JPH03134532A - Pressure detecting apparatus and pressure sensor - Google Patents

Abstract

PURPOSE:To save labor by storing reference data for determining correct pressure in a nonvolatile memory with a data processing means beforehand, using the reference data in measurement, and computing the correct data. CONSTITUTION:The usable temperature range of a pressure sensor 1 is classified, and boundary temperatures are set at T0 - TM. Pressure is applied in the sensor 1 by using a standard pressure generator for each value of the temperatures T0 - TM. The output data of an A/D converter 2 with respect to the pressures P0 - PN are read out with a CPU 3. The data are written into a nonvolatile RAM 7 as reference data. When unknown pressure PX is applied into the sensor 1 in use, temperature data DTV associated with the temperature TV of the sensor 1 and the pressure data based on the sensor 1 are read with the CPU 3 and stored in the RAM. Then, the reference data written in the RAM 7 are checked so as to compute the pressure PX. When the pressure PX is determined, the pressure is sent into an external display device and a control device and used for controlling various devices in the computer 3 itself.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a pressure detection device and a pressure sensor that can be used or manufactured labor-savingly without any troublesome adjustment work, and that hardly require voltage gain adjustment, zero point adjustment, or temperature compensation adjustment. The purpose of the present invention is to provide a pressure detection device and a pressure sensor that operate reliably without any noise, and for this purpose, a pressure sensor, a temperature measuring means for measuring the temperature in the vicinity of the pressure sensor, an analog quantity based on the output of the pressure sensor, and a pressure sensor. It has an A/D converter that converts the analog value obtained by the temperature measuring means into a digital value, a computer that reads the digital value, and a non-volatile memory that can be read and written by the computer, and the operating temperature range is divided into an appropriate number and each When a discrete standard state pressure is applied to the pressure sensor in advance for each boundary temperature of the section, reference data obtained from the A/D converter is stored in the nonvolatile memory, and at the time of measurement, the temperature measurement means and the A pressure detection device is configured that includes data processing means for calculating approximately correct data by referring to the reference data corresponding to the boundary temperature from the data obtained from the pressure sensor. Further, a pressure sensor is constructed by providing a pressure sensor element, an amplification element for amplifying the output of the pressure sensor element, and a data storage element in a single package. Furthermore, a pressure sensor having a built-in temperature sensor is configured in the package.

[Industrial application field]

The present invention relates to a pressure detection device and a pressure sensor that can be used or manufactured labor-savingly without any troublesome adjustment work.

[Conventional technology]

Pressure sensors are used to measure the intake pressure of automobile engines and to measure atmospheric pressure, and bridge circuits made of semiconductor strain gauges are commonly used as pressure sensors. FIG. 10 is a block diagram showing an example of a conventional pressure detection device equipped with such a pressure sensor. In the same figure, the output of pressure sensor 1 is output from operational amplifier OP.
The output signal is amplified by an amplifier based on I, and the offset of the output of the amplifier is adjusted by an offset adjustment circuit based on an operational amplifier OP2.

The output of the offset adjustment circuit is input to the analog input terminal of the A/D converter 2, and the A/D converter 2 converts the analog amount into, for example, an 8-bit digital value. It is designed to be read by a computer 3 such as a board computer or a personal computer.

The digital data read by the computer is displayed as pressure data on a display panel (not shown), and pressure-related equipment connected to the output port of the combiator is controlled.

[Problem to be solved by the invention]

By the way, due to manufacturing technology, it is difficult to obtain a completely uniform pressure sensor l, and there are generally variations in characteristics. is the pressure sensor 1
It is necessary to adjust the gain adjustment of the amplifier by the operational amplifier OPI with the variable resistor V R+ so that the A/D converter converts the maximum value when the voltage is applied to the signal.

Furthermore, it is necessary to perform so-called zero point adjustment by adjusting the variable resistor VRz of the offset adjustment circuit by the operational amplifier OP2 so that the A/D converter outputs zero when no pressure is applied to the pressure sensor I.

However, since the adjustments of the variable resistors VRI and VR2 are mutually correlated, adjusting one will destroy the other, and it is necessary to narrow down the points over and over again to find a compatible point until both adjustments are compatible. First, there are problems in that the work efficiency is poor and it takes time. Further, the variable resistor VR+
As an alternative to VRz, there is a known trimming method in which a film resistor formed on a silicon substrate or a ceramic substrate along with the amplifier etc. is cut and adjusted using a laser trimmer, but this method also does not cause the above-mentioned problems. Similar problems exist, as well as the need for expensive equipment for trimming.

Furthermore, since semiconductor strain gauge type pressure sensors do not have good temperature characteristics, various temperature compensation methods have been proposed to alleviate temperature fluctuations and obtain stable operation. As one such temperature compensation method, it is known that by setting the impurity concentration in the gauge part of the pressure sensor to about 3.3×1020 (atoms/o+1), it is possible to suppress fluctuations in output due to temperature changes.However, due to manufacturing technology, It is quite difficult to obtain a pressure sensor that has a uniform and accurate target impurity concentration, and it is also known that even if the target can be achieved, the temperature range that can be compensated is narrow. In order to improve the temperature characteristics to a level that does not pose a practical problem, it was necessary to adopt a circuit technology-based temperature compensation method.However, such a circuit technology-based temperature compensation method does not respond to temperature changes. On the other hand, it is necessary to adjust the compensation resistance to match the target temperature characteristics, and the same adjustment work has to be repeated over and over again.Furthermore, the temperature changes over time are very slow, which is not satisfactory. There is a problem in that it takes a lot of time and effort to obtain the desired temperature characteristics.

SUMMARY OF THE INVENTION In view of these problems, it is an object of the present invention to provide a pressure detection device and a pressure sensor that operate reliably with almost no need for voltage gain adjustment, zero point adjustment, or temperature compensation adjustment.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a pressure sensor, a temperature measuring means for measuring the temperature in the vicinity of the pressure sensor, an analog quantity based on the output of the pressure sensor, and a digital value of the analog quantity obtained by the temperature measuring means. It has an A/D converter that converts the digital value into a digital value, a computer that reads the digital value, and a nonvolatile memory that can be read and written by the computer. When a standard state pressure is applied, reference data obtained from the A/D converter is stored in the nonvolatile memory, and during measurement, data obtained from the temperature measuring means and the pressure sensor corresponds to the boundary temperature. A pressure detection device is provided which includes a data processing means for calculating approximately correct data by referring to the reference data. Further, a pressure sensor is constructed by providing a pressure sensor element, an amplification element for amplifying the output of the pressure sensor element, and a data storage element in a single package. Furthermore, a pressure sensor having a built-in temperature sensor is configured in the package.

[For production]

The data processing means stores the reference data in the nonvolatile memory only once before the pressure detection device is assembled, wired, etc. and shipped from the factory. On the user side, during measurement, data obtained from the temperature measuring means and the pressure sensor is referred to the reference data corresponding to the boundary temperature to determine approximately correct data. As a result, the determined data can be used as correct pressure data regardless of the ambient temperature in which the pressure sensor is placed.

Further, since the pressure sensor is equipped with a data storage element, once the pressure sensor is calibrated by the user, the data storage element stores reference data. Thereafter, a pressure sensor that outputs correct pressure data during measurement can be obtained.

Furthermore, if the data storage element is provided with reference data written in it, the data storage element stores the reference data and does not require any calibration work on the user's side. A pressure sensor that immediately outputs correct pressure data can be obtained by simply attaching it to a device.

In addition, in the case of a pressure sensor with a built-in temperature sensor, the pressure sensor itself outputs an analog value corresponding to the temperature, so there is no need to separately install a temperature sensor, making it easier to replace a malfunctioning sensor.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an example of the pressure detection device of the present invention.

Hereinafter, in the figure, the same members as those described in the prior art section will be described with the same numbers.

The pressure detection device includes a pressure sensor 1 having a bridge configuration.
The output of the pressure sensor 1 is connected to a constant gain amplifier 4 through a resistor R1.
, R2. Note that the resistor R3 is a fixed resistor for feedback.

The output of the amplifier 4 is input to the negative analog input terminal of the A/D converter 2, and the A/D converter 2 converts the analog quantity into, for example, an 8-bit digital value, and the converted digital value is sent to the CPU. The information is readable by a computer 3 such as a board computer or a personal computer.

Further, a temperature sensor 8 such as a thermistor is disposed near the pressure sensor 1. One end of the temperature sensor 8 is grounded, and the other end is connected to a positive power line (not shown) via a resistor R6.

The junction between the temperature sensor 8 and the resistor Rh is connected via a resistor R1 to a non-inverting input terminal of a constant gain amplifier (operational amplifier) 9, and the inverting input terminal of the amplifier 9 is connected via a resistor Ri. It is grounded. In addition, the resistance R
9 is a fixed resistor for feedback.

The A/D converter 2 is provided with another analog input terminal, into which the output of the amplifier 9 is input. Although not shown in the figure, the A/D
The converter 2 has a built-in multiplexer for selecting the two analog input systems, and the combinator selects the required system depending on the state of the control line connected to the computer.

On the other hand, the computer 3 is equipped with an input port,
A switch 5 and one end of a resistor R4 are connected to the port Po, and the other end of the resistor R4, although not shown, is connected to a positive power supply line. Further, the other end of the switch 5 is grounded. By operating this switch 5, it is possible to switch between a calibration mode and a measurement mode, which will be described later.

Port P1 also has an operation circuit made up of a switch 6 and a resistor R5 in the same way as Po (Po). is instructed to the computer 3.

The computer 3 is RO like a normal computer.
M and RAM, but in addition to these, non-volatile R
It has AM7. Note that the CP of the computer 3
If the U itself has a built-in non-volatile RAM, this non-volatile RAM becomes the non-volatile RAM 7, and it can be used regardless of whether it is external or built-in. Also,
The non-volatile RAM 7 is EEPROM or OTPRO.
M can be suitably used.

the pressure sensor (pressure sensor element) 1, the amplifier 4,
the temperature sensor 8, the amplifier 9 and the non-volatile RA
M (data storage element) 7 can be formed as a single pressure sensor in a single package, shown surrounded by dotted lines in FIG. Note that when the temperature sensor 8 and the amplifier 9 are externally attached, they may be configured as a type of pressure sensor that is not included in the package, and the temperature sensor 8, the amplifier 9, and the nonvolatile RAM 7
If these are externally attached, they can be formed as a type of pressure sensor that is not included in the package.

The entire pressure sensor including the pressure sensor element formed in a single package has a so-called hybrid IC structure. The pressure sensor element (1), the differential operation amplifier (4, 9), and fixed resistors (R1, R2, R3, R6, R7, R8, R1) are mounted on a substrate made of alumina or the like.
, the temperature sensor 8 and the EEPROM (7) are assembled.

The pressure detection device according to the present invention, which has been assembled, wired, etc., is calibrated in accordance with the following procedure before being shipped from the factory. Moreover, the pressure sensor configured as described above is shown in FIG.
It is connected to a computer via a /D converter and calibrated using the following procedure.

First, the switch 5 is operated (closed in the case shown) in order to put the pressure detection device into the calibration mode. Then, the state of the input port changes from 'H' to 'L11'. As a result, the CPU in the computer
Start execution of the calibration program written in OM. Thereafter, the operating temperature range is divided into an appropriate number and determined, and the pressure in the standard state is applied to the pressure sensor for each boundary temperature of each division, and the output of the A/D converter 2 in response to the pressure is applied each time. data (digital conversion value) to the CP
Let U read it. Thereby, the CPU creates a correspondence table of data for each pressure in one temperature state in the nonvolatile RAM 7 according to the program.

After creating a correspondence table of data for each pressure in one temperature state, create a similar correspondence table for the next temperature state, and create a correspondence table for the boundary temperature of all the categories determined in an appropriate number. Once completed, a correspondence table of the entire reference data will be created. That is, its operation will be explained with reference to FIG.

The operating temperature range of the pressure sensor 1 is divided, and the boundary temperatures thereof are defined as T0 to T7. First, a boundary temperature T0 is set in a constant temperature bath, etc., and constant pressure differences such as Pa, P+, Pz~PH are taken and sequentially applied to the pressure sensor 1 using a standard pressure generator. go. Then, the output data [loo, DOI, D02 to DON] of the A/D converter 2 corresponding to each of these pressures is read out by the CPU.

At this time, in order to read each data for each pressure, the switch 6 is operated (closed) when the pressure is applied to the pressure sensor 1 and the state becomes stable. As a result, the state of the boat Po changes from "H" to "L".

In response to this state change, the CPU first
Temperature data is read from the D converter 2 and written to the nonvolatile RAM 7. Next, the program switches the state of the multiplexer of the A/D converter 2 to the side where the signal based on the pressure sensor 1 is input, takes in the output data of the A/D converter 2, and stores it in the nonvolatile RAM 7. Write while corresponding to the pressure. The temperature data is read every time the pressure data is read, but if the error is practically negligible compared to the previous data, the first temperature data obtained is given priority and is not written to the non-volatile RAM 7. After writing the correspondence table between the pressure applied to the pressure sensor 1 and the output data of the A/D converter 2 regarding the boundary temperature To, operate a switch similar to the switch 6 (not shown) to set the boundary temperature. The CPU
Let me know. Next, a similar correspondence table is written for the boundary temperature TI. Thereafter, similar correspondence tables are sequentially written until the boundary temperature TM is reached. Thus, the predetermined region of the nonvolatile RAM 7 has a boundary temperature T. The above A/ for each pressure PG-PN for each boundary temperature TH.
The output data of the D converter 2 is written. The data thus obtained is used as reference data to be referred to in order to obtain the correct pressure in the measurement mode described later.

As described above, reference data is written in the nonvolatile RAM 7, shipped from the factory, and delivered to the user. Note that the switch 5 and the switch 6 are both shipped from the factory in an open state (measurement mode). Although the switch 5 and the switch 6 are not shown in FIG. 2, they are connected to a control line (not shown) and the computer 3 so as to perform the same function. Furthermore, in the pressure sensor shown in FIG. 2, the reference data may not be written in the nonvolatile RAM 7 at the time of factory shipment, and the reference data may be written by the user.

In use, the user applies an unknown pressure PX to the pressure sensor l. The CPU receives temperature data D related to the temperature TV of the pressure sensor 1 at that time from the A/D converter.
Read pressure data based on TY and pressure sensor l and save them in a register or RAM. and,
To calculate the unknown pressure px, the non-volatile R
With reference to the reference data created in AM7, the T0 to T1. ! Temperature data corresponding to DT, ~DT? l
Two pieces of data that are close in size to the digital data DTv are selected from among them by comparison. Now, among these data, the smaller one is DT, and the larger one is DT.

shall be. The temperatures corresponding to these are T and T
m*1. The temperature Tv can be expressed by the following equation.

・ ・ ・ [1] Once the above Ty is determined, create a data string DI/Q to D'/N. To create this data string, perform the following calculations.

The pressures applied are Pn and P,l, respectively. Then, the unknown pressure Px can be expressed by the following equation.

・ ・ ・ [2] Similarly, ・ ・ ・ [3] From now on, the calculation formula will be omitted, but the same calculation will be performed, and finally, ・ ・ ・ [4] will be obtained.

After calculating the above data string D yO"" D yN,
The unknown pressure Px is determined by the following procedure. That is, among the data string D yO-D yN, the two closest to the output data DX of the A/D converter corresponding to the pressure Px
The smaller one is Dy, the larger one is D yn, and so on. Corresponding to each...
[5] In order to make these relationships easier to understand, a graph is shown in FIG. 4.

A program for calculating each of the above formulas is written in the ROM of the computer 3 using a conventional method.
U executes this program.

As a result, the unknown pressure px is determined and sent to an external display device or control device, or to the computer 3.
The data itself can be used as data to control various devices.

In the example in the calibration mode described above, the non-volatile RAM
The output data DOG""-DMN of the A/D converter 2 with respect to the pressure PG-PN is written in the predetermined area of FIG. 7 for each of the boundary temperatures 'ro to TH. The reference data is as shown.

The relationship between the pressure at each temperature and the output data DOO""DMH of the A/D converter 2 is linearly regressed to obtain the following equation. However, P and D generally indicate the output data.

To:P=ao+βoD T+:P=α1+β+D TM:P=αH+3M D Here, αo1α, -α. and β. , β1 ... β
A is the regression coefficient.

From these equations, we obtain the following general equation.

P=α(T)+β(T) The relationship between regression coefficients α and β and T is linearly regressed to obtain the following equation.

α(T)=a+bT β(T)=c+dT Substituting these into the above general formula, the pressure P is P=a+bT+
D (c+dT) It is also possible to obtain the values of a, b, c, and d from the previous two and write these into the nonvolatile RAM 7, and then calculate the pressure P for the temperature T and data D found at the time of measurement. In this case, the reference data to be saved are a, b,
Only four items c and d are required, which saves memory space. Furthermore, the regression coefficient can also be determined using the temperature data DT, and can be expressed as shown in the following equation.

Obtain P=a"+b"DT+D (c'+d'DT).

In this case, when determining Px in the measurement mode, calculation for determining the actual temperature T is not necessary.

Furthermore, if regression is performed not linearly but quadraticly using the temperature data DT, the following equation can be obtained.

P = a o + a t DT + a z DT
2+D (be ten b+ DT+bz DT2)+D
2 (c(1+C+ DT+c2 DT2) Calculate the regression coefficient of this equation separately and calculate ao, al, azbe −,
By writing the nine regression coefficients of tel, l)2, co % CI, and C2 in the nonvolatile RAM 7, it is possible to determine the unknown pressure with higher accuracy in relation to the temperature data DT obtained during measurement. .

The temperature sensor 8 shown in FIG. 1 can be built into the chip of a semiconductor strain gauge, which is the pressure sensor 1, using a diffused resistor, for example, as shown in FIG. 6. Also,
As shown in FIG. 7, the temperature sensor 8 in the pressure sensor shown in FIG. 2 can also be built into the chip of the semiconductor strain gauge, which is the pressure sensor 1, using, for example, a diffused resistor.

FIG. 8 is a block diagram showing an example in which the pressure sensor 1 itself is used as a temperature sensor.

The gauge resistance of the semiconductor strain gauge that is the pressure sensor 1 has a resistance temperature coefficient of about 1500 ppm,
If the bridge is driven at a constant current by a constant current source I and the voltage change at the current carrying terminal of the constant current source I is amplified by the amplifier 9, data relating to temperature can be obtained based on the output thereof.

Further, as shown in FIG. 9, if the pressure sensor shown in FIG. 2 is driven at a constant current by a constant current source I and the voltage change at the current carrying terminal of the constant current source I is amplified by an amplifier 9, the output Data related to temperature can be obtained based on .

In the calibration mode, the switch 5 and the switch 6 can be replaced by a microcomputer, a sequencer, or a programmable controller, and the temperature data,
Automatic calibration can be performed by reading pressure data.

Moreover, it is possible to automatically adjust several dozen units at once. Therefore, almost no time is required for adjustment.

〔Effect of the invention〕

As described above in detail, according to the present invention, reference data for determining the correct pressure is stored in a non-volatile memory in advance by the data processing means, and the reference data is referred to during measurement to obtain approximately correct pressure. Since the pressure detection device is configured to calculate , it is possible to provide a pressure detection device that can be produced labor-savingly without any troublesome adjustment work, which is economically advantageous and enables cost reduction. Moreover, a pressure sensor is obtained in which the main parts necessary for executing the data processing means are housed in a single package, and when a malfunction occurs in the pressure sensor, it is simply replaced and there is no need for readjustment.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram showing an example of the pressure detection device of the present invention, FIG. 2 is a configuration diagram for pressure detection including a pressure sensor according to the present invention, and FIG. 3 is an explanation for explaining the calibration mode. Fig. 4 is an explanatory diagram showing how to obtain parameters for obtaining an unknown pressure, and Fig. 5 shows pressure data D for pressure Po=Ps for each of the boundary temperatures To to Ti. . ~[)P4
FIG. 6 is a block diagram showing another embodiment of the pressure detection device of the present invention, and FIG. 7 is a pressure detection device including a pressure sensor as another embodiment of the present invention. FIG. 8 is a block diagram showing another embodiment of the pressure detection device of the present invention, and FIG. 9 is a configuration diagram for pressure detection including a pressure sensor as another embodiment of the present invention. , FIG. 1O is a block diagram of a conventional pressure detection device. ■... Pressure sensor, 2... A/D converter, 3... Computer, 5... Switch, 6... Switch, 7... Non-volatile RAM, 8... ...Temperature sensor.

Claims (1)

[Claims] 1) A pressure sensor, a temperature measuring means for measuring the temperature near the pressure sensor, an analog quantity based on the output of the pressure sensor, and converting the analog quantity obtained by the temperature measuring means into a digital value. It has an A/D converter, a computer that reads the digital values, and a non-volatile memory that can be read and written by the computer, and divides the operating temperature range into an appropriate number and sets the pressure sensor in a discrete standard state in advance for each boundary temperature of each division. When a pressure of 1. A pressure detection device comprising a data processing means for calculating substantially correct data by referring to data for the pressure detection device. 2) A pressure sensor characterized in that a pressure sensor element, an amplification element for amplifying the output of the pressure sensor element, and a data storage element are provided in a single package. 3) A pressure sensor according to claim 2, wherein the data storage element is an EEPROM with a serial interface. 4) A pressure sensor characterized in that a pressure sensor element, an amplification element for amplifying the output of the pressure sensor element, a data storage element, and a temperature sensor for detecting the temperature in the vicinity of the pressure sensor element are provided in a single package. sensor. 5) The pressure sensor according to claim 4, wherein the temperature sensor is formed within the pressure sensor element. 6) The pressure sensor according to claim 4, wherein the pressure sensor element itself plays the role of the temperature sensor. 7) The pressure sensor according to claim 2, wherein reference data for determining the measured temperature and the measured pressure are stored in the data storage element.