Method for a loop-fed measuring device

Abstract

Method for a loop-fed measuring instrument (100) for level measurement, limit level determination, pressure measurement and / or temperature measurement, wherein the measuring instrument (100) comprises a sensor device (120) arranged in a two-wire loop (180), the method comprising the steps: Determining a first voltage (U) init ) on the sensor device (120); Determining a current voltage (U) sensor ) on the sensor device (120); and when the current voltage (U sensor ) by more than a predefined voltage amount (U diff ) from the first voltage (U init ) differs, issuing an alarm, where the predefined voltage amount (U) diff ) depending on a time series of current voltages (U sensor ) is determined.

Description

Field of invention

[0001] The invention relates to a measuring device, e.g., a field device or control cabinet device, with a sensor – e.g., an attached sensor – for level measurement, limit level determination, flow measurement, pressure measurement, and / or temperature measurement. In particular, the invention relates to a loop-fed measuring device, field device, or measuring system, a method, a use, a program element, and a computer-readable medium. background

[0002] For level measurement, limit level determination, flow measurement, pressure measurement, and / or temperature measurement, measuring devices, such as field devices and / or measuring systems, are often used that are connected to a sensor via a two-wire loop. The measuring device may include other components—such as a display unit—that are also located in the two-wire loop. The measuring device can, for example, supply power to the sensor and, if applicable, other connected components in the measuring loop, as well as process the measurement signal. If, for any reason, the resistance in the two-wire loop is increased—for example, due to corrosion—the functionality of at least some types of sensors and / or the transmission of the sensor's measured values ​​may be impaired.

[0003] Document DE 10 2006 047 262 A1 relates to a method for testing an electronic unit for determining and / or monitoring a process variable. Document DE 10 2019 208 431 A1 concerns sensors for level measurement, limit level determination, detection of the topology of a product surface, pressure measurement, and / or flow measurement.

[0004] Document DE 10 2015 223 670 A1 concerns a sensor device for monitoring a fill level in a liquid container.

[0005] Document DE 10 2018 123 787 A1 concerns a measuring arrangement and a method for detecting defects in an industrial plant. Summary

[0006] The object of the invention is to improve, at least partially, the functionality of a measuring instrument, a field device, and / or a measuring system. This object is achieved by the subject matter of the independent claims. Further developments of the invention are described in the dependent claims and the following description.

[0007] A first aspect concerns a method for a loop-fed measuring device, e.g., a field device and / or a measuring system, for level measurement, limit level determination, pressure measurement, flow measurement, and / or temperature measurement. The measuring device includes a sensor device arranged in a two-wire loop. Depending on the application, the sensor device can use various types of sensors, for example, an impedance limit switch, a vibration limit switch, a high-frequency front end, e.g., a radar sensor, and / or other types of sensors. The method comprises the following steps: Determining an initial voltage at the sensor device; Determining a current voltage at the sensor device; and If the current voltage differs from the initial voltage by more than a predefined voltage amount, an alarm is triggered.

[0008] The two-wire loop can be implemented, for example, as a 4–20 mA current loop. The two-wire loop can be powered by a so-called power supply unit, such as a measuring instrument. For at least some measuring instruments, the available power in a two-wire loop may be limited, for example, because the power supply unit itself has a power limitation. This applies, for example, to intrinsically safe isolating barriers or (Ex) transmitter power supplies (power supply units) used to power the two-wire loop, for example, in applications in potentially explosive atmospheres ("Ex"). This limitation can be used, for example, to reduce the power supplied to the measuring instrument, to extend the lifespan of a power supply battery, and / or for safety reasons. Other devices can also be connected in the two-wire loop, such as a display device and / or a communication device (e.g., wireless).The other devices can be arranged in the same housing as the sensor device and / or in separate housings. The method can be implemented in the power supply unit—especially if it is designed as a power supply and control unit—but the method can also be implemented in the display device and / or in one of the other devices. The sensor device has at least one sensor, e.g., one of the sensors mentioned above. It can also possess its own intelligence, meaning that, for example, a control unit or another type of computer and / or communication device can be located near, e.g., in the housing, of the sensor device. The sensor can be designed for process automation or factory automation. It can physically measure, for example, temperature, pressure, fill level, limit level, and / or flow rate. The sensor device converts the measured value, for example, into a current in the range of 4 mA to 20 mA.The sensor device thus provides the loop current, which is in turn measured and evaluated by another device, e.g., a measuring device, such as a power supply and / or control unit. The two-wire loop can support, for example, so-called SMART protocols such as the HART protocol (Highway Addressable Remote Transducer), the so-called "Brain Protocol" (Yokogawa), Baily (STC02), Foxcom, and / or other similar protocols.

[0009] The initial voltage can be measured, for example, during manufacturing, during commissioning (e.g., during initial startup), and / or at another defined point in time. This initial voltage is sometimes referred to as the initial voltage. It can also be considered a reference voltage and stored, for example, in non-volatile memory.

[0010] The current voltage is sometimes referred to as the actual voltage. Determining the current voltage at the sensor device can be done, for example, cyclically and / or on demand. Determining a voltage at the sensor device—for example, the initial voltage or the current voltage—can be done, for instance, by measuring directly at the sensor device, and / or at devices such as the power supply unit and / or other devices that, for example, indirectly infer the voltage at the sensor device from their own measured values.

[0011] Determining a voltage at the sensor device (U sensor ) and its transmission to the measuring device can also take place via a communication interface such as HART. In this case, the necessary data can be exchanged, for example, in master / slave mode. Determining a voltage at the sensor device (U sensorThe measurement and its transmission to the measuring device can also occur via a wireless communication interface such as Bluetooth or LoRa. The data is transmitted wirelessly from the sensor to the measuring device. Determining the current voltage is sometimes referred to as a monitoring function. This monitoring function can include the device monitoring the terminal voltage(s) and / or the loop current and drawing conclusions about the state of the current loop or two-wire loop. If the current voltage is lower than the initial voltage by a predefined amount and / or if changes occur outside a specified limit, an alarm, for example in the form of a warning message, can be issued and / or transmitted. The predefined voltage threshold can be adjustable.The alarm can include, for example, the following actions: illuminating a yellow and / or red light on the sensor device, another device and / or an external device, e.g., a control room; emitting a sound; sending a message and / or a data sequence, especially if the measuring device, field device and / or measuring system is part of an IoT-based automation system (IoT: Internet of Things); displaying a status, a message and / or a pictogram on a display device; updating a database, especially in a central unit such as a control system.

[0012] This allows load problems in the current loop to be detected advantageously in a timely manner. Such problems can occur in the short term – e.g., transiently – but they can also develop gradually – e.g., insidiously – and only after some time reach and / or exceed a critical value for the current loop (or for the function of the measuring device and / or measuring system). The change in the current voltage compared to the initial voltage can be caused, for example, by corrosion, e.g., at at least one of the connection terminals. For example, corrosion at the connection terminals can increase the resistance in the current loop to such an extent that the power supply can no longer provide sufficient voltage at a high loop current to ensure the operation of the connected sensor and any loads that may be located in the current loop. Changes in temperature during operation can also negatively affect the loop balance, e.g.,Because an increased temperature can lead to higher overall loads on the current loop, at least in some systems. For example, the current loop might still function adequately at 20°C, but not at 60°C due to altered, increased line resistances within the loop. Subsequent modifications to the current loop, such as the installation of additional loads or the replacement of existing devices, can also affect the current balance of the two-wire loop. This also enables the sensible expansion of IoT concepts with their associated advantages. For example, load changes in the loop caused by temperature changes can be transmitted to third-party systems such as diagnostic systems.In addition to the diagnostic messages, switching off "consumers" can also ensure that the loop balance remains in the "green" range and that the current loop, and thus the relevant part of the system, continues to function properly.

[0013] In some embodiments, the measuring device further comprises a consumer device arranged serially to the sensor device (120) in a two-wire loop (180). The consumer device can have a single or multiple functional units, for example, a measuring resistor (e.g., a HART resistor), a measuring device, a display, a backlight, a communication unit, a radio unit, a processing unit, and / or a memory. The functional units can be arranged in a housing, e.g., together with other functional units and / or the sensor device. The spatial distribution of the functional units can be influenced by a measurement concept. The alarm can further include switching off one or more of the functional units.The shutdown process can be determined by a sequence based on power consumption and / or functional priority of the functional units and / or other devices; for example, the sensor device and / or the sensor can be the last device to be switched off.

[0014] In numerous embodiments, the measuring device also includes a power supply and control unit. This power supply and control unit can, for example, be a transmitter power supply. The transmitter power supply can be externally powered and / or supplied by a separate power supply. The transmitter power supply can, for example, be connected to a passive PLC analog input card (PLC: programmable logic controller). The transmitter power supply can also be passive, i.e., without an external supply voltage, and, for example, be implemented and / or connected as an active PLC analog input card. The power supply and control unit can, for example, be a power supply and control unit such as VEGAMET or VEGATOR, a isolating barrier such as VEGATRENN, and / or loop-powered display devices such as VEGADIS.

[0015] In numerous embodiments, the measuring device or measuring system is part of a process automation or factory automation system. In some embodiments, the system includes a central control station and / or a database.

[0016] In some embodiments, the predefined voltage level is freely selectable and / or adjustable. This advantageously allows for easy adaptation, for example, to a system optimized for a customer. In these cases, the predefined voltage level can be set, for example, by a practitioner familiar with this system and / or another expert.

[0017] In some embodiments, the predefined voltage level is determined by means of a simulation. The simulation can, for example, include specifications of the sensor, the cable, the power supply and control unit, the power consumption of other devices, temperature ranges, tolerance ranges and / or other factors.

[0018] In some embodiments, the predefined voltage level is determined based on a time series of current voltages. For example, to assess the power balance of the two-wire loop, the voltage at 4 mA and the voltage at 20 mA, or even intermediate voltage values, can be recorded at the start of the loop installation. These can be stored in an internal list as initial reference values. If these reference values ​​fall below the predefined voltage level over time, this may indicate increased resistance in the current loop, for example, due to corrosion. This method can be combined with a method that frequently and / or continuously records measurements in devices such as VEGATRENN / VEGATOR / VEGAMET / VEGADIS, etc.The data is recorded in order to detect deviations over the operating time of the system and to interpret these deviations as corrosion and / or to provide them to the user as a diagnostic message.

[0019] The time series can be stored, for example, in one of the devices of the measuring system and / or in a central database. The time series can include equidistant measurements of current voltages and / or measurements with varying intervals, where, for example, voltage measurements in critical situations are overrepresented. The time series can be collected on demand, predefined, and / or periodically – for example, in periods of seconds, minutes, etc., up to months. Using a time series, the effects of gradual deterioration, such as corrosion, can be observed and / or predicted. It can also be used to implement preventive maintenance concepts regarding potential problems, for example, through linear interpolation or by using another interpolation function. These concepts allow, for example, maintenance to be planned and / or carried out more effectively.Furthermore, the high costs resulting, for example, from a plant or sub-plant shutdown can at least be mitigated. Problems of gradual deterioration can also be clearly distinguished from short-term and / or transient problems. This can be advantageously used, for example, to detect unexpected problems that result, for instance, from the addition of an extra device—such as a functional unit—to the two-wire loop, perhaps because its power consumption was miscalculated. It can also be advantageously used to implement warm redundancy concepts. For example, if a short-term and / or transient problem is detected, in an "emergency mode," only critical fill levels (e.g., overflow) are measured by another, potentially less expensive, measuring system maintained in cold or warm redundancy; this avoids the need for costly and / or energy-intensive hot redundancy.

[0020] Furthermore, by triggering an alarm – for example, through notification, visualization of the problem, and / or other measures as described above and / or below – the plant operator can specifically correct their individually configured current loop. They can plan work and / or maintenance proactively and do not have to react immediately to a potentially much more expensive plant shutdown later on. Additionally, wireless communication channels or connections to wired communication channels can be integrated into the concept, as described above and / or below. Furthermore, the generated messages can be stored in a database, e.g., in a cloud, to provide centralized diagnostic information. This can form a basis for evaluating the reliability and / or availability of specific system configurations and / or measuring devices.

[0021] The methods explained above for determining the predefined voltage level can, in principle, be combined.

[0022] One aspect concerns a loop-fed measuring device, field device, and / or measuring system for level measurement, limit level determination, pressure measurement, flow measurement, and / or temperature measurement. The measuring system comprises a sensor device and a power supply and control unit arranged in a two-wire loop, wherein the power supply and control unit and / or the sensor device is configured to perform a procedure as described above and / or below.

[0023] In some embodiments, the measuring system further comprises a consumer device arranged in series with the sensor device in the two-wire loop. The power supply and control unit, the sensor device, and / or the consumer device are configured to perform a method as described above and / or below. The consumer device can comprise a variety of functional units, for example, a measuring resistor (e.g., a HART resistor), a measuring device, a display, a backlight, a communication unit, a radio unit, a processing unit, and / or a memory.

[0024] In some embodiments, the alarm is transmitted via a wireless communication unit. The wireless channel can be implemented, for example, as a low-power wide area network (LPWAN) or as a short-range network, such as Bluetooth. This can be an alternative or additional method to transmission via a two-wire loop and / or another wired method. The transmission can be made, for example, to a display and / or to a central control system. The central control system can also analyze voltage time series. This can advantageously be used as described above, for example, to detect creeping, transient, and / or other problems.

[0025] In one embodiment, the current voltage at the sensor is transmitted to the measuring device via a wired and / or wireless communication interface. The wired communication interface can, for example, support a protocol such as HART. The wireless communication interface can, for example, support protocols such as Bluetooth, LoRa, etc.

[0026] In one embodiment, the power supply and control unit of the measuring system has an output voltage of approximately 24 V or a maximum of approximately 17 V (typically for intrinsically safe measuring instruments). The power supply and control unit can, for example, be implemented as a transmitter power supply. Power supplies approved for a maximum of 17 V, or 16–17 V (e.g., due to explosion limit characteristics), can be intrinsically safe devices certified for use in potentially explosive atmospheres. Other power supplies with limited supply voltages can also be used. This can make the field devices suitable and / or certifiable for critical applications, such as those in potentially explosive atmospheres.

[0027] One aspect concerns the use of a measuring instrument, field device, and / or measuring system as described above and / or below, or a method as described above and / or below, for level measurement, limit level determination, pressure measurement, flow measurement, and / or temperature measurement, and / or for measurements in a potentially explosive atmosphere, particularly one with intrinsic safety protection. The potentially explosive atmosphere may include an environment as defined by Exi IIC. This allows, for example, the implementation of current loops that require relatively low supply voltage from the transmitter power supply. At least one of the aforementioned methods can be used as an aid in fault detection.

[0028] One aspect concerns a program element which, when executed on a measuring device, field device and / or measuring system as described above and / or below, instructs the field device to perform a procedure as described above and / or below.

[0029] One aspect concerns a computer-readable medium on which a program element is stored as described above.

[0030] To further illustrate the invention, it is described with reference to embodiments depicted in the figures. These embodiments are to be understood as examples only, not as limitations. The representations in the following figures are schematic and not to scale. In the figures, identical reference numerals denote identical or similar elements. Brief description of the characters

[0031] It shows: Fig. 1 a schematic sketch of a loop-fed measuring device according to one embodiment; Fig. 2 a schematic sketch of a loop-fed measuring device according to a further embodiment; Fig. 3 a schematic sketch of a loop-fed measuring device according to a further embodiment; Fig. 4 a method according to one embodiment. Detailed description of embodiments

[0032] Fig. Figure 1 shows a schematic sketch of a loop-fed measuring device, field device, and / or measuring system 100 according to one embodiment. The measuring system 100 has a two-wire loop or current loop 180. A sensor device 120 and a power supply and control device 200 are arranged in the two-wire loop 180. The power supply and control device 200 can be, for example, a power supply and control device such as VEGAMET or VEGATOR, a barrier such as VEGATRENN, and / or loop-fed display devices such as VEGADIS. The sensor device 120 is symbolically depicted as a radar device. However, an impedance limit switch, a vibration limit switch, a level sensor with a high-frequency front end (e.g., like the radar front end shown), an ultrasonic front end, or a laser front end, or a radiometric measuring device can also be used as the sensor, alternatively or additionally.

[0033] The power supply and control unit 200 outputs a voltage U Loopoff. A voltage U is applied to sensor device 120. Sensor Optionally, a consumer device 140 can be arranged in series with the sensor device 120 in the two-wire loop 180. The power supply and control unit, the sensor device, and / or the consumer device are configured to perform a procedure as described above and / or below. The consumer device can have a variety of functional units, for example, a measuring resistor (e.g., a HART resistor), a measuring device, a display, a backlight, a communication unit, a radio unit, a processing unit, and / or a memory.

[0034] Fig. Figure 2 shows a schematic sketch of a loop-fed measuring device 100 according to a further embodiment. The measuring device 100 shown comprises a power supply and control unit 200 and a sensor unit 120; see the explanations above. The power supply and control unit 200 is supplied with a voltage U PS (PS: power supply); this can be mains voltage, or the device 200 is powered ("autonomously") by a battery. The power supply and control unit 200 and the sensor unit 120 are connected by means of the two-wire loop 180. The line has a line resistance R L Accordingly, each of the conductor sections has a conductor resistance of approximately R. L / 2. A voltage U drops across the entire line resistance. RL off. This results in a voltage of 120 at the sensor device: U Sensor = U Loop - U RL For a correct measurement, the voltage U must be below a certain value. SensorThe current at sensor device 120 should not fall below a value specified for this sensor device. With a correct measurement, the loop current I Loop determined by the sensor device 120. In the illustrated embodiment, the power supply and control unit 200 can assume a monitoring function. For this purpose, the device can use the following information: its own terminal voltage U Loop , the magnitude of the loop current I Loop and the sensor terminal voltage U Sensor The terminal voltage U Loop and the loop current I Loop The current sensor terminal voltage U can be measured by the device, for example, using A / D conversion. SensorThe sensor can transmit the data to the power supply and control unit 200, e.g., using the two-wire loop protocol 180 (e.g., via the HART protocol) and / or via a second transmission path such as radio. If communication with the sensor is not possible, it is also possible to measure the sensor terminal voltage U when commissioning the current loop. Sensor Different current values ​​can be communicated directly to the device as reference values. From this information, the current line resistance R can be calculated. L The following will be calculated: R L = (U Loop - U Sensor ) / I Loop This calculated resistance value can be recalculated regularly, e.g., continuously. R LThe resistance value should always remain constant within predefined tolerance limits. Larger deviations may indicate a change in the resistance value. As explained above, the causes can vary; for example, corrosion at the terminals, a faulty sensor with a changed terminal voltage, and / or other factors may be responsible. Because the measuring device (e.g., the 100) can issue a diagnostic message in such a case, a system operator can, for instance, address the cause early on, such as corroded terminals, and / or schedule planned maintenance.

[0035] Fig. Figure 3 shows a schematic sketch of a loop-fed measuring device 100 according to a further embodiment. Compared to Fig. 2 This embodiment additionally features a consumer device 140, which is arranged in series with the sensor device 120 in the two-wire loop 180. The consumer device 140 can, for example, comprise a loop-fed display instrument. In this embodiment, the loop-fed consumer device 140 (and / or the power supply and control device 200) can perform the monitoring function. For this purpose, the device can use the following information: its own terminal voltages U L1 and U L2 , the magnitude of the loop current I Loop , the sensor terminal voltage U Sensor and the terminal voltage U Loop The terminal voltage U L1 and U L2 and the loop current I Loop can be measured by the device itself, e.g., using A / D conversion. The current sensor terminal voltage U SensorThe sensor can transmit the data to the power supply and control unit 200, e.g., using the two-wire loop protocol 180 (e.g., via the HART protocol) and / or via a second transmission path such as radio, and / or – as described above – by inputting reference values ​​at different currents. From this information, the current line resistance R can be calculated. L1 and R L2 The resistance value can be calculated. This calculated resistance value can be recalculated regularly, e.g., continuously. L1 and R L2The resistance values ​​should always remain constant within predefined tolerance limits. Larger deviations may indicate a change in the resistance value. The causes for this can vary, as explained above. Because the display unit issues a diagnostic message in such cases, the system operator can address the cause (e.g., corroded terminals) early on. Additionally, it is possible to maintain the operation of the current loop by automatically switching off components in the consumer unit 140 (e.g., the display backlight), thereby stabilizing the U value. V , which drops at the consumer device 140, can be reduced and thus an increased value of U L1 and U L2 can be balanced out.

[0036] Fig. Figure 4 shows a method 300 according to one embodiment. In step 301, a first voltage U is applied. init on the sensor device 120 (see Fig.1 to 3). The first voltage U init is a sensor terminal voltage U Sensor , which is measured, for example, during the manufacture and / or commissioning of the measuring device 100. In step 302, a current voltage U is measured. Sensor The current voltage U is determined on the sensor device 120. In step 303, it is checked whether the current voltage U is... Sensor by more than a predefined voltage amount U diff from the first voltage U init differentiating. If the difference is greater – for example, the sensor terminal voltage U – Sensor If the voltage falls below a specified value, the system branches to step 304. In step 304, an alarm is triggered. The alarm can include, for example, a visual signal, an audible signal, a message via a communication channel, and / or other outputs. If the difference U diffIf the value is smaller, the process branches to step 305. In step 305, for example, normal operation of measuring device 100 continues. Steps 304 and / or 305 can then continue with step 302.

[0037] It should also be noted that the different embodiments can be combined with each other, unless this is explicitly excluded and / or prohibited by technical impossibility. List of reference symbols 100 loop-fed measuring device, e.g. field device 120 Sensor, sensor device 140 consumer device 200 power supply and control unit 300 Flowchart 301 - 305 steps

Claims

[1] Method for a loop-fed measuring instrument (100) for level measurement, limit level determination, pressure measurement and / or temperature measurement, wherein the measuring instrument (100) comprises a sensor device (120) arranged in a two-wire loop (180), the method comprising the steps: Determining a first voltage (U) init ) on the sensor device (120); Determining a current voltage (U) sensor ) on the sensor device (120); and when the current voltage (U sensor ) by more than a predefined voltage amount (U diff ) from the first voltage (U init ) differs, issuing an alarm, where the predefined voltage amount (U) diff ) depending on a time series of current voltages (U sensor ) is determined. [2] Method according to claim 1, wherein the measuring device (100) further comprises a consumer device (140) arranged in series with the sensor device (120) in a two-wire loop (180). [3] Method according to claim 2, wherein the consumer device comprises a measuring resistor, a measuring device, a display, a light, a communication unit, a radio unit, a computing unit, and / or a memory. [4] Method according to one of the preceding claims, wherein the measuring device (100) further comprises a power supply and control unit (200). [5] Method according to any of the preceding claims, wherein the predefined voltage amount (U) diff ) is freely selectable and / or adjustable. [6] Method according to any of the preceding claims, wherein the predefined voltage amount (U) diff ) is determined by means of a simulation. [7] Method according to one of the preceding claims, wherein the current voltage at the sensor (U sensor ) is transmitted to the measuring device via a wired and / or wireless communication interface. [8] Method according to one of the preceding claims, wherein the power supply and control unit (200) provides an output voltage (U Loop ) of approximately 24 V or of a maximum of approximately 17 V. [9] Loop-fed measuring instrument, field instrument and / or measuring system (100) for level measurement, limit level determination, flow measurement, pressure measurement and / or temperature measurement, comprising: a sensor device (120) and a power supply and control device (200) arranged in a two-wire loop (180), wherein the power supply and control unit (200) and / or the sensor unit (120) is configured to perform a method according to one of the preceding claims. [10] Loop-fed measuring system (100) according to claim 9, further comprising a consumer device (140) arranged in series with the sensor device (120) in the two-wire loop (180), wherein the power supply and control device (200), the sensor device (120) and / or the consumer device (140) is configured to perform a method according to any one of claims 1 to 8. [11] Loop-fed measuring system (100) according to claim 9 or 10, wherein the alarm is transmitted by means of a wireless communication unit. [12] Loop-fed measuring system (100) according to claim 9, 10 or 11, wherein the power supply and control unit (200) provides an output voltage (U Loop ) of approximately 24 V or of a maximum of approximately 17 V. [13] Use of a measuring instrument, field device and / or measuring system (100) according to any one of claims 9 to 12 or a method according to any one of claims 1 to 8 for level measurement, limit level determination, pressure measurement, flow measurement and / or temperature measurement, and / or for measurements in a potentially explosive atmosphere. [14] Program element which, when implemented on a measuring instrument and / or field device (100) according to any one of claims 9 to 12, instructs the measuring instrument and / or field device (100) to perform a method according to any one of claims 1 to 8. [15] Computer-readable medium on which a program element according to claim 14 is stored.

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