JPS61239135A - Differential pressure transmitter - Google Patents

Abstract

PURPOSE:To obtain a transmitter which is not damaged by an excessive pressure without providing a protective mechanism especially, by using two pieces of hydrostatic pressure sensors of the same kind. CONSTITUTION:A low pressure chamber 3 and a high pressure chamber 4 are formed on both sides of a partition of a columnar body 5, and the inside of both the chambers is filled with an incompressive fluid such as an Si oil, etc. Seal diaphragms 1, 2 are welded to both end faces of the body 5. Hydrostatic pressure sensors 6, 7 are constituted of a semiconductor material having a hydrostatic pressure sensitivity. By hermetic sealing parts 8, 9, lead wires 61, 71 which is connected to the hydrostatic sensors 6, 7 are fetched to the outside of the body 5. A temperature detecting element 10 detects a temperature of the sensors 6, 7, and a lead wire 101 fetches this electric signal. Also, a pressure of a fluid to be measured is led to the chambers 3, 4, and a signal corresponding to a differential pressure of the chambers 3, 4 is obtained by calculating a variation of a resistance of the sensors 6, 7. Also, even if excessive pressures PH, PL are impressed to a transmitter, an external force which gives a damage is not applied at all to the sensors 6, 7 since the chambers 3, 4 are surrounded by a solid wall of the body 5.

Description

[Detailed Description of the Invention] A. ``Objective of the Invention'' [Industrial Application Field] The present invention uses a semiconductor material whose resistance value changes due to hydrostatic pressure, and which is resistant to destruction even when excessive pressure is applied. It concerns a differential pressure transmitter.

[Conventional technology]

FIG. 3 shows a general means of measuring flow rate using an orifice. In the figure, 11 is an orifice, 12 is a pipe, 13 is a liquid, 14 is a pressure conduit, 15 is a valve, 16 is a differential pressure transmitter, and 11 is a differential pressure sensor. Orifice 11
When measuring the flow rate of liquid 13 using Measure pressure. Then, by calculating the equation (1), the current IQ
can be found.

Q-K JkoPs-〒-1) mko/H (1) Q: Flow rate: Constant PH: Upstream pressure PL: Downstream pressure There is a problem with the configuration of the conventional differential pressure transmitter as shown in Figure 3. This is because even if the differential pressure (PHPL) is small, if PH and PL are high pressures, high pressure may be applied to the differential pressure sensor 17 of the differential pressure transmitter 16 depending on the valve operation. be. For example, PH-101bar rpL-100ba
In the case of r, even if the differential pressure is 1 bar, depending on the valve operation, 100 bar, which is 100 times the differential pressure, may be applied to the differential pressure transmitter 16 as a differential pressure, and as a result, it may be destroyed. .

In order to prevent such a situation, conventionally, an overpressure protection mechanism is provided.

Figure 4 shows overpressure 1! It is a figure showing an example of composition of a differential pressure transmitter provided with a mechanism. In the configuration shown in FIG. 4, when excessive differential pressure (including reverse pressure) is applied, the overload protection valve 20 shown in the figure moves to close the hole provided in the body 29, so the high pressure side The pressure on the low pressure side is equalized, and the silicon sensor 22 is protected.

[Problem that the invention seeks to solve]

However, the differential pressure transmitter as shown in FIG. 4 has many problems such as a complicated overpressure protection mechanism, characteristic error factors, and increased cost.

SUMMARY OF THE INVENTION An object of the present invention is to provide a differential pressure transmitter that uses two hydrostatic pressure sensors of the same type and is not damaged by excessive pressure without the need for an excessive pressure protection mechanism.

``Structure of the Invention'' [Means for Solving the Problems] In order to solve the above problems, the present invention includes a body with a low pressure chamber and a high pressure chamber formed on both sides by a partition,
The pressure of the fluid to be measured is introduced into the low-pressure chamber and the high-pressure chamber, and static pressure sensors made of a semiconductor material having a resistance change characteristic corresponding to the hydrostatic pressure are placed in the low-pressure chamber and the high-pressure chamber, respectively. The change in resistance of the static pressure sensor is then calculated to obtain a signal corresponding to the differential pressure between the low pressure chamber and the high pressure chamber.

〔Example〕

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a diagram showing an example of the configuration of main parts of a differential pressure transmitter according to the present invention. In the figure, 1 and 2 are seal diaphragms. 3 is a low pressure chamber, and 4 is a high pressure chamber, both of which are filled with an incompressible fluid such as SL oil. 5
is a cylindrical body with a partition in the center, and the above-mentioned low pressure chamber 3 and high pressure chamber 4 are formed on both sides of this partition. The seal diaphragms 1 and 2 are, for example, welded to both end surfaces of the body 5. Static pressure sensors 6 and 7 are made of a semiconductor material sensitive to hydrostatic pressure.

This static pressure sensor 6.7 is connected to a low pressure chamber 3 and a high pressure chamber 4, respectively.
will be installed in 8 and 9 are hermetic seal parts,
Lead wire 6+ electrically connected to static pressure sensor 6.7
, 7+ to the outside of the body 5. 1
0 is a temperature detection element that detects the temperature of the static pressure sensor 6.7,
Reference numeral 101 is a lead wire for taking out an electric signal from this temperature detection element 10.

Figure 2 shows each lead wire 6+ + 7++1 shown in Figure 1.
01 is an electrical circuit to which it is connected, and a signal corresponding to the differential pressure can be obtained from the output terminal of this circuit. In FIG. 2, E is a constant voltage source and U is an amplifier. R+, R
2 is the resistance of the static pressure sensor 6.7 shown in FIG. That is, the static pressure sensor 6 is represented by a resistor R1, and the static pressure sensor 7 is represented by a resistor R2. However, the present invention can be achieved even if the static pressure sensor 6 is the resistor R2 and the static pressure sensor 7 is the resistor R1, contrary to the above. C is a logarithmic converter, D is a divider,
F is an adder.

Resistor R1 is connected to the inverting input terminal of amplifier U, and resistor R2 is connected between the output terminal and the inverting input terminal of the amplifier. A constant voltage source E is connected between the other end of the resistor R+ and the non-inverting input terminal of the amplifier U.

The output terminal and non-inverting input terminal of amplifier U are connected to logarithmic converter C. The output voltage e2 of the logarithmic converter C and the output voltage of the adder F are connected in series and introduced into a divider. Further, a signal from the temperature detection element 10 is introduced into another input terminal of the divider.

The operation of the device in which the differential pressure transmitter of FIG. 1 and the electric circuit of FIG. 2 configured as described above are combined will be described below.

Assuming that the static pressure sensor shown in FIGS. 1 and 2 is constructed of a semiconductor material sensitive to hydrostatic pressure, and assuming that this semiconductor is an intrinsic semiconductor, the static pressure sensor 6.7 (in FIG. 2, the resistance R+,
The conductivity σ weight and σ2 of R2> are expressed by equations (2) and (3).

σ+-nL+ ・e ・(ue +tlp)
(2) σz=nLz see (μe+μp)
(3) Here, e is the electron elementary charge ue is the electron mobility μp is the hole mobility (2), nil and nL2 in equation (3) are the intrinsic carrier concentration of the semiconductor material, and the following equation It is expressed as

nt + -no TT eXri (-" aim-)
(4)kT''1-n=2-no TT eXp (2 to 1) (S) Here, nO is temperature, material constant not related to band energy E o + *E G2 is band gap energy of semiconductor material Resistance to hydrostatic pressure, i.e. nff
The reason why the 1 ratio changes is mainly because the bandgap energy Eo changes with pressure. The resistance values R+ and R2 of the static pressure sensor 6.7 are (6).

It is expressed by equation (7).

When this static pressure sensor 6.7 is immersed in silicone oil as shown in Fig. 1 and pressures PH and PL are applied, the resistance values R+ and R
2 changes. When this is amplified by amplifier U in Fig. 2,
The output el of the amplifier U is expressed by equation (8).

e I-"'e g (8)
R.

e, is the voltage of constant voltage source E. If the temperatures in the low pressure chamber 3 and high pressure chamber 4 shown in FIG. 9)
It can be replaced with the expression u1.

1B+ -61o-eXp(, KT (EG 2-Eo
+))...(9) By taking the resistance ratio (R2/R1) as described above, it is possible to obtain the signal e in which the influence of the first temperature (T-T) has been eliminated.

When el is passed through a logarithmic converter C, a signal e2 of the formula 00 is obtained.

e2-In I e+ l -to +1 EG2 Eol) OΦIn addition,
In eo = A When a constant signal of -A from adder F is added to this e2 signal, the signal transferred to the divider is
+). When this signal is divided by the temperature signal (1/T) from the temperature KT detection element 10,
A signal eouL expressed by equation (11) is obtained.

eouL-01'(Eo2-Eol) el
) That is, it is possible to obtain signal voltages proportional to the outputs of the static pressure sensors on the high-pressure side and the low-pressure side. Also, as mentioned above, the second
The influence of temperature can also be easily eliminated by division.

FIGS. 5 and 6 show an example of a change in the band gap energy EG depending on the pressure P. FIG. 5 shows the change in resistance due to pressure of black phosphorus, and FIG. 6 shows the change in resistance due to pressure of InSb. In addition, in Fig. 5, the characteristics of the a-axis and the a-axis are a
This is a case where electrodes are formed parallel to the a-axis and the a-axis.

Figure 7 shows the (+) data for various materials.

Here, the difference in resistance value due to the pressure difference will be briefly explained.

First, the following equation holds true.

When black phosphorus is used as a static pressure sensor, "jp" --24X 10-' ev/barK
T −0,0245ev (at 300°K) Therefore, tR 1[/n= −0,05%,'bar・For example, P
In the case of H-101 bar and PL -100 bar, the change in resistance is ΔR2/R2--5,05%ΔR+/
R+ -5,00%, and the difference between the two is a value that can be detected with sufficient accuracy.

FIG. 8 is a diagram showing another embodiment of the present invention.

The difference between Fig. 8 and Fig. 1 is that Fig. 1 has a seal diaphragm so that the fluid to be measured does not directly touch the static pressure sensor, but in Fig. 8, the seal diaphragm is used. The structure is such that the fluid to be measured directly comes into contact with the static pressure sensor.

In addition, although the temperature detection element 10 is arranged in the partition part of a pipe in the above, it may be integrated with a static pressure sensor.

Furthermore, according to the configurations shown in FIGS. 1 and 8, the excessive pressure PH
, PL is applied to the differential pressure transmitter, since the low pressure chamber and the high pressure chamber are surrounded by the solid wall of the body 5, there will be no damage to the static pressure sensor 6.7 placed inside. No external force is applied. Therefore, according to the configurations shown in FIGS. 1 and 8, there is no need to particularly provide an overpressure protection mechanism.

C. "Effects of the Present Invention" As described above, according to the present invention, the following effects can be obtained.

■ A differential pressure transmitter that does not require an overpressure protection mechanism can be realized.

■ In addition to differential pressure signals, static pressure and temperature signals can be obtained.

If further correction is performed using a microprocessor, a highly accurate differential pressure transmitter can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the main part configuration of a differential pressure transmitter according to the present invention, and FIG. 2 shows each lead wire 6 + + shown in FIG. 1.
7 + and 10 + are connected; Figure 3 is a diagram showing a general means of measuring flow rate using an orifice;
Figure 4 is a diagram showing an example of the configuration of a differential pressure transmitter equipped with an overpressure protection mechanism. Figures 5 and 6 are diagrams showing an example of changes in bandgap energy Eo due to pressure P.
The figure shows data on (+) for various materials.
FIG. 8 is a diagram showing another embodiment of the present invention. 1.2... Seal diaphragm, 3... Low pressure chamber, 4
...High pressure chamber, 5...Body, 6,7...Static pressure sensor, 8゜9...Hermetic seal part, 10...Temperature detection element, 61.7+, 1oI...Lead wire , R+
, R2-resistance, U...amplifier, C...logarithmic converter,
D...divider, F...adder. Ward ■ ΔR/R('/,)

Claims (2)

[Claims] (1) A means having a low-pressure chamber and a high-pressure chamber through which the pressure of the fluid to be measured is introduced, and a semiconductor material that is placed in the low-pressure chamber and the high-pressure chamber, respectively, and whose resistance changes in response to hydrostatic pressure. A differential pressure transmitter comprising: a static pressure sensor; and means for calculating a change in resistance of the static pressure sensor to obtain a signal corresponding to a differential pressure between a low pressure chamber and a high pressure chamber. (2) The differential pressure according to claim 1, wherein a temperature detection element for detecting the temperature of each static pressure sensor is provided in the differential pressure transmitter, thereby correcting a change in resistance due to a temperature change. transmitter.