JPS59151031A - Pressure sensor - Google Patents

Abstract

PURPOSE:To raise the sensitivity and to make a pressure detecting circuit simple and inexpensive by providing a pressure detector for adding an outputting a varied portion against a reference set value by pressure of each of plural bridge resistors for forming a strain gauge. CONSTITUTION:A strain of a diaphragm influenced by pressure is tansmitted to a strain gauge, and varies a resistance of a bridge resistor 10. Especially, resistances r1-r4 are varied to a compressed state, its resistance value is decreased, and resistances R1-R4 are varied to an expanded state and its resistance value is increased. When a strain is generated in this pressure detecting circuit, a balance of the bridge resistor 10 is varied, a resistance varied portion of each bridge is added, input voltage of a non-inversion input terminal of an operational amplifier OP1 is increased, and an increased portion against a reference voltage value Vz is obtained as an output from its output terminal. In this way, the sensitivity is raised and the pressure detecting circuit is made simple and inexpensive without damaging a temperature characteristic of a metallic strain gauge.

Description

Detailed Description of the Invention The present invention relates to a pressure sensor, in which pressure is converted into stress, displacement, etc. by a deformable flat plate (diaphragm), and then converted into an electrical signal by a strain gauge formed on the surface of the diaphragm. The present invention relates to a pressure sensor.

A pressure sensor is one of the most important sensors among automotive sensors, and is used to measure intake manifold pressure, atmospheric pressure, transmission oil pressure, brake oil pressure, engine oil pressure, and the like.

As a pressure sensor, there are two strain gauges on the diaphragm.
A bridge circuit is generally used, which converts the strain caused in the diaphragm due to pressure into an electrical signal.This strain gauge is made of metal wire, There are two types of strain gauges: one is a metal strain gauge using a continuous metal film or a discontinuous metal film, and the other is a semiconductor strain gauge using a cermet or a semiconductor.

However, while metal strain gauges have extremely excellent temperature characteristics, their sensitivity is inferior.On the other hand, semiconductor strain gauges have several dozen times the sensitivity of metal strain gauges, but on the other hand, they have temperature characteristics unique to semiconductors. In this famous test, a temperature compensation circuit was essential. In addition, this temperature compensation circuit has the disadvantage that it is very complex and expensive, depending on the usage of the pressure sensor.

Therefore, in order to make full use of the excellent temperature characteristics of the metal strain gauge and further compensate for its sensitivity, it is conceivable to provide an amplifier to amplify the entire signal to a predetermined level. This amplifier is generally an operational amplifier, but the output of a metal strain gauge is small and is usually used as a sensor for automobiles.
The ones used for this purpose can only obtain an output of several tens of mV. Furthermore, since the input value required by various control devices for automobiles is several volts, the amplification factor of the amplifier must be about a few digits to about 100 times. However, these operational amplifiers have temperature drift, and this temperature drift is also amplified by the above amplification factor (there are some with small temperature drift, but they are extremely expensive), and the operating temperature of automotive sensors is - Considering that the temperature is about -40 to 120°C, there is a drawback that the influence of this temperature drift becomes extremely large at high temperatures, and the accuracy of use deteriorates.

The primary purpose of the present invention is to improve the sensitivity of metal strain gauges without impairing their excellent temperature characteristics.The present invention has a pressure detection circuit that is simple and inexpensive to configure, and is extremely effective even under a wide range of temperature conditions. The second purpose is to operate with high precision.

In order to achieve the above object, in the present invention, a strain gauge is formed of a plurality of bridge resistors, a reference setting value of the bridge resistor at zero pressure is determined in advance, and each bridge resistor is It is equipped with a pressure detection circuit that adds up all the changes made to the reference resistance value due to pressure and outputs the result. According to this, since the respective outputs of the plurality of bridge resistors are all added together and output, the output increases by a minute amount of the formed bridge resistors, and as a result, the sensitivity improves. Further, according to the present invention, in addition to the above configuration, the reference set value changes in a direction opposite to the change direction of the change due to pressure, and further includes a pressure detection circuit that adds and outputs the change. Therefore, the output of the pressure detection circuit is the change due to the pressure of each bridge resistor plus the change due to the pressure of the standard setting value itself,
Sensitivity is further improved.

Furthermore, in the preferred embodiment of the present invention, these pressure detection circuits can be constructed easily and inexpensively by simply constructing an adder using an operational amplifier. Furthermore, since an operational amplifier is used as an adder, a high degree of amplification is not required, and the influence of fnIv drift can be made extremely small.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. m
FIG. 1 shows the circuit configuration of one embodiment. The bridge circuit 1.0 shown in FIG. 1 is a strain gauge formed on a guiaflame, and in this embodiment consists of four bridge resistors. Each bridge resistor has a resistor r14
Resistance r2. R2, resistance r3, R3, resistance r4,
The connection point of each resistor is input to the non-inverting input terminal of the operational amplifier op1. The inverting input terminal of the operational amplifier OPI has a power supply voltage V c c f
A reference set value vz divided by the resistors Rx and Ry is input. Here, the resistor Rx and the resistor R7 are set equal to the combined resistance value of each resistance '] + '2' + '3 + '4 and the combined resistance value of the resistors Rq, R2', Ra', and Pv. Further, the resistor Rf is a feedback resistor.

The diaphragm is strained by pressure, and this strain is transmitted to the strain gauge, changing the resistance of the bridge resistor 10 (7J).

In particular, the resistance r1 * R2 * '3 + '4 Gjl
+ Changes to a reduced form 7 and its resistance value decreases, and the resistance "i"
+R-2'+R3+R4 changes to an extended state and its resistance value increases. The upward and downward arrows in FIG. 1 indicate increases and decreases in resistance, respectively.

In the pressure detection circuit configured in this way, when distortion occurs, the balance of the bridge resistor 10 changes,
According to the resistance value change as described above, the operational amplifier OPI
The input voltage at the inverting input terminal a increases. Therefore, from the output terminal of the operational amplifier OPI, the increment with respect to the reference setting value (2), which is the input voltage of the inverting input terminal, is obtained as an output.

In this way, all the changes in each bridge of the bridge resistor lO are added together and output as a change with respect to the reference setting value.

Next, a second embodiment of the present invention is shown in FIG.

The strain gauge 20 includes a plurality of bridge resistors 21, 22, 28, 24 formed on a diaphragm, and each of the bridge resistors 2, 22, 23, 24 changes into a compressed state due to the strain of the diaphragm. The resistance rI+"l whose resistance value decreases, the resistance r2, 'r2, the resistance Q l rs, the resistance '4 e '4, and the resistance R,, R whose resistance value increases ', 1. Resistor R2, y!2, resistor R4, R', has 7. The contact point of each resistor is connected to the power supply voltage V
cc, ground GND, and the inverting input terminal and non-inverting input terminal of the operational amplifier OP2. Right, resistance R
C is a feedback resistance.

Furthermore, each bridge resistor 21, 22, 23.

24 and the operational amplifier OP2 will be explained. As shown in Fig. 2 by the upward and downward arrows indicating the increase and decrease in resistance value, each resistor has a connection point where the partial pressure value increases due to an increase or decrease in the resistance that changes due to the distortion of the diaphragm. The connection points that are input to the inverting input terminal and at which the divided voltage value decreases are respectively input to the inverting input terminal.

In the pressure detection circuit configured in this way, when distortion occurs in the diaphragm, the input voltage at the non-inverting input terminal of the operational amplifier OP2 is
The input voltage of the inverting input terminal is the sum of all the increases among the changes of 24, and the input voltage of the inverting input terminal is the voltage of each bridge resistor 21 , 22 , 23 .

Of the 24 changes, all the decreases are added together. Therefore, the output of the operational amplifier OP2 is obtained as the sum of the increase and decrease of the changes in the bridge resistors 21, 22, 23, and 24, respectively. Therefore, in this embodiment, the input to the inverting input terminal of the operational amplifier OP2, that is, the reference set value V''2 changes with pressure, and this change is roughly added to the change in the bridge resistor itself, so that The output will be a larger value.

Next, FIG. 8 shows an example of a pattern when the strain gauge (bridge resistor) according to this embodiment is formed on a diaphragm by sputtering. In the figure, the part connected to the inverting input terminal of operational amplifier OP2 is indicated by ←).
Further, the portion connected to the non-inverting input terminal is shown by (1), and the other resistors are shown corresponding to the respective resistors in FIG.

This diaphragm is gripped all along its edges and is subjected to pressure over its entire surface 1, so that in the strain gauge 20, the resistance that is stretched by pressure is located in the center (R1r ``l + R2L bird.

R3+ ``s 'l R41R'4), the pressure resistance is placed in the peripheral part ('I 1 '';
l '21 '21 '31 r2+ '4, r:)
.

There are various techniques for manufacturing strain gauges using patterns, but for example, if a sputtering method is used as in this embodiment, it is relatively simple and inexpensive, and is suitable for large-scale production. Furthermore, there is no need to use adhesive between the strain gauges and the diaphragm, and therefore the sensitivity can be further improved.

Next, an eighth embodiment of the present invention is shown in FIG. In this example, bridge resistors 81 .
．． 32, 33, and 84 are constructed in the same manner as the bridge resistors 21, 22, 23, and 24 of the second embodiment described above, so the explanation thereof will be omitted. The characteristic configuration of this embodiment is that the input resistance R is connected between this bridge resistor and the operational amplifier OP8.
j, R+2, Rt3'; Ri4, 'R'i
1, R′i1. This is because Ri2, Y@, and R″i4 are arranged, and the use of these input resistors is normally done.The basic configuration of the present invention is the same as the second embodiment, including a plurality of bridge resistors and Since these are resistors with the operational amplifier, their explanations will also be omitted.

FIG. 5 shows an example of the strain gauge pattern of the eighth embodiment.

Here again, the connection points with the inverting input terminal and the non-inverting input terminal of the operational amplifier OP8 are indicated by (e) and ←), respectively. Further, other resistors and others are shown corresponding to FIG.

In order to form the strain gauge pattern as described above on the diaphragm, it is preferable to use a sputtering method. That is, according to the sputtering method, even when using the input resistor in the eighth embodiment, it is sufficient to form it on the diaphragm together with the strain gauge, and the use of the input resistor does not increase the manufacturing process. At this time, it is preferable that the input resistor be located at a portion where the stress on the diaphragm is zero.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and FIG. 8 is a plan view showing a strain gauge of the second embodiment. FIG. 4 is a circuit diagram showing a third embodiment of the present invention, and FIG. 5 is a plan view showing a strain gauge according to an eighth embodiment. 10... Strain gauge (multiple bridge resistors), 20...
...Strain gauge 9.21122 gkou8,24...Bridge resistor, 80...Gold gauge, 81.32,83
．． 34...Bridge resistor, opl, ()p2. O
F2 ・”Operation amplifier, VZ, 'V'z, V
C...Standard value Figure 4 30! 191- Figure 5

Claims (3)

[Claims] (1) In a pressure sensor that measures pressure with a strain gauge formed on a diaphragm, the strain gauge is shaped like a plurality of bridge resistors, and the pressure causes each bridge resistor to respond to a basic set value by 7. A pressure detection circuit that adds up the 7 changes and outputs it? Equipped with pressure sensor. (2) The pressure detection circuit is a pressure detection circuit that changes the reference set value force $ pressure in a direction opposite to the change direction of the change amount, adds the change amount together, and outputs the result. f#, pressure sensor described in disciple (1). (3) The pressure sensor according to claim (1), wherein the strain gauge is a thin film resistor formed by a sintering method.