JPS59168331A - pressure transducer - Google Patents

Abstract

PURPOSE:To make it possible to perform zero-point temperature compensation without the effect of previous adjustment and without dispersion in zero-point temperature characteristics, by performing the temperature characteristic compensation at a zero point in correspondence with the expansion and contraction of the gas in a reference pressure chamber due to temperature change. CONSTITUTION:A reference pressure chamber, which is partitioned by diaphragm, is filled with a gas such as helium at reference pressure. The resistance value of a temperature dependent resistor RA is changed with the variation in volume of the gas due to temperature change. A bridge circuit B2 is formed by the resistor RA in a resistor Ralpha and resistors R6-R8. A temperature compensating output is outputted through the bridge circuit B2 and an operation amplifier OP2. The temperature compensation at a zero point of the strain gage bridge circuit B1 for measuring the pressure provided in the diaphragm is performed, including the offset compensation of the amplifier OP2 and an operation amplifier OP1, which generates the output corresponding to the pressure accompanied by the temperature change. In this constitution, the zero-point temperature compensation can be performed without the effect of the previous adjustment caused by the dispersion in strain gage characteristics and without the dispersion in zero-point temperature characteristics in a broad range.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a diaphragm pressure transducer that compensates for the temperature characteristics of the zero point to obtain a stable zero point against temperature changes. It is suitable for a high-sensitivity pressure transducer equipped with a silicon diaphragm (strain-generating part) in which a diffusion type strain gauge is arranged in a fractional manner.

[Prior art]

Conventionally, the temperature characteristics, especially the temperature characteristics at the zero point, in high-sensitivity pressure transducers equipped with silicon pressure-sensitive diaphragms are caused by slight differences in temperature characteristics between strain gauges arranged in the form of a bridge circuit on the diaphragm. do. In particular, products where silicon pressure sensitive diaphragms are used.

Most of the 18 degree pressure transducers require compensation of the zero point temperature characteristics.

The conventional method used to compensate for this temperature characteristic is to use a resistor RX (such as a thermistor, metal film resistor, or diffused resistor) with a temperature coefficient of resistance different from that of the strain gauge, as shown in Figure 1. Thus, it is inserted into a bridge circuit composed of strain gauges 5GI-SG4, and this bridge circuit is given an unbalanced temperature characteristic to compensate for it. In this case, the output level of the bridge circuit changes due to the insertion of the resistor RX, so to compensate for this, a resistor RY with the same or similar temperature characteristics as the strain gauge is inserted. It may also be inserted next to an edge. Although this conventional method is direct and simple, it has the following drawbacks.

■ Since other resistors RX and RY are inserted into the bridge circuit consisting of strain gauges S01 to SG4, the values adjusted in the previous adjustment process, such as sensitivity, may be affected and readjustment may be necessary. arise. In particular, this effect becomes more significant as the values of the resistors RX and RY increase.

(2) If fluctuations in the zero-point temperature characteristics of individual pressure transducers occurring in the output of the strain gauge bridge circuit become a problem, it becomes necessary to adjust the zero-point temperature characteristics of each pressure transducer individually. At this time, in this conventional method, the zero point temperature characteristics are adjusted by setting the resistance values of the resistors RX and RY for each pressure transducer. However, since the temperature characteristics between the resistance R× or RY and the strain gauge are different, the zero point temperature characteristics may curve (
In other words, the temperature characteristics are not linear). The greater the variation in the slope of the zero point yla degree characteristic, the greater the variation in the curve of the zero point temperature characteristic caused by the above-mentioned adjustment.

[Mejiro 9] Therefore, the purpose of the present invention is to eliminate the above-mentioned drawbacks, do not affect the zero point temperature characteristic compensation or the adjustment process before that, and at the same time reduce the variation in the curve of the zero point temperature characteristic due to the adjustment of the zero point temperature characteristic. The object of the present invention is to provide a pressure transducer that eliminates the

[Key points of the invention]

In order to achieve such an object, the present invention provides a reference pressure chamber integrally with the diaphragm, and provides this base with 1. A gas is sealed in a pressure chamber, and the temperature dependence of the zero point accompanying the expansion and contraction of this gas due to temperature changes is utilized to compensate for the temperature characteristics of the zero point.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 2 shows an example of the configuration of the pressure transducer of the present invention, in which SGI to SG4 are connected to a diaphragm IA formed on a silicon chip 1 shown in i3, and a bridge circuit B1, respectively.
It is a strain gauge configured and arranged in the form of.

To explain this in more detail with reference to FIG. 3, a diaphragm IA is created by etching the central part of the silicon chip l, and four strain cases SGI to SG4 are placed on the unetched inner surface of the diaphragm IA.
built in through expansion. At this time, a pair of strain gauges SGI and SG3 are arranged at the periphery of diaphragm IA, and the remaining strain gauges SG2 and SG4 are arranged at the center of diaphragm IA. Reference numeral 2 is a container whose inside is a reference pressure chamber 2A, and this container 2 keeps the reference pressure chamber 2A airtight.
By filling A with an inert gas such as helium gas, a predetermined reference pressure P is generated. The measuring pressure is conducted to the etched outer surface 1B of the diaphragm IA.

Furthermore, as shown in FIG. 2, strain gauge SG1
Connect the connection point between and SG4 to electric WVc, and
The connection point between strain gauges SG2 and SG3 is connected to the ground potential G.
Make it ND. In addition, the connection point between the strain gauges SG3 and SG4 is used as one output terminal of the strain gauge bridge circuit B1, and one output amplifier OP is connected via the resistor R1.
The connection point between the strain gauges SGI and S02 is connected as the other output terminal of the strain gauge bridge circuit B1 to the non-inverting input terminal of the operational amplifier OPI via a resistor R2. The output terminal of the other operational amplifier OP2 and the above-mentioned operational amplifier (P OP
A resistor R3 is connected between the + non-inverting input terminal, and a feedback resistor R4 is connected between the inverting input terminal of the operational amplifier OP1 and its output terminal.

In this way, the operational amplifier OPI and the resistors R1 to R4 constitute a differential amplifier. Here, each of the above-mentioned resistors R1 to
Let the resistance value of R4 be R1-R2 and R3=R4,
Generally, the resistance values of the resistors R1 and R2 are set to a sufficiently large value compared to the output impedance of the strain bridge circuit Bl. In this case, let the output voltage of the input range bridge circuit B1 be Vin, and let the output of the amplifier OP2 be v.
The pressure transducer output voltage vO obtained from the output terminal of the operational amplifier OPI is expressed by the following equation (1).

3 VO= -Vin + -V
(1)I Next, a resistor R5 is connected between the voltage '#vc and the ground potential G'ND.
and R6 are connected in series, and resistors R5 and R6 are connected in series.
The common connection point with the OP2 is connected to the non-inverting input terminal of the operational amplifier OP2. Further, the resistor R7 and a resistor RA having a large positive temperature characteristic (for example, a positive temperature characteristic thermistor) are connected in parallel, and these two resistors R7 and RA are collectively referred to as Rα. Furthermore, a resistor R is connected between the power supply VC and the ground potential GND.
α and R8 are connected in series, and a resistor R8 is connected between the common connection point of the resistors Rα and R8 and the inverting input terminal of the operational amplifier OP2.

A feedback resistor R1 (+) is connected between the inverting input terminal of the operational amplifier OP2 and its output terminal.

In this way, the resistors R5, R6, Rα and R8 constitute a full bridge circuit B2, and the output voltage of this bridge circuit B2 is connected to the operational amplifier OP2 and the resistors Rα and R8 to R8.
It is amplified by an amplifier consisting of IO. Here, resistance R
The potential of the common connection point of 5 and R6 is Vya, and the resistors Rα and R8 are
The potential of the common connection point with V- is set as V-, and the relationship between the resistance values of resistors Rα, R8, and R9 is expressed by the following equation (2). ) is expressed by the formula.

In the circuit configuration shown below, for example, P at 27°C.
mm) Ig (absolute pressure) based on helium gas 1!・If one person enters the pressure chamber 2A, the standard pressure chamber 2A
By changing ji by 1 degree, this group Qli pressure P changes according to the Hoyle-Charles law. That is, if the temperature change at that time is ΔT, the change ΔP7 in the reference pressure P due to the temperature change ΔT is expressed by the following equation (4).

Temperature compensation at the zero point of the pressure transducer output is performed over the span (
Perform this after adjusting the output voltage range and compensating for the span temperature characteristics. In this case, if the sensitivity of the pressure transducer to a change in the measured pressure is a, then the sensitivity to a change in the filling pressure of the semi-pressure chamber 2A is -a. In the fire example, the sign of this sensitivity a is Since it is positive, the shift due to temperature change ΔT (
(Pressure transducer output voltage VO due to change in pressure P ΔP
The change ΔVOI is expressed by the following equation (5).

Each strain gauge s1 to S forming the bridge circuit Bl
4 usually have temperature characteristics that differ by 1·Y·.

Therefore, the zero point output voltage of the strain gauge circuit Bl has temperature dependence. Furthermore, the offset voltages of the 7iif calculation amplifiers DPI and OR3 also have temperature dependence. Temperature characteristics due to these temperature j & dependences (however, the
If b is the value of white, then this /I
The change ΔVO2 in the pressure transducer output voltage vO due to the temperature change T due to the slope b of the J-degree characteristic is expressed by the following equation (6): 3 ΔVO2= −b ΔT (6) 1 Resistor bridge circuit B configured in the previous stage
Since the resistor RA in No. 2 has a large positive temperature characteristic, the resistance value of the resistor RA increases as the temperature rises. Along with this, the potential V- at the common connection point of the resistors Rα and R8 decreases, and as shown in the above equation (3), the operational amplifier OP2
Since the output voltage v of increases, the pressure transducer output voltage vO also increases as shown in equation (1). Here, if the slope of the temperature characteristic of the pressure transducer output voltage vO due to the temperature characteristic of this resistance RA is C, then the temperature change ΔT due to this slope C
The change ΔVO3 in the pressure transducer output voltage vO due to the change in pressure transducer output voltage vO is expressed by the following equation (7). However, the sign of the slope C of the temperature characteristic is positive.

ΔVO3=cXΔT (?)
As described above, in this embodiment, the three factors expressed by the above-mentioned equations (5) to (7) are the main causes of the temperature dependence of the zero point. Therefore, according to equations (5) to (7), the change ΔvO in the zero point of the pressure transducer output' voltage vO due to the temperature change ΔT can be calculated as follows (8)
It is expressed by the formula.

ΔVO=ΔVO1+ΔVO2+ΔVO3 Therefore, it can be seen that in order to eliminate the slope of the zero point temperature characteristic of the pressure converter output voltage vO, the following equation (9) needs to be satisfied.

300 ('k) R1 - Shallowly, in the case of a high-precision diffusion type semiconductor pressure changer or I device like this embodiment, the strain cage bridge circuit B
Variations in the slope b of the temperature characteristic of the second term on the right side of equation (8) due to variations in the temperature dependence of the average point output voltage of l and fluctuations in the temperature dependence of the offset voltage of the calculation increase l1Ii ÷ (1) However, this variation in the slope b can be compensated for by adjusting the base pressure P in the reference pressure chamber 2A, which is represented by the right-hand side force 1Jf4 of equation (8).

Furthermore, since the first term on the right side of equation (8) is only a negative fraction and is 1μ, in this embodiment, the basic pressure P in the reference pressure chamber 2A is The resistors RA and R7 shown in the second diagram
~Choose the resistance value of RIO appropriately to give the value of slope C (constant value) described in 1-. At that time, Jl! l; The resistance values of the anti-RA and RIO can be selected so as to satisfy the above-mentioned conditions and at the same time, to eliminate variations in the curve of the zero point temperature characteristic.

Note that if the above-mentioned slope b of the temperature characteristic is always positive, the equation (9) is satisfied even if the slope C of the temperature characteristic is C=O. That is, in this case, it is possible to compensate for the slope of the zero point temperature characteristic even without a compensation circuit that generates the slope of the zero point temperature characteristic as described above.

Further, when the value of the reference pressure P is adjusted, the zero point output voltage of the pressure transducer changes accordingly. Change in reference pressure P ΔP
The change in zero point ΔvOP accompanying this is expressed by the following equation (10).

△VOP = −a−△P (1
0) This zero point change ΔvOP is determined by the resistance R5 or R6.
By appropriately changing the resistance value of the resistors R5 and R6, the potential V+ at the common connection point of the resistors R5 and R6 in equation (3) is changed, and the output voltage vL of the operational amplifier OP2 is thereby compensated for by selecting an appropriate value. Ru.

Next, in the circuit configuration of FIG. 2, the sensitivity a to changes in measured pressure is 4. mV/°C1 measurement pressure range is 1
FIG. 4 shows a general example of the distribution of variations in the slope R3/R1·b (second term on the left side of equation (9)) of the zero point temperature characteristic when the absolute pressure is 50 to 7 eOmmHg (absolute pressure). Zarani, 2nd V! p, t in the circuit configuration of J; 1
Slope of zero point temperature characteristic of output due to 1Oi pressure P = aP/
An example of the relationship between 300('k) (the first term on the left side of equation (8)) and the base ξ pressure P is shown in FIG. Normally, (the mold pressure P is in the sonic pressure range (100 to 780+n in this example)
IIT can be set arbitrarily within the same pressure range as mHg).

According to FIG. 4, the slope R3/R1·b of the zero point temperature characteristic is generally distributed in a range of -2 to +2 mV/°C.

Therefore, as can be seen from Fig. 5, in order to adjust all the pressure transducers, it is sufficient to move the reference pressure P within a range of 300 mml (g. In other words, for example, the slope of the temperature characteristic
Assuming that C is +4mV/'C, ), (mold pressure P is 150
If you move it in the range of n++nHg to 450m+nHg (
9) The right side of the equation can be set to zero. In this way, according to this embodiment, a sufficiently wide compensation range can be obtained for variations in the slope of the zero point temperature characteristic.

Note that 2 (if the gas sealed in the pressure booster chamber 2A is close to an ideal gas, such as helium, changes in temperature and changes in reference pressure can be considered to be in a proportional relationship according to the Hoyle-Charles law). Furthermore, the temperature characteristic of the sensitivity of a pressure transducer is generally compensated within the operating temperature range, and in that case, the sensitivity a of the pressure transducer to changes in measured pressure does not depend on temperature. In other words, the temperature characteristic caused by the helium gas in the pressure chamber 2A at that time is only the slope of the temperature characteristic,
No bending of temperature characteristics occurs. Therefore, when adjusting the zero-point temperature characteristics of individual pressure transducers by changing the reference pressure P as in the unimplemented example, there is an advantage that variations in the bending of the one-complexity characteristic do not occur. .

〔effect〕

As described above, according to the present invention, a gas at a predetermined pressure is sealed in a reference pressure chamber, and the pressure is adjusted by utilizing the temperature dependence of the zero point as the gas expands, contracts, and contracts due to temperature changes. Since we compensated for the temperature characteristics at the zero point of the converter, the compensation for the temperature characteristics at the zero point overshadowed the previous adjustment process! YJI has developed a pressure transducer that allows the zero point temperature characteristic to be adjusted and does not cause variations in the curve of the zero point temperature characteristic due to adjustment of the zero point temperature characteristic.

Furthermore, in the present invention, it is possible to easily compensate for the temperature characteristics of the zero point over a wide adjustment range as described above, and by selecting, for example, helium as the gas to be sealed in the reference pressure chamber, the gas in the reference pressure chamber can be adjusted using a helium leak detector. Density can also be easily measured.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of the main circuit configuration of a conventional pressure transducer, FIG. 2 is a circuit diagram showing an example of the circuit configuration of the pressure transducer of the present invention, and FIG. 3 is a circuit diagram showing an example of the circuit configuration of the pressure transducer of the present invention. FIG. 4 is a characteristic diagram showing an example of the variation distribution of the slope R3/R1・b of the zero point temperature characteristic in the circuit configuration of FIG. 2, and FIG. It is a characteristic diagram showing an example of the relationship between the slope of the zero point temperature characteristic -aP/300('k) and the base (pressure P) in the circuit configuration of 1...Silicon chip, IA...Diaphragm, 2. ...Container, 2A...Reference pressure chamber, 5GI-9G4...Strain cage, OPI, OR3
... Performance 1p, amplifier, R1 to RIO, Rα... resistance, RA, RX, RY... temperature dependent resistance, Vc...
・Power supply, GND...Earth voltage, vO...Output voltage, Bl, B2...Bridge circuit, Reference pressure...P. Figure 1 Figure 3 Figure 4 1'b (mV/'C) 1

Claims (1)

[Claims of Claims] 1) A tire flamm equipped with a switch/range bridge circuit and a reference pressure chamber provided integrally with the diaphragm, and gas at a predetermined pressure sealed in the reference pressure chamber. The temperature dependence of the zero point of the range bridge circuit is changed by the expansion and contraction of the gas due to the temperature change, and the zero point temperature characteristic of the pressure transducer output is compensated according to the temperature dependence. A pressure transducer characterized by: 2. In the pressure transducer according to claim 1,
A pressure transducer characterized in that the gas is helium. 3) In the pressure transducer according to claim 1,
A pressure transducer characterized in that the pressure in the reference pressure chamber at room temperature is set to a pressure within a constant pressure range.