JPH0546488B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a strain sensor that receives the pressure of a liquid or the like with a diaphragm and converts the strain into an electrical signal using a strain-sensitive resistor set on the diaphragm.

BACKGROUND ART Conventionally, pressure sensors have been widely used for measuring the pressure of liquids, etc., which receive pressure with a diaphragm and extract strain as a change in electrical resistance using a strain-sensitive resistor formed on the diaphragm. In addition to metal gauges and semiconductor gauges, strain-sensitive resistors include those with a silicon semiconductor diaphragm and a diffused resistance layer formed on the diaphragm. When the strain-sensitive resistor is made of a semiconductor such as silicon, the resistance and gauge factor are particularly strongly affected by the operating temperature, so it is necessary to compensate for temperature more strictly. It has the advantage of being more sensitive than 10 times.

FIG. 8 shows an example of a conventional pressure sensor, and is a sectional view of the main part in which a semiconductor gauge is stuck on a diaphragm. The strain-sensitive resistors 3 and 5 are formed on the diaphragm. Reference numerals 4 and 6 indicate electrode portions at both ends of the strain-sensitive resistor, respectively. In order to compensate for the temperature, the strain-sensitive resistor is usually connected to a bridge circuit as shown in FIG. 9. In Figure 9, 1
1 and 12 are strain sensitive resistors, 13 and 14 are metal resistors, 4
1 indicates a constant voltage power supply section. A power source 41 is connected to bridge ends a and c, and bridge voltage outputs are obtained from b and d.

In addition, if there is a difference in the resistance temperature characteristics of the strain-sensitive resistors, the voltage between the bridge output voltages b and d can be adjusted by connecting metal resistors in series or in parallel to the resistor parts that constitute the bridge, as necessary. It is known to compensate for variations due to temperature at the zero point.

On the other hand, the output sensitivity is proportional to the gauge factor of the strain-sensitive resistor, but since the gauge factor is affected by the ambient temperature, it is necessary to compensate for the operating temperature.
As shown in the figure, the thermistor element 15 has a metal resistor 1
A known method is to externally connect 6 and 17 in series and in parallel to the bridge, and connect this to the constant voltage power supply 42. However, with the above method, it is quite complicated and time-consuming to precisely adjust the resistance-temperature characteristics of the external thermistor element to match the resistance-temperature characteristics of the strain-sensitive resistor. In many cases, it is difficult to obtain sufficient sensitivity compensation in a wide operating temperature range. There is also the inherent problem that errors resulting from mismatched output sensitivity compensation cause bridge output voltage zero point fluctuations, and there are many cases in which this zero point fluctuation cannot be ignored. Further, the desired thermistor element cannot necessarily be made small, and the sensor as a whole has disadvantages such as an increase in size.

Purpose of the Invention Therefore, the purpose of the present invention is to:
It is an object of the present invention to provide a small strain sensor that facilitates temperature compensation of sensitivity while keeping the zero point fluctuation of a bridge output voltage made of a strain-sensitive semiconductor resistor to a minimum.

Structure of the Invention In the present invention, a strain-sensitive semiconductor resistor is connected in a bridge circuit on a diaphragm, electrically connected to the midpoint of two strain-sensitive semiconductor resistors connected in series to one of the bridge output terminals, and the zero point of the bridge output voltage is compensated,
In a strain sensor in which a temperature-sensitive resistor made of the same material as the strain-sensitive semiconductor resistor is provided on a portion of the diaphragm that is not subjected to strain, the temperature-sensitive resistor is connected in series to the bridge input end and serves as a constant current source. Alternatively, connect the series circuit of the temperature-sensitive resistor and the metal resistor in parallel to the bridge input terminal and connect it to a constant voltage source, and measure the bridge output voltage and the voltage of the temperature-sensitive resistor. A compact strain sensor is provided that detects temperature-corrected pressure after comparison in a computer calculation unit.

Embodiment FIG. 1 shows a cross-sectional view of essential parts of an embodiment of the strain sensor of the present invention. In Figure 1, 1 is a metal diaphragm made of stainless steel, 2 is an electrical insulating layer made of resin, ceramic, glass, etc., 3, 5, 7
indicates a strain-sensitive semiconductor resistor made of silicon, germanium, etc. formed on the insulating layer. The strain-sensitive resistors 3 and 5 are strain sensor sections that receive strain generated in the diaphragm 1, and electrical resistance changes due to strain are extracted from electrodes 4 and 6 at both ends of the resistors 3 and 5. The resistor 7 is a temperature-sensitive sensor portion formed in a portion of the diaphragm 1 that is not subjected to strain, and approximately senses the temperature of the strain-sensitive resistors 3 and 5, and detects the change in electrical resistance at the electrodes 8 at both ends of the resistor 7.
Take it out.

The resistors 3, 5, and 7 are formed of the same semiconductor material on the same diaphragm, and can be easily miniaturized.

FIG. 2 shows an example of the bridge circuit connection in FIG. A temperature-sensitive resistor made of the same material as the semiconductor resistor, and 43 a constant current power supply section, respectively. In FIG. 2, the metal resistor connection portion for temperature compensation of the bridge voltage output zero point is omitted from the figure, but it is assumed that the bridge output voltage zero point temperature compensation between b and d is sufficiently compensated. Furthermore, the dotted line portion 20 indicates a portion that is integrated as a strain sensor and is used at the same ambient temperature.

Figure 3 shows the bridge output voltage V ₁ in Figure 2.
The relationship between P and the pressure P applied to the diaphragm is shown using the ambient temperature T as a parameter. In the figure, T ₀ indicates 20°C. Figure 4 is the second
This figure shows the relationship between the voltage V ₂ between both ends c and e of the resistor 25 in the figure and the temperature T. As shown in FIG. 3, the zero point fluctuation of the bridge output voltage due to ambient temperature is suppressed to a sufficiently low level. Further, the bridge output voltage V ₁ with respect to the pressure P is expressed as V ₁ α{1-β(T-T ₀ )}P, where α and β are constants.

Also, from Fig. 4, the voltage V ₂ is V ₂ with V ₀ and γ as constants.
It is expressed as V ₀ e ^rT . Therefore, by measuring the voltages V ₁ and V ₂ , the pressure applied to the diaphragm can be calculated from PV ₁ /α{1−β(T−T ₀ )}. First, the pressure value at voltage V ₁ measured using the ambient temperature as a parameter shown in Fig. 3 is stored in the calculation section of the computer, and the relationship between the ambient temperature and voltage V ₂ as shown in Fig. 4 is compared. By doing so, it is possible to calculate the true pressure value.

FIG. 5 shows another embodiment of the bridge circuit connection in FIG. In the figure, 31 and 32 are 3 and 5
, 33, 34, and 36 are metal resistors, 35 is a temperature-sensitive resistor corresponding to 7, and 45 is a constant voltage power supply section, respectively. (Similar to Figure 2, the metal resistor connection part for temperature compensation at the bridge voltage output zero point is omitted, but it is assumed that the bridge output voltage zero point temperature compensation between b and d is sufficient.) The dotted line portion 30 indicates a portion that is integrated as a strain sensor and is used at the same ambient temperature. In the case of FIG. 5, the voltage between the bridge output voltage b and d _is
The relationship with the ec' voltage V ₂ also has the same characteristics as in FIGS. 3 and 4. Therefore, the value of pressure P can be calculated by measuring voltages V ₁ and V ₂ . If necessary, in order to linearize the resistance-temperature characteristics of the temperature-sensitive resistors 25 and 35 in FIGS. It is also possible to add resistors 26, 27 and 38, 39 in series and parallel. The metal resistor 36 is a shared voltage resistor for the constant voltage power supply.

Although this embodiment shows the case where the diaphragm is made of metal, similar excellent effects can be obtained when the diaphragm is made of a semiconductor such as silicon single crystal.

Furthermore, in the embodiments of the present invention, the power supply applied to the temperature-sensitive resistor section was the same as the power supply for the strain-sensitive resistor section.
Of course, each may be driven by a separate power source.

Effects of the Invention As described above, in the present invention, a strain-sensitive semiconductor resistor is connected in a bridge circuit on a diaphragm, and is electrically connected to the midpoint of two strain-sensitive semiconductor resistors connected in series to one of the bridge output terminals. In a strain sensor in which the voltage zero point is temperature-compensated and a temperature-sensitive resistor made of the same material as the strain-sensitive semiconductor resistor is provided on a portion of the diaphragm that does not receive strain, the temperature-sensitive resistor is connected in series with the bridge input end. or connect a series circuit of the temperature-sensitive resistor and metal resistor in parallel to the bridge input end and connect it to a constant voltage source to maintain the ambient temperature shown in Figure 3. The relationship between the bridge output voltage and the measured pressure, which are parameters, is stored in advance in the calculation section of the computer.
By comparing the voltage of the temperature-sensitive resistor part shown in FIG.
The present invention provides a small strain sensor that can accurately measure pressure.

[Brief explanation of the drawing]

FIG. 1 shows a sectional view of the main parts of an embodiment of the strain sensor of the present invention. FIG. 2 shows an example of the bridge circuit connection in FIG. 1. Figure 3 shows the relationship between the bridge output voltage V ₁ and the pressure P applied to the diaphragm in Figure 2 using the ambient temperature T as a parameter, where the vertical axis shows the output voltage and the horizontal axis shows the pressure. . FIG. 4 shows the temperature characteristics of the voltage V ₂ between the temperature-sensitive resistors in FIG. 2, where the vertical axis shows the voltage and the horizontal axis shows the temperature. FIGS. 5, 6 and 7 respectively show bridge circuit connection examples of other embodiments of the strain sensor of the present invention. FIG. 8 is a sectional view of essential parts of an example of a conventional strain sensor. 9 and 10 show examples of bridge circuit connections of conventional strain sensors. 3, 5, 11, 12, 21, 22, 31, 32
...Strain sensitive semiconductor resistor, 25, 35... Temperature sensitive resistor, 41, 42, 45, 46... Constant voltage power supply section,
43, 44... constant current power supply section.

Claims (1)

[Claims] 1. A strain-sensitive semiconductor resistor is connected in a bridge circuit on the diaphragm, and is electrically connected to the midpoint of the two strain-sensitive semiconductor resistors connected in series to one of the bridge output terminals,
In a strain sensor in which the bridge output voltage zero point is temperature-compensated and temperature-sensitive resistors 25 and 35 made of the same material as the strain-sensitive semiconductor resistor are provided on a portion of the diaphragm that is not subjected to strain, the temperature-sensitive resistor is Connect in series to the input end and connect to a constant current source, or connect a series circuit of the temperature sensitive resistor and metal resistors 36 and 38 in parallel to the bridge input end and connect to a constant voltage source, A strain sensor characterized in that a bridge output voltage V ₁ and a voltage (V ₂ ) of the temperature-sensitive resistor are measured and compared to detect a temperature-corrected pressure. 2. The strain sensor according to claim 1, wherein the temperature-sensitive resistor is formed by connecting a metal resistor in series 26, 38 or in parallel 27, 39.