JPH0635156Y2 - Pressure sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a capacitance-type pressure sensor useful for detecting a liquid level position in a tank, a water head in a pipe or the like.

[Conventional technology]

When detecting a change in fluid pressure, it is possible to detect the change in the lift amount by receiving the pressure on the diaphragm and to electrically detect it as a change in the capacitance between the movable electrode plate and the fixed electrode plate connected to the diaphragm. Has been done. A conventional air pressure detection sensor having such a detection mechanism has, for example, a structure as shown in FIG. 3, and in order to secure the parallelism between the fixed electrode plate 21 and the movable electrode plate 22, the movable electrode plate 22 is It is fixed to the diaphragm 23 with solder or adhesive 24. The fixed electrode plate 21 and the diaphragm 23 are fixed by a fixed frame body 25 and a diaphragm support plate 26 attached to the bottom of the fixed frame body 25, and a pressure P is applied from a pressure introduction pipe 27 provided on the bottom surface thereof. The capacitance between the fixed electrode plate 21 and the movable electrode plate 22 is measured between the output lead wire 28 directly drawn from the fixed electrode plate 21 and the output lead wire 29 drawn from the movable electrode plate 22. It is like this.

In measuring the electrostatic capacitance, for example, as shown in FIG. 4, a variable frequency oscillator (OSC) is used in response to a change in the capacitance C.
Is used, and the output frequency is converted into a voltage by the V converter (-V) and detected, but the scale of the indicating instrument is of course set based on the pressure P applied to the diaphragm. There is.

In such a conventional air pressure detection sensor, the influence of the external environment on the fixed electrode plate 21 and the movable electrode plate 22 is blocked by surrounding the sensor portion with the shield body 30. There were no problems.

However, when such a pressure measurement method is used to detect the water level, the environment is often high in humidity, so air with high humidity enters and leaves the sensor as the temperature changes, etc. An error may occur in the measured value of the capacitance.

[Problems to be solved by the device]

The present invention solves the problem that the measurement error becomes large when using such a capacitance type pressure sensor in a bad environment, for example, when detecting the water level in a hot water tank, and it is highly accurate even in a bad environment. The present invention aims to provide a highly reliable pressure sensor that can maintain the above.

That is, an object of the present invention is to provide a pressure sensor that can always detect pressure with high accuracy even if there are changes in temperature and humidity.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, in the present invention, an insulator is attached to a diaphragm which is sealed to the bottom plate in a shield case electrically connected to a metal bottom plate having a pressure introduction hole. A movable electrode plate fixed through the fixed electrode plate, a fixed electrode plate supported in parallel to the movable electrode plate, and an output circuit mounting board for converting a change in capacitance between the electrode plates into an electric signal. In the pressure sensor provided with, the bottom plate and the mounting substrate are respectively coupled and fixed by three or more coupling arms that are alternately extended in a vertical direction from a peripheral edge of a metal frame plate provided in the middle of them. A structure in which the fixed electrode plate is sandwiched and fixed by a pair of electrically insulating annular spacers provided between the bottom plate and the frame plate is introduced.

Further, the insulator for fixing the electrically insulating annular spacer and the movable electrode plate to the diaphragm is formed of a ceramic molded body, and the heater is fixed to the back surface of the fixed electrode plate to further improve reliability. realizable.

The pressure sensor of the present invention will be described with reference to the examples shown in FIGS. 1 and 2.

Reference numeral 1 is a metal bottom plate, and a pressure introducing hole 1a is provided in the center thereof. Reference numeral 2 is a metal diaphragm, and its peripheral edge is welded to the bottom plate 1. 3 is a ceramic chip insulator, the lower surface of which is soldered to the center of the diaphragm 2 and the upper surface of which is soldered to the center of the movable electrode plate 4.

Reference numerals 5a and 5b are ceramic annular insulators, respectively, and spacers for maintaining the fixed electrode plate 6 sandwiched between them in a position parallel to the movable electrode plate 4 and at a predetermined interval. Has become.

Reference numeral 7 denotes a metal frame plate, which is formed in a substantially circular plate shape having a size capable of being crimped onto the upper surface of the annular spacer 5b, and has three connecting arms 7a and 7c extending alternately vertically from the periphery thereof. There is. The tip 7b of the connecting arm 7a is divided into two by a slit,
The ring spacers 5a, 5b and the fixed electrode plate 6 are fixed between the bottom plate 1 and the frame plate 7 at the correct positions by being inserted into the coupling holes 1b of the bottom plate 1 and fixed by caulking. . An engaging portion 7d is formed at the tip of the coupling arm 7c, and an output for detecting the electrostatic capacitance between the fixed electrode plate 6 and the movable electrode plate 4 and converting it into an output signal such as a voltage. It engages with the engaging portion 8a of the circuit mounting board 8 and is joined by soldering.

The conducting wire 8b from the movable electrode plate 4 is coupled to one of the input terminals of the output circuit mounting board 8, and the fixed electrode plate 6 is coupled to the other.
The terminal pin 6a extending from the edge portion of is connected. Reference numeral 8c is a cable for inputting / outputting an output signal, power source power and the like.

Further, a window portion 7e is provided in the center of the frame body 7, and a heater 9 composed of a PTC thermistor heating element capable of automatically controlling temperature is fixed to the back surface of the fixed electrode plate 6 corresponding to the window portion 7e. Therefore, the fixed electrode plate 6 is kept warm within a predetermined temperature range.

Reference numeral 10 denotes a metal shield case, which is sealed in the bottom plate 1 and electrically coupled thereto.

In the pressure sensor of the present invention configured as described above, the whole is shielded by the bottom plate 1 and the shield case 10, and the output circuit portion and the electrode portion are mutually shielded by the frame plate 7, Since the fixed electrode plate 6 is fixed at accurate positions by the annular spacers 5a, 5b made of ceramics, the capacitance value is extremely stable and the error is small, so that highly accurate pressure measurement can be performed. If the heater 9 is fixed to and kept at a temperature higher than room temperature, dew condensation due to invading moisture is prevented and a more stable sensor output can be obtained.

[Effect of device]

In the pressure sensor of the present invention, a fixed electrode plate is securely sandwiched and fixed between a pair of annular spacers by a metal bottom plate and a metal frame plate having a function as a shield plate inside a shield case, and an output circuit mounting board. Since it is also supported and fixed, not only the assembly is easy, but the assembly accuracy is also improved. Further, in combination with the use of a ceramic molded body as the insulating material such as the annular spacer and fixing the heater to the fixed electrode plate, the effect of temperature and humidity is further reduced, and high accuracy is achieved even in a bad environment. It has the feature that pressure can be measured.

[Brief description of drawings]

FIG. 1 is a sectional view of an example of a pressure sensor of the present invention, FIG. 2 is an explanatory diagram showing its assembly structure, FIG. 3 is a sectional view of an example of a conventional pressure sensor, and FIG. 4 is a capacitance type pressure. It is a block diagram of the example of the output circuit in a sensor. 1 ... bottom plate, 2 ... diaphragm, 3 ... chip insulator, 4 ... movable electrode plate, 5a, 5b ... annular spacer, 6 ...
... fixed electrode plate, 7 ... frame plate, 8 ... output circuit mounting board,
9 ... Heater, 10 ... Shield case, 21 ... Fixed electrode plate, 22 ... Movable electrode plate, 23 ... Diaphragm, 25 ... Fixed frame body, 30 ... Shield case, P ... Pressure, C ... … Capacitance, OSC… Variable frequency oscillator, –V… V converter.

Claims (4)

[Scope of utility model registration request] 1. A movable electrode plate fixed in a shield case electrically connected to a metal bottom plate having a pressure introducing hole to a diaphragm which is sealed to the bottom plate to form a pressure chamber through an insulator. And a fixed electrode plate that is supported in parallel to face the movable electrode plate, and an output circuit mounting substrate that converts a change in capacitance between the electrode plates into an electric signal. The bottom plate and the mounting substrate are respectively coupled and fixed by three or more coupling arms extending vertically from a peripheral edge of a metal frame plate provided in the middle thereof, and the fixed electrode plate and the bottom plate. A pressure sensor which is sandwiched and fixed by a pair of electrically insulating annular spacers provided between the frame plate and the frame plate. 2. The pressure sensor according to claim 1, wherein the annular spacer is formed of a ceramic molded body. 3. The pressure sensor according to claim 1, wherein the insulator is formed of a ceramic molded body. 4. The pressure sensor according to claim 1, wherein a heater is fixedly attached to the back surface of the fixed electrode plate.