temperature sensor which has a high resolution, can extract a low frequency output signal, and can accurately detect temperature without being affected by noise or harmonics.

[Means for solving problems]

A crystal temperature sensor according to the present invention is a crystal temperature sensor that detects a temperature change based on a change in the resonant frequency of a crystal resonator, and includes a first crystal resonator whose resonant frequency changes almost linearly with respect to the temperature change. a first filter that passes a frequency component in a predetermined band from the oscillation frequency components of the temperature-sensitive crystal oscillator, and a second crystal whose resonant frequency changes with respect to temperature changes. a resonator, and the temperature of the second crystal resonator is controlled so that the change in the resonant frequency of the second crystal resonator is one thousandth or less of the change in the resonant frequency of the first crystal resonator. A constant temperature crystal oscillator that maintains a substantially constant temperature, a second filter that passes a frequency component in a predetermined band from the oscillation frequency components of the constant temperature crystal oscillator, and outputs from the first filter and the second filter are input. It is characterized by comprising a mixer that outputs a frequency difference between oscillation frequencies, and a third filter that passes frequency components in a predetermined band from the output of the mixer.

[Effect]

A frequency component in a predetermined band among oscillation frequency components from a temperature-sensitive crystal oscillator including a crystal oscillator whose resonant frequency changes approximately linearly with respect to temperature changes is passed through the first filter. On the other hand, a constant-temperature crystal that suppresses the temperature change of the internal crystal resonator so that the change in the resonant frequency output is less than one-thousandth of the change in the resonant frequency output from the temperature-sensitive crystal oscillator. Among the oscillation frequency components from the oscillator, frequency components in a predetermined band are passed through the second filter. Next, the mixer inputs the outputs from the first filter and the second filter, and outputs the frequency difference between the oscillation frequencies output from both filters. Among the output frequency components from the mixer, frequency components in a predetermined band are passed through the third filter.

Then, the third filter outputs a low frequency signal that does not contain noise components or harmonic components.

〔Example〕

Hereinafter, the present invention will be explained based on drawings showing embodiments thereof. FIG. 1 is a block diagram showing a crystal temperature sensor of the present invention, and in the figure, reference numeral 1 indicates a temperature-sensitive crystal oscillator that is installed in the deep sea and measures the temperature of seawater.

Figure 2 shows the oscillation frequency (output signal) of temperature-sensitive crystal oscillator 1.
FIG. 3 also shows the temperature characteristics of the oscillation frequency. In FIG. 3, the horizontal axis shows the temperature T, and the vertical axis shows the frequency f, and the frequency at the reference temperature T0 is fo. The temperature-sensitive crystal oscillator 1 includes a crystal oscillator whose resonant frequency changes linearly with changes in ambient temperature (see FIG. 3). It is desirable that the temperature characteristics of the temperature-sensitive crystal oscillator 1 be as straight as possible and have a large slope. In order to achieve good linearity, it is necessary to use a crystal oscillator whose second- and third-order coefficients are smaller than the first-order resonant frequency temperature coefficient. It is necessary to use a crystal resonator with large absolute values of the following coefficients.

As a crystal resonator that satisfies these conditions, an LC cut crystal resonator or an AC cut crystal resonator as described above is most suitable. Note that the frequency change rate of the temperature-sensitive crystal oscillator 1 (ΔL/fo: where Δfo is the temperature change from To to ΔT
When ΔT is 20° C., the amount of change in the oscillation frequency of the temperature-sensitive crystal oscillator 1 is approximately 10 −3 .

The oscillation frequency output from the temperature-sensitive crystal oscillator 1 passes through a filter 2, and resonance frequency components outside a predetermined band are removed. The filter 2 is a bandpass filter whose center frequency is fo and whose passband width is approximately 2·Δfo.

3 is a thermostatic crystal oscillator that is housed in a thermostatic bath and installed in the deep sea like the temperature-sensitive crystal oscillator 1, and is composed of a crystal resonator, a temperature sensor, a heater, a temperature change suppression circuit, and the like. The constant-temperature crystal oscillator 3 is designed so that the temperature of its internal crystal oscillator is kept substantially constant and outputs a substantially constant resonant frequency even if there is a change in ambient temperature. 4 shows the frequency characteristics of the oscillation frequency (output signal) of the constant temperature crystal oscillator 3, and FIG. 5 shows the temperature characteristics of the oscillation frequency of the constant temperature crystal oscillator 3. In FIG. 5, the horizontal axis represents the temperature T, and the vertical axis represents the frequency f, which is the reference temperature T. The frequency at is f, and this frequency f1 is equal to the temperature T. It is approximately equal to the frequency f0 of the temperature-sensitive crystal oscillator l in . In the constant temperature crystal oscillator 3, the temperature of the crystal oscillator is kept almost constant even if the ambient temperature changes, and the change in the resonant frequency output is equal to the change in the resonant frequency output from the temperature sensitive crystal oscillator 1. It can be suppressed to less than one-fold. In other words, the frequency change rate (Δf, /f
, : However, Δf1 is the amount of change in the oscillation frequency of the constant temperature crystal oscillator 3 when the temperature changes from To to ΔT, and is extremely small compared to Δf0) is about 10-7 to 10-9.

The oscillation frequency output from the constant temperature crystal oscillator 3 passes through a filter 4, and resonance frequency components outside a predetermined band are removed. The filter 4 is a bandpass filter whose center frequency is rl and whose passband width is on the order of 10 to f.

The oscillation frequency output signals output from the filters 2 and 4 are input to the mixer 5, and the mixer 5 outputs the frequency difference between each oscillation frequency. The frequency difference signal output from the mixer 5 passes through a filter 6, and resonance frequency components outside the predetermined band are removed. Filter 6 is a low-pass filter that removes all frequency components higher than a predetermined frequency, and removes harmonics (spurious) of the output from mixer 5.
remove.

Next, the principle of temperature detection by the crystal temperature sensor having such a configuration will be explained. Temperature T now. Assuming that a temperature change occurs by ΔT from , the oscillation frequencies of the temperature-sensitive crystal oscillator 1° and the constant temperature crystal oscillator 3 are f0+Δfo, respectively.

It becomes f1+Δf1. And at temperature T0+ΔT,
Frequency difference output f. ut is expressed by the following equation (1).

rOut-(fo+Δfo)-(f++Δr+)-u
, b) + (8 fo - ΔL) ・ut Here, fl to fo, Δfo〉〉Δf I ・(21
Therefore, the above equation (1) becomes the following equation (3).

fout −Δf O·(3) Therefore, only the amount of frequency change of the temperature-sensitive crystal oscillator 1 can be obtained as an output signal.

Next, the operation will be explained. The output signal of the oscillation frequency from the temperature-sensitive crystal oscillator 1 whose resonant frequency changes with changes in the ambient temperature is passed through the filter 2 to a frequency f. Frequency components whose band is only within the range of 2·Δfo centered on are passed and input to the mixer 5. On the other hand, the output signal of the oscillation frequency from the constant-temperature crystal oscillator 3 is passed through a filter 4 whose frequency is centered around fl and whose band is 10.DELTA.f, and only frequency components within the range are passed and input to the mixer 5. The frequency difference between the oscillation frequencies from the filters 2 and 4 is output from the mixer 5, and the harmonics (spurious) are removed from the output of the frequency difference by the filter 6. ut(#Δfo) is output.

Then, the temperature is detected based on the output frequency change amount (Δf0) of the temperature-sensitive crystal oscillator 1.

Here, since the output signal from the filter 6 is the oscillation frequency difference between the temperature-sensitive crystal oscillator 1 and the constant temperature crystal oscillator 3,
Low frequency output is possible. Further, since the frequency change due to temperature change of the temperature-sensitive crystal oscillator 1 is obtained as an output signal, high resolution is achieved and the time for measuring temperature change is short. Furthermore, temperature sensitive crystal oscillator 1. Regarding the output from the thermostatic chamber controlled crystal oscillator 3 and the mixer 5, only the components having frequencies in a predetermined band are passed through the filter, so the temperature can be accurately detected without the influence of high frequency noise or harmonics. .

〔effect〕

As described in detail above, the crystal temperature sensor of the present invention has high resolution and can extract a low frequency output signal in a short time measurement.

Additionally, temperature can be detected accurately without the effects of high frequency noise or harmonics.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the crystal temperature sensor of the present invention, Fig. 2 is a frequency characteristic diagram of the output signal of the temperature-sensing crystal oscillator, Fig. 3 is a temperature characteristic diagram of the oscillation frequency of the temperature-sensing crystal oscillator, and Fig. The figure is a frequency characteristic diagram of the output signal of the constant temperature type crystal oscillator, and FIG. 5 is the temperature characteristic diagram of the oscillation frequency of the constant temperature type crystal oscillator. 1... Temperature sensitive crystal oscillator 3... Constant temperature crystal oscillator 5... Mixer 2, 4.6... Filter patent applicant Sumitomo Metal Industries Co., Ltd. agent Patent attorney Noboru Kono ΔS/- ! Y-center μ 9 Δ Bi-center

Claims (1)

[Claims] 1. In a crystal temperature sensor that detects temperature changes based on changes in the resonant frequency of a crystal resonator, a first crystal resonator whose resonant frequency changes almost linearly with respect to the temperature change is provided. a temperature-sensitive crystal oscillator, a first filter that passes a frequency component in a predetermined band from the oscillation frequency components of the temperature-sensitive crystal oscillator, and a second crystal vibration whose resonant frequency changes with respect to temperature changes. the temperature of the second crystal oscillator so that the change in the resonant frequency of the second crystal oscillator is one thousandth or less of the change in the resonant frequency of the first crystal oscillator. A constant temperature crystal oscillator that is kept constant, a second filter that passes a frequency component in a predetermined band from the oscillation frequency component of the constant temperature crystal oscillator, and outputs from the first filter and the second filter are input. A crystal temperature sensor comprising: a mixer that outputs a frequency difference between oscillation frequencies; and a third filter that passes frequency components in a predetermined band from the output of the mixer.