JPH10281912A - Pressure sensor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensor device in which the increase in size or cost and complicated processing are suitably avoided, and a more precise sensor value corrected in dispersion of a characteristic or mechanical difference every sensor can be provided. SOLUTION: This device has a pressure sensor 100 having a pressure information extracting bridge circuit 1, a temperature information extracting bridge circuit 2, and a standard information extracting bridge circuit 3. In an EPROM 12 which is a nonvolatile memory, the temperature coefficient (a) related to temperature information T, the offset value (b) of the temperature information T at a standard temperature, the temperature characteristic coefficient (c) to pressure information D, the sensitivity (d) to the pressure information D at the standard temperature, the temperature coefficient (e) in the offset of the pressure information D, and the offset value (f) of the pressure information D at the standard temperature are prepared as correction data. A microcomputer 11 calculates a final pressure P according to P= (T/A-b)×(-e/a)+(D/ A-f)}/ (T/A-b)×(c/a)+d} (wherein A represents the standard information extracted by the bridge circuit 3).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor device for processing a pressure sensor signal by a processing device such as a microcomputer, and more particularly to a pressure sensor device structure for more efficiently obtaining a more accurate sensor value. Is what you want to do.

[0002]

2. Description of the Related Art In recent years, microcomputers have been introduced for various controls and processes, and the output of sensors for detecting various information for such controls and processes is usually processed by the microcomputer. It is being done.

[0003] Conventionally, as a sensor device having a sensor and a processing device such as a microcomputer for processing the sensor signal, for example, Japanese Patent Application Laid-Open No. 3-688 is disclosed.
The device described in Japanese Patent Publication No. 15 is known.

Incidentally, the sensor device has a search table (map) in its processing unit (microcomputer), and performs association (map calculation) in the search table in accordance with information input from the sensor side. To obtain the desired sensor value.

[0005]

As described above, by processing the sensor signals by the microcomputer or the like, various calculations can be performed extremely flexibly, and the obtained values can be easily corrected. For example, a more reliable sensor value can be obtained.

Generally, when a plurality of pressure sensors are manufactured, even if the specifications are the same, there are variations in characteristics and machine differences among the sensors. For this reason, in a processing device such as a microcomputer, if the above calculations and corrections are uniformly applied to the outputs of these sensors, a desired accuracy may not be obtained as a sensor value.

Therefore, when such high precision is required, it is necessary to accurately correct variations in characteristics of each sensor and machine differences. However, if data for compensating for variations in the characteristics of each sensor and machine differences are written in the above-described processing device, the processing becomes complicated. If correction and absorption are to be performed internally, some processing circuit for that purpose is required inside the sensor, and the sensor itself is inevitably increased in size and cost.

[0008] The present invention has been made in view of such circumstances, and it has been made possible to preferably avoid the increase in size, increase in cost, and complicated processing, and to compensate for variations in characteristics of each sensor and machine differences. It is an object of the present invention to provide a pressure sensor device that can obtain a highly accurate sensor value.

[0009]

According to the first aspect of the present invention, the temperature information extracting means, the reference information extracting means, and the nonvolatile memory are provided, and pressure information D, temperature information T, reference information A, By performing the calculation based on the correction data a to f, it is possible to suitably remove the influence of the temperature characteristic of the sensor itself and other characteristic variations.

That is, as the correction data, the temperature coefficient a relating to the temperature information T and the temperature information T at the reference temperature
An offset value b, a temperature characteristic coefficient c of sensitivity to pressure information D, a sensitivity d to pressure information D at a reference temperature, and a temperature coefficient e of offset of pressure information D,
An offset value f of the pressure information D at the reference temperature is prepared, and the calculating means calculates P = {(T / A−b) × (−e / a) + (D / A−f)} / ｛(T / A−b) × (c / a) + d｝ (1) The final pressure P is calculated. By employing such an arithmetic structure, it becomes possible to obtain an extremely accurate sensor value for the pressure P to be detected.

That is, the pressure information D, the temperature information T, and the reference information A are represented by the following formulas using the above-mentioned a to f when the temperature is t: D = {(ct + d) P + et + f} × β (t) (2) T = (at + b) × β (t) (3) A = β (t) (4) In the equation (2), (ct + d) P is a sensitivity term relating to pressure, f is an offset amount, and et
Is a correction term of the shift amount, and a correction coefficient is multiplied by a term of xβ (t). In the equation (3), b is an offset amount, at represents sensitivity to temperature, and a correction coefficient is multiplied by a term of xβ (t). Equation (4) indicates that the reference information A is represented by the temperature characteristic (non-linearity) of the circuit section.

[0012] Then, from the equations (2), (3) and (4), when solving for P in order to obtain the final pressure P, the above equation (1) is obtained. Thus, the final pressure P can be easily obtained by expressing the sensitivity with respect to the temperature t by a linear function.

The above-mentioned reference temperature can be, for example, room temperature. Here, according to the second aspect, it is possible to suitably remove the influence of the temperature characteristic of the sensor itself and other characteristic variations.

That is, the pressure data itself to be detected can be obtained as a frequency difference between the oscillation outputs of the first and second CR oscillation circuits to which the time constant change is given by the pressure information extracting means. This is usually due to the error due to the temperature characteristics of the sensor itself, the temperature characteristics of the first and second CR oscillation circuits, the frequency difference calculating means, and the like (variations in characteristics between the first and second systems, etc.). The error is also included.

According to the third aspect of the present invention, based on the high sensitivity of the bridge circuit and the high oscillation accuracy of the pass transistor type CR oscillation circuit,
Each of the above-described pressure information, temperature information, and reference information can be obtained more efficiently and accurately.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the pressure sensor device according to the present invention.

The pressure sensor device of this embodiment is configured as a device that can obtain a more accurate sensor value by correcting variations in characteristics of each sensor, machine differences, and the like. Hereinafter, the configuration and operation of the pressure sensor device according to this embodiment will be sequentially described with reference to FIG.

As shown in FIG. 1, the pressure sensor device comprises a pressure sensor 100 and a microcomputer 11 for processing the sensor signal as required. The pressure sensor 100 has three full bridge circuits of a pressure information extraction bridge circuit 1, a temperature information extraction bridge circuit 2, and a reference information extraction bridge circuit 3 as portions for extracting physical information to be detected. doing.

Among them, the pressure information extraction bridge circuit 1
FIG. 1 corresponds to the application of pressure to be detected.
, The pressure-sensitive resistance elements R11, R12, R13, and R14 whose resistance values change due to the piezoresistance effect.

For this reason, the midpoint potential of the resistance elements R11 and R12 decreases according to the applied amount of the pressure, and conversely, the midpoint potential of the resistance elements R13 and R14 decreases according to the applied amount of the same pressure. Get higher. Then, the potential difference between these midpoint potentials is taken out as a bridge output by the bridge circuit 1. The output voltage of the bridge circuit 1 depends on the temperature of the sensor in addition to the applied pressure.

On the other hand, the temperature information extraction bridge circuit 2
As a bridge circuit in which the temperature-sensitive resistance elements R21 and R24, which generate a resistance value change according to the temperature of the sensor itself, and the resistance elements R22 and R23, which basically do not have temperature characteristics, are connected in the manner shown in FIG. It is configured.

For this reason, a potential difference corresponding to the temperature of the sensor itself occurs between the midpoint potentials of the resistance elements R21 and R22 and the midpoint potentials of the resistance elements R23 and R24. To be extracted as a bridge output. Note that this bridge circuit 2
Output voltage basically depends only on the temperature of the sensor.

The reference bridge circuit 3 for extracting reference information, which is the third bridge circuit, includes resistance elements R31, R32, R33, and R34, each of which basically has no temperature characteristic, as shown in FIG. It is configured as a bridge circuit connected by.

For this reason, in the bridge circuit 3,
Normally, there is no potential difference between the midpoint potential of the resistance elements R31 and R32 and the midpoint potential of the resistance elements R33 and R34. This is because the time value conversion circuit (time A
-D) If any time measurement value of the output (potential difference) of the bridge circuit 3 is obtained in 9, the measurement value is determined by the following circuits, the CR oscillation circuits 5 and 6, the frequency divider circuits 7 and 8, and This means that the temperature value conversion circuit 9 shows temperature characteristics and other variations. The “other variations” include variations in characteristics between the first and second systems in the CR oscillation circuit and the frequency divider circuit.

The selector 4 outputs the respective bridge outputs of the pressure information extraction bridge circuit 1, the temperature information extraction bridge circuit 2, and the reference information extraction bridge circuit 3 to a selection signal given from a control circuit 10 described later. This is a circuit for selectively outputting based on sel. As shown in FIG. 1, the selected bridge outputs are supplied to the MOS transistors (hereinafter referred to as pass transistors) T5 and T6 of the CR oscillation circuits 5 and 6 as voltages of opposite polarities, respectively. Become.

The first and second CR oscillating circuits 5 and 6 configured as these pass transistor type CR oscillating circuits have a frequency (or period) according to a change in on-resistance of each of the pass transistors T5 and T6. The circuit oscillates a changing alternating signal (a pulse signal in this example).

Incidentally, in such a CR oscillation circuit, the oscillation frequency f is determined as f = 1 / 2πCR (5).
If the on-resistance R of T6 is large, an alternating signal of a low frequency (long cycle) is oscillated, and if the on-resistance R of the pass transistors T5 and T6 is small, a pulse signal of a high frequency (short cycle) is oscillated.

Therefore, for example, when the bridge output of the pressure information extraction bridge circuit 1 is selected, the first C
The pass transistor T5 on the side of the R oscillation circuit 5 has a low potential on the P-channel electrode and a high potential on the N-channel electrode, and has a low on-resistance. The pass transistor T6 on the side of the second CR oscillation circuit 6 has a high potential on the P-channel electrode and a low potential on the N-channel electrode, and has a large on-resistance. In such a case, a pulse signal having a relatively high frequency (short cycle) is output from the first CR oscillation circuit 5, and a pulse signal having a lower frequency (cycle) is output from the second CR oscillation circuit 6. Pulse signal is oscillated and output.

The bridge output of the bridge circuit 2 for extracting temperature information and the bridge output of the bridge circuit 3 for extracting reference information also have a pulse signal having a frequency (period) corresponding to the potential difference in a manner similar to this. Is oscillated from the first and second CR oscillation circuits 5 and 6.

The pulse signals oscillated from the first and second CR oscillation circuits 5 and 6 in this manner are both the first and second CR oscillation circuits.
Are divided into, for example, several hundred times the time width by the frequency dividing circuits 7 and 8, and are taken into the time / numerical value converting circuit 9.

The time value conversion circuit 9 obtains the frequency difference (period / time difference) based on the divided two oscillation pulses of the first and second CR oscillation circuits 5 and 6, and converts this to a digital signal. Circuit. FIG. 2 shows an example of the processing mode.

That is, as shown in FIG. 2, the first CR oscillation circuit 5 outputs a pulse having a relatively high frequency (short period) as shown as a frequency divided output in FIG. A signal is output, and the other second CR oscillation circuit 6 outputs a pulse signal having a lower frequency (longer cycle) than that shown in FIG. 2C, the difference (T1−T2) between the cycle times T1 and T2 is calculated in the time numerical value conversion circuit 9 in the manner shown in FIG. 2C, and the calculated time difference (T1−T2) is calculated. It is converted into a digital signal at a predetermined resolution. The same-time numerical conversion circuit 9
For more information, please refer to the IEICE Transactions CI
I Vol. J78-C-II No. 6 pp. 36
6-374 June 1995 "Time A / D conversion LSI enabling high precision and multiple pulse measurement by digital processing" written by Takamoto Watanabe et al. " I do.

In this way, the frequency difference (period-time difference) is obtained for the two input pulse signals, and the digital-to-digital converted time / numerical value conversion circuit 9 outputs this to the microcomputer 11 as frequency difference (period-time difference) information fs. I do. In the following, for the sake of convenience, the frequency difference (period / time difference) information fs obtained for the bridge output of the pressure information extraction bridge circuit 1 is referred to as pressure information D, and the bridge output of the temperature information extraction bridge circuit 2 is referred to as pressure information D. The obtained frequency difference (period time difference) information fs is referred to as temperature information T, and the frequency difference (period time difference) information fs obtained for the bridge output of the reference information extraction bridge circuit 3 is referred to as reference information A. say.

In this embodiment, the frequency dividers 7 and 8 and the time value converter 9 constitute a frequency difference calculator. The control circuit 10 controls selection of a bridge output through the selector 4 and activation of the time value conversion circuit 9. The microcomputer 11 as an arithmetic means corrects the obtained pressure information D, temperature information T, and reference information A for variations in characteristics of the sensor itself and machine differences which are stored in advance in the EPROM 12 which is a nonvolatile memory. Calculation by adding correction data (constants a to f) for the final pressure value P
Is a circuit that outputs.

Specifically, the correction data stored in advance in the EPROM 12 include: a temperature coefficient a relating to the temperature information T; an offset value b of the temperature information T at the reference temperature; a temperature characteristic coefficient c of sensitivity to the pressure information D; Six data (constants) of sensitivity d to pressure information D at the reference temperature, temperature coefficient e at offset of pressure information D, and offset value f of pressure information D at reference temperature are prepared. Normally, all of these data differ depending on manufacturing variations of the sensor, etc., and in the apparatus of the embodiment, the correction data a to f
The data is written to the OM12.

The microcomputer 11 includes a CPU 11
a, a ROM 11b as a program memory,
And the RAM 11c as a data memory, etc., and collectively collects the separated and demodulated correction data a to f, the pressure information D, the temperature information T, and the reference information A into predetermined areas of the RAM 11c, ROM11
The arithmetic program illustrated in FIG. 3 pre-registered in b is executed through the CPU 11a.

That is, in the calculation routine shown in FIG. 3, the CPU 11a reads the pressure information D, the temperature information T, the reference information A, and the correction data a to f stored in the RAM 11c in steps 201 and 202. Thereafter, in step 203, the calculation P = {(T / A−b) × (−e / a) + (D / A−f)} / ｛(T / A−b) × (c / a) + d … (6) is executed to calculate the final pressure information P.

The equations which are the basis of the calculation of the equations are the above-mentioned equations (2) to (4), which are as described above, and the description thereof will be omitted here. In addition, "D /
A "and" T / A "are the first and second CRs in the sensor for the pressure information D and the temperature information T, respectively.
This is a process for normalizing the temperature characteristics of the oscillation circuits 5 and 6, the frequency divider circuits 7 and 8, and the time value conversion circuit 9 and the variation in characteristics between the systems. As described above, the reference information A is information corresponding to temperature characteristics in these circuits and characteristic variations between systems.

As described above, the pressure information D (output voltage) extracted through the pressure information extraction bridge circuit 1 depends not only on the pressure applied to the sensor but also on the temperature of the sensor itself. However, by performing the calculation of the above equation (6) on such pressure information D,
An extremely accurate sensor value for the pressure P, which is physical information to be detected, can be obtained. Specifically, the accuracy can be set within 2% FS.

As described above, according to the pressure sensor device of this embodiment, (1) the bridge circuit 1 for extracting pressure information, the bridge circuit 2 for extracting temperature information, and the bridge circuit 3 for extracting reference information. In addition to providing three bridge circuits, an EPROM 12 storing correction data a to f is provided, and pressure information D obtained through the pressure information extraction bridge circuit 1 is provided.
Is compensated for by the temperature information T obtained through the temperature information extraction bridge circuit 2, the reference information A obtained through the reference information extraction bridge circuit 3, and the correction data a to f. The effects of temperature characteristics and other characteristic variations can be suitably removed. Specifically, by calculating the final pressure P based on the above equation (6), an extremely accurate value can be obtained as the physical information.

In the embodiment, the pressure-sensitive resistance elements are used for all the resistance elements constituting the pressure information extraction bridge circuit 1. For example, only one of the resistance elements R11 and R12, or A configuration in which the pressure-sensitive resistance element is used for only one of the resistance elements R13 and R14 is also possible as appropriate. In short, any configuration may be used as long as a potential difference corresponding to the application of pressure can be obtained through the bridge output.

Similarly, the temperature information extracting bridge circuit 2 can be configured to use a temperature-sensitive resistance element only for the resistance element R24, for example. In other words, it is only necessary that a potential difference corresponding to the temperature of the sensor be obtained through the bridge output.

In this embodiment, a pass transistor type CR oscillation circuit is used as the first and second CR oscillation circuits. However, a resistance element is inserted in place of the pass transistor, and the resistance is changed according to the CR time constant. An oscillation circuit of a type that oscillates an alternating signal having a predetermined cycle can be appropriately employed.

In this case, including the pressure information,
The means for extracting temperature information and reference information need not necessarily constitute a bridge circuit, but may be any means for extracting pressure information. What can be given to the first and second CR oscillation circuits. Also, if it is a means for extracting temperature information, it can apply different time constant changes corresponding to the temperature of the sensor to the first and second CR oscillation circuits. If the means for extracting the reference information is: the first and second time constant changes different from each other regardless of the application of the pressure to be detected and the temperature of the sensor;
That can be given to the CR oscillation circuit. It just needs to be.

The means for storing and holding the correction data unique to the sensor is not limited to the EPROM 12, but may be another rewritable ROM (EEPROM or flash ROM) or a nonvolatile memory such as an SRAM. Can be.

As a circuit for digitizing the oscillation frequency, a method of counting the number of oscillation pulses in a single time is often used in addition to the above embodiment. Instead of using the microcomputer 11, an arithmetic processing circuit having the same function may be formed on a chip constituting the pressure sensor 100, and the whole may be formed into one chip.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a pressure sensor device according to the present invention.

FIG. 2 is a time numerical value conversion circuit (time A-
4 is a time chart illustrating the processing mode of D).

FIG. 3 is a flowchart illustrating a sensor value calculation procedure.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Bridge circuit for extracting pressure information, 2 ... Bridge circuit for extracting temperature information, 3 ... Bridge circuit for extracting reference information, 5 ...
1st CR oscillation circuit, 6 ... second CR oscillation circuit, 7 ... first frequency divider circuit, 8 ... second frequency divider circuit, 9 ... time value conversion circuit, 11 ... microcomputer, 11a ... CPU,
11b ROM, 11c RAM, 12 EPROM.

Claims (3)

[Claims] A pressure information extracting unit that extracts pressure information according to the application of a pressure to be detected; a temperature information extracting unit that extracts temperature information according to a temperature of a sensor; A reference information extracting means for extracting reference information irrelevant to the application and the temperature of the sensor; a non-volatile memory in which data for correcting variations in characteristics of the sensor, machine differences, and the like are stored in advance; Calculating means for calculating a final pressure based on temperature information T, reference information A and correction data, wherein the correction data includes a temperature coefficient a relating to temperature information T, and temperature information at a reference temperature. T offset value b, temperature characteristic coefficient c of sensitivity to pressure information D, sensitivity d to pressure information D at a reference temperature, and offset of pressure information D And temperature coefficient e that, prepared and offset value f of the pressure information D at the reference temperature, said computing means, P = {(T / A-b) × (-e / a) + (D / A-
f) A pressure sensor device wherein the final pressure P is calculated by {/ {(T / A−b) × (c / a) + d}. 2. A first CR oscillation circuit that oscillates an alternating signal having a period according to a capacitance (C) -resistance (R) time constant, and a period according to the capacitance-resistance time constant. A second CR oscillating circuit for oscillating an alternating signal having the first and second CR oscillating circuits, wherein the pressure information extracting means performs different time constant changes according to the application of pressure to be detected. The temperature information extracting means applies different time constant changes according to the temperature of the sensor to the first and second CR oscillation circuits, and the reference information extracting means provides Different time constant changes are applied to the first and second CR oscillation circuits irrespective of the pressure applied and the temperature of the sensor, and the time constant change is given by the pressure information extracting means. 1 and 2nd C A frequency difference between oscillation outputs of the R oscillation circuit, a frequency difference between oscillation outputs of the first and second CR oscillation circuits to which a time constant change is given by the temperature information extracting means, and a time constant of the reference information extracting means. 2. The pressure sensor device according to claim 1, further comprising: frequency difference calculating means for calculating a frequency difference between oscillation outputs of the first and second CR oscillation circuits to which a change has been given. 3. The pressure information extracting means includes: a first pressure-sensitive resistance element that changes a resistance value in a first direction in response to application of a pressure to be detected; A second pressure-sensitive resistance element that generates a resistance change in a second direction opposite to the first direction in accordance with the first direction. A second bridge circuit including a temperature-sensitive resistance element that changes a resistance value according to the temperature of the sensor and a resistance element that basically does not have a temperature characteristic; A third bridge circuit configured by a resistance element having no temperature characteristic, wherein the first and second CR oscillation circuits are configured such that output voltages of the first to third bridge circuits have respective opposite polarities. MOS transistor applied 3. The pressure sensor device according to claim 2, wherein the pressure sensor device is a MOS transistor type CR oscillation circuit in which a cycle of the oscillating alternating signal changes according to a change in on-resistance of the MOS transistor.