JPS6367536A - Pressure sensor - Google Patents

Abstract

PURPOSE:To detect the quantity of strain of a pressure receiving diaphragm caused by the pressure under a noncontact system by projecting an optical pulse signal on a reflection film of the pressure receiving diaphragm and detecting the phase difference between both optical pulse signals which are reflected before and after the pressure is applied to the pressure receiving diaphragm. CONSTITUTION:Only the reflection film 3 is provided to the pressure receiving diaphragm 2 and the optical pulse signal projected 13 from a signal processing means 11 is reflected on the reflection film 3. The reflected optical pulse signal is received 14 by the signal processing means 11. Then, the phase difference between the optical pulse signals which are received 14 in both cases before the pressure is applied to the pressure receiving diaphragm 2 and when the pressure is applied to the diaphragm 2 and the strain takes place thereon is detected. In this way, the quantity of strain of the pressure receiving diaphragm 2 caused by the applied pressure is detected under the noncontact system by the optical pulse signal. Accordingly, the pressure applied to the pressure receiving diaphragm is detected with high accuracy without being influenced by a temperature change, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention 1 (Field of Industrial Application) The present invention relates to a pressure sensor used, for example, in a pressure transmitter.

(Prior Art) A conventional pressure sensor will be explained using FIG. 6, taking a semiconductor pressure sensor as an example.

In FIG. 6, reference numeral 31 denotes a Si semiconductor chip, and the semiconductor chip 31 has a recess formed in the center of the back surface thereof to form a thin pressure-receiving diaphragm 32.

On the surface of the semiconductor chip 31 and on the pressure receiving diaphragm 32
A diffusion layer resistance is formed around the periphery of the chip by doping with an impurity having a conductivity type opposite to that of the semiconductor constituting the chip, and piezoresistors 33 and 34 are formed by this diffusion layer resistance.

35 is a base, 36 is a holding plate fixed to the base 35,
The semiconductor chip 31 is attached to the holding plate 3 at the thick part around it.
6 is airtightly fixed. The recess space of the semiconductor chip 31 communicates with the atmosphere through an atmospheric pressure inlet 37 provided through the holding plate 36 and the base body 35 .

38a and 38b are external takeout bins, and piezoresistors 33
．． A bonding pad is formed at the part 34 with an A-shape (not shown), and the wire 3 is connected to this bonding pad.
One end of 9 is bonded, and the other end is externally removed from the bin 3.
8a and 138b, respectively.

Since the piezoresistors 33 and 34 extract the resistance change as a voltage change, a bridge circuit is formed by the piezoresistors 33 and 34 and other resistances.

When pressure is applied to the pressure receiving diaphragm 32, it bends and distortion occurs on its surface, causing each piezoresistor 3
The resistance value of 3.34 changes depending on the amount of strain. Due to the change in the resistance value of the piezoresistors 33 and 34, a voltage proportional to the amount of strain is taken out from the bridge circuit, and due to this voltage, the resistance value is The influence of temperature changes is relatively large, and its resistance temperature characteristics have nonlinearity.

Such correction of resistance temperature characteristics is generally performed by adding a temperature compensation circuit, but it is difficult to sufficiently correct this.

Therefore, the semiconductor pressure sensor described above has a semiconductor chip 3.
1, it is necessary to form a diffusion layer resistor and a bonding pad, and to bond a thin wire 39 for bonding to the bonding pad.In addition to the problem that the structure is complicated and the failure rate is relatively high, There have been problems in that it is difficult to sufficiently compensate for the influence of changes, and it is difficult to detect pressure with high accuracy.

The present invention has been made based on the above circumstances, and an object of the present invention is to provide a pressure sensor having a relatively simple structure of the sensor main body and having high detection accuracy.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention includes a pressure-receiving diaphragm provided with a reflective film, a light pulse signal projected onto the reflective film, and a light pulse signal projected onto the reflective film. Receives the optical pulse signal reflected by the membrane (
) and signal processing means for detecting the phase difference between the optical pulse signals received before and when pressure is applied to the pressure receiving diaphragm.

(Function) The pressure receiving diaphragm only needs to be provided with a reflective film, and the optical pulse signal projected from the signal processing means is reflected by the reflective film.

A signal processing means receives this reflected optical pulse signal and calculates the position between the received optical pulse signals both before pressure is applied to the pressure receiving diaphragm and when the pressure is applied and distortion occurs. A phase difference is detected.

The amount of strain in the pressure receiving diaphragm caused by the pressure applied in this manner is detected in a non-contact manner using an optical pulse signal.

Therefore, the pressure applied to the pressure receiving diaphragm can be detected with high precision without being affected by temperature changes or the like.

(Example) Embodiments of the present invention will be described below based on the drawings.

1 to 4 are diagrams showing an embodiment of the present invention.

Figure 1 is a configuration diagram showing the sensor body in longitudinal section, Figure 2 is a configuration diagram of the optical pulse signal transmission/reception unit, Figure 3 is a block diagram of the signal processing unit, and Figure 4 is the sensor body. FIG.

First, to explain the structure, in FIG. 1, reference numeral 1 denotes a Si semiconductor chip, and the semiconductor chip 1 has a thin pressure receiving diaphragm 2 formed by processing four parts of the central part of the back surface of the semiconductor chip 1.

The thickness of the pressure receiving diaphragm 2 is adjusted so that the amount of strain is approximately 10 to 20 μm within the measurement pressure range.

A reflective film 3 is formed on the back surface of the pressure receiving diaphragm 2 opposite to the side to which pressure is applied, that is, on the bottom surface of the recess, of a silver vapor-deposited film or the like having a large light reflection coefficient.

The semiconductor chip 1 is hermetically fixed to the base 4 at a thick portion around the semiconductor chip 1. The recessed space of the semiconductor depth 1 is
The base body 4 is connected to the atmosphere through an atmospheric pressure inlet 5 provided through the base body 4 .

The semiconductor chip 1 having the pressure-receiving diaphragm 2 and the base 4 to which it is hermetically fixed form the sensor main body 6.
is configured.

Almost at the center of the base 4, at a position facing the reflective film 3,
A light pulse signal transmitting/receiving section 7 is fixed with an adhesive 8.

The transmitting/receiving section 7 is connected to a signal processing section 11 via a cable 9, and an amplifier 12 is connected to an output terminal of the signal processing section 11. The amplifier 12 outputs a measured pressure signal converted into an electrical signal.

The signal processing unit 11 controls the transmitting/receiving unit 7 to transmit an optical pulse signal having a constant repetition frequency, and also causes the pressure receiving diaphragm 2 to receive an optical pulse signal reflected by the reflection 1!513 and received. A signal processing function is provided to detect the phase difference between the optical pulse signals before and after pressure is applied.

The above transmitting/receiving section 7 and signal processing section 11 constitute a signal processing means.

FIG. 2 shows the details of the configuration of the transmitter/receiver section 7, which includes an optical transmitter 13, an optical receiver 14, a half mirror 15, and a convex lens 16. The convex lens 16 has a function of focusing the light emitted from the optical transmitter 13 onto the reflective film 3.

Further, FIG. 3 shows the details of the configuration of the signal processing section 11, and shows a pulse oscillator 1 that oscillates a pulse signal of a constant frequency.
7 is connected to the processing/memory section 18, and the processing/memory section 1
8 is connected to an advance credit amplifier 19 and an optical receiving amplifier 21. The advance credit amplifier 19 is connected to the optical transmitter 13 via a cable 9a, and the optical receiving amplifier 21 is connected to the optical receiver 14 via a cable 9b.

A pulse signal with a constant repetition frequency generated by the pulse oscillator 17 is sent to the advance credit amplifier 19 via the processing/memory section 18, and the optical transmitter 13 is driven by the amplitude-amplified pulse signal.

The processing/memory unit 18 transmits the phase difference between the transmitted pulse signal and the received pulse signal reflected by the reflective film 3 and received via the optical receiver 14 and the optical reception amplifier 21 to the pressure receiving diaphragm 2. It is equipped with a memory function that digitally counts and detects both before and after pressure is applied and stores the counted values.

The output terminal of the processing/memory section 18 is connected to a comparator 22 , and the output terminal of the comparator 22 is connected to the amplifier 12 via a D/A converter 23 .

A comparator 22 digitally detects the phase difference between the optical pulse signals received before and when pressure is applied to the pressure receiving diaphragm 2.

24 is a zero adjustment switch, and this zero adjustment switch 24
By turning on, a phase difference of "zero" is created by the meter program in the processing/memory unit 18, and the output is forced to be 0%.

Further, 25 is a span adjustment switch, and by turning on this span adjustment switch 25, a phase difference of 100% is created by the calculation program within one day of the processing/memory unit, and the output is forced to 100%.

Next, the action will be explained.

A pulse signal with a constant repetition frequency is sent from the processing/memory section 18 to the advance credit amplifier 19, and the optical transmitter 13 is driven by the amplitude-amplified pulse signal, and the optical pulse signal with a constant repetition frequency is transmitted to the reflective film. Projected to 3.

The projected optical pulse signal is reflected by the reflective film 3, direction-changed by the half mirror 15, and received by the optical receiver 14. The received optical pulse signal is converted into the original electrical pulse signal by the optical receiver 14, and then sent to the optical receiving amplifier 2.
1, the signal is amplified to an appropriate amplitude level and inputted to the processing/memory section 18 again.

The processing/memory section 18 digitally counts and detects the phase difference between the above-described transmitted pulse signal and received pulse signal.

The counting and detection task of this phase difference in the processing/memory unit 18 is performed before pressure is applied to the pressure receiving diaphragm 2, as shown at 2a in FIG. 4(B), and before pressure is applied to the pressure receiving diaphragm 2, 2
As shown in b, this is carried out for both cases where pressure is applied to the pressure receiving diaphragm 2 and strain ml is generated.

The phase difference data in both cases is once stored in the processing/memory section 18 and then sent to the comparator 22 for comparison.

Then, the comparator 22 outputs a phase difference signal corresponding to the amount of distortion as a digital value, which is converted into an analog value by the D/A converter 23,
The magnitude of the pressure applied to is detected.

Next, FIG. 5 shows another embodiment of the present invention.

In this embodiment, a metal pressure receiving diaphragm 26 is used, an O-ring 27 is interposed between the pressure receiving diaphragm 26 and the base 4, and the pressure ring 27 is tightened with a retaining ring 28. It is airtightly fixed. A reflective film is formed by the metal pressure receiving diaphragm 26 itself.

The structure of the parts other than the above is almost the same as that of the previous embodiment.

Further, the pressure detection function is also substantially the same as that of the first embodiment.

This embodiment has the advantage that the pressure receiving diaphragm 26, which has a different thickness depending on the range of measured pressure, can be easily replaced, and the range of measured pressure can be easily expanded.

[Effects of the Invention] As explained above, according to the configuration of the present invention, the pressure receiving diaphragm only needs to be provided with a reflective film, and the amount of distortion of the pressure receiving diaphragm caused by the applied pressure can be reduced by the optical processing means. It is detected in a non-contact manner using optical pulse signals sent and received. Therefore, there is an advantage that the structure of the sensor main body is relatively simple and the failure rate is reduced, and that the pressure applied to the pressure receiving diaphragm can be detected with high accuracy without being affected by temperature changes or the like.

[Brief explanation of the drawing]

Figure 1 and Figure 4 show an embodiment of the pressure horn sensor according to the present invention. Figure 1 is a configuration diagram showing the sensor main body in longitudinal section, and Figure 2 is a diagram showing the structure of the sensor main body in longitudinal section. Block diagram of the receiving section,
Fig. 3 is a block diagram of the signal processing section, Fig. 4 is a partial view of the sensor main body and is a diagram for explaining the operation, and Fig. 5 is a block diagram of the signal processing section.
The figure shows another embodiment of the present invention, and is a configuration diagram showing a sensor body section in longitudinal section, and FIG. 6 is a longitudinal sectional view showing a conventional pressure sensor. 2.26: Pressure receiving diaphragm, 3: Reflective film, 6: Sensor body, 7: Optical pulse signal transmission/reception section, 11: Signal processing section, 13: Optical transmitter, 14: Optical receiver, 18: Processing・Memory part. Agent Patent Attorney Noriyuki Chika Agent Patent Attorney Hiroshi Mitsumata 1st diagram 2nd figure 8th figure 4th figure 6th figure

Claims (1)

[Scope of Claims] A pressure receiving diaphragm provided with a reflective film; a light pulse signal is projected onto the reflective film, the light pulse signal reflected by the reflective film is received, and pressure is applied to the pressure receiving diaphragm. and signal processing means for detecting the phase difference between the optical pulse signals received before and when applied.