JP2012002742A - Physical quantity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the output accuracy of a physical quantity sensor in a determined temperature segment.SOLUTION: A physical quantity sensor includes a memory part 133 for storing data relating to higher correction formula g1, g2 which are quadratic equations or larger than them for determining the correction value of the physical amount detection value by a physical amount detection element 11 in a corresponding partial temperature segment for each of a plurality of partial temperature segments selected from the determined temperature region and a correction processing part 13-i (wherein i is equal to 1 or 2) for correcting the physical quantity detection value based on a correction value of the corresponding partial temperature segment based on data of the correction formula g1, g2 corresponding to one of the partial temperature regions.

Description

  One embodiment of the present invention relates to a technique for sensing physical quantities such as pressure, temperature, and humidity.

  As a pressure sensor (dual pressure sensor) for detecting two measured pressures, for example, a technique described in Patent Document 1 below is known. The dual pressure sensor described in Patent Document 1 has two pressure-sensitive diaphragm chips, and two measured pressures introduced from two pressure guiding tubes are applied to the respective pressure-sensitive diaphragms. By converting the displacement of the pressure-sensitive diaphragm at this time into an electrical signal using, for example, a diffusion strain gauge, a detection signal corresponding to the pressure to be measured can be obtained.

  Since such a dual pressure sensor can detect two measured pressures, it can also be used as a differential pressure sensor for obtaining a difference between them, that is, a differential pressure. As an example of the required differential pressure, there is a pressure difference (that is, differential pressure) between fluids upstream and downstream of the flow control valve. As an example of the flow control valve, one described in Patent Document 2 below is known.

JP 2009-31003 A JP 2009-115302 A JP 2004-294110 A JP 2004-294110 A

  The difference (differential pressure) between the fluid pressure upstream and downstream of the flow control valve can be used to determine the flow rate of the fluid flowing through the flow control valve. Here, the pressure sensor using a pressure-sensitive diaphragm is configured to detect the pressure of the fluid by utilizing the physical displacement of the pressure-sensitive diaphragm according to the applied pressure. It has a temperature characteristic in which an offset occurs and the output gain changes.

  Therefore, in order to accurately determine the flow rate of the fluid, it is required to perform appropriate correction (compensation) according to the temperature of each pressure sensor on the sensor output. As temperature correction methods, for example, the methods described in Patent Documents 3 and 4 are known.

  In the method described in Patent Document 3 (hereinafter referred to as “correction method 1”), a temperature characteristic curve for obtaining a sensor output correction value is divided into a plurality of temperature sections in a predetermined temperature range, and each temperature section is divided. Assuming that a correction value corresponding to the intermediate temperature in the temperature section exists on a straight line connecting the correction values at both ends, a correction value corresponding to the temperature of the sensor is obtained from the straight line, and temperature correction is performed.

  Further, in the method described in Patent Document 4 (hereinafter referred to as “correction method 2”), a high-order approximate expression closest to a temperature characteristic curve for obtaining a correction value of the sensor output in a predetermined temperature range is obtained. A correction value corresponding to the temperature of the sensor is obtained from the approximate expression to perform temperature correction.

  By the way, when the flow control valve described in Patent Document 2 is applied to a heat source supply system of an air conditioning system, a low-temperature fluid [for example, cold water (about 5 ° C. to 20 ° C.)] ] Or a high-temperature fluid [for example, warm water (about 40 ° C. to 60 ° C.)] selectively flows. Therefore, it can be said that the sensor temperature rarely falls within the intermediate temperature range (20 ° C. to 40 ° C.) (hereinafter referred to as “split range”).

  In such a situation, if temperature correction is to be performed by the correction method 1, the entire temperature range including the split range is divided into a number of temperature sections, so that necessary temperature correction is performed according to the number of divisions. The number of values increases, and the capacity of the memory that stores the temperature correction value increases. That is, there is a trade-off relationship between the accuracy required for temperature correction and the memory capacity. Moreover, in the correction method 1, since the temperature correction value of the intermediate portion is complemented by linearly approximating the temperature correction values at both ends of each temperature interval, the temperature correction accuracy of the intermediate portion other than both ends of the temperature interval deteriorates. Cheap.

  On the other hand, in the case where the split range exists, if temperature correction is performed by the correction method 2, the temperature characteristic curve of the entire range of the predetermined temperature range including the split range is approximated by a single higher-order expression. As compared with the correction method 1, a temperature interval in which a predetermined temperature correction accuracy cannot be obtained is likely to occur. For example, if the higher-order equation is determined so that the accuracy is obtained at the median value of one temperature range of the low temperature fluid and the high temperature fluid, the temperature correction accuracy for the other temperature range cannot be increased.

  It should be noted that the deterioration of the temperature correction accuracy as described above is not limited to the pressure sensor that detects (measures) the fluid pressure, but may occur in common with a physical quantity sensor having nonlinear temperature characteristics.

  Accordingly, one of the objects of the present invention is to improve the accuracy of the output temperature correction of the physical quantity sensor in a predetermined temperature section.

  In addition, the present invention is not limited to the above-described object, and other effects of the present invention can be achieved by the functions and effects derived from the respective configurations shown in the embodiments for carrying out the invention which will be described later. It can be positioned as one of

  One aspect of the physical quantity sensor of the present invention includes a physical quantity detection element that detects a predetermined physical quantity having temperature characteristics, and the physical quantity detection in the partial temperature section for each of a plurality of partial temperature sections selected from a predetermined temperature range. A storage unit that stores data relating to a correction equation of a second or higher order for obtaining a correction value of the physical quantity detection value by the element, and the partial temperature interval based on the data of the correction equation corresponding to any of the partial temperature intervals And a correction processing unit that obtains the correction value and supplies the correction value to the physical quantity detection value.

  Here, the physical quantity sensor further includes a temperature detection element that detects a temperature of the physical quantity detection element, and the correction processing unit includes the first partial temperature section including a temperature detection value by the temperature detection element and the first partial temperature section. A correction calculation unit that obtains the correction value in each of the first and second partial temperature intervals based on data relating to the correction formula corresponding to each of the second partial temperature intervals not including the temperature detection value. And a selection output unit that selectively outputs the physical quantity detection value given the correction value corresponding to the first partial temperature section in which the temperature detection value is included.

  In addition, each of the correction formulas corresponding to the partial temperature section may be a correction formula that can obtain a correction value with higher accuracy than the other for the median value of the partial temperature section.

  According to the above-described aspect of the present invention, the detection value of the physical quantity detection element is calculated using a correction equation of a second or higher order corresponding to each of a plurality of partial temperature sections selected from a predetermined temperature range. Since the correction value is obtained, a highly accurate correction value can be obtained in each of the selected partial temperature sections. Therefore, the physical quantity detection accuracy by the physical quantity detection sensor can be improved.

It is a block diagram which shows the structural example of the pressure sensor unit concerning one Embodiment. FIG. 2 is a block diagram illustrating a configuration example of a correction calculation unit illustrated in FIG. 1. 3 is a graph illustrating a relationship between a load applied to the pressure sensor illustrated in FIG. 1 and an output after correction of the pressure sensor. 3 is a graph illustrating an example of pressure characteristics of the pressure sensor illustrated in FIG. 1. 3 is a graph illustrating an example of temperature characteristics of the pressure sensor illustrated in FIG. 1. 3 is a graph illustrating the relationship between the pressure-corrected output (PV) and pressure of the pressure sensor illustrated in FIG. 1. 3 is a graph illustrating the relationship between an output (OUT) after correction of the pressure sensor illustrated in FIG. 1 and an output (PV) after temperature correction; It is a figure which shows an example of the temperature vs. output error of the pressure sensor unit illustrated in FIG. It is a figure which shows an example of the temperature versus output error of the conventional pressure sensor unit.

  Embodiments of the present invention will be described below with reference to the drawings. However, the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described below. In other words, the present invention can be implemented with various modifications (combining the embodiments, etc.) without departing from the spirit of the present invention. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. The drawings are schematic and do not necessarily match actual dimensions and ratios. In some cases, the dimensional relationships and ratios may be different between the drawings.

(One embodiment)
FIG. 1 is a block diagram illustrating a configuration example of a pressure sensor unit according to an embodiment. The pressure sensor unit 1 shown in FIG. 1 can be attached to, for example, a flow control valve. For example, the pressure sensor 11, the temperature sensor 12, the correction processing units 13-1 and 13-2, the selector 14, Is provided.

  The pressure sensor 11 is an example of a physical quantity detection element that detects the pressure of a fluid that is one of physical quantities. For example, a semiconductor substrate (silicon) on which a pressure-sensitive diaphragm is formed as an example of a pressure-sensitive part, and a diffusion-type strain gauge. And a semiconductor chip comprising The diffusion strain gauge detects strain due to the pressure to be measured of the pressure-sensitive diaphragm using the piezoresistive effect, and outputs an electrical signal (voltage signal) corresponding to the detected value (strain amount). The output signal of the pressure sensor 11 is input to each of the two correction processing units 13-1 and 13-2.

  The temperature sensor (temperature detection element) 12 detects the temperature of the pressure sensor 11 (pressure-sensitive diaphragm) and outputs an electrical signal corresponding to the detected temperature. An example of the temperature sensor 12 is a temperature measuring resistance element provided in the vicinity of the pressure-sensitive diaphragm of the pressure sensor 11, and outputs an electrical signal corresponding to a temperature change in the resistance value of the resistance element. The output signal of the temperature sensor 12 is input to the correction processing units 13-1 and 13-2 and the selector 14, respectively.

  The correction processing unit 13-i (i = 1 or 2) calculates the output signal of the pressure sensor 11 based on the output signal (pressure detection value) of the pressure sensor 11 and the output signal (temperature detection value) of the temperature sensor 12. Find the correction value. Therefore, the correction processing unit 13-i exemplarily includes a multiplexing unit (MUX) 131, an analog-digital converter (ADC) 132, a storage unit 133, and a correction calculation unit 134.

  The multiplexing unit 131 multiplexes the output signal of the pressure sensor 11 and the output signal of the temperature sensor 12, for example, in a time division manner, and outputs the multiplexed signal to the ADC 132. An amplifier that amplifies the time division multiplexed signal may be provided between the multiplexing unit 131 and the ADC 132.

  The ADC 132 performs analog-to-digital conversion on each of the output signal of the pressure sensor 11 and the output signal of the temperature sensor 12 that are time-division multiplexed and outputs the result to the correction calculation unit 134.

  The storage unit 133 stores data relating to a correction formula for obtaining a correction value to be given to the output signal of the pressure sensor 11. For example, an EEPROM can be used as the storage unit 133. The “correction formula” can be determined based on “pressure characteristics” and “temperature characteristics” of the pressure sensor 11. Here, “correction” means to obtain a constant output (OUT) for a certain load (in this example, for example, pressure) as shown in FIG. 3, for example. Further, the “pressure characteristic” is a characteristic (see FIG. 4) in which the output (pressure) changes according to the applied load, and the “temperature characteristic” is a characteristic in which the output changes in accordance with the temperature (FIG. 5). Reference).

  The “pressure characteristic” and the “temperature characteristic” can be divided into a gain representing the amount of change (slope) of the output with respect to the load and an offset at which the output changes while the load is constant. “Pressure characteristics” and “temperature characteristics” are characteristics inherent to the pressure sensor 11 and include a linear change and a non-linear change. When correcting non-linear characteristics, the order of the correction formula is different depending on the pressure sensor 11 depending on whether it is secondary or tertiary.

Therefore, the gain and offset correction coefficients for the pressure and temperature for the respective orders are expressed as follows. However, n is illustratively assumed to be an integer of 2 or more.
Correction factor of pressure gain for the nth order: Gp_n
Correction coefficient of pressure offset for the nth order: Op_n
nth-order temperature gain correction coefficient: Gt_n
Correction coefficient of temperature offset for the nth order: Ot_n

In the following description, the temperature (use environment temperature) of the pressure sensor 11 is represented by “Temp”, and the difference (that is, the temperature difference) between the reference temperature (for example, 25 ° C.) and the use environment temperature (Temp) of the pressure sensor 11. ) Is represented by “ΔT”. Further, the output (pressure) that is affected by the temperature difference ΔT (before temperature correction) is represented by “PV (ΔT)”.

First, temperature correction is performed so that a constant output can be obtained at any temperature. Here, the temperature-corrected coefficients (Gt_n and Ot_n) when PV (ΔT) and Temp are variables are obtained with PV being the temperature-corrected output. As a result, PV = f (PV (ΔT), Tem
p) and this equation can be used as a temperature correction equation. For example, the temperature correction unit 134a shown in FIG. 2 performs the calculation based on the temperature correction formula.

  Next, pressure correction will be described. From FIG. 3 and FIG. 6, the relationship between the corrected output (OUT) and the temperature corrected output (PV) can be expressed as shown in FIG. 7, for example. From the pressure characteristics illustrated in FIG. 7, a relationship (expression) between the corrected output and the temperature corrected output is derived using the least square method or the like, and the pressure correction coefficient (Gp_n, OP_n) is calculated from the relationship (expression). Can be derived.

Therefore, the corrected output (OUT) can be expressed by a composite function of the output PV (ΔT) before correction and the temperature output Temp, OUT = g (f (PV (ΔT), Temp)). For example, the pressure correction unit 134b shown in FIG. The storage unit 133 can store each of the correction coefficients Gp_n, Op_n, Gt_n, and Ot_n as an example of “data related to a correction formula”.

  However, the function g need only be a correction formula optimized for a part of the temperature range (partial temperature range) selected from the temperature range rather than the entire range of the predetermined temperature range of the fluid to be measured. For example, when a flow control valve to which the pressure sensor unit 1 is attached is applied to a heat source supply system of an air conditioning system, the fluid to be pressure-measured is a low-temperature fluid [cold water (5 ° C. to 20 ° C.)] and a high temperature depending on the time Since one of the fluids [warm water (about 40 ° C. to 60 ° C.)] (split range occurs), a correction formula optimized for each partial temperature section may be used individually.

  For example, the function g1 is a correction equation optimized for a temperature interval (5 ° C. to 20 ° C.) that a low temperature fluid can take, and a function that is a correction equation optimized for a temperature interval (40 ° C. to 60 ° C.) that a high temperature fluid can take. Represented as g2. Then, a correction coefficient that determines one of the functions g1 and g2 is stored in the storage unit 133 of one correction processing unit 13-1, and a correction coefficient that determines the other is stored in the storage unit 133 of the other correction processing unit 13-2. Remember it. In other words, the correction processing unit 13-1 is a correction formula g1 optimized for a low temperature fluid, and the correction processing unit 13-2 is a correction value g2 optimized for a high temperature fluid. Ask for.

  The correction equations (functions) g1 and g2 can be obtained, for example, by calculating (for example, fitting) based on individual pressure data measured in advance at a plurality of temperatures in each partial temperature section. Further, the correction equations g1 and g2 do not have to be functions that can obtain a correction value with a predetermined accuracy in all of the corresponding partial temperature sections. For example, a function approximated so as to obtain a correction value with higher accuracy than any other temperature in the partial temperature interval at any temperature in each partial temperature interval, for example, the median value (12.5 ° C. or 50 ° C.). (Approximate expression).

  Next, as illustrated in FIG. 2, the correction calculation unit 134 includes the temperature correction unit 134 a and the pressure correction unit 134 b described above, and the digital signal input from the ADC 132, that is, the output signal of the pressure sensor 11 and the temperature sensor 12. Based on the time-division multiplexed signal with the output signal and the correction coefficient (function) gi (i = 1 or 2) stored in the storage unit 133, a correction value in the corresponding temperature interval is obtained.

  That is, the correction calculation unit 134 of each of the correction processing units 13-1 and 13-2 includes the first partial temperature section in which the temperature detection value by the temperature sensor 12 is included and the second partial temperature in which the temperature detection value is not included. A correction value in each partial temperature section is obtained based on a correction coefficient related to the correction formula corresponding to each section. The obtained correction value is given to the output signal of the pressure sensor 11.

  The selector 14 selectively outputs the output of each correction processing unit 13-i (correction calculation unit 134), that is, the output signal of the pressure sensor 11 corrected using the correction equations for low temperature fluid and high temperature fluid, respectively. To do. The selection of the output signal can be controlled by the output signal of the temperature sensor 12, for example. For example, when the output signal of the temperature sensor 12 indicates a temperature within the temperature interval (5 ° C. to 20 ° C.) of the low temperature fluid, the selector 14 is connected to the correction processing unit 13-1 (correction calculation unit 134) for the low temperature fluid. The output signal is output as a corrected detected pressure. On the other hand, when the output signal of the temperature sensor 12 indicates the temperature within the temperature zone (40 ° C. to 60 ° C.) of the high temperature fluid, the selector 14 outputs the correction processing unit 13-2 (correction calculation unit 134) for the high temperature fluid. The signal is output as a corrected detected pressure.

  However, the selection by the selector 14 may be controlled by predetermined setting information. For example, information indicating the current time (spring, summer, autumn, winter) and date and time is automatically or manually given to the selector 14 as setting information to control which correction formula based on which correction calculation result is valid. You may do it.

  As described above, according to the pressure sensor unit 1 of the present embodiment, the correction target is compared with a case where the entire range of a predetermined temperature range (for example, 5 ° C. to 60 ° C.) is corrected with one correction equation. Since the correction formulas optimized for each of the partial temperature intervals (for example, the temperature interval of 5 to 20 ° C. and the temperature interval of 40 to 60 ° C.) are selectively used, the correction value in each temperature interval is made highly accurate. The pressure detection accuracy of the pressure sensor 11 can be improved.

  For example, when the entire temperature range of 5 ° C. to 60 ° C. is corrected with a single correction formula, as illustrated in FIG. 9, an error of about 1% occurs at the maximum. According to this embodiment, By selectively using a correction formula optimized to obtain the highest correction accuracy at the median value (12.5 ° C. or 50 ° C.) of each partial temperature interval of 5 to 20 ° C. and 40 to 60 ° C., As illustrated in FIG. 8, the maximum correction error in each partial temperature section can be suppressed to about 0.25%.

  In other words, by narrowing down the temperature section to be corrected, it is not necessary to consider the correction accuracy outside the temperature section, so that the correction accuracy in the temperature section can be increased. In addition, since the width of each temperature section can be narrowed by narrowing down the temperature section to be corrected, it becomes easy to fit the correction formula in each temperature section to the actual temperature characteristic curve of the pressure sensor 11. Therefore, it is possible to minimize deterioration of correction accuracy due to approximation.

  The configuration of the pressure sensor unit 1 shown in FIG. 1 is merely an example. For example, some or all of the components of the correction processing unit 13-i may be shared by each temperature section. For example, the storage area (address) of one storage unit 133 may be divided according to the function gi to store each coefficient.

  In addition, the multiplexing unit 131, the ADC 132, and the correction calculation unit 134 are also shared by each temperature section, and the correction formula gi used in the correction calculation unit 134 is selectively switched according to the output signal of the temperature sensor 12 and the setting information. Also good. In this case, the correction calculation unit 134 may perform switching determination, or a separate control unit may be provided to give a switching instruction from the control unit to the correction calculation unit 134. By using the correction processing unit 13-i in common, the scale and power consumption of the pressure sensor unit 1 can be reduced.

  In the above-described embodiment, the case where the physical quantity to be detected is a fluid pressure has been described. However, the above-described embodiment may be applied to a physical quantity having other temperature characteristics such as humidity and having temperature characteristics.

  DESCRIPTION OF SYMBOLS 1 ... Pressure sensor unit, 11 ... Pressure sensor (physical quantity detection element), 12 ... Temperature sensor (temperature detection element), 13-1, 13-2 ... Correction processing part, 14 ... Selector, 131 ... Multiplexing part (MUX), 132 ... Analog-to-digital converter (ADC), 133 ... Storage unit, 134 ... Correction calculation unit, 134a ... Temperature correction unit, 134b ... Pressure correction unit

Claims (3)

A physical quantity detecting element for detecting a predetermined physical quantity having temperature characteristics;
A memory for storing data relating to a correction equation of a second or higher order for obtaining a correction value of a physical quantity detection value by the physical quantity detection element in the partial temperature section for each of a plurality of partial temperature sections selected from a predetermined temperature range And
A correction processing unit that obtains a correction value in the partial temperature section based on the data of the correction formula corresponding to any of the partial temperature sections, and corrects the physical quantity detection value by the correction value;
A physical quantity sensor. A temperature detection element for detecting the temperature of the physical quantity detection element;
The correction processing unit
Based on the data related to the correction formula corresponding to each of the first partial temperature section in which the temperature detection value by the temperature detection element is included and the second partial temperature section in which the temperature detection value is not included, A correction calculation unit for obtaining the correction value in each of the first and second partial temperature sections;
A selection output unit that selectively outputs the physical quantity detection value given a correction value corresponding to the first partial temperature section in which the temperature detection value is included;
The physical quantity sensor according to claim 1, comprising:   3. The physical quantity sensor according to claim 1, wherein each of the correction formulas corresponding to the partial temperature section is a correction formula for obtaining a correction value with higher accuracy than the other for the median value of the partial temperature section. .

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