Method, measuring arrangement and computer program product for controlling a valve

Abstract

The invention relates to a method for controlling a valve (1) which is arranged in a line (6) for conducting a gas, in particular a gas mixture, comprising the method steps of: - determining a current measured value of a gas property of the conducted gas, in particular a measured density value, preferably by means of a density sensor (2); - determining a current measured flow rate value by means of a flow rate sensor (3); - determining at least one control parameter of a controller (4), in particular a continuous linear controller (4), depending on the current measured value, in particular the measured density value, by means of a measuring and operating circuit (5); - generating an operating signal for operating the valve (1) for a set target flow rate value taking into consideration the at least one control parameter and the current measured flow rate value by means of the controller (4); and - operating the valve (1) by means of the operating signal.

Description

[0001] Method, measuring arrangement and computer program product for controlling a valve

[0002] The invention relates to a method for controlling a valve which is arranged in a line for carrying a gas, in particular a gas mixture, a measuring arrangement for controlling a flow of a gas, in particular a gas mixture, in a line and a computer program product for controlling a valve.

[0003] Common mass flow meters, such as thermal flow meters, and mass flow controllers must be calibrated to the medium being monitored in order to measure accurately. Gas mixtures can also only be measured if the composition of the mixture is known, if it does not change, and if the mass flow meter and mass flow controller have been calibrated accordingly. However, this is not always the case. Furthermore, precisely because of these requirements, commissioning and use by laypersons is impossible.

[0004] The invention is based on the object of remedying the problem.

[0005] The object is achieved by the method according to claim 1, the measuring arrangement according to claim 9 and the computer program product according to claim 14.

[0006] The method according to the invention for controlling a valve which is arranged in a line for carrying a gas, in particular a gas mixture, comprises the method steps:

[0007] - Determining a current measured value of a gas property of the guided gas, in particular a density measured value, preferably by means of a density sensor;

[0008] - Determining a current flow measurement value using a flow sensor;

[0009] - Determining at least one control parameter of a controller, in particular a continuously linear controller, as a function of the current measured value, in particular the density measured value, by means of a measuring and operating circuit;

[0010] - generating an operating signal for operating the valve for a set target flow value, taking into account the at least one control parameter and the current flow measurement value by means of the controller; and

[0011] - Operating the valve using the operating signal.

[0012] This solution has the advantage that precise control of the valve is possible even with gas mixtures and even when the user does not know the exact gas properties. Furthermore, the method according to the invention also reacts automatically to changes in the gas properties, such as a change in gas composition or a change in density, without the need for manual parameter adjustment. Advantageous embodiments of the invention are the subject of the dependent claims.

[0013] One embodiment provides that the at least one control parameter comprises a first control parameter, wherein the first control parameter is a zero point offset Koff of the operating signal.

[0014] The valve only opens at a certain valve current or coil current, and closes at a certain valve current or coil current. Therefore, a zero point offset is provided, which shifts the zero point of the manipulated variable in percent by a defined number of percentage points (relative to the maximum coil current). This improves the time it takes for the valve to rise from approximately 0 sccm to the desired flow rate, since the controller does not first have to adjust the current from 0 mA to the actual zero point of the valve.

[0015] From measurements with various gases, it can be determined that the controller parameters and the zero point offset Koff are gas-dependent. After manually adjusting the parameters for the various gases, it can be determined that the parameters are proportional to the density of the gases. This allows a multiplication factor (the slope) and a zero crossing of the Y-axis to be calculated, which, based on the density of the current gas, can be used to calculate at least one control parameter for the offset. This means that any gas or binary gas mixture within the density range of the previously measured gases can be controlled without having to manually adjust any parameters.

[0016] One embodiment provides that the first control parameter is determined from a provided first linear function.

[0017] One embodiment provides that the controller comprises a P-element and an I-element, wherein the at least one control parameter comprises a second and a third control parameter, wherein the second control parameter is a controlled variable Kp of the P-element, wherein the third control parameter is a controlled variable Ki of the I-element.

[0018] It has proven advantageous to select the second control parameter of the P-element and the third control parameter of the I-element, in addition to or alternatively to the first control parameter, depending on the currently measured gas property, in particular the gas density, rather than fixed during commissioning. This prevents over-regulation of the valve due to changing gases or incorrectly specified mixing ratios. One embodiment provides that the second control parameter is determined from a provided second linear function, and / or wherein the third control parameter is determined from a provided third linear function.

[0019] One embodiment provides that the controller further comprises a D-element, wherein the at least one control parameter comprises a fourth control parameter, wherein the fourth control parameter is a controlled variable Kd of the D-element.

[0020] It has been found that a controller without a D element tends to settle rather slowly, especially at low reference variables. To improve the settling time and achieve faster adjustment of the setpoint, it is advantageous to implement a PID controller instead of a PI controller.

[0021] One embodiment provides that the fourth control parameter is determined from a provided fourth linear function.

[0022] One embodiment provides that the first, second, third and / or fourth linear function is determined for a fixed pressure.

[0023] A measuring arrangement according to the invention for regulating a flow of a gas, in particular a gas mixture, in a line comprises:

[0024] - a valve to regulate the flow;

[0025] - a sensor for determining a current measured value of a gas property, in particular a density sensor for determining a current measured value of the gas density;

[0026] - a flow sensor for determining a current flow measurement value;

[0027] - a measuring and operating circuit for operating the valve by means of an operating signal, wherein the measuring and operating circuit comprises a controller, in particular a continuously linear controller, wherein the controller is configured to generate the operating signal for a set target flow value as a function of the current flow measured value and at least one control parameter, wherein the measuring and operating circuit is configured to determine the at least one control parameter as a function of the current measured value, in particular the current density measured value. One embodiment provides that the at least one control parameter comprises a first control parameter, wherein the first control parameter is a zero point offset Koff of the operating signal, wherein the measuring and operating circuit is configured to determine the first control parameter as a function of the current measured value, in particular the density measured value.

[0028] One embodiment provides that the controller comprises a P-element and an I-element, wherein the at least one control parameter comprises a second and a third control parameter, wherein the second control parameter is a controlled variable Kp of the P-element, wherein the third control parameter is a controlled variable Ki of the I-element, wherein the measuring and operating circuit is set up to determine the second and third control parameters as a function of the current density measurement value.

[0029] One embodiment provides that the controller further comprises a D-element, wherein the at least one control parameter comprises a fourth control parameter, wherein the fourth control parameter is a controlled variable Kd of the D-element, wherein the measuring and operating circuit is configured to determine the fourth control parameter as a function of the current density measurement value.

[0030] One embodiment provides that the first control parameter is determined from a provided first linear function, and / or wherein the second control parameter is determined from a provided second linear function, and / or wherein the third control parameter is determined from a provided third linear function, and / or wherein the fourth control parameter is determined from a provided fourth linear function.

[0031] A computer program product according to the invention for controlling a valve, configured to carry out the following method steps when executed on a computer: - receiving a current measured value of a gas property, in particular a current density measured value, preferably determined by means of a density sensor;

[0032] - Receiving a current flow measurement value, in particular determined by means of a flow sensor;

[0033] - Determining at least one control parameter depending on the current measured value, in particular the current density measured value;

[0034] - generating an operating signal for operating the valve for a set target flow value, taking into account at least one control parameter and the current flow measurement value; and

[0035] - Providing the operating signal.

[0036] One embodiment provides that the at least one control parameter comprises a first control parameter, wherein the first control parameter is a zero point offset Koff of the operating signal.

[0037] One embodiment provides that the at least one control parameter comprises a second and a third control parameter, wherein the second control parameter is a controlled variable Kp which comprises a proportional part of the control, wherein the third control parameter is a controlled variable Ki which comprises an integral part of the control.

[0038] One embodiment provides that the at least one control parameter comprises a fourth control parameter, wherein the fourth control parameter is a controlled variable Kd which comprises a differential component of the control.

[0039] One embodiment provides that the first control parameter is determined from a provided first linear function, and / or wherein the second control parameter is determined from a provided second linear function, and / or wherein the third control parameter is determined from a provided third linear function, and / or wherein the fourth control parameter is determined from a provided fourth linear function.

[0040] The invention is explained in more detail with reference to the following figures. They show:

[0041] Fig. 1 : a perspective view of an embodiment of the measuring arrangement according to the invention;

[0042] Fig. 2 : a flow chart of an embodiment of the method according to the invention;

[0043] Fig. 3 : a graph showing the density dependence of the zero point offset (in %) of the coil current; and

[0044] Fig. 4 : a graph showing the density dependence of the control parameters of the coil current.

[0045] Fig. 1 shows a perspective view of an embodiment of the measuring arrangement according to the invention. The measuring arrangement is designed to regulate the flow of a gas, in particular a gas mixture, in a line 6. The line 6 can be, for example, a hose or a pipe.

[0046] In order to regulate the gas flow, the measuring arrangement comprises a valve 1 for regulating the flow. The valve 1 is designed to shut off the flow of gas through line 6 or to control it according to a reference variable. The valve 1 can be a proportional solenoid valve. Proportional valves enable sensitive flow control compared to shut-off valves, which can only be fully opened or closed. The opening rate is controlled proportionally to the current strength, whereby a higher current strength leads to a higher flow rate. These valve types are based on electromagnetic switching valves in which a spring presses the lifting armature onto the valve seat and thus keeps the valve closed when de-energized (normally closed). A seal at the base of the valve ensures that no medium escapes.The current flow through the coil creates a magnetic field that lifts the plunger and opens the valve. By varying the switching solenoid valves, a balance between spring and magnetic force can be achieved for any desired flow rate. Specifically, valve 1 can be a plunger valve. The flow rate can be a flow-velocity-dependent measured variable—such as flow velocity, volume flow, or mass flow. Valve 1 is connected to line 6.

[0047] Another component required to control the flow is a flow sensor 3 for determining a current flow measurement. Using the current flow measurement, a comparison can be made with the reference variable – in this case, the target flow value – in order to control valve 1 in the event of a deviation so that a future flow measurement is closer to the value of the reference variable. The flow sensor has two connections via which it is connected to line 6. The flow sensor 3 can be a thermal flow meter. This works according to the calorimetric principle and can therefore detect not only the flow velocity but also the flow direction.

[0048] According to the invention, the measuring arrangement has a further component that is necessary for regulating the flow. This is a sensor for determining a current measured value of a gas property. The gas property can be the thermal conductivity, viscosity, pressure, temperature, or density of the gas. The sensor is, in particular, a density sensor 2 for determining a current measured value of the gas density. Like the flow sensor, the density sensor 2 can also have two connections and be integrated into the line 6. Alternatively, the density sensor 2 can also be arranged in a lateral opening in the outer surface of the line 6.

[0049] The sensor for determining the current measured value of the gas property of the gas around a density sensor 2 can be arranged together with the flow sensor 3 in a common housing 8. An example of this is taught by DE 202022107233 U1, which teaches a density sensor in combination with a flow sensor. Reference is made in full to DE 202022107233 U1. The flow sensor disclosed therein is a thermal flow meter. Thermal flow meters are usually calibrated to a specific gas, since the determined measured value is influenced by the thermal conductivity and heat capacity of the gas. Thus, a specially calibrated thermal flow meter is required for each gas, or the manufacturer stores special correction factors for different gases in the thermal flow meter. Consequently, the thermal flow meter must always first be informed which gas is currently being measured.However, if the gas composition changes during a measurement, existing thermal flowmeters are unable to accurately determine the flow. The density sensor taught in DE 202022107233 U1 comprises an oscillator (e.g., a quartz tuning fork or a cantilever beam oscillator) and is designed as a MEMS sensor element. However, the density sensor does not have to be integrated into line 6. Alternatively, the density sensor can also be connected to a gas tank from which the gas is fed into line 6.

[0050] In addition, a measuring and operating circuit 5 for operating the valve 1 by means of an operating signal (e.g. a current or voltage signal or a digital signal) with a microcontroller is provided. The measuring and operating circuit 5 can be arranged near, on or in the flow sensor, sensor, in particular density sensor 2, valve 1 or remote from the sensors and the valve. In addition, the measuring and operating circuit 5 is in communication with the valve 1, the flow sensor and the sensor, in particular the density sensor. Furthermore, the measuring and operating circuit 5 has a controller 4, in particular a continuously linear controller. The controller 4 can be, for example, a PI controller with a P-element and an I-element or a PID controller with a P-element, I-element and D-element.The PID controller is a widely used control algorithm that combines proportional, integral, and derivative control measures to enable fast, accurate, and stable control of a process variable. The proportional part adjusts the control output based on the current deviation between the desired setpoint and the measured flow rate. The derivative part increases or decreases the control value based on the change in the control deviation to improve the settling time, and the integral part accumulates the deviation over time to reduce the deviation. The controller is designed to generate the operating signal for a set target flow value (= setpoint) depending on the current flow measurement and at least one control parameter.The measuring and operating circuit 5 is also designed to determine the at least one control parameter as a function of the current measured value, in particular the current density measured value.

[0051] The at least one control parameter can comprise a first control parameter, which is a zero-point offset Koff of the operating signal. The zero-point offset Koff is the minimum value of the operating signal that must be set for valve 1 to open. When using a lifting armature valve, the operating signal can be a coil current, and the zero-point offset Koff can be the minimum coil current that must be applied to raise the lifting armature and thus allow the gas to pass through. The zero-point offset Koff can describe an absolute current or a relative current (e.g., to the maximum possible coil current). The measuring and operating circuit 5 is configured to determine the first control parameter as a function of the current measured value, in particular the density measured value. The zero-point offset Koff is therefore dependent on the density of the gas.The coil current required to open Valve 1 decreases with increasing gas density. This can be explained by the fact that the denser gas displaces the armature of Valve 1 more strongly and thus provides more support than the less dense gas. Therefore, with denser gas, a lower minimum coil current is required to displace the valve's armature.

[0052] The at least one control parameter may furthermore or alternatively comprise a second and a third control parameter. If the controller is at least a PI controller, the second control parameter may be a controlled variable Kp of the P-element, and the third control parameter may be a controlled variable Ki of the I-element. Both control parameters are dependent on the density of the gas. Therefore, the measuring and operating circuit 5 can be configured to determine the second and third control parameters depending on the current measured density value.

[0053] The at least one control parameter can further comprise a fourth control parameter. In this context, controller 4 can be a PID controller with a D-element, and the fourth control parameter can be a controlled variable Kd of the D-element. The fourth control parameter set for optimal control of the valve also depends on the current measured density value of the gas. Therefore, the measuring and operating circuit 5 is configured to determine the fourth control parameter depending on the current measured density value.

[0054] The at least one control parameter, in particular the four control parameters, can always be stored in connection with a density measurement value in a look-up table in the measuring and operating circuit 5. The at least one control parameter, in particular the four control parameters, can each be determined from a provided polynomial function, in particular from a provided third, second, or first degree polynomial function.

[0055] Alternatively, the first control parameter can be determined from a provided first linear function. Furthermore, the second control parameter can be determined from a provided second linear function. Furthermore, the third control parameter can be determined from a provided third linear function. Furthermore, the fourth control parameter can be determined from a provided fourth linear function. The four linear functions differ from one another. The individual linear functions each have a gradient and can each have an offset. The linear functions can each be stored as an equation in an electronic memory in the measuring and operating circuit 5.

[0056] Fig. 2 shows a flow diagram of an embodiment of the method according to the invention for regulating a valve arranged in a line for conveying a gas, in particular a gas mixture. The embodiment comprises the following five method steps, which can be carried out using the measuring arrangement shown in Fig. 1. The order of the five method steps may differ from the order used.

[0057] I. Determining a current measured value of a gas property of the guided gas, in particular a density measured value or a density-dependent measured variable, preferably using a density sensor. The gas property can be the thermal conductivity, viscosity, pressure, temperature, or density of the gas. The determined current measured value is provided to a measuring and operating circuit and serves as the basis for determining at least one control parameter. Determining means measuring using a sensor.

[0058] II. Determining a current flow measurement using a flow sensor. The flow sensor can be, for example, a thermal flowmeter, a magnetic-inductive flowmeter, an ultrasonic flowmeter, a vortex flowmeter, or a Coriolis flowmeter. Alternatively, a mechanical-volumetric flowmeter can be used to determine the current flow measurement.

[0059] III. Determining at least one control parameter of a controller, in particular a continuously linear controller, as a function of the current measured value, in particular the measured density value, by means of a measuring and operating circuit. The at least one control parameter can be a zero point offset Koff (= first control parameter) of the operating signal. Alternatively or additionally, the at least one control parameter comprises a second and a third control parameter, wherein the second control parameter is a controlled variable Kp of the P-element and the third control parameter is a controlled variable Ki of the I-element. The P-element multiplies the control deviation by its controlled variable Kp and outputs this value. The I-element sums or integrates the control deviation over time and multiplies the sum or integral by the controlled variable Ki.Alternatively or additionally, the at least one control parameter comprises a fourth control parameter, wherein the fourth control parameter is a controlled variable Kd of the D-element. The D-element adds the output of the P-element to a D component resulting from the change in the control deviation. The change in the control deviation (difference or time derivative) is multiplied by the controlled variable Kd, and the calculated value is added to the output of the P-element. All four control parameters are determined from a provided first linear function, which was previously determined in an adjustment process.

[0060] IV. Generating an operating signal for operating the valve for a set target flow value, taking into account the at least one control parameter and the current flow measurement value by means of the controller; and

[0061] V. Operating the valve using the operating signal.

[0062] Fig. 3 shows a graph showing the density dependence of the zero point offset of the minimum coil current (in % of the maximum coil current) for a density measurement value between 0.15 and 2 kg / m 3 Fig. 4 shows a graph illustrating the density dependence of the coil current control parameters for a density measurement value between 0.15 and 2 kg / m 3All measurements were carried out under the same conditions. To determine the control parameters, the valve was flooded with helium (He), air, nitrogen (N2), argon (Ar), and carbon dioxide (CO2) at a pressure of 4 bar. To determine the zero point offset (see Fig. 3), the minimum coil current required to open or close the valve was determined for each of the different gases. It can be seen that the measured data can be described with a straight line with a negative slope. To determine the density-dependent controlled variables, the value of the controlled variable Kp was varied, while the other controlled variables were set to zero. The Kp values ​​of the controller for the different gases were determined through iterative tests. With these values, the controller has a good settling time with no or very little overshoot.In order to reduce the remaining error, the values ​​of the controlled variable Ki and the controlled variable Kd were adjusted next. It turns out that there is a linear relationship between the controlled variables and the density. This relationship can be described by a straight line with a constant slope (multiplication factor) and an offset (Y-axis shift). The dependence of the controlled variable on the density can be explained by the fact that the denser the gas, the heavier it is, which makes the valve sluggish. With the zero point offset Koff, the zero point, i.e. the coil current needed to keep the valve closed, is lower when the gas density is higher. This could in turn be because a heavier gas presses the valve open more firmly when closed than a lighter gas.Using the determined and stored multiplication factor and Y-axis shift of the line, the controlled variables can be automatically adjusted to the current gas properties. The measurement results shown were all determined at the same pressure. To determine the ideal controlled variables, the current pressure in the line can also be taken into account. For this purpose, an additional sensor, namely a pressure sensor, can preferably be installed in the line. This sensor communicates with the measuring and operating circuit and is configured to provide a current measured value of the pressure in the line. The measuring and operating circuit can be configured accordingly to determine the controlled variables as a function of the density and pressure.

Claims

PATENT CLAIMS 1 . Method for controlling a valve (1) which is arranged in a line (6) for carrying a gas, in particular a gas mixture, comprising the method steps: - determining a current measured value of a gas property of the guided gas, in particular a density measured value, preferably by means of a density sensor (2); - Determining a current flow measurement value by means of a flow sensor (3); - determining at least one control parameter of a controller (4), in particular a continuously linear controller (4), as a function of the current measured value, in particular the density measured value, by means of a measuring and operating circuit (5); - generating an operating signal for operating the valve (1) for a set target flow value, taking into account the at least one control parameter and the current flow measurement value by means of the controller (4); and - Operating the valve (1) using the operating signal.

2. The method according to claim 1, wherein the at least one control parameter comprises a first control parameter, the first control parameter being a zero point offset Koff of the operating signal.

3. The method according to claim 2, wherein the first control parameter is determined from a provided first linear function.

4. Method according to one of claims 1 to 3, wherein the controller comprises a P-element and an I-element, wherein the at least one control parameter comprises a second and a third control parameter, where the second control parameter is a controlled variable Kp of the P-element, where the third control parameter is a controlled variable Ki of the I-element.

5. The method according to claim 4, wherein the second control parameter is determined from a provided second linear function, and / or wherein the third control parameter is determined from a provided third linear function.

6. The method according to claim 4 or 5, wherein the controller further comprises a D-element, wherein the at least one control parameter comprises a fourth control parameter, wherein the fourth control parameter is a controlled variable Kd of the D-element.

7. The method according to claim 6, wherein the fourth control parameter is determined from a provided fourth linear function.

8. The method according to any one of claims 2 to 7, wherein the first, second, third and / or fourth linear function is determined for a fixed pressure.

9. Measuring arrangement for regulating a flow of a gas, in particular a gas mixture, in a line, comprising: - a valve (1) for regulating the flow; - a sensor for determining a current measured value of a gas property, in particular a density sensor (2) for determining a current measured density value of the gas; - a flow sensor (3) for determining a current flow measurement value; - a measuring and operating circuit (5) for operating the valve (1) by means of an operating signal, wherein the measuring and operating circuit (5) comprises a controller (4), in particular a continuously linear controller, wherein the controller (4) is designed to generate the operating signal for a set target flow value as a function of the current flow measured value and at least one control parameter, wherein the measuring and operating circuit (5) is designed to determine the at least one control parameter as a function of the current measured value, in particular the current density measured value.

10. Measuring arrangement according to claim 9, wherein the at least one control parameter comprises a first control parameter, wherein the first control parameter is a zero point offset Koff of the operating signal, wherein the measuring and operating circuit (5) is configured to determine the first control parameter as a function of the current measured value, in particular the density measured value.

11. Measuring arrangement according to claim 9 or 10, wherein the controller (4) comprises a P-element and an I-element, wherein the at least one control parameter comprises a second and a third control parameter, wherein the second control parameter is a controlled variable Kp of the P-element, wherein the third control parameter is a controlled variable Ki of the I-element, wherein the measuring and operating circuit (5) is set up to determine the second and third control parameters as a function of the current density measurement value.

12. Measuring arrangement according to claim 11, wherein the controller further comprises a D-element, wherein the at least one control parameter comprises a fourth control parameter, wherein the fourth control parameter is a controlled variable Kd of the D-element, wherein the measuring and operating circuit (5) is set up to determine the fourth control parameter as a function of the current density measurement value.

13. Measuring arrangement according to at least one of claims 10 to 12, wherein the first control parameter is determined from a provided first linear function, and / or wherein the second control parameter is determined from a provided second linear function, and / or wherein the third control parameter is determined from a provided third linear function, and / or wherein the fourth control parameter is determined from a provided fourth linear function.

14. Computer program product for controlling a valve (1), arranged to carry out the following method steps when executed on a computer: - receiving a current measured value of a gas property, in particular a current density measured value, preferably determined by means of a density sensor (2); - receiving a current flow measurement value, in particular determined by means of a flow sensor (3); - Determining at least one control parameter depending on the current measured value, in particular the current density measured value; - generating an operating signal for operating the valve (1) for a set target flow value, taking into account the at least one control parameter and the current flow measurement value; and - Providing the operating signal.

15. The computer program product of claim 14, wherein the at least one control parameter comprises a first control parameter, wherein the first control parameter is a zero point offset Koff of the operating signal.

16. The computer program product according to any one of claims 14 to 15, wherein the at least one control parameter comprises a second and a third control parameter, wherein the second control parameter is a controlled variable Kp which comprises a proportional part of the control, wherein the third control parameter is a controlled variable Ki which comprises an integral part of the control.

17. The computer program product according to claim 16, wherein the at least one control parameter comprises a fourth control parameter, wherein the fourth control parameter is a controlled variable Kd which comprises a derivative component of the control.

18. Computer program product according to at least one of claims 15 to 17, wherein the first control parameter is determined from a provided first linear function, and / or wherein the second control parameter is determined from a provided second linear function, and / or wherein the third control parameter is determined from a provided third linear function, and / or wherein the fourth control parameter is determined from a provided fourth linear function.

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