JPH03248028A - Pressure sensor unit - Google Patents

Abstract

PURPOSE:To facilitate temperature compensation of the entire pressure sensor and to omit the requirement for correction due to time change by providing two sensors having approximately same constitution wherein tuning-fork type quartz resonators are sealed in pressure response container, and detecting the pressure based on the difference in resonant frequencies outputted from the output terminals of the sensors. CONSTITUTION:When pressure is applied on a pressure sensor 1a which is assembled in an oscillating circuit 31, the resonant frequency of a tuning-fork type quartz resonator which is a pressure sensor element is changed, and the frequency outputted from the oscillating circuit is changed. The frequencies corresponding to the temperature and the atmospheric pressure at every time are outputted from an oscillating circuit 33 on the side of a reference device 1b. The frequencies of both outputs are divided in frequency dividing circuits 32 and 34 and counted in a counter 41. The pressure value corresponding to the difference in counted values obtained in an operating circuit 42 is read out of a memory 43 and displayed on a display circuit 44. Since the sensors having the same constitution are used for the pressure sensor 1a and the reference device 1b, the correction of the temperature characteristics are automatically performed.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a pressure sensor unit that uses a tuning fork type crystal resonator made of an XY cut crystal plate as a pressure sensor element, and more specifically relates to this tuning fork type crystal unit. The vibrator is hermetically sealed in a pressure-responsive container that houses this tuning-fork crystal resonator in a non-mechanical contact state, and the volume of this pressure-responsive container fluctuates due to fluctuations in external pressure. The present invention relates to a pressure sensor unit that detects external pressure based on changes in the resonance frequency of a tuning fork crystal resonator due to internal pressure fluctuations.

Note that the term "response" used in the present invention means acting in response to an external action.

(Prior Art) The resonant frequency of a tuning fork crystal resonator has a characteristic that changes approximately linearly with changes in pressure in the surrounding atmosphere, and this characteristic is used to measure pressure. - For boat fishing, in order to protect the electrode film on the surface of the crystal oscillator, the crystal oscillator that functions as a pressure sensor element is not placed directly under the measured atmospheric pressure, but is placed inside a pressure-responsive container such as a bellows. Internal pressure fluctuations within this container are detected.

Tuning fork crystal resonators have frequency-temperature characteristics that follow a negative quadratic curve, and this has to be corrected when measuring pressure.

The prior art will be explained with reference to FIG. 1, which shows the general structure of a pressure sensor, and FIG. 3, which shows the structure of a pressure gauge using this pressure sensor in a Pronk diagram. In FIG. 1, the pressure sensor 1a includes a bellows 11 that is a pressure-responsive container, a base 12 that is joined to the bellows 11, and a tuning fork-type crystal vibrator that is a pressure sensor element installed in the base 12. Child 13
It consists of a base 14 that holds this tuning fork type crystal resonator, and lead terminals 15.

The pressure gauge includes a pressure sensor 1a and an oscillation circuit 5 that drives it.
1, the frequency dividing circuit 52, the counter 53, and the clock 5.
It consists of a memory 55 that stores date, frequency pressure data, and frequency temperature data, an arithmetic circuit 56 that calculates a pressure value from the pressure data from the pressure sensor 1a and the temperature data from the temperature sensor 54, and a display circuit 57.

(Problem to be Solved by the Invention) However, the tuning fork type crystal resonator has a frequency temperature characteristic expressed by a negative quadratic curve, and this is a matter that must be corrected when measuring pressure. Ta. In addition, the gas (SFs) and bellows surrounding the tuning fork crystal resonator, which is the pressure sensor element, expand and contract in response to temperature changes, and these affect the frequency changes of the tuning fork crystal resonator. In some cases, the pressure value obtained only by temperature compensation for the crystal resonator does not represent the actual pressure value.

In addition, with the above configuration, if you want to detect pressure with high accuracy, it is necessary to take temperature parameters into consideration.
There was a need to select a highly accurate temperature sensor and a larger memory capacity.

Also, when writing frequency pressure characteristics, etc. to a memory such as ROM, the characteristics are written under a predetermined atmospheric pressure (for example, 1 atm), but in actual use, the atmospheric pressure may be different from the above predetermined atmospheric pressure. Highly sexual. In such cases, the accuracy of the relative predetermined pressure measurement may be reduced. For example,
When you want to find a relative pressure value, such as measuring the amount of hot water in a bathtub, the detected pressure value differs depending on the atmospheric pressure, resulting in measurement errors.

Furthermore, it is necessary to correct changes in the pressure sensor and temperature sensor during treatment, which poses a problem in usability.

The present invention has been developed to solve the above problems, and it is possible to easily perform temperature compensation for the entire pressure sensor without using a high-performance temperature sensor or increasing the memory capacity. It is an object of the present invention to provide a pressure sensor unit that does not require correction due to changes over time.

(Means for Solving the i! Problem) The pressure sensor unit according to the present invention consists of two sensors having substantially the same configuration in which a tuning fork-type crystal oscillator is enclosed in a pressure-responsive container, and one sensor is placed under the pressure to be measured. , the other sensor is installed in the atmosphere or a desired standard atmospheric pressure to be used as a reference device, and the pressure is detected by the resonance frequency difference output from the output terminals of each sensor. .

(Function) Since one of the sensors with the same configuration is used as a pressure sensor and the other as a pressure or temperature reference device, by finding the difference between the frequency output from the pressure sensor and the frequency output from the pressure reference device, Correction of the temperature characteristics of the pressure sensor unit is automatically performed. In other words, when no pressure is applied, the effect of changing the frequency of the tuning fork crystal resonator due to temperature on the pressure sensor and pressure reference device (frequency change due to heat of the tuning fork crystal resonator itself, thermal expansion of the bellows, gas inside the sensor) 01ij extension, etc.) is applied in the same way to both, and there is no difference in the frequency output from both. When pressurizing, the sensor detects a frequency change with respect to the pressure applied to the pressure sensor. This frequency change corresponds to pure pressure excluding effects caused by other factors such as temperature.

Furthermore, when the reference device side is opened to atmospheric pressure, relative pressure measurement can be performed, and measurement errors can be minimized, for example, when measuring the amount of hot water in a bathtub. Furthermore, since the changes over time of both sensors are considered to be approximately equal, the calibration period becomes longer.

As mentioned earlier, the frequency Wl temperature characteristic of a tuning fork crystal resonator is expressed by a negative quadratic curve, but in practical use it is
In order to shift this quadratic curve to the high temperature side so that the left side of the quadratic curve falls within the practical temperature range, a cutting angle that is rotated several degrees counterclockwise around the X axis is used.

(Example of the invention) Embodiments according to the present invention will be described with reference to the drawings.

Note that the same components as those described in the prior art section will be described using the same drawings and the same numbers. FIG. 1 is a sectional view showing the structure of the pressure sensor, and FIG. 2 is a block diagram showing the pressure measurement system.

The pressure sensor 1a has a cylindrical shape as a whole, and includes a metal bellows 11 with one end open, which is a pressure-responsive container;
A metal base 1 connected to the opening of this bellows 11
2, and a tuning fork type crystal resonator 13 installed on this base 12.
, a base 14 , and a lead terminal 15 . The tuning fork crystal oscillator 13, which functions as a pressure sensor element, consists of an XY cut plate rotated by ±10° counterclockwise around the (The electrode arrangement is omitted.) A base 14 fixes this tuning fork type crystal resonator 13, and is connected to an oscillation circuit to be described later through a lead terminal 15 integrated with the base. The inside of the bellows is filled with SFs gas 16.

The reference device 1b also has the same configuration, and both sensors having the same configuration are housed in a case 2, respectively, as shown in FIG. The case 2 is provided with a pressure to be measured inlet 21 and an atmospheric pressure inlet 22.

In addition, both of these sensors have the external dimensions of the tuning fork type crystal oscillator,
It is necessary to configure the components with the same resonance frequency, electrode configuration, bellows material, spring constant, etc. Furthermore, it is preferable to use the same manufacturing conditions.

Next, the pressure measurement process will be explained.

When pressure is applied to the pressure sensor la incorporated in the oscillation circuit 31, the resonance frequency of the tuning fork crystal resonator, which is the pressure sensor element, changes, and the frequency output from the oscillation circuit changes. On the other hand, the oscillation circuit 33 on the side of the reference device 1b outputs a frequency corresponding to the current temperature and atmospheric pressure. In addition,
Depending on selection, the inside of the case on the reference device side may be fixed at a predetermined pressure.

The frequencies of both outputs are divided by frequency dividing circuits 32 and 34, respectively, and counted by a counter 41. 45
is a reference clock. The difference between these counts is determined by the arithmetic circuit 42, the pressure value corresponding to this difference between counts is read out from the memory 43, and this is sent to the display circuit 44, where the pressure value is displayed.

In addition, in the above pressure processing system, the pressure sensor 1a
By frequency-dividing one of the outputs from the reference device 1b and multiplying the other, it is also possible to count using one of the frequency outputs as a reference. In this case, the clock 45 becomes unnecessary.

Although the present invention uses a bellows as the pressure-responsive container, the present invention is not limited to this, and for example, a diaphragm or the like may be used.

(Effects of the Invention) According to the present invention, since a sensor with the same configuration is used as the pressure sensor and the reference device, the temperature characteristics of the entire pressure sensor are automatically corrected, and there is no need to provide a complicated temperature compensation circuit. Pressure can be measured with extremely high accuracy without the need for In connection with this, there is no need to store temperature-related data in advance, so the memory capacity can be reduced. Further, when the reference device side is opened to atmospheric pressure, pressure measurement relative to the current atmospheric pressure can be performed, and measurement errors can be minimized. Furthermore, since two sensors with the same configuration are used, it is considered that the changes over time are approximately the same, and there is no need to calibrate the memory.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a pressure sensor using a tuning fork type crystal resonator, Fig. 2 is a block diagram showing a pressure measurement system using the pressure sensor unit according to the present invention, and Fig. 3 is a diagram showing a conventional pressure measurement system. It is. 1a...Pressure sensor 1b...Reference device 13...Tuning fork type crystal oscillator Drawing Fig. 1 Fig. 2

Claims (1)

[Claims] It consists of two sensors with almost the same configuration, each with a tuning fork-type crystal oscillator sealed in a pressure-responsive container.One sensor is used under the pressure to be measured, and the other sensor is used as a reference device under atmospheric pressure or a desired reference pressure. A pressure sensor unit, which is installed at the bottom of each sensor, and detects pressure based on a resonance frequency difference output from an output terminal of each sensor.