JPH03156333A - Pressure detecting apparatus - Google Patents

Abstract

PURPOSE:To make it possible to output a voltage which is inversely proportional to an applied pressure directly through one connecting point of four connecting points by providing a pressure sensor element wherein four resistors are connected in a bridge pattern through four connecting points. CONSTITUTION:In a pressure sensor element 2A, four resistors R1 - R4 are connected in a bridge pattern through four connecting points 2a - 2d. A DC driving power source 1 applies a DC voltage to the first connecting point 2a of the element 2A. The output terminal of an operational amplifier 7 is connected to the second connecting point 2b of the element 2A, and the inverted input terminal of the amplifier 7 is connected to the fourth connecting point 2d. These parts are provided. The voltage which is inversely proportional to the directly applied pressure can be directly outputted through the third connecting point 2c of the element 2A. The reliability of the apparatus can be also improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pressure detection device that can directly output a voltage that is inversely proportional to pressure without using a special conversion characteristic element.

[Prior Art] Generally used semiconductor pressure sensors are designed to obtain a DC voltage that is directly proportional to the applied pressure. In this case, the obtained signal 1 is usually converted into the desired characteristics through a logarithmic amplifier or a complex non-linear amplifier.

The configuration of a conventional example will be explained with reference to FIG.

FIG. 2 is a circuit diagram showing a conventional pressure detection device.

In FIG. 2, the conventional pressure detection device includes a driving DC power source (1), a pressure sensor element (2) connected in parallel to the driving DC power source (1), and a pressure sensor element (2) connected in parallel to the driving DC power source (1).
an operational amplifier (4) whose one input terminal is connected to the buffer amplifier (3) and whose other input terminal is grounded; and one input terminal of the operational amplifier (4). A logarithmic conversion diode (
5) and an output terminal (6) connected to the output terminal of the operational amplifier (4).

Next, the operation of the above-mentioned conventional example will be explained.

Figure 2 shows a typical example that has been commonly used in the past.The output voltage obtained from the pressure sensor element (2) itself is an electrical signal that is directly proportional to the applied pressure. Electrical signals having a reciprocal relationship are obtained by a signal conversion circuit.

This signal conversion circuit uses a logarithmic amplifier that takes advantage of the nonlinearity of diodes and transistors, and FIG. 2 shows an example of a circuit that uses diodes.

First, the pressure sensor element (2) provides an output voltage proportional to the applied pressure. The output voltage of the pressure sensor element (2) is applied to the operational amplifier (4) via the FIL amplifier (3). Further, a current proportional to the output voltage of the yL amplifier (3) flows through the logarithmic conversion diode (5). That is, the current of the logarithmic conversion diode (5) is proportional to the output voltage of the pressure sensor element (2).

Since the output voltage of the operational amplifier (4) is equal to the voltage across the logarithmic conversion diode (5), the diode current is eventually converted into voltage along the voltage-current characteristic curve of the diode.

Generally, there is a relationship between the diode current I and the voltage across the diode (I = I-(log(qVr/kT) 1 ) (where I8 is the reverse saturation current). The output voltage is in logarithmically transformed form.

Since the polarity is inverted by the operational amplifier (4), the output voltage is logarithmically compressed in the relationship of the reciprocal of the input voltage of the operational amplifier (4), that is, the output voltage of the pressure sensor element (2).

Therefore, if the logarithmically compressed output voltage of the operational amplifier (4) is returned to its original state by an inverse conversion circuit (not shown) using a diode (the logarithmically compressed signal is expanded to its original form), eventually , the output is inversely proportional to the input.

However, the above-mentioned conventional example has the disadvantage that the circuit is complicated, unreliable, and expensive.

[Problems to be Solved by the Invention] In the conventional pressure detection device as described above, the conversion circuit using a logarithmic amplifier or special conversion element generally has poor temperature characteristics, and the conversion characteristics are approximate, so reliability is low. There was a problem with the lack of.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain a pressure detection device that can improve reliability with a simple circuit configuration.

[Means for Solving the Problems] A pressure detection device according to the present invention includes the following means.

(i) A pressure sensor element in which four resistors are connected in a bridge form via four connection points.

(ii) A driving DC power source that applies a DC voltage to the first connection point of the pressure sensor element.

(iii) An operational amplifier having an output terminal connected to the second connection point of the pressure sensor element and an inverting input terminal connected to the fourth connection point.

[Operation] In the present invention, a pressure sensor element in which four resistors are connected in a bridge shape through four connection points applies pressure from one of the four connection points. A voltage that is inversely proportional to is directly output.

[Embodiment] The configuration of an embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and the driving DC power source (1) is completely the same as that of the conventional device described above.

In FIG. 1, one embodiment of the present invention includes a driving DC power source (1), a pressure sensor element (2^) connected to the driving DC power source (1), and a pressure sensor element (2^) connected to the driving DC power source (1). )
and an operational amplifier (7) whose inverting input terminal and output terminal are connected to the pressure sensor element (2^) and whose non-inverting input terminal is grounded.

In addition, the pressure sensor element (2^) has four resistors (R, ,
R3, R1, R4) is formed into a bridge shape, and (
2a) and (2b) are drive voltage application terminals, (2c
) and (2d) are output terminals for voltage detection.

Next, the operation of the above embodiment will be explained.

If the voltage of the driving DC power supply (1) is E, the output voltage E2 of the operational amplifier (7) is given by the following equation.

R2-E, (R, /R,) Furthermore, the voltage Eab between the drive voltage application terminal (2aχ and (2b>) is expressed as Eab=E, -R2 -E, (t +R2/R+).

Here, since the voltage Eab is divided by the resistors R1 and R1, the terminal voltage Eac of the resistor R3 is expressed by the following equation.

Eac=E+ (1+R2/R1) ・Ry/ (R1
+R4) Therefore, the connection point of resistors R5 and R4 (2c
) and GND (ground), that is, the voltage at the output terminal (68)■. uT2 is Vouy2=E1-Eae=E, (1-R,/R,・(R+◆R2)/(R
, +R, )).

For bridge type pressure sensor element (2^), R+/R4
= R2/Rs=k Furthermore, since it is possible to make k and K constant by <RI + R2) / (R3 + R4) = K, substituting this relationship yields the following equation.

Voutz = E+ (K/to -Rt/R+ 1) Furthermore, since R, +R, is constant, R+ + RzR
o, then Voutz=-E+ (K/k-Ro/R+-to/to-1) where K/k-R,=K.

If +1 = 6 is set for K/, Vouyz = E+ (Ko/R1ko), and the output voltage is ■. U, is inversely proportional to El, and in the end,
A signal that is the reciprocal of the applied pressure can be obtained.

As described above, one embodiment of the present invention incorporates the conventional bridge-type pressure sensor element (2^) into a part of the amplifier, and directly outputs a signal inversely proportional to the applied pressure from the output terminal of the pressure sensor element (2^). This has the effect that it is possible to obtain an output voltage of 100%, and to obtain nonlinear (inversely proportional) characteristics only with an operational amplifier without using any special conversion characteristic element.

[Effects of the Invention] As explained above, the present invention provides a pressure sensor element in which four resistors are connected in a bridge shape via four connection points, and a first connection point of the pressure sensor element. Since it is equipped with a driving DC power supply that applies a DC voltage, and an operational amplifier whose output terminal is connected to the second connection point of the pressure sensor element and whose inverting input terminal is connected to the fourth connection point, This has the advantage that a voltage inversely proportional to the applied pressure can be directly output from the third connection point of the pressure sensor element, and reliability can be improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional pressure detection device. In the figure, (1) ... driving DC power supply, (2^) ... pressure sensor element, (,6^) ... output terminal, (7) ... operational amplifier. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A pressure sensor element in which four resistors are connected in a bridge shape through four connection points, a driving DC power supply that applies a DC voltage to a first connection point of the pressure sensor element, and the pressure sensor element. an operational amplifier having an output terminal connected to a second connection point of the pressure sensor element and an inverting input terminal connected to a fourth connection point of the pressure sensor element; A pressure detection device characterized by direct output.