DE102011002038B3 - Filling level sensor for determination of filling level in toroidal container, has evaluation unit determining total filling level measurement value, and total filling level output outputting total filling level measurement values - Google Patents

Abstract

The sensor (10) has a communication unit (22) receiving data packets with source information and single filling level measurement values at a communication input (24). The single filling level measurement values are read from the data packets, the source information assigned to storage and the received data packets are output at a communication output (26). An evaluation unit (20) determines a total filling level measurement value from the single filling level measurement values. A total filling level output (28) i.e. analog output, outputs the total filling level measurement values.

Description

The invention relates to a filling level sensor according to the preamble of claim 1.

There are a number of known level sensors based on such different principles as a mechanical float, the detection of the medium by capacitance change, or the propagation time of electromagnetic pulses. In the case of the last-mentioned time-based measuring methods, time domain reflectometry (TDR) is often preferred because of uncontrolled wave propagation. It is based on the determination of propagation times of an electromagnetic signal to determine the distance of a continuity of the line wave resistance, as it occurs at the interface between air and the medium whose level is to be measured. The difference to the radar principle also used for level applications is that the electromagnetic waves are not emitted to the outside, but are guided along a conductor.

Special challenges are the measurement of the fill level on a turbulent surface in a moving container. This occurs, for example, in reservoirs of a bottling plant, which are in rotational motion and thereby urge the liquid due to the inertia of the outer wall. This creates in connection with the sometimes highly dynamic regulated inflow and outflow a constant, irregular wave motion. The punctual measurement of the level sensor is then not representative of the actual level, so that the level is determined only with a large measurement error.

A conventional solution is to measure the level in several places by means of several level sensors distributed over the circumference of the reservoir. Since the level sensors detect the rotational movement, the measurement information must be transmitted via sliding contacts to a central control.

Several sliding contacts are problematic because of their susceptibility to wear. In addition, several level sensors require a corresponding number of connections to the central control, which is usually designed as a PLC (programmable logic controller) and in which the number of necessary connections again leads to higher costs.

For these reasons, it is desirable to pre-consolidate the measurement information and then output bundled over a single wiper. But usual level sensors are not designed for this purpose. In a conventional configuration, multiple level sensors based on reed contacts are connected in series. The cumulative resistance, which is dependent on the local fill levels, is converted by an auxiliary device into an equivalent current value and thus transmitted by means of the sliding contact. It not only needs an additional device, but this additional device must also be adapted to the specific configuration, in particular the number of sensors involved. The whole system is error prone and inflexible. If the series connection is interrupted, for example because one of the sensors fails, then no meaningful measured value is generated anymore. There is no information about the distribution of the individual measured values or about the status of the sensors involved.

From the US 2004/0052450 A1 For example, an optical ring architecture is known. In this case, sensors, such as cameras, equipped with microprocessors, which are connected to each other via bidirectional optical fibers to form a communication ring.

The DE 198 03 686 A1 describes a communication of equal stations of an annular, serial optical fiber bus. In addition, process data can be exchanged quickly and strictly time-cyclically.

In the DE 40 25 025 A1 a synchronized, computer-aided digital measuring system with several distributed measuring points is disclosed. Therein, a master node sends synchronization messages to a plurality of slave nodes that are interconnected by transmission links to form a ring.

It is therefore an object of the invention to determine a level at locally different level.

This object is achieved by a level sensor according to claim 1. The invention is based on the basic idea to equip the level sensor for communication in the ring with other level sensors. The level sensor, like each level sensor involved in the ring, measures its own single level reading, and these single level readings are then exchanged across the ring between the participating level sensors by receiving data packets from a predecessor in the ring and passing it on to a follower in the ring. The level sensor extracts one or more individual level measurement values from the data packet as well as source information which serves to identify the origin of the individual level measurement values. The source information becomes For example, generated from the serial number of the level sensor. From the various individual level readings, each containing the local level of the level sensor measuring there, the level sensor calculates a total level reading and provides it at a total level output. The total level measurement, for example, the average of the individual level readings, but also weights are conceivable to compensate for known irregularities of the surface of the medium to be measured.

The invention has the advantage that due to the simple ring structure there is no need to implement a concept for the use of a common transmission medium. As a result, the communication remains very simple and can be implemented particularly cost-effectively.

Although it is conceivable according to the invention, it is not absolutely necessary for a filling level sensor in the ring to assume the role of a communications master, as in the case of a bus. Instead, preferably, a peer-to-peer communication ring is established using point-to-point communication. Each participating level sensor continuously accumulates all achievable single level readings during operation, calculates the total level reading, and provides it at its total level output. From the point of view of the participating level sensors, it does not matter if a total level output is connected at all and which level sensor has been selected for it. The level sensors are thus completely identical and interchangeable with each other, and the variety of variants is reduced. It eliminates any parameterization of the level sensors, regardless of the number, position or role in the ring composite. The system is scalable and allows flexible adaptation to the specific application without having to change anything on the system side. The ring composite behaves outward like a single sensor. There is no additional computational or processing effort in the control computer despite the multiple participating level sensors.

The communication unit is preferably configured to use the received data packets to build up a dynamic list of all the fill level sensors participating in the communication and to store the current single fill level reading in the list for each participating fill level sensor. The level sensor thus needs no advance information about the participants in the ring network. The relevant information, such as the number and identity of the participants, their status and current measured value and the like, are successively obtained as equitable participants as a dynamic list (Dictionary) from the received data packets. This considerably reduces the setup effort.

The communication unit is preferably designed to build up the dynamic list and keep it up to date that upon receipt of a first data packet with source information of a previously unknown subscriber, a new entry is created in the list and upon receipt of further data packets with source information of already known subscribers the existing entry is overwritten with the current single level reading. Thus, data packets are processed correctly regardless of whether the data packet sending the subscriber was previously known or not. The Ringverbund organizes itself.

The communication unit is preferably designed to output and receive the dynamic list in a data packet. Instead of accommodating only the current individual measured value of the respective transmitting level sensor in a data packet, the parts of the dynamic lists or even the entire dynamic lists are exchanged in this preferred development. Each participant feeds the communication within the ring network with additional or even all current information available to him on the entire ring network. One possible implementation is that there is always only one data packet revolving in which each participating level sensor makes updates as it is relayed, and from which each participating level sensor makes use of the information it requires.

The data packet preferably contains a time stamp, wherein the communication unit is designed to compare the time stamps of known and received single level measurement values and to process only the latest single level measurement values in each case. The timestamp is used to determine how current a single level reading is. It is possible that the level sensor has more recent information available from earlier data packages.

The communication unit is preferably designed to no longer forward data packets with a time stamp from a predetermined age. This prevents a data packet from blocking unnecessary communication capacity even though its information is already outdated.

The communication unit is preferably designed to no longer forward a repeatedly received data packet. When a data packet is received a second time, it has already passed each subscriber in the ring, so that this data package promises nowhere or an information gain.

The communication unit is preferably designed to no longer forward a received data packet if it contains the source information of its own fill level sensor. In principle, this represents a special case of an already known data packet. As long as each participant reliably ensures that their own data packets circulate only once through the ring network, the measures described in the preceding paragraphs are therefore superfluous. But they serve a redundant protection against unnecessary communication. The level sensor can use the time slot for the no longer passed on to generate a new, separate data package with a current single level reading and output in the ring network.

The communication unit is preferably designed to output and receive data packets containing additional diagnostic data. In addition to the single level measurement, for example, failure messages, error messages, maintenance requests or checksums for the integrity of the data packet are exchanged. The participants then not only know the various individual level readings, but also the status of the other participants.

The communication unit is preferably designed to cyclically generate and output its own data packet with a current single-level measured value of its own sensor. For example, a data packet is output every 50 ms. The cycle can be adapted to exploit the gaps between the received and to be forwarded data packets for the output of new, separate data packets.

The communication unit is preferably designed to quickly forward received data packets. This achieves rapid communication via the ring network and thus a short response time for generating a total level measurement. Data packets can be forwarded within a few milliseconds and in any event within ten milliseconds.

The communication input and the communication output is preferably formed by the separate communication lines of an IO-Link connection.

The IO-Link is in itself designed for bidirectional communication and is separated in this advantageous development. The incoming communication link of the previously bidirectional port is connected to a preceding level sensor, the outgoing communication link to a successor level sensor. Thus, the ring communication can be realized very easily on the basis of an already previously provided IO-Link connection. At the same time, the subscribers work as repeaters, so that range limits of the IO-Link protocol of, for example, at most 20 m no longer apply to the ring network as a whole, but possibly even the distance between two participating level sensors.

Alternatively, the communication input and the communication output are connected to a common bus line. This creates a classic ring bus. This also allows the necessary communication, but requires relatively more effort.

The total level output is preferably an analog output, in particular a 4-20 mA output. Thus, the entire ring assembly connected across the full level output of a participating level sensor is backward compatible with a single level sensor providing its reading at a corresponding analogue output.

The fill level sensor preferably has a diagnostic output for outputting diagnostic information via a ring connection, in which the fill level sensor participates. In addition to the overall level value, status and other information of the participants can be output. The diagnostic output is the existing total level output or a separate, in particular digital output.

The sensor unit preferably has a transmitter and a receiver for emitting and receiving an electromagnetic signal, in particular a microwave signal, wherein the evaluation unit is adapted to determine the single level reading based on a transit time of the electromagnetic signal up to an interface of a medium located in the container. Such radar and TDR sensors provide very precise and robust single level readings.

In an advantageous embodiment, a ring network of several inventive level sensors is provided, which are each annularly connected via their communication input to the communication output of the predecessor and their communication output to the communication input of the successor, the total level output of at least one level sensor is connected to a higher-level control for reading the total level measurement , This ring compound determines the level multiple points as a single level reading of the participating level sensors, collects the individual measured values by means of communication in the ring network, and outputs a calculated total level measurement to a higher-level control, such as a plant control, a meter or a display.

The ring composite is preferably mounted on a moving container, which is part of a filling plant, wherein the container in particular performs a rotational movement, and wherein the overall level output is connected via a sliding contact with the non-moving superordinate control. The measuring medium in such a container is restless and therefore by a local, punctual measurement usually no meaningful level can be determined. The ring composite according to the invention nevertheless allows a robust and accurate measurement of the entire fill level by merging a plurality of individual measured values.

In an alternative embodiment to a self-organized communication structure equal participants recognizes the level sensor whose total level output is connected to the parent control, this connection preferably automatically and then takes the role of a communication master, the remaining level sensors take the role of communication slaves.

The invention will be explained below with regard to further advantages and features with reference to the accompanying drawings with reference to embodiments. The figures of the drawing show in:

1 a schematic sectional view of an embodiment of a level sensor according to the invention; and

2 a schematic block diagram of a ring composite of several level sensors according to 1 on a toroidal reservoir.

1 shows an embodiment of a level sensor according to the invention 10 , The fill level sensor shown by way of example 10 works on the TDR principle. Likewise, however, other measuring principles known per se for determining a filling level are conceivable, some of which were mentioned in the introduction.

The level sensor 10 has a probe 12 , which is immersed in the measuring medium, and a sensor head 14 with the required electronics on. To the probe 12 is a transmitter 16 for coupling microwave pulses and a receiver 18 for receiving signals from the probe 12 and converting to an electronic signal. An evaluation unit 20 controls the transmitter 16 and determines the signal propagation time between the transmission of a microwave pulse and the reception of a reception pulse from an interface of the medium to be measured. From this, a measured value for the level of the medium is derived via the speed of light. Other electronics, such as amplifiers or transmitter controls, is in 1 omitted for simplicity.

A communication unit 22 is with the evaluation unit 20 as well as with a communication input 24 and a communication output 26 connected. Via the communication connections 24 . 26 Data packets from other level sensors are received and forwarded to other level sensors. Preferably, the communication ports are 24 . 26 realized by a standardized IO-Link port is split, so that a pin as a communication input 24 and the other pin as the communication output 26 is used. This uses the IO-Link physics to the OSI layer 1 to realize, and thus find standardized output drivers for the generation of binary signals for data exchange use. In order to improve the interference immunity of the transmission, push / pull stages can be used for transmission.

Using the information from the data packets and their own measured value, the evaluation unit calculates an overall measured value and outputs it to an output 28 out, which is preferably designed as a 4-20 mA analog output. Another exit 30 , in particular a digital output, may be provided to output diagnostic data.

2 shows a ring network of several, here four exemplary level sensors 10a -D, which is distributed on a toroidal storage container 32 a bottling plant are attached. The storage tank 32 is in rotational motion. Therefore, due to wave motions and the like, a rough surface of the liquid in the reservoir is generated 32 , which is also forced outward due to centrifugal forces. Because of this dynamic, the level in the reservoir can be 32 with a point measurement not reliably determine, but there are several local measurements of the level sensors 10a -D merged.

The level sensors 10a -D are at the reservoir 32 mounted and therefore carry out the rotation with. One behind the other are the level sensors 10a -D each from communication output 26 to communication input 24 to a Ring composite joined together. The exit 28 one of the level sensors 10d is connected via a only roughly indicated sliding contact to a higher-level control.

The level sensors 10a -D communicate via the ring network using data packets 36 , Each participating level sensor 10a -D generates data packets 36 containing at least source information and measurement information. For example, contains each data packet 36 a packet identifier, process data and a checksum. The packet identifier is designed in such a way that the data packet 36 clearly the sending level sensor 10a can be assigned. For this purpose, for example, a unique serial number of the level sensors 10a -D used. Furthermore, the packet identifier may contain a serial number containing the data packet 36 identified.

The process data primarily includes a level value. This is the self-measured fill level value, but optionally also known further fill level values of other participating fill level sensors 10a d. Moreover, with the data package 36 additional information such as error conditions or warnings are transmitted.

The checksum represents a data package-specific value that determines the consistency of the data packet 36 checked or a corrupt data packet 36 can be repaired. Possibilities of the checksum are CRC checks or other checksums, for example, from a logical combination of the individual bits of the data packet 36 arise. The individual bytes of the data packet 36 can be secured with a parity bit.

For a clear synchronization between the participating level sensors 10a -D, it may be useful to provide the whole package with a start and end identifier that is unique and can not occur in the variable data stream. Synchronization may be due to the asynchronous participating level sensors 10a -D required. For example, a level sensor could 10a -D get a reset, or the level sensors 10a -Wake at different times from a reset, and a level sensor 10a Therefore, -d only receives part of a data packet 36 , Furthermore, very strong interference on the communication lines can cause an apparent start condition of a byte to be triggered.

Each level sensor 10a -D sends its own data packets 36 with the last measured level value, for example cyclically every 50 ms. In addition, received data packets 36 evaluated and quickly forwarded within a few milliseconds. The data package 36 is checked for consistency and, if necessary and possible, corrected with the help of the checksum. Corrupt data packets 36 are discarded.

With this communication, depending on the number of participating level sensors 10a -D total cycle times, in which all required information was updated via the ring network, of a few 100 ms or even less. This results in response times for updated total level readings at the output 28 in a similar order of magnitude.

Receives a level sensor 10a -D your own data package 36 , so it has the ring compound once completely happened and is therefore no longer passed. The same is preferably true for any already known data packet 36 of whatever origin. If, for example, the packet identifier is changed due to transmission errors, no level sensor detects 10a -D the data packet 36 still as his own. Yet another alternative to the ring communication of no longer needed data packets 36 Freeing is a timestamp for each data packet 36 , whereby data packets with a certain age are no longer passed on.

Each level sensor 10a -D keeps a dynamic list of the remaining participating level sensors 10a -D are listed. To every level sensor 10a -D is from the evaluation unit 20 its measured level value and any other status data stored that the data packet 36 contains. This list is extended by one entry each, if a data packet 36 a previously unknown participant is received. data packets 36 an already known subscriber are used to update its information and in particular its fill level reading. Each level sensor 10a Thus d has complete information about the other participants, their measurements and their status.

The evaluation unit 20 in every level sensor 10a -D calculates a total level in the reservoir from the level measurements 32 , for example, by simple or weighted averaging. Various filters, for example to detect different container geometries, outlets and inlets, sensor types, probe lengths and the like, can be individually in each level sensor 10a -D before sending a data packet 36 as well as during averaging. For example, it is known in a bottling plant that in the region of the outflows of the filling ring, a lower, dependent on the filling speed level value is measured, and this can compensate for a filter.

The ring composite is able to output at least one more total level of lower accuracy despite various errors occurring. For example, if the ring is interrupted at one point, the still connected ring segment can continue working. Each level sensor 10a Therefore, -d preferably transmits its data packets 36 even if he himself receives nothing. Then there is a chance that the level sensor connected to the higher-level controller 10d still data packets 36 Arrive. Even if this level sensor 10d no data packets at all 36 arrive more, at least one more level due to its own measurement at the output 28 be issued. The system thus remains operational, albeit with a reduced process quality.

Are from a level sensor 10a -D only corrupt data packets 36 receive, so this level sensor 10a -D are set inactive in the dynamic list and the mean value is nevertheless formed from the other measured values.

Such error conditions can be on the diagnostic output 30 be reported to the higher-level control. This then knows that the measurement function is limited or no longer available. A corresponding error signal can also be output 28 output as fail-high or fail-low. The system allows increased availability of the system due to limited operation. Required repairs can be moved to scheduled maintenance times. If no operation is possible any more, this will be reported immediately.

Is an additional digital diagnostic output 30 provided, its communication line is usually in a cable with the analog connection to the output 28 laid. Then the bit representation or modulation should be designed so that the interference caused by capacitive coupling of the digital communication line to the analog line disappear on average. Also, the slew rate of the digital drivers should be as low as possible.

As an alternative to the previously described ring communication among equal participants, one of the level sensors could also be used 10a -D become a master. The master roll preferably takes over that level sensor 10d that is due to the impedance at its output 28 detects that there is a connection to a higher-level controller. As another alternative, instead of the connection via a separate IO-Link interface, a common bus line can be used to connect the level sensors 10a -D to join together to form a ring.

Claims (19)

Level sensor ( 10 ) for determining the level in a container ( 32 ), with a sensor unit ( 12 . 16 . 18 ) for generating a dependent of the level measurement and with an evaluation unit ( 20 ), which is designed to determine from the measurand a single fill level measurement for the fill level, characterized in that the fill level sensor ( 10 ) a communication input ( 24 ) for connecting a predecessor in a ring network of several level sensors ( 10a -D), a communication output ( 26 ) for connecting a successor in the ring network and a communication unit ( 22 ), which is adapted to the communication input ( 24 ) Data packets ( 36 ) with at least one source information and at least one single level measurement value, single level measurement values from the data packet ( 36 ) and to store the associated source information and received data packets ( 36 ) at the communication output ( 26 ) that in the evaluation unit ( 20 ) a total level measurement value can be determined from the individual level measurements and that the level sensor ( 10 ) a total level output ( 28 ) to output the total level measurement. Level sensor ( 10 ) according to claim 1, wherein the communication unit ( 22 ) is designed to be based on the received data packets ( 36 ) a dynamic list of all filling level sensors participating in the communication ( 10a -D) and in the list to each participating level sensor ( 10a -D) to store its current single level reading. Level sensor ( 10 ) according to claim 2, wherein the communication unit ( 22 ) is designed to build the dynamic list and keep it up to date that upon receipt of a first data packet ( 36 ) with source information of a previously unknown participant ( 10a -D) a new entry is created in the list and upon receipt further data packets ( 36 ) with source information of already known participants ( 10a -D) the existing entry is overwritten with the current single-level measurement value. Level sensor ( 10 ) according to claim 2 or 3, wherein the communication unit ( 22 ) is designed to store the dynamic list in a data packet ( 36 ) to spend and receive. Level sensor ( 10 ) according to one of the preceding claims, wherein the data packet ( 36 ) contains a timestamp, and wherein the communication unit ( 22 ) is adapted to compare the time stamps of known and received single level measurements and to process only the latest single level measurements. Level sensor ( 10 ) according to claim 5, wherein the communication unit ( 22 ) is designed to store data packets ( 36 ) with a time stamp from a given age no longer pass. Level sensor ( 10 ) according to one of the preceding claims, wherein the communication unit ( 22 ) is adapted to receive a repeatedly received data packet ( 36 ) no longer pass. Level sensor ( 10 ) according to one of the preceding claims, wherein the communication unit ( 22 ) is adapted to receive a received data packet ( 36 ) when the source information of its own level sensor ( 10 ) contains. Level sensor ( 10 ) according to one of the preceding claims, wherein the communication unit ( 22 ) is designed to store data packets ( 36 ) and receive additional diagnostic data. Level sensor ( 10 ) according to one of the preceding claims, wherein the communication unit ( 22 ) is designed to cycle its own data packet ( 36 ) with a current single level measurement of the own sensor ( 10 ) to generate and output. Level sensor ( 10 ) according to one of the preceding claims, wherein the communication unit ( 22 ) is adapted to receive received data packets ( 36 ) to pass on quickly. Level sensor ( 10 ) according to one of the preceding claims, wherein the communication input ( 24 ) and the communication output ( 26 ) is formed by the separate communication lines of an IO-Link connection. Level sensor ( 10 ) according to one of claims 1 to 11, wherein the communication input ( 24 ) and the communication output ( 26 ) are connected to a common bus line. Level sensor ( 10 ) according to any one of the preceding claims, wherein the total level output ( 28 ) is an analogue output, in particular a 4-20 mA output. Level sensor ( 10 ) according to one of the preceding claims, which has a diagnostic output ( 30 ) for outputting diagnostic information via a ring connection, on which the filling level sensor ( 10 ) participates. Level sensor ( 10 ) according to one of the preceding claims, wherein the sensor unit ( 12 . 16 . 18 ) a transmitter ( 16 ) and a receiver ( 18 ) for emitting and receiving an electromagnetic signal, in particular a microwave signal, and wherein the evaluation unit ( 20 ) is adapted to measure the single level measurement based on a transit time of the electromagnetic signal up to an interface of one in the container ( 32 ) to determine medium. Ring compound of several level sensors ( 10a D) according to one of the preceding claims, wherein the level sensors ( 10a -D) in each case via their communication input ( 24 ) with the communication output ( 26 ) of the predecessor and via its communication output ( 26 ) with the communication input ( 24 ) of the successor are annularly connected, and wherein the total level output ( 28 ) at least one level sensor ( 10d ) is connected to a superordinate controller for reading the total level reading. Ring composite according to claim 17, wherein the ring composite on a moving container ( 32 ), which is part of a filling plant, wherein the container ( 32 ) performs in particular a rotational movement, and wherein the total level output is connected via a sliding contact with the non-moving superordinate control. Ring assembly according to claim 17 or 18, wherein the level sensor ( 10d ), whose total level output is connected to the higher-level control, recognizes this connection automatically and then assumes the role of a communications master, the remaining level sensors ( 10a -C) assume the role of communication slaves.

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