JPH0337537A - Pressure sensor - Google Patents

Abstract

PURPOSE:To prevent trouble due to an abnormal sensor output by forming a plurality of pressure sensitive parts with a plurality of strain resistors formed on a diaphragm, and using the signal from the pressure sensitive side without abnormality as the output of the sensor. CONSTITUTION:A plurality of strain resistors are formed at positions, where the amounts of strains due to deformations are different, on a diaphragm which is deformed by receiving pressure. The resistors are connected in bridge forms, and a plurality of pressure sensitive parts 61 and 62 are formed. When wire breakage or a fault occurs in the pressure sensitive part (e.g. 61) which is provided at the position where the amount of strain is large by the application of excessive pressure on the diaphragm, an abnormality indicating signal is outputted from an abnormality judging means 63 which receives the signal from the pressure sensitive part 61. Meanwhile, since there is no wire breaking or the like on the pressure sensitive part 62 where the amount of strain is small, a signal indicating no abnormality is outputted from an abnormality judging means 64. The signal from the pressure sensitive part 61 is cut out in a judging means 65 which receives the signal. The normal signal is outputted from the pressure sensitive part 62.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a pressure sensor using a strain gauge.

(Prior art) Semiconductor pressure sensor using diffused type semiconductor strain sensor-1 = Sugaru (September 1980, Japan Science and Technology Foundation, Japan Science and Technology Museum publication 1 Japanese Science and Technology) 9 (See October issue, pages 54 and 55).

To explain this, as shown in FIG. 11, four strain resistors 24 to 27 whose resistance value changes depending on the amount of strain are diffused and formed in the surface layer of the silicon diaphragm 23. 24 to 27 are used to assemble the Wheatstone bringe as shown in FIG. The back surface of the Deno main body 21 is hollowed out as shown in FIG. 13, and the thin part located above serves as a diaphragm 23.

When pressure is applied from above as shown, the silicon diaphragm 23 deforms, causing strain in the strain resistors 24-27. Here, a large resistance change occurs in the strain resistors 24 to 27 due to the piezoresistance effect, and an output proportional to the pressure is obtained from the buritsuno.

(Problems to be Solved by the Invention) By the way, in such a pressure sensor, if excessive pressure is applied, poor connection or disconnection may occur between the strain resistors or the connection wire to the power supply voltage. In that case, an erroneous signal will be output, and if that signal is used to perform pressure control (for example, control of a hydraulic device system), it may cause problems such as runaway.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a device that does not cause troubles such as runaway even if a pressure sensor breaks or breaks down.

(Means for Solving the Problems) As shown in FIG. 1, the present invention forms a plurality of strain resistors at positions where the amount of strain due to deformation differs on a diaphragm that deforms under pressure, and each strain resistor A means 63, 64 for configuring a plurality of pressure sensing parts 61, 62 by connecting the wires using the body, and determining whether there is an abnormality in the signal from each pressure sensing part 61, 62; Multiple pressure sensitive parts 6
Means 65 is provided for inputting the signal from 1.62 and inputting the signal from the determination means 63 and 64 as a selection signal, and for selecting the signal from the pressure sensing section on the side where there is no abnormality as the sensor output. Ta.

(Function) When excessive pressure is applied to the diaphragm, the pressure sensitive part (for example 61) provided at the position where the amount of distortion is large
If a disconnection or failure occurs in the pressure sensitive section 61, the determination means 63 that receives the signal from the pressure sensitive section 61 outputs a signal indicating that there is an abnormality.

On the other hand, since there is no wire breakage in the pressure sensitive section 62 with the smaller amount of distortion, the determination means 64 outputs a signal indicating that there is no abnormality.

The selection means 65 that receives these signals cuts off the signal from the abnormal pressure sensing section 61 and outputs a normal signal from the pressure sensing section 62.

(Example) FIG. 2 is a sectional view of an example. For example, the sensor main body 1 made of silicon wafer or metal consists of a cylindrical base 2 and a thin film-shaped diaphragm 3 on the top.When a gas to be measured is introduced from below, the diaphragm part deforms. arise.

4 FIG. 3 is a plan view of the sensor body 1, in which two strain resistors A and B are located approximately at the center of the diaphragm 3, and the base 2 at the lower right
Two strain resistors C and D are each formed by diffusion near 90 degrees apart. These four strain resistors A-D are connected to #X5 via each electrode 4 formed at both ends of the strain resistor.
This wiring 5 is further connected to an electrode 6. A bonding wire 7° is connected to lead #111 via electrode 10. These connections are for constructing the bridge shown in FIG. Here, one pressure sensitive part 31 (see Fig. 7) is connected from four strain resistors A-D connected in a bridge.
is configured.

Note that the electrode 10 is formed on a wiring board 8 fixed via an insulator 9.

Similarly, four strain resistors A' to D' are formed on the upper left side of the diaphragm 3, and these strain resistors A' to D'
is electrode 15. A bridge connection is made as shown in FIG. 5 via the wiring 16 and the like. However, unlike the corresponding strain resistors A and B, the strain resistors A' and B' are formed at positions slightly shifted outward in the radial direction from the center of the diaphragm 3.

Here, a pressure sensing section 32 (see FIG. 7) different from the pressure sensing section described above is provided.
is configured.

The arrangement of the strain resistors A' and B' takes into consideration the strain distribution on the diaphragm. When this strain distribution is shown in FIG. 6, the horizontal axis represents the distance radially outward from the center of the diaphragm 3, and the vertical axis represents the amount of strain. From the same figure, the amount of strain (tension) is maximum at the center position of the diaphragm 3,
It decreases toward the outside in the radial direction, and a negative amount of strain (compression) occurs near the base 2. From this, the strain resistors A and B are provided in the portions where the amount of strain is the largest, whereas the strain resistors A' and B' are provided in the portions where the amount of strain is smaller than that. Here, according to the bridge shown in FIG. 4 that includes strain resistors A and B, pressure can be measured with high precision.

However, from the perspective of damage, the part where the amount of strain is maximum is also the part where the possibility of damage is highest when excessive pressure is applied.

In this case, if strain resistors A' and B' are formed at positions slightly away from the center position where the amount of strain is greatest6, even if strain resistors A and H are damaged due to excessive pressure. Even if this happens, the strain resistors A' and B' will not be damaged. In other words, strain resistors A', B'
The position of is determined in response to expected overpressure so that it will not be destroyed, and the higher the overpressure, the further outward in the radial direction the position is placed. This is the so-called 7erse 7, and from the point of view of measurement accuracy, the strain resistors A' and B
Although the accuracy is slightly lower at the position where ' is provided compared to the center position of the Guia 7 ram, it is more resistant to damage and increases the reliability of the dage.

FIG. 7 is a block diagram of a circuit for processing signals from a pressure sensor having two pressure sensitive parts 31,32.

In the same figure, 33.34 is an amplification/shaping circuit, in which the pressure value (minimal signal) sensed by the pressure sensitive part 31.32 is amplified, and the correspondence between the pressure value and the voltage value and the offset 111I Adjustments will be made.

35.36 is a comparator, amplification/shaping circuit 33.3
By comparing the voltage value from 4 and a predetermined value, it is determined whether the detected pressure value is outside the predetermined normal pressure range, and if it is outside the normal pressure range, the corresponding sensor pressure A signal (for example, a high level signal) indicating that there is an abnormality is output to the sections 31 and 32.

For example, in Fig. 8, if the constant voltage Vcc applied to the blinno is 6V, if the wire breaks at point E as shown in the figure, no output will be output (that is, 0■), and if the wire breaks at point F, it will be approximately 6V. A voltage close to is output. In this case, 0
■The reference value S L l (for example, 0.4 V) is slightly larger than
), the reference value 5L2, which is a little smaller than 6■ (for example, 5.
8 V), and if the output voltage of the amplification/shaping circuits 33 and 34 is below S L l or above SL2, it is determined that there is an abnormality. In other words, the comparators 35 and 36 have the number of comparators 35 and 36 corresponding to possible cases of disconnection or failure of the Blinno. These comparators 35 and 36 are connected to the abnormality determining means 63 in FIG.
．． It is a part that performs 64 functions.

37 is a selection circuit, here it is an amplification/shaping circuit 33.34
In addition to inputting two output voltages from , it receives signals from comparators 35 and 36 as selection signals,
When an abnormality signal is output from either comparator 35 or 36, the output voltage from the amplification/shaping circuit with the abnormality is cut off, and the output voltage from the remaining amplification/shaping circuit is detected. Send it as output. Sorting circuit 3
The sensor output from 7 is used, for example, as a feedbank signal in a pressure control system of a hydraulic device system (not shown). It should be noted that if there is no abnormality in any of the pressure sensitive sections 31 and 32, it is determined in advance which pressure sensitive section the output voltage is to be selected. This selection circuit 37 functions as the signal selection means 65 in FIG.

Furthermore, although the signals from the comparators 35 and 36 can be treated as abnormal signals as they are, the two signals from the comparators 35 and 36 are input to the OR block 38 here. The signal from the OR block 38 is output to, for example, a 9-alarm device (not shown) and is output to a comparator 35.
．． When a signal indicating that there is an abnormality is output from at least one of 36, the alarm device is activated.

Here, the effect when excessive pressure is applied to the sensor will be explained.

When excessive pressure is applied to the diaphragm 3, the strain resistors A to D, which are shaped at positions where the amount of strain is large,
If a disconnection or failure occurs, this is determined by the comparator 35, and the comparator 35 outputs a signal indicating that there is an abnormality.

On the other hand, since there is no disconnection in the strain resistors A' to D', the comparator 36 outputs a signal indicating that there is no abnormality.

In the selection circuit 37 that receives these signals, the output voltage from the amplification/shaping circuit 33 is cut off, and the output voltage from the amplification/shaping circuit 34 is cut off.
Outputs the output voltage from. In other words, one pressure sensitive part 31
Even if the pressure sensitive part 32 is damaged or malfunctions, the sensor output from the other pressure sensitive part 32 that is not damaged is selected, and according to the selected normal sensor output, pressure control is continued. − I can do it. Here, troubles due to the use of abnormal sensor outputs are prevented.

Further, from the signal from the OR block 38, it can be known that there is a disconnection or a failure in any of the pressure sensitive parts 31, 32.

FIGS. 9 and 10 show other embodiments. In this example, as shown in FIG. 9, the thickness of the diaphragm 25 provided on the right is made thicker than the thickness of the diaphragm 26 provided on the left, and as shown in FIG. The strain resistors A' to D' are formed by diffusion.

(Effects of the Invention) In this invention, a plurality of pressure sensitive parts having different measurement sensitivities are configured on a diaphragm that deforms under pressure, and
It is determined whether or not there is an abnormality in the signals from each pressure sensing part, and if an abnormality is found, the signal from the normal pressure sensing part is selected as the sensor output. Therefore, even if one pressure sensing part is damaged or malfunctions, pressure control can be continued using the sensor output from the other pressure sensing part that is not damaged. This prevents troubles caused by the use of sensor outputs.

[Brief explanation of drawings]

FIG. 1 is a claim correspondence diagram of this invention, t! Figure tJ2 and Figure 3 are a cross-sectional view and plan view of the sensor body of one embodiment, respectively, Figure 14 and Figure fIS5 are circuit diagrams showing the Brisono of this embodiment, and Figure 6 shows the strain distribution of this embodiment. Characteristic diagram, Figure 7 is a block diagram of the signal processing circuit of this embodiment,
FIG. 8 is a circuit diagram for explaining the disconnection point in this embodiment, and FIGS. 0 and 10 are a sectional view and a plan view of other embodiments, respectively. FIG. 11 is a plan view of a conventional sensor main body, FIG. 12 is a circuit diagram showing a conventional sensor, and FIG. 13 is a sectional view of a conventional sensor main body. ”...Sensor body, 3...Diaphragm, 4,6...
・Electrode, 5...Wiring, 15.17...Electrode, 16...
Wiring, A-D...Strain resistor, A'-D'...Strain resistor, 25゜26...Diaphragm, 31.32-Pressure sensitive part, 33゜]2 34...Amplification/shaping Circuit, 35.36...Comparator, 37...Selection circuit, 38...OR block, 61.62...Pressure sensing section, 63.64...Abnormality determination means, 65...Signal Sorting means. 3 Fig. 10 2 (7//--wo/'---=;〉Kuini, 17 JP 37537 (8) Fig. 11 Fig. 12 Fig. 13

Claims (1)

[Claims] A plurality of strain resistors are formed at positions with different amounts of strain due to deformation on a diaphragm that deforms under pressure, and each strain resistor is connected in a bridge to form a plurality of pressure sensitive parts. means for determining whether or not there is an abnormality in the signal from the pressure section; inputting the signals from the plurality of pressure sensing sections; inputting the signal from the determining means as a selection signal; 1. A pressure sensor comprising: means for selecting a signal from a pressure sensitive section as a sensor output.