JPS6280533A - Pressure measuring instrument - Google Patents

Abstract

PURPOSE:To simplify the constitution of an analog circuit and to improve measurement precision by processing digitally the output of a ridge circuit which has a semiconductor strain gauge. CONSTITUTION:A pressure receiving diaphragm 2 deforms according to the pressure for measurement to strain the semiconductor strain gauge 5 which varies in resistance value by piezoresistance effect. A bridge circuit 9 has the semiconductor strain gauge 5 incorporated in a bridge 92 and outputs a signal corresponding to the resistance value of the semiconductor strain gauge 5. The voltage-division value obtained by dividing this output signal by the input voltage VA of the bridge 92 by a voltage dividing circuit 1 is selected and digitized by an A/D converting circuit 14. Then, the output of the circuit 14 is inputted to calculate the ratio of the 1st digital signal corresponding to the output voltage of the circuit 9 and the 2nd digital signal corresponding to the voltage division by an arithmetic circuit 15, thereby outputting a pressure measurement digital signal corresponding to measured pressure.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a pressure measuring device that detects pressure or differential pressure with a piezoresistive element and outputs a signal corresponding to the pressure or differential pressure as a digital signal. It is something.

[Conventional technology]

Figures 3 to 5 show conventional devices of this kind, in which (1) is a sensor main body having a chamber with a vertical cross section such as a circular or oval shape, and (2) is a sensor unit. It is a pressure receiving diaphragm that separates the chamber in the main body (1) into a first chamber (3) and a second chamber (4), and the edge is held by the sensor main body (1) to detect pressure or differential pressure. , it is displaced in one direction in the direction of arrow A in the figure. (5) is a piezoresistive effect element having a piezoresistive effect provided on the pressure receiving diaphragm (2), such as a semiconductor strain gauge;
) is a first capillary for introducing pressure that communicates with the second chamber (4), and (7) is a second capillary for introducing pressure that communicates with the second chamber (4). (8) is a sensor part, and the above-mentioned code (1)
It is composed of the components shown in ~(7). (9
) is a bridge circuit having a bridge (92) constructed using a semiconductor strain gauge (5), and α is an amplifier circuit that amplifies the output of the bridge circuit (9) and outputs the differential signal. .

The bridge circuit (9) includes a constant current circuit (91) and a bridge (92) having a semiconductor strain gauge (5). For example, in this bridge (92), among opposing resistor pairs that are not directly connected, only one resistor pair is composed of a semiconductor strain gauge (5 n), and the other resistor pair (92A ), (92B) are fixed resistors.The amplifier circuit OI includes an amplifier (1oo) that non-inverts and amplifies the output voltage on the positive side of the bridge (92), and an output voltage on the negative side of the bridge (92). It consists of an amplifier (101) that performs non-inverting amplification, a coefficient unit (102) that calculates the difference between the outputs of both amplifiers (10s, (1o1), and outputs the difference. (105) is a variable resistor for span adjustment. The terminals are connected between the (-) input terminals of the amplifiers (10 and (101)).

(104) is a variable resistor for zero point adjustment, and (105) is an amplifier that amplifies the voltage adjusted by the variable resistor (10) and supplies it to the (+1 input terminal) of the coefficient unit (102).

Next, the operation will be explained. Measuring pressure PA is introduced into the first chamber (3) via the first capillary (6).

Moreover, the measurement pressure PB is introduced into the second chamber (4) via the second capillary (7). Pressure receiving diaphragm (2
) deforms according to the pressure difference between the introduced measurement pressures PA and PB. Due to this deformation, semiconductor strain gauge (5)
undergoes strain and changes its resistance value due to the piezoresistive effect. The bridge circuit (9) outputs a signal corresponding to the resistance value of the semiconductor strain gauge (5) to the amplifier circuit 01. The output voltage of the bridge (92) of the bridge circuit (9) is
00) and (101) to increase the difference, and the difference is calculated by a coefficient unit (102) and output. In addition, when starting this pressure measurement, the measurer adjusts the resistance value of the variable resistor (104) to adjust the zero point, and then adjusts the resistance value of the variable resistor (105) to adjust the span. Make adjustments.

Furthermore, in the conventional example described above, there is also a conventional device in which one of the measuring pressure P and Pa is kept constant and the measuring pressure is applied to the pressure receiving diaphragm from one direction.

[Problem that the invention seeks to solve]

Conventional pressure measuring devices have the above-mentioned configuration, so the processing circuit is configured in an analog manner, and since many analog elements are used, the measured value is greatly influenced by temperature and measurement errors are likely to occur. In addition, there are other problems such as the adjustment of the zero point and span is complicated and tends to cause temperature drift.

This invention was made to solve the above-mentioned problems, and by digitally processing the output of a bridge circuit having an element exhibiting a piezoresistive effect, it simplifies the configuration of an analog circuit and improves measurement accuracy. The purpose is to obtain a pressure measuring device with increased pressure.

[Means for solving problems]

The pressure measuring device according to the present invention applies strain to the piezoresistive element according to the measurement pressure by a processing means, and changes the output of a bridge circuit having a bridge incorporating the piezoresistive effect element according to the measurement pressure. , the input voltage for the bridge is divided by the voltage divider circuit and the output of the bridge circuit is digitized by the analog-to-digital conversion circuit, and the ratio of both digitized signals is calculated to calculate the voltage according to the measurement pressure. A pressure measurement digital signal is output from an arithmetic circuit.

[For production]

The pressure measuring device in this invention changes the output signal of the bridge circuit by piezoresistive effect according to the measurement pressure,
The output signal of the bridge of the bridge circuit and the divided voltage value obtained by dividing the input voltage of the bridge are A-to-D converted by the A-to-digital conversion circuit, and the output signal of the bridge digitized by the arithmetic circuit and the divided voltage of the input voltage of the bridge are converted. A highly accurate pressure measurement signal is output by calculating the ratio with the pressure value and eliminating errors caused by fluctuations in the input voltage of the bridge.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall block diagram of an embodiment of the present invention, and FIG. 2 is a detailed circuit diagram from the bridge circuit to the amplifier circuit in FIG. 1. In the figure, symbols (1) to (9)
, (92) are the same or equivalent parts as in the conventional example, and their explanations are omitted. However, it should be noted that a normal power supply is used as the power supply for the bridge circuit (9). , supply voltage +v on the input side of the bridge (92)
I'm giving an A. 0υ is a resistor connected in series (111)
, (N2), and the input voltage of the bridge (92) is ten VA.
The voltage divider circuit α2, which divides the voltage between
The two output voltages (V5), (v4) and the ground level voltage (vl) are selectively input and output. Note that the switch circuit α opens and opens a predetermined switch in response to a selection control signal from an arithmetic circuit (l!9), which will be described later. wide operational amplifier (151), non-inverting side input resistance (1
iS2) and a feedback resistor (133);
α( is an analog-digital converter (hereinafter referred to as A-D converter) whose input side is connected to the output side of the non-inverting amplifier circuit α, (I!9 is the output of the analog-digital converter I) This is an arithmetic circuit that receives input and performs arithmetic operations according to a predetermined formula, and is composed of, for example, a microprocessor, a work memory, a program memory that stores programs, etc., and also controls the switch circuit a2. αQ is a symbol C1 to I
This is an A-D conversion circuit shown in FIG.

Next, the operation of one embodiment of the present invention will be explained.

Due to the deformation of the pressure receiving diaphragm (2) due to the pressure difference between the measurement pressures PA%PB or the pressure on one side, the resistance value of the semiconductor strain gauge (5) changes due to the piezoresistive effect. In the case of PA master FB, the pressure receiving diaphragm (2) is curved and deformed, so the semiconductor strain gauge (5) receives tension, and its resistance value increases from the resistance value when PA=PB. This semiconductor strain gauge (5
) changes so that the difference between the output voltages v2 and v4 of the bridge (92) of the bridge circuit (9) increases.

First, the switch circuit aZ is controlled by the arithmetic circuit (l!9).
selects the divided output voltage (vl) of the voltage dividing circuit μυ and inputs it to the amplifier circuit. This divided output voltage (vl) is amplified by an amplifier circuit Q3, and then converted into a digital signal VD1 by an A-D converter I, taken into an arithmetic circuit, and temporarily stored. This conversion is performed to monitor variations in the level of power supply voltage +VA. In the same manner as described above, next, the relatively larger output voltage v2 of the bridge (92) is converted into a digital signal VD2, then the ground level voltage v3 is converted into a digital signal VD3, and then , the relatively smaller output voltage v4 of the bridge (92)
is converted into a digital signal VD4. The arithmetic circuit Sumio takes in the digital signals vD2, ■D5, and VD4 for each conversion and temporarily stores them.

Here, the measurement pressure P applied to the pressure receiving diaphragm (2)
If P is the differential pressure or pressure between A and Pa, then equation (1) holds true. In formula (1), the molecule is a bridge (92
), and includes the influence of fluctuations in the power supply voltage +V^ and the ground level voltage v5, and error components due to temperature drift of the amplifier circuit. The denominator is the power supply voltage of 1VA and the ground level voltage of v5.
This is a voltage difference component including an error component of 11' V +l q L. As shown in equation (1), by taking the ratio of the two, the influence 2 due to fluctuations in the power supply voltage +VA and ground level voltage v3 and the error component of the temperature drift of the amplifier circuit are eliminated, resulting in a fluctuation component that does not include the error component. This is the differential pressure P
is proportional to. Therefore, the arithmetic circuit α9 performs an arithmetic operation by multiplying the arithmetic expression on the right side of equation (1) by an appropriate digital constant from the stored digital signals VD1 to VD1, etc., and outputs a pressure measurement signal corresponding to the differential pressure or pressure. do.

As described above, by removing the error component, it becomes unnecessary to adjust the zero point due to fluctuations in the power supply voltage and ground level, and since the span adjustment is performed by calculation, the span adjustment becomes unnecessary.

S, analog voltages v1, vl, v3, v4 may be converted in the order of A/D (this order may be used).Furthermore, the conversion of the ground level voltage v3 is not necessarily required.

〔Effect of the invention〕

As described above, according to the present invention, the pressure for measurement is converted into a resistance change by the piezoresistive effect element, the output of the bridge having the piezoresistive effect element is changed, and the output voltage of the bridge and the power supply voltage for the bridge are changed. The structure is configured to convert the signal into a digital signal, calculate the ratio of the converted digital signal, and output a pressure measurement signal corresponding to the measurement pressure.This simplifies the analog processing circuit and performs digital processing. It eliminates the error component of temperature drift that occurs in the analog processing circuit, which may cause temperature drift in the measured value, so it is possible to obtain a highly accurate pressure measurement signal, and it also eliminates the need for zero point adjustment and span adjustment. There are benefits to be gained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional configuration diagram showing an embodiment of the present invention, FIG. 2 is a detailed circuit diagram of the bridge circuit etc. in FIG. 1, and FIG. , Figures 4 and 5 are detailed circuit diagrams of the bridge circuit etc. in Figure 3. In the figures, (1) is the sensor body, (2) is the pressure receiving diaphragm, and (5) is the piezoresistive effect element. , (9) is a bridge circuit, αυ is a voltage dividing circuit, α is a switch circuit, (141
is an A/D converter, 19 is an arithmetic circuit, and αQ is an A-D conversion circuit. In addition, in the drawings, the same or equivalent parts are indicated.

Claims (1)

[Claims] a bridge circuit consisting of a straining means that deforms and applies strain to the piezoresistive element according to the measurement pressure; a bridge incorporating the piezoresistive element; and a power supply for the bridge; and a bridge circuit that divides the output voltage of the power supply. an analog-to-digital converter circuit that sequentially selects and digitizes the output voltage of the bridge circuit and the divided voltage value of the voltage divider circuit; an arithmetic circuit that outputs a pressure measurement digital signal according to the measurement pressure by calculating a ratio between a first digital signal corresponding to the output voltage of the bridge circuit and a second digital signal corresponding to the partial pressure; Pressure measuring device with.