Device and method for calibrating measured values

Abstract

An apparatus is shown having an input terminal, an analog-to-digital converter (ADC), and a processor. The input terminal is configured to read in an analog signal, the ADC is configured to convert the analog signal into a digital value, and the processor is configured to determine a measured value of the digital value. Furthermore, the processor is configured to derive a calibrated digital value from the digital value using a linear calibration function, and to derive a measured value of the digital value from the calibrated digital value using a non-linear measurement function. In response to the calibration signal, the processor modifies the linear calibration function based on an algorithm and a predetermined number of comparative measurements, the algorithm being based on the non-linear measurement function.

Description

Technical Field

[0001] This invention relates to apparatus and methods for calibrating measured values. More particularly, it relates to apparatus and methods for calibrating measured values ​​in the field. Background Technology

[0002] On the production side, the measurement converter can be calibrated to a specific range of measurement values ​​and / or specific measurement values. For example, a linear calibration function can be predetermined on the production side, which assigns calibration values ​​to the original values. If events occurring in the field deviate from the predictions made for the calibration performed on the production side, or from the environment in which the calibration is applied on the production side, then adapting the calibration on the user side in the field to the events that occur may be necessary or advantageous. Summary of the Invention

[0003] The first device according to the invention includes an input terminal, an analog-to-digital converter (ADU), and a processor. The input terminal is configured to read in an analog signal, the ADU is configured to convert the analog signal into a digital value, and the processor is configured to determine a measured value of the digital value. The processor is designed to derive a calibrated digital value from the digital value using a linear calibration function, and to derive the measured value of the digital value from the calibrated digital value using a nonlinear measurement function. Furthermore, the processor is designed to change the linear calibration function based on an algorithm and a predetermined number of comparative measurements as a response to a calibration signal, the algorithm being based on the nonlinear measurement function.

[0004] As used herein, the concept of "device" in this specification and claims refers particularly to an input / output module, i.e., an I / O module. Within the scope of this specification, the concept of "I / O module" specifically refers to a module that can be serially connected to a front-end, or is already serially connected to a front-end, which connects one or more field devices (e.g., sensors and / or actuators) to the front-end and, if necessary (through the front-end), to a higher-level controller. Furthermore, as used within the scope of this specification and claims, the concept of "front-end" refers to a component of a modular fieldbus node whose task is to make data and / or services of the I / O modules serially connected to the front-end available via a fieldbus connected to the front-end.

[0005] Furthermore, the concept of "input terminal" as used in the specification and claims specifically refers to an electrical connection through which electrical signals (e.g., voltage and / or current values) can be read (and thus further processed in the device). Additionally, the concept of "analog-to-digital converter" as used in the specification and claims specifically refers to a circuit that determines which of a number of value ranges an analog value falls into and outputs a digital value corresponding to that range. This digital value may, for example, be output as a bit string.

[0006] Furthermore, the concept of "processor" as used in the specification and claims specifically refers to a circuit configured to process instructions from an instruction set allocated to the processor, wherein the order of the instructions (and, if necessary, variables allocated to the instructions) is predetermined by an algorithm executed by the processor. Additionally, the concept of "non-linear measurement function" as used in the specification and claims specifically refers to a non-linear allocation rule (e.g., a calculation rule) by means of which a measured value can be assigned to a digital value. The measured value can, for example, be quantitatively reported through a physical parameter, such as the temperature at a specific location. The measured value can, for example, be a numerical value provided digitally by the processor.

[0007] Furthermore, the concept of "calibration signal" as used in the specification and claims refers in particular to a signal that can be manually triggered, for example by pressing a button on the housing of the device, or can be received via a data interface, and that the signal initiates a calibration procedure.

[0008] The comparison measurement may include two analog signals corresponding to known measurement values.

[0009] For example, a temperature sensor can be connected to the input terminal and subjected to two known temperatures (in succession) to determine the measurement value to be generated (within the measurement accuracy range), and the linear calibration function can be used to reduce or compensate for deviations.

[0010] The changes include repeatedly adjusting the calibration function.

[0011] For example, in the shrinking step, the parameters of the calibration function can be adjusted until the generated measurement value is fully consistent with the generated physical value.

[0012] The iterative adjustment can be interrupted if the preset number of steps is reached, or if the deviation between the known measurements and the measurements calculated using the adjusted calibration function meets a specific standard, or if an interruption request is received.

[0013] For example, the repeated adjustments can be interrupted when the deviation falls below the measurement accuracy limit of the sensor.

[0014] The processor can be designed to change the linear calibration function by determining a first value in a first process and a second value in a second process, multiplying the first value by the value assigned to the analog signal, adding the second value to the product of the value and the first value, or subtracting the second value from the product.

[0015] It should be noted that the ordinal numbers such as "first" and "second" used in the specification and claims do not indicate a temporal order, but are merely used to distinguish features.

[0016] For example, the second value can be determined first in the second process, and then the first value can be determined in the first process.

[0017] The processor may further be designed to determine the value by multiplying the numerical value by a third value and by adding or subtracting a fourth value.

[0018] The linear calibration function can therefore be implemented using two consecutively connected functions. For example, the first function can be predetermined on the production side and calibrates the signal path from the input (i.e., the measurement converter), while the second function calibrates the signal path up to the input and is adjustable in the field.

[0019] For example, the sensor may be a resistance temperature sensor or a thermistor, and for the resistance temperature sensor or thermistor, calibration of the signal path to the input terminal may be necessary.

[0020] The second device according to the invention has an input circuit for a sensor, particularly a temperature sensor, and also includes an ADU, a first function block, a second function block, a third function block, a fourth function block, and a correction function block. The input circuit is used to output an analog voltage. The ADU is used to input an analog voltage and output a digital value. The first function block is used to perform a first calibration of the digital value related to the ADU based on a first calibration function to output a first calibration value. The second function block is used to perform an application-related second calibration of the first calibration value based on a second calibration function to output a second calibration value. The third function block is used to input the second calibration value and output a physical value of the sensor based on the second calibration value. The fourth function block is used to compare the physical value of the sensor with a predetermined nominal value and output a comparison result. The correction function block is used to change the application-related second calibration function based on the comparison result.

[0021] The function block can be implemented using specific hardware, software, or a combination of specific hardware and software. For example, the function block can be implemented using one or more signal processors.

[0022] According to the invention, a method for configuring an electronic measurement component located in the field downstream of a sensor, the electronic measurement component derives a calibration value from a sensor signal by means of a linear calibration function, and derives a measurement value from the calibration value by means of a nonlinear measurement function, the method comprising changing the linear calibration function based on a first sensor signal value and a second sensor signal value, the first sensor signal value and the second sensor signal value corresponding to a known measurement value.

[0023] The change may include repeatedly adjusting the calibration function, either when a preset number of steps has been reached, or when the deviation between the known measurements and the measurements calculated with the adjusted calibration function applied meets a specific criterion, or when the repeated adjustments are interrupted upon receiving a request to interrupt.

[0024] The change may include determining a first value, and may include determining a second value, multiplying the first value by a value assigned to the second sensor signal value, adding the second value to the product of the value and the first value, or subtracting the second value from the product.

[0025] The value can be determined by multiplying the third value determined by the second sensor signal value with the fourth value and by adding or subtracting the fifth value.

[0026] The first sensor signal value can be zero or correspond to the sensor’s minimum absolute output value.

[0027] For example, the sensor signal value can be selected such that the value becomes zero, or the absolute value of the value becomes the minimum.

[0028] It goes without saying that the features described in relation to the device can also be features of the method, and vice versa. Attached Figure Description

[0029] The present invention will now be described in detail with reference to embodiments, wherein the following figures are provided:

[0030] Figure 1 A block diagram of a fieldbus system is shown, which includes multiple modular fieldbus nodes;

[0031] Figure 2 A block diagram of a modular fieldbus node is shown, the fieldbus node including a front end and multiple I / O modules, and a fieldbus device connected to the I / O modules is shown;

[0032] Figure 3 A block diagram of an I / O module equipped with electronic measurement components is shown;

[0033] Figure 4a and Figure 4b The flowchart illustrates the process of adjusting the parameters of the calibration function for linearity; and

[0034] Figure 5 The process is shown for configuring an electronic measurement component (downstream of a sensor) located in the field.

[0035] Here, the same or similar components in the diagram are labeled in the same way. Detailed Implementation

[0036] Figure 1 A block diagram of a fieldbus system is shown. The fieldbus system 10 includes a higher-level control unit 20 and modular fieldbus nodes 100 interconnected via a fieldbus 30 (in signal technology). The higher-level control unit 20 can be used to both monitor and regulate devices (not shown) controlled via the fieldbus system 10. When the higher-level control unit 20 monitors the devices, it can periodically or non-periodically receive status data from the fieldbus nodes 100. This status data describes the status of the devices and generates error or alarm signals when the status of the devices deviates (substantially) from a desired / permissible state or range. When the higher-level control unit 20 (not only monitors but also regulates) the devices, it can periodically or non-periodically receive status data from the fieldbus nodes 100 and determine the control data to be transmitted to the fieldbus nodes 100, taking into account the status data.

[0037] Figure 2 A block diagram of a modular fieldbus node is shown. Fieldbus node 100 includes a front end 110 and two I / O modules 120 and 130 serially connected to the front end 110. Sensors and actuators 140, 150, 160, and 170 are signal-technically connected to I / O modules 120 and 130. During operation, the I / O modules 120 and 130 read sensor signals and generate status data from the sensor signals, which is transmitted to the front end 110 via a local bus 180. The front end 110 is capable of processing the status data locally and / or (in an improved form if necessary) forwarding the status data to a higher-level control unit 20. The higher-level control unit 20 (or the front end 110 in the case of local processing) is then capable of generating control data taking the status data into account.

[0038] Control data generated by the upper-level control unit 20 can then be transmitted via fieldbus 30 to (the same or another) front-end. The control data transmitted to front-end 110 (or generated by front-end 110) is then (in an improved form if necessary) forwarded / transmitted to I / O modules 120 and 130. I / O modules 120 and 130 receive the control data and output control signals corresponding to the control data at their output terminals connected to the actuators. Data communication between components of the fieldbus system 10, mapping of sensor signals to status data, and mapping of control data to control signals can be adapted to different usage scenarios through the configuration of fieldbus nodes 100.

[0039] Figure 3 A block diagram of an apparatus configured as an I / O module according to the present invention is shown. I / O module 130 includes input terminals 132 and 134. Sensor 150 is connected to I / O module 130 via input terminal 134. Sensor 150 may be, for example, a temperature sensor or a thermistor, such as a resistance temperature sensor. Input terminal 134 is connected to input circuitry 200. Input circuitry 200 can be designed to apply a defined voltage to sensor 150 or generate a defined current through sensor 150. Input circuitry 200 can also be designed to detect the current through sensor 150, or measure the voltage drop across sensor 150, or generate an analog voltage proportional to said current or voltage drop. I / O module 130 further includes ADU 300. ADU 300 is designed to convert analog voltages into digital values.

[0040] The digital value is mapped to a calibration value through calibration function block 400. Calibration function block 400 applies a linear calibration function k(x), i.e., a calibration function of the form k(x) = a·x + b, where x represents the numerical value corresponding to the digital value. Calibration function block 400 may include function blocks 410 and 420, wherein function block 410 applies a first linear calibration function k1 = a1·x + b1 to the numerical value, and function block 420 applies a second linear calibration function k2(k1(x)) = a2·k1(x) + b2 to the output value of function block 410, i.e., the result of the first linear calibration function.

[0041] The first linear calibration function k1(x) can be adapted to, for example, an ADU 300, so that when there is no interference on the signal path cut off at input 134, the result of the first linear calibration function (within the measurement accuracy range) no longer requires further calibration. The second linear calibration function k2(k1(x)) is set accordingly to adapt the electronic measurement components of the I / O module 130 to the signal path cut off at input 134. Alternatively, only one linear calibration function can be used, without associating the two linear calibration functions.

[0042] The calibration value is mapped to the measured value via function block 500. The measured value can correspond to a physical parameter, such as temperature. This mapping is performed using a nonlinear measurement function, such as a second-order or higher-order polynomial m(y) = d + e·y + f·y² + ... where y = k²(k₁(x)). When a² = b² = 0, the nonlinear measurement function will yield the correct measured value when there is no interference in the signal path to input terminal 134. When there is interference in the signal path to input terminal 134, the interference can be reduced or compensated by the appropriate selection of a² and b². Therefore, I / O module 130 is designed to change the linear calibration function based on an algorithm and a certain number of predetermined comparative measured values ​​as a response to the calibration signal 700, the algorithm being based on the nonlinear measurement function.

[0043] I / O module 130 may be equipped with button 136, and calibration signal 700 may be triggered by the initiator via button 136. Alternatively or additionally, I / O module 130 may also be designed such that calibration signal 700 can be triggered by the initiator when a corresponding message is received by I / O module 130 (via local bus 180). If comparison and correction function block 600 receives calibration signal 700, comparison and correction function block 600 repeatedly changes b2 and / or a2 until an interruption criterion is met, or until the initiator interrupts the process.

[0044] The comparison and correction function block 600 may include a function function block 610 and a correction function block 620. The function function block 610 may be configured to compare the measured value with a predetermined nominal value and output the comparison result. The correction function block 620 may be configured to change (application-related) the calibration function k2(k1(x)) of the second linearity based on the comparison result.

[0045] The calibration function block 400, the function function block 500, and the comparison and correction function block 600 can be implemented by means of defined hardware or by software executed on the processor 800.

[0046] Figure 4aThe diagram illustrates the process that runs twice to adjust a2 and b2, where... Figure 4b In the diagram, the first run is shown in the first row, and the second run is shown in the second row. During the first run, a first comparison value 970 is determined in step 910, and an initial value (e.g., b2 = 0) is determined for b2 in step 920. b2 is increased in step 930. The degree of increase may decrease in each subsequent step 930. For example, the degree of increase may be half that in the previous step 930 in each subsequent step 930. Furthermore, a waiting time (e.g., one second) may be provided between the loops.

[0047] If the measured value 972 is detected to be greater than the comparison value 970 in decision box 940, the previous increase is withdrawn in step 950. If the maximum number of loops is reached, the process can be interrupted in step 960. Furthermore, the process can be interrupted when the runner receives an interrupt signal. Figure 4b As shown, the comparison value 970 can be chosen such that the slope of the second linear calibration function k2(k1(x)), i.e., a2, has the smallest possible impact on the calibration of the "compensation". For example, the comparison value 970 can be chosen such that k1(x) is close to zero. Figure 4b (The first row is shown by circles). This could be, for example, a case where the sensor signal value is zero or a case corresponding to the sensor's minimum absolute output value.

[0048] During the second run, a second comparison value 980 is determined in step 910, and an initial value (e.g., a2 = 0) is determined for the "gain" a2 in step 920. a2 is increased in step 930. The degree of increase may decrease in each step 930. For example, the degree of increase may be half that in the previous step 930 in each subsequent step 930. Furthermore, a waiting time (e.g., one second) may be provided between the loops.

[0049] If the measured value 982 is detected to be greater than the comparison value 980 in decision box 940, the previous increase is withdrawn in step 950. If the maximum number of loops is reached, the process can be interrupted in step 960. Furthermore, the process can be interrupted when the initiator receives an interrupt signal. Figure 4b As shown, the comparison value 980 can be chosen such that the slope of the second linear calibration function k2(k1(x)), i.e., a2, has the largest possible influence. For example, the comparison value 980 can be chosen such that k1(x) is almost maximized. Figure 4b (The second row is shown by circles). This could be, for example, the case where the sensor signal value is at its maximum.

[0050] Figure 5The process is illustrated for configuring an electronic measurement component located in the field downstream of the sensor 150. The method includes step 1000 of changing the linear calibration function k2(k1(x)) based on two sensor signal values ​​corresponding to measured values ​​972 and 982.

[0051] List of reference numerals

[0052] 10 Fieldbus System

[0053] 20 Control Units

[0054] 30 Fieldbus

[0055] 100 Fieldbus Nodes

[0056] 110 Front-end / Fieldbus Coupler

[0057] 120 I / O modules

[0058] 130 I / O modules

[0059] 132 input terminal

[0060] 134 Input Terminal

[0061] 140 Field Equipment

[0062] 150 Field Equipment

[0063] 160 Field Equipment

[0064] 170 Field Equipment

[0065] 180 Local Bus

[0066] 200 Input Circuit

[0067] 300 Analog-to-Digital Converter

[0068] 400 Calibration Function Block

[0069] 410 Function Block

[0070] 420 Function Block

[0071] 500 Function Blocks

[0072] 600 Comparison and Correction Function Blocks

[0073] 610 Function Block

[0074] 620 Correction function block

[0075] 700 calibration signal

[0076] 800 processor

[0077] 910 steps

[0078] 920 steps

[0079] 930 steps

[0080] 940 judgment

[0081] 950 steps

[0082] 960 judgment

[0083] 970 comparison value

[0084] 972 Measured values

[0085] 980 comparison value

[0086] 982 Measured Value

[0087] 1000 steps

Claims

1. An apparatus (130) for calibrating measured values, comprising: The input terminal (134) is configured to read in analog signals; Analog-to-digital converter (300), configured to convert analog signals into digital values; and Processor (800), whose settings are used to determine the measured value of the digital; The processor (800) is designed to derive a calibrated digital value from the digital value using a linear calibration function (k(x)); and The processor (800) is designed to derive the measured value of the digital value from the calibrated digital value by means of a nonlinear measurement function (m(y)); Its features are, The processor (800) is designed to change the linear calibration function (k(x)) based on an algorithm and a certain number of predetermined comparison measurements as a response to the calibration signal, the algorithm being based on the nonlinear measurement function (m(y)).

2. The apparatus (130) according to claim 1, wherein, The comparison measurements include two analog signals corresponding to known measurements.

3. The apparatus (130) according to claim 2, wherein, The changes include repeatedly adjusting the calibration function (k(x)).

4. The apparatus (130) according to claim 3, wherein, The iterative adjustments shall be interrupted in the following circumstances: The preset number of steps has been reached, or the deviation between the known measurements and the measurements calculated using the adjusted calibration function (k(x)) meets a specific standard; or An interrupt request has been received.

5. The apparatus (130) according to claim 4, wherein, The processor (800) is designed to change the linear calibration function (k(x)) by determining a first value in a first process and a second value in a second process, multiplying the value assigned to the analog signal by the first value, adding the second value to the product of the value and the first value, or subtracting the second value from the product.

6. The apparatus (130) according to claim 5, wherein, The processor (800) is further designed to determine the numerical value by multiplying the numerical value (x) by a third value and by adding or subtracting a fourth value.

7. A device (130) for calibrating measured values, having The input circuit (200) for the sensor (150) is used to output an analog voltage. An analog-to-digital converter, or ADU (300), is used to input analog voltages and output digital values ​​(x). A first function block (410) is configured to perform a first calibration on the digital value (x) relative to the ADU (300) based on a first calibration function (k1(x)) to output a first calibration value. The second function block (420) applies a related second calibration to the first calibration value based on the second calibration function (k2(y)) to output the second calibration value. A third function block (500) is configured to take the second calibration value as input and output the physical value of the sensor (150) based on the second calibration value. The fourth function block (610) compares the physical values ​​of the sensor (150) with predetermined nominal values ​​and outputs the comparison result. The correction function block (620) is used to change the application-related second calibration function (k2(y)) based on the comparison result.

8. The apparatus according to claim 7, wherein, The sensor (150) is a temperature sensor.

9. A method for configuring an electronic measuring component located in the field downstream of a sensor (150), the electronic measuring component deriving a calibration value from a sensor signal by means of a linear calibration function (k(x)) and deriving a measured value from the calibration value by means of a nonlinear measurement function (m(y)), the method comprising: Based on the linear calibration function (k(x)) of the change in the first sensor signal value and the second sensor signal value (1000), the first sensor signal value and the second sensor signal value correspond to the known measured value.

10. The method according to claim 9, wherein, The change includes repeatedly adjusting the calibration function (k(x)), interrupting the repeated adjustments in the following situations: The preset number of steps has been reached, or the deviation between each known measurement and the measurement calculated using the adjusted calibration function (k(x)) meets a specific standard; or An interrupt request has been received.

11. The method according to claim 9 or 10, wherein, The change includes determining a first value and determining a second value, multiplying the first value by a value assigned to the second sensor signal value, adding the second value to the product of the value and the first value, or subtracting the second value from the product.

12. The method according to claim 11, wherein, The value is determined by multiplying a third value, which is determined from the second sensor signal value, with a fourth value and by adding or subtracting a fifth value.

13. The method according to claim 12, wherein, The first sensor signal value is zero or corresponds to the minimum absolute output value of the sensor (150).

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