JPS63262537A - Pressure measuring apparatus - Google Patents

Abstract

PURPOSE:To dispense with or simplify a linearity correction or instrumental error correction circuit, by directly adhering a small capacity pressure sensor having a specific shape to a printed wiring board. CONSTITUTION:The peripheral part of a diaphragm, whose effective diameter is 15mm or less, having a movable electrode plate 2 having a diameter 20mm or less fixed thereto is adhered to the periphery of the bottom surface part of a housing 5 made of a synthetic resin to form a pressure chamber. The fixed electrode plate 1 with an effective diameter of 20mm or less opposed to the movable electrode plate 2 is supported by the peripheral edge part of the housing. The movable electrode plate 2 and the fixed electrode plate 1 are constituted so that the initial electrostatic capacity value therebetween becomes 7.5-9.5pF and the capacity change to pressure change of 300mmHg being 4-7pF.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] The present invention relates to a pressure measuring device for use in, for example, blood pressure measurement.

Conventionally, when detecting changes in fluid pressure, pressure is received by a diaphragm and converted into a change in lift amount, and electrically detected as a change in capacitance between a movable electrode plate and a fixed electrode plate connected to the diaphragm. Detection is being done. A conventional air pressure detection sensor having such a detection mechanism has a structure as shown in FIG. 3, for example. In order to ensure the parallelism between the fixed electrode plate 21 and the movable electrode plate 22,
2 is fixed to the diaphragm 23 with solder 24 or the like. The diaphragm 23 is fixed to the diaphragm support plate 25 by soldering or the like, and an O-ring 2 is provided between the diaphragm support plate 25 and the housing 20.
6, and is fixed by a set screw 27 so as to be airtight. In such a pressure sensor, the distance between the fixed electrode plate 21 and the movable electrode plate 22 changes due to the pressure introduced from the pressure introduction pipe 20' provided at the bottom of the housing 20, and the resulting change in the capacitance between the electrodes is reflected by the output conductor 28. and 29 to the measuring circuit.

When measuring capacitance, for example, as shown in Figure 4, a variable frequency oscillator (O3C) is used in response to changes in capacitance C.
A method is used in which the output frequency is converted into a voltage by an fV converter (fV) and detected.

It has been proposed to use such a capacitance type pressure sensor to detect fluctuations in air pressure within the cuff by assembling it into a blood pressure monitor, for example (for example, Japanese Patent Laid-Open No. 61-2206
No. 27). In such cases, the blood pressure monitor itself must be made smaller, so measures such as integrating the device for amplifying the output of the pressure sensor and outputting the measured pressure value and mounting it on a wiring board are adopted. At the same time, pressure sensors also need to be made smaller. However, if a conventional capacitive pressure sensor is simply made smaller in size and placed close to the output device, stray capacitance between the pressure sensor and the wiring board or output circuit increases. In addition to impairing the linearity of the pressure sensor's output, there is also large instrumental error in stray capacitance. Conventionally, it has been necessary to incorporate a correction circuit into the output device for compensating the linearity of these outputs and adjusting instrumental errors, and furthermore, it has been inconvenient that human labor is required to adjust the correction circuit.

Under the above-mentioned circumstances, the present invention hardly requires correction of the instrumental error of stray capacitance, and also eliminates the need to add a circuit for correcting linearity in the output circuit. The purpose of this invention is to provide a pressure measuring device that can perform

[Structure of the invention]

. In order to achieve the above-mentioned purpose of determining the pressure value, the present invention includes mounting and fixing a small capacitive pressure sensor and an integrated circuit that outputs the output as a measured pressure value on a wiring board. In this pressure measuring device, a pressure chamber is formed by bonding the periphery of a diaphragm with an effective diameter of 1'5 tm or less to which a movable electrode plate with a diameter of 20 m or less is fixed to the bottom of a housing made of synthetic resin. A fixed electrode plate having an effective diameter of 2 (ln or less) facing the electrode plate is supported at the periphery of the housing, and the initial capacitance value between the movable electrode plate and the fixed electrode plate is 7.
．． A small pressure sensor configured to have a capacitance of 5 to 9.5 pF and a capacitance change of 4 to 7 pF with respect to a pressure change of 300 mHg is directly attached to the wiring board.

In the pressure measuring device of the present invention having such a configuration, the pressure sensor is mounted directly on the wiring board, so that the stray capacitance becomes almost constant and at the same time becomes a low value, resulting in a straight line of capacitance change in the pressure change range. sex is improved.

Examples of small pressure sensors used in the pressure measuring device of the present invention are shown in FIGS. 1 and 2.

Here, reference numeral 1 denotes a fixed electrode plate, which is fixed to the peripheral edge of a housing 5 made of hard plastic using set screws 6. Reference numeral 2 denotes a movable electrode plate, which is fixed to the diaphragm 3 at its central position with solder 4, and the peripheral portion 3' of the diaphragm 3 is bonded to the upper surface of the bottom of the housing 5 with a hardening polymer adhesive. . Further, 7 is an output pin whose one end is welded to the diaphragm peripheral part 3' and is drawn out through the bottom of the housing 5, and 1' is formed by punching out the peripheral part of the fixed electrode plate 1 as one piece.
This is the output pin obtained by bending this.

Here, the effective diameters of the fixed electrode plate I and the movable electrode plate 2 are both 16 fins, and the outer diameter of the diaphragm 3 is the same <1
It is 6mm. And also, the spacing between the fixed electrode plate 1 and the movable electrode plate 2 is adjusted so that the capacitance between the electrodes is slightly below 8.5 pF, so that it is within the range of 0.2 to 0.3 W. was obtained.

Further, the outer diameter of the housing 5 is 22fi excluding the protruding portion, and the thickness of the bottom portion thereof is 2.5 mm.

Furthermore, two output pins 1' from the fixed electrode plate 1.

1' and one output pin 7 from the movable electrode plate 2 are both rigid and have sufficient strength to fix the miniature pressure sensor to the printed circuit board.

The small pressure sensor of this example has a stray capacitance of 1 pF or less when mounted on a rigid wiring board equipped with electronic components for pressure measurement and fixed with solder, and has almost no instrumental error. It won't happen. Therefore, means for correcting linearity in the pressure measurement amplifier circuit is no longer necessary.

〔Effect of the invention〕

The pressure measuring device of the present invention has a small pressure sensor of a specific shape and small capacity directly attached to a wiring board, and circuits for linearity correction and instrumental error correction are unnecessary or simplified, and further miniaturization is achieved. This was achieved.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an example of a small pressure sensor used in the pressure measuring device of the present invention, Fig. 2 is a perspective view of a fixed electrode plate used therein, and Fig. 3 is a conventional capacitance type pressure sensor. FIG. 4 is a configuration diagram of an example of a capacitance measuring circuit used in combination with a capacitance type sensor. 1.21...Fixed electrode plate, 1'...Output bin, 2゜22...Movable electrode plate, 3,23...Diaphragm,
4゜24...Solder, 5,20...Housing, 7
...Output pin, 25...Diaphragm support plate, 26
...0 ring, C...capacitance, OSC...oscillator,
f-V...fV converter. Patent applicant: Saginomiya Seisakusho Co., Ltd. Figure 4

Claims (1)

[Claims] In a device in which a small capacitive pressure sensor and an integrated circuit for amplifying and calculating the output of the sensor and outputting a measured pressure value are placed and fixed on a wiring board, a movable electrode plate with a diameter of 20 mm or less is fixed. A pressure chamber is formed by gluing the peripheral part of a diaphragm with an effective diameter of 15 mm or less around the bottom of a housing made of synthetic resin, and a fixed electrode plate with an effective diameter of 20 mm or less facing the movable electrode plate is attached to the periphery of the housing. , the initial capacitance value between the movable electrode plate and the fixed electrode plate is 7.5 to 9.5 pF, and 300 m
A pressure measuring device characterized in that a small pressure sensor configured so that a capacitance change is 4 to 7 pF with respect to a pressure change of mHg is directly mounted on the wiring board.