JPS60138433A - Pressure transducer - Google Patents

Abstract

PURPOSE:To compensate the bend of temperature characteristic of a zero point by using a resistance having a large temperature dependent property, as a part of a strain gauge bridge. CONSTITUTION:A resistance RA having a large temperature dependent property is connected in series to a resistance R7, and a resistance R8 is connected in parallel to these resistances R7, RA. Also, a resistance RB having a large temperature dependent property is connected in series to a resistance R9, and a resistance R10 is connected in parallel to these resistances R9, RB. The resistance RA and RB have a temperature dependent property of the same tendency. A strain gauge bridge is constituted of these resistances and resistances R4, R5, and its output side is connected to an input side of an operational amplifier OP.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention converts pressure into electricity by the output of a strain gauge bridge consisting of regions of opposite conductivity type formed in a semiconductor pressure-sensitive diaphragm of one conductive station. Concerning highly sensitive pressure transducers.

[Prior art and its problems]

The temperature characteristics of a high-sensitivity pressure transducer equipped with a silicon pressure-sensitive diaphragm, and the temperature characteristics at the zero point, are affected by the slight difference in temperature characteristics between the strain gauges that are inserted into the diaphragm and configured as a bridge. Occur. Particularly when silicon pressure-sensitive diaphragms are used in high-precision pressure transducers, compensation of the zero-point temperature characteristics is essential in most of them.

The conventional method used for this temperature compensation is
Insert a resistor RX (e.g. a thermistor, gold-plated film resistor, diffused resistor, etc.) with a temperature coefficient of resistance different from that of the strain meter into the bridge circuit consisting of strain gauges SG1 to SG4 as shown in Figure 1. This is a method of compensating for the unbalance of the bridge by giving it a temperature characteristic. In this case the resistance R
Inserting x changes the bridge output level, so to compensate for this, a resistor R7 with the same or similar temperature characteristics as the strain meter may be inserted on the side adjacent to the side where the resistor flx is inserted. . This method is direct and f
Although this method is easy to use, it has the following drawbacks.

A bridge circuit consisting of a +11 strain meter and another resistor RX.

Inserting an RV may affect the values adjusted in the previous adjustment process (for example, span) and require readjustment. In particular, this effect becomes more significant as the value of Rx+Ry increases.

(2) This compensation method cannot compensate for the curvature of the temperature characteristics. Although there is a curvature in the temperature characteristic even when Rx and Ry are not inserted, a curvature in the temperature characteristic also occurs when Rx and Ry are inserted. This is due to the fact that strain gauges and compensation resistance values do not change linearly with temperature. It is very rare that these two curvatures cancel each other out and result in a temperature characteristic with no curvature, and curvature of the temperature characteristic is usually observed.

[Object of the Invention] An object of the present invention is to eliminate the above-mentioned drawback Tl) so that zero point temperature characteristic compensation does not affect the previous adjustment process, and at the same time eliminate the drawback (2) to improve the zero point temperature characteristic compensation. An object of the present invention is to provide a pressure transducer that compensates for bending.

[Key points of the invention]

In the pressure transducer according to the present invention, the output side of a resistor bridge has a resistor with a large temperature dependence and a resistor with no temperature dependence connected in series and parallel to the resistor in both adjacent arms. The above object is achieved by also connecting the output side of the strain meter bridge to the input side of the operational amplifier.

[Embodiments of the invention]

FIG. 2 is a circuit diagram showing one embodiment of this circuit.

A resistor RA with high temperature dependence is connected in series with the resistor R7, and a resistor R8 is connected in parallel with the two resistors. These three resistances are collectively referred to as Rα. A resistor RB with high temperature dependence is connected in series with the resistor R9, and a resistor RIO is connected in parallel with the two resistors.

These three resistances are collectively referred to as V. RA (!: R
B is a resistance having the same tendency of temperature dependence. For example, if eight people have positive temperature dependence, RB also has positive temperature dependence. Resistors R4 and R5 are connected in series between power supply VC and ground potential. Resistance Rα, Rβ and resistance R
4, R5 constitutes a full bridge. A resistor R11 is connected between the node 1 of Rα and J and the negative input terminal 5 of the operational amplifier OP.A resistor R6 is connected between the node 2 of OR4 and R5 and the positive input terminal 6 of the operational amplifier OP. Signal voltage v from strain meter bridge output between 0 terminals 3 and 40
in is added. This Vin may be the strain meter bridge output voltage itself, or may be a voltage obtained by amplifying the strain meter bridge output by a differential amplifier. A resistor R1 is connected between the terminal 3 and the negative input terminal 5 of the operational amplifier OP, and a resistor R2 is connected between the terminal 4 and the positive input terminal 60 of the operational amplifier OP.

Further, a feedback resistor R3 is connected between the negative input terminal 5 and the output terminal 6 of the operational amplifier OP.

The present invention will be described in detail with the above configuration. Here, it is assumed that the resistance values and temperature characteristics of the resistors RA and RB are equal, and that their temperature characteristics have a positive temperature gradient and a downward convex curve as shown in Figure 3. . Further, it is assumed that resistances other than RA and RB have substantially no temperature dependence. As the temperature rises, the resistance value of Rh increases,
Along with this, the resistance value of the elbow also increases. In this case, the slope of the temperature characteristic of resistor Rα becomes larger when the resistance value of R7 is small and when the resistance value of R8 is large. RA in Figure 4
(27℃) = 7 holes, R7 = 2 holes, R8 = 4 phases as the standard (line 41), @42 = 0, R8
When Ω is set to =4, according to line 43, R7=2KXl
, shows the temperature characteristics of the resistance Rα when R8 = 6KJ'l (resistance value at 27°C is 1).
If the resistance value of R7 is increased and at the same time the resistance value of R8 is increased, the temperature characteristics of the resistor Rα will tend to convex downward.On the other hand, if the resistance value of R7 is decreased and the resistance value of R8 is decreased at the same time, The temperature characteristics of the resistance Rα tend to be upwardly convex.

FIG. 5 shows an example in which the slope of the temperature characteristic of the bait was kept constant and only the curve was changed. That is, RA=7, R7=
2 to Ω, set the case of R8 = 4 ribs as the reference line 51, and line 5
2 shows the temperature characteristics of the resistance Rα when R7=O, R8-2, 2 and Ω, and the line 53 shows R7=6−1 and R8=10.4 and Ω. In this way, the resistance R
7. By changing R8, the slope and curve of the temperature characteristic of the resistance Rα can be changed. Of course RA is RB
The same thing can be said if R7 is replaced by R9 and R8 is replaced by RIO. That is, by changing the resistors R9 and RIO, the slope of the temperature characteristic of the resistor Rβ and the curve can be changed.

If the temperature characteristics of the resistors Rα and RA are equal, the voltage VT at the connection point 1 between Hiro and RA has no temperature dependence. Next, the resistance R
When the temperature characteristics of α and RA are different, the relationship between the temperature characteristics of RC and RA and the temperature characteristics of VT will be described with reference to FIG. If the slope of the temperature characteristic of resistance Rα is positive compared to the slope of the temperature characteristic of RA, vT has a negative slope of temperature characteristic (
(Fig. 6(a)), conversely, if the slope of the temperature characteristic of the resistance Rα is also negative, then VT has a positive slope of the temperature characteristic (Fig. 6(b)). .

Furthermore, if the temperature characteristics of RC are convex downward as well as those of RA, then VT has temperature characteristics convex upward (Fig. 6(c)).
), conversely, if the temperature characteristics of RC are upwardly convex than those of RA, VT has downwardly convex temperature characteristics (6th
Figure (d)). In this way, resistors R7, R8, R9, RIO
By selecting the value of and giving appropriate temperature characteristics to the resistors Rα and Rβ, it is possible to give the voltage VT at the connection point 1 of RC and RA a predetermined slope and curve of the temperature characteristics.

Let the voltage at the connection point 2 between resistors R4 and R5 be VL, and to simplify the explanation, R4) (-R4/R5)<<
R6゜R4+R5 R3=R6, and assuming that the average value of the voltage between input terminal 3 and ground, and the voltage between input terminal 4 and ground is always equal to half of the power supply VC, the pressure transducer output ■0 is calculated by the following formula ( 1).

As mentioned above, VT in the second term of formula (1) is R7, R8
.

By selecting the values of R9 and R1O, it is possible to provide a predetermined slope and curvature of the temperature characteristics. Also, the formula (1
) by changing the value of resistor R11 in the second term of JJ,
It is possible to adjust the degree to which the pressure transducer output of the
The slope and curve p of the temperature characteristic of VT can be determined according to the zero point temperature characteristic due to terms other than the term, and the slope and curve p of the zero point temperature characteristic of the pressure transducer output yo can be compensated for.
7. By changing the resistance values of R8, R9, and RIO,
The zero point of the pressure transducer output VO is affected, but R4, R
By setting 5 to an appropriate value, the zero point can be set to a predetermined value.

If the curve of the zero point temperature characteristic due to a term other than the second term of equation (1) is only convex upward or convex downward, one of R7, R8, R9, RIO is selected. One resistor can be omitted. For example, if there is only a downward convexity, resistor R7
It is possible to compensate for the zero point temperature characteristic of the pressure transducer output yo by replacing y with a short and giving the second term of equation (1) an upwardly convex curve.

FIG. 7 shows another embodiment, in which resistors RC and RD with large temperature dependence are inserted into two arms of a resistor bridge connected to the plus input terminal 6 of the operational amplifier OP. By appropriately selecting temperature-independent resistors R14, R15, R16, and R17 connected in series and parallel to RC and RD, the same effects as in the embodiment shown in FIG. 2 can be obtained.

FIG. 8 shows yet another embodiment υ, the power supply V of the resistor bridge
This is a case where a resistor Re l RA with large temperature dependence is inserted into the two arms connected to C. Resistor R14,
By appropriately selecting R15, R7, and R8, the same effect as in the embodiment shown in pS FIG. 2 can be obtained. A similar effect can also be obtained when a temperature-dependent resistor is inserted between the two arms connected to the ground potential of the resistor bridge.

FIG. 9 shows still another embodiment, in which the resistors R4 and R5 in the embodiment of FIG. 2 are omitted, and the positive input terminal 6 of the operational amplifier OP is connected to the ground via the resistor R6. . By appropriately selecting three or more of the resistors R7, R8, R9, and RIO, the slope of the zero point temperature characteristic,
It is possible to compensate for and curvature and adjust the zero point. However, compared to the embodiment shown in FIG. 2, the compensable range is narrower.

FIG. 10 shows yet another embodiment, in which the connection method of the resistors in each of the adjacent arms of the resistor bridge in which temperature-dependent resistors are interposed is different from the embodiment of FIG. 2. In other words, a resistor R21 that has no temperature dependence is connected in parallel to the resistor RA that has a large temperature dependence, and a resistor R2 that has no temperature dependence is connected in series with this parallel resistance.
0 is connected, and these three resistors constitute one arm.

In addition, a resistor R23 that has no temperature dependence is connected in parallel to the resistor RB that has a large temperature dependence, and a resistor R22 that has no temperature dependence is connected in series with this parallel resistor. The arm is configured. By appropriately selecting the resistors R20, R21, R22, and R23, the same effect as the embodiment shown in FIG. 2 can be obtained. If the connection method of one of the adjacent arms is different from the connection method of the other arm, for example, in the circuit shown in FIG.
It is also effective to replace Rα in the embodiment shown in the figure.

[Effects of the Invention] According to the present invention, as is clear from the above-mentioned embodiments,
The output component of the resistance bridge, which has a temperature-dependent resistor connected in series and parallel to it on both arms adjacent to the pressure transducer, and a temperature-independent resistor connected in series and parallel to the resistor bridge, is the output component of the strain meter bridge. It is equipped with a circuit using an operational amplifier that is superimposed on the Temperature characteristics of resistance with temperature dependence.

By appropriately selecting the resistance value and the resistance value of both resistors that have no temperature dependence, it is possible to compensate for the slope and curvature of the zero point temperature characteristic of the output of the p1 operational amplifier. Furthermore, the individual arms constituting the resistive bridge, for example Rα, RA, i4 in the embodiment of FIG. The resistance value of Rs is the resistance inserted between the input terminal of the operational amplifier, that is, R6, R
By selecting the resistance value sufficiently small compared to the resistance value of No. 11, it is possible to sufficiently reduce the influence that the zero point temperature characteristic compensation has on the previous adjustment process, such as span adjustment.

In addition, the operational amplifier used to amplify the output of the distortion meter bridge is
Since it also has the function of superimposing a temperature compensation voltage signal, for example VT, on the strain bridge output component, a highly accurate pressure transducer can be obtained with a simple circuit configuration, and its effects are extremely high.

[Brief explanation of the drawing]

FIG. 1 is a compensation circuit diagram of zero point temperature characteristics according to the prior art, FIG. 2 is a circuit diagram of an embodiment of the present invention, and FIG. 3 is a temperature characteristic diagram of resistors RA and RB in the embodiment of FIG. FIG. 4 is a diagram when the slope of the temperature characteristic of the resistor Rα is changed in the embodiment shown in FIG. 2, and FIG. The line diagram when
Figures 6(a) and (b). (c) and (d) are the resistances Rα in the embodiment of FIG.
, FIG. 7, FIG. 8, FIG. 9, and FIG. 10 are circuit diagrams showing different embodiments of the present invention, respectively. be. RA , RB4D , , , , ・Resistance with large temperature dependence, R7゜R8, R9, R10, R14, R1
5, R20, R21, R22, R23...
-Resistor without temperature dependence, 3, 4... Output terminal of strain meter bridge, OP... Operational amplifier. Figure 21 F? i 2 years old + M, good ('C) 4 years old 77 figures R1 8 years old 101 yen)

Claims (1)

[Claims] 1) - In a device that converts pressure into electricity by the output of a strain gauge bridge consisting of regions of opposite conductivity type formed in a conductivity type semiconductor diaphragm, both adjacent arms each have a resistance with a large temperature dependence and a A pressure transducer characterized in that the output side of a resistance bridge in which a temperature-independent resistor connected in series and parallel is inserted, and the strain meter bridge are connected to the input side of an operational amplifier.