DE102023116641A1 - Method for establishing a wireless communication connection between a field device and a mobile terminal and system - Google Patents

Abstract

The invention relates to a method for establishing a wireless communication connection between a field device (1a; 1b) of automation technology and a mobile terminal (2a; 2b), for switching the field device (1a; 1b) by the mobile terminal (2a; 2b) using the wireless communication connection. The field device is switched on the basis of a current distance estimate (Xid _ti ). The invention further relates to a system (100) of automation technology, comprising such a field device (1a; 1b) and such a mobile terminal (2a; 2b).

Description

The invention relates to a method for establishing a wireless communication connection between an automation technology field device and a mobile terminal. The invention further relates to an automation technology system comprising such a field device and such a mobile terminal.

Field devices are often used in process automation technology as well as in production automation technology. In principle, field devices are all devices that are used close to the process and that provide, process and/or display process-relevant information. Field devices are used, for example, to record and/or influence process variables. Measuring devices or sensors are used to record process variables. These are used, for example, for pressure and temperature measurement, conductivity measurement, flow measurement, pH measurement, level measurement, etc. and record the corresponding process variables pressure, temperature, conductivity, pH value, level, flow, etc. Actuators are used to influence process variables. These are, for example, pumps or valves that can influence the flow of a liquid in a pipe or the level in a container. In addition to the measuring devices and actuators mentioned above, field devices also include remote I/Os, radio adapters or general devices that are arranged at the field level. A large number of such field devices are produced and distributed by the Endress+Hauser Group.

• - die hohen Kosten für die verwendeten Hardwarekomponenten, den Anschluss und/oder die Montage;
• - den Aufwand für die erforderliche Abdichtung eines Gehäuses des Feldgeräts, welche ggf. gemäß entsprechender Normen ausgebildet sein muss, etwa im Hygienebereich.
• - Darüber hinaus sind aufgrund des prozessnahen Einsatzes physische Schalt- und/oder Bedienelemente eines in einer Prozessanlage eingebauten Feldgeräts ggf. schwer oder gar nicht zugänglich.
• - Zuletzt weisen physische Schalt- und/oder Bedienelemente eine begrenzte Lebensdauer und/oder eine gewisse Ausfallwahrscheinlichkeit auf.

Many such field devices have physical switching and/or operating elements, by means of which, for example, a switching process can be triggered. The switching and/or operating elements are designed, for example, as touch displays and/or as knock sensors and/or switches. These switching and/or operating elements are used to trigger certain actions on the field device, for example switching a display on a display unit such as a display or setting parameter values, etc. Such physical switching and/or operating elements have a number of disadvantages, including

• - the high costs of the hardware components used, the connection and/or assembly;
• - the effort required for the required sealing of a field device housing, which may have to be designed in accordance with relevant standards, for example in the hygiene sector.
• - In addition, due to the process-related use, physical switching and/or operating elements of a field device installed in a process plant may be difficult or even impossible to access.
• - Finally, physical switching and/or control elements have a limited lifespan and/or a certain probability of failure.

The DE 10 2020 120 297 A1 discloses a method for extending the operating functionality of a field device of automation technology from one operating device to at least one further operating device.

The invention is based on the object of specifying a possibility to switch a field device without using a physical switching and/or operating element of the field device.

The problem is solved by a method for establishing a wireless communication connection between a field device of automation technology and a mobile terminal, for switching the field device by the mobile terminal by means of the wireless communication connection.

Advantageous embodiments are specified in the dependent claims.

• - Bereitstellen eines Feldgeräts der Automatisierungstechnik, wobei das Feldgerät aufweist:
  • -- eine programmierbare Rechen-/Steuereinheit
  • -- eine Feldgerät-Sende/Empfangseinheit, die von der Rechen-/Steuereinheit ansteuerbar ist;
• - Bereitstellen eines mobilen Endgeräts, mit einer Endgerät-Sende-/Empfangseinheit, wobei die Feldgerät-Sende-/Empfangseinheit und die Endgerät-Sende-/Empfangseinheit dazu ausgestaltet sind, mittels einer drahtlosen Kommunikationsverbindung, insb. unter Benutzung eines vorherbestimmten Frequenzbereichs, insb. gemäß eines standardisierten Kommunikationsprotokolls, miteinander zu kommunizieren;
• - Übermitteln von Telegrammen von der Endgerät-Sende-/Empfangseinheit an die Feldgerät-Sende/Empfangseinheit und/oder von der Feldgerät-Sende/Empfangseinheit an die Endgerät-Sende-/Empfangseinheit über die drahtlose Kommunikationsverbindung;
• - Ermitteln eines aktuellen Distanzschätzwerts anhand der übermittelten Telegramme, welcher aktuelle Distanzschätzwert mit einer aktuellen physischen Distanz zwischen dem Feldgerät und dem mobilen Endgerät korreliert; und
• - Schalten, insb. automatisiertes Schalten, des Feldgeräts, auf Basis des aktuellen Distanzschätzwerts.

The method according to the invention comprises the steps:

• - Providing a field device for automation technology, wherein the field device has:
  • -- a programmable computing/control unit
  • -- a field device transmitting/receiving unit that can be controlled by the computing/control unit;
• - Providing a mobile terminal with a terminal transmitting/receiving unit, wherein the field device transmitting/receiving unit and the terminal transmitting/receiving unit are designed to communicate with each other by means of a wireless communication connection, in particular using a predetermined frequency range, in particular according to a standardized communication protocol;
• - Transmitting telegrams from the terminal transmitting/receiving unit to the field device transmitting/receiving unit and/or from the field device transmitting/receiving unit to the terminal transmitting/receiving unit via the wireless communication link;
• - Determining a current distance estimate based on the transmitted telegrams, which current distance estimate correlates with a current physical distance between the field device and the mobile device; and
• - Switching, especially automated switching, of the field device based on the current distance estimate.

The mobile device is, for example, a smartphone, a tablet or a wearable, e.g. a smartwatch or data glasses, or a mobile device specific to process automation, such as the FieldXpert distributed by the applicant.

Modern field devices often have a radio interface via which the field devices can communicate using such mobile devices. For this purpose, the field device and the mobile device are equipped with specially designed transmitting/receiving units. The transmitting/receiving units are designed in such a way that they are tuned to a predetermined frequency range. Common communication frequencies are usually 2.4 GHz. The transmitting/receiving units are therefore preferably designed to transmit data or telegrams according to a wireless protocol, e.g. Bluetooth LE and/or WiFi.

The programmable computing/control unit can be assigned, in particular at least partially, to a transmitter unit which serves to process and/or forward a measurement signal recorded by the field device. The programmable computing/control unit can also be assigned, in particular at least partially, to a module which is separate from the transmitter unit and which comprises the field device transmitting/receiving unit, for example a Bluetooth module.

The distance estimate is used to determine the physical proximity of the field device to the mobile device. Preferably, the field device is automatically switched using the mobile device based on the current distance estimate, so that the field device can be switched or operated using the mobile device even without the use and/or secure accessibility of physical switching and/or operating elements. In particular, the field device can be free of physical switching and/or operating elements.

• - Vergleich des aktuellen Distanzschätzwerts mit einem vorgegebenen oder vorgebbaren Grenzwert;
• - Für den Fall, dass zumindest der aktuelle Distanzschätzwert den Grenzwert entweder über- oder unterschreitet: Schalten des Feldgeräts.

In one embodiment of the procedure, this comprises the following steps:

• - Comparison of the current distance estimate with a given or predefinable limit value;
• - In the event that at least the current distance estimate either exceeds or falls below the limit value: Switching the field device.

The limit value is selected, for example, such that if a physical distance between the field device and the mobile terminal estimated using the distance estimate is smaller than a maximum distance, e.g. is estimated to be less than 1.5 m, in particular less than 0.5 m, preferably less than 0.2 m, the field device can be switched using the mobile terminal, in particular is switched automatically.

• - Schalten des Feldgeräts in einen aktiven Kommunikationsmodus, in welchem eine vergrößerte Reichweite der Feldgerät-Sende/Empfangseinheit vorliegt, im Vergleich zu der Reichweite der Feldgerät-Sende/Empfangseinheit außerhalb des aktiven Kommunikationsmodus, wobei die Reichweite insb. auf zumindest das 2-fache, bevorzugt zumindest auf das zumindest 10-fache vergrößert wird, im Vergleich zu der Reichweite der Feldgerät-Sende/Empfangseinheit außerhalb des aktiven Kommunikationsmodus;
• - Aktivieren und/oder Ändern einer, insb. optischen und/oder akustischen, Anzeige, die an einer Feldgerät-Anzeigeeinheit angezeigt wird.

In one embodiment of the method, at least one of the following steps is carried out during switching:

• - Switching the field device to an active communication mode in which there is an increased range of the field device transmitting/receiving unit compared to the range of the field device transmitting/receiving unit outside the active communication mode, wherein the range is increased in particular to at least 2 times, preferably at least 10 times, compared to the range of the field device transmitting/receiving unit outside the active communication mode;
• - Activating and/or changing a display, in particular an optical and/or acoustic display, that is shown on a field device display unit.

Outside of the active communication mode, the range of the wireless communication connection of the field device transmitter/receiver unit is limited to a maximum of 1 m, especially 0.5 m, for example for security reasons, in order to prevent the field device from communicating with a mobile device further away. The limitation of the range therefore serves as protection against manipulation.

In active communication mode, the range can be increased, for example, by increasing the transmission power. The range outside of active communication mode is limited to a reduced value below a technically possible transmission power and an associated range. For example, a range of 100 m or even more is technically possible for Bluetooth. Even in active communication mode, the range may not be increased to the maximum technically possible value - for example, in order to continue to guarantee conformity with a standard laid down in the relevant norms.

The field device display unit includes, for example, an optical display unit, e.g. a physical or virtual display, such as an LCD display, an LED, etc. and/or an acoustic display unit such as a loudspeaker.

Activating and/or changing an optical display includes, for example: flashing, changing the color and/or brightness, switching through measurement and/or status values determined by the field device on a display, etc.

Activating and/or changing an acoustic indication includes, for example, playing and/or changing a sound, e.g. a beep, etc.

• - Aussenden eines Distanzschätzwert-Telegramms durch die Endgerät-Sende-/Empfangseinheit und Empfangen des Distanzschätzwert-Telegramms von der Feldgerät-Sende-/Empfangseinheit;
• - Ermitteln einer Signalstärke des Distanzschätzwert-Telegramms durch die Rechen-/Steuereinheit;
• - Bestimmen des aktuellen Distanzschätzwerts, basierend auf zumindest der ermittelten Signalstärke des Distanzschätzwert-Telegramms durch die Rechen-/Steuereinheit.

In one embodiment of the procedure, the procedure comprises the following steps:

• - Sending a distance estimate telegram by the terminal device transmitting/receiving unit and receiving the distance estimate telegram from the field device transmitting/receiving unit;
• - Determination of a signal strength of the distance estimation telegram by the computing/control unit;
• - Determining the current distance estimate based on at least the determined signal strength of the distance estimate telegram by the computing/control unit.

In this embodiment, the computing/control unit assigned to the field device preferably determines the current distance estimate itself. The field device is not switched using a distance estimate determined by the mobile device. Preferably, the mobile device does not estimate the distance and does not have to be designed to do so.

• - die Endgerät-Identifikationsinformation,
• - die Empfangszeitpunkt-Zeitinformation.

In one embodiment of the method, the distance estimate telegram comprises terminal identification information specific to the mobile terminal and/or the field device transmitting/receiving unit determines reception time information specific to a time of reception of the distance estimate telegram by the field device transmitting/receiving unit, wherein at least one of the following pieces of information is transmitted from the field device transmitting/receiving unit to the computing/control unit together with the determined signal strength:

• - the terminal identification information,
• - the reception time information.

The distance estimate is estimated specifically for the respective mobile terminal by the field device. This is done, for example (see the following embodiments), by storing the distance estimate as a distance estimate specific to a respective mobile terminal, by always linking it to the terminal identification information in a memory of the field device.

• - die Signalstärke, die Endgerät-Identifikationsinformation, die Empfangszeitpunkt-Zeitinformation, und den aktuellen Distanzschätzwert,

in einem schreib- und auslesbaren Speicher der Rechen-/Steuereinheit gespeichert.In one embodiment of the method, a data set comprising at least one of the following:

• - the signal strength, the terminal identification information, the reception time information, and the current distance estimate,

stored in a writable and readable memory of the computing/control unit.

• - Wiederkehrendes Aussenden von Distanzschätzwert-Telegrammen durch die Endgerät-Sende-/Empfangseinheit und Empfangen der wiederkehrend ausgesandten Distanzschätzwert-Telegramme von der Feldgerät-Sende-/Empfangseinheit.

In one embodiment of the procedure, this includes the step:

• - Recurrent transmission of distance estimate telegrams by the terminal device transmitting/receiving unit and reception of the recurrently transmitted distance estimate telegrams by the field device transmitting/receiving unit.

• - Löschen des Datensatzes aus dem Speicher, wobei das vorgegebene Grenz-Zeitintervall kleiner als fünf Minuten, insb. kleiner als eine Minute, und bevorzugt kleiner als eine halbe Minute ist.

In one embodiment of the method, this comprises the step: In the event that for a time interval which is greater than a predetermined limit time interval, no distance estimate telegrams are received from the field device transmitting/receiving unit which comprise terminal identification information matching terminal identification information of a data set stored in the memory:

• - Deleting the data record from memory, whereby the specified limit time interval is less than five minutes, in particular less than one minute, and preferably less than half a minute.

A time interval is therefore determined which has passed since the last reception of a distance estimate telegram sent by a respective mobile device. The time interval is determined, for example, on the basis of the time information at the time of reception and with the aid of a time recording unit (e.g. timer) which the field device, in particular the computing/control unit, has; see also the system mentioned below, which is also included in the invention. The limit time interval ensures that the memory is regularly emptied in the event that no more distance estimate telegrams are received from the respective mobile device. In this way, the memory is prevented from filling up, or the memory can be designed to be correspondingly small.

• - Ermitteln einer zuletzten Signalstärke, welche zuletzte Signalstärke der Signalstärke eines zuletzt empfangenen Distanzschätzwert-Telegramms entspricht;
• - Ermitteln eines zuletzten Zeitpunkts, welcher zuletzte Zeitpunkt dem Zeitpunkt des Empfangs des zuletzt empfangenen Distanzschätzwert-Telegramms entspricht;
• - Auslesen des vorherigen Distanzschätzwerts und des vorherigen Zeitpunkts aus dem Speicher;
• - Ermitteln einer Zeitdifferenz zwischen dem zuletzten Zeitpunkt und dem vorherigen Zeitpunkt; und
• - Bestimmen des aktuellen Distanzschätzwerts als ein geglätteter Schätzwert, wobei der aktuelle Distanzschätzwert sowohl von der zuletzten Signalstärke als auch von dem vorherigen Distanzschätzwert derart abhängt, dass der Beitrag der zuletzten Signalstärke und des vorherigen Distanzschätzwerts zu dem aktuellen Distanzschätzwert mittels eines Glättungskoeffizienten berücksichtigt werden, welcher Glättungskoeffizient von der Zeitdifferenz abhängt.

In one embodiment of the method, in the event that a previous distance estimate is stored in the memory, which previous distance estimate was determined on the basis of a previous distance estimate telegram received at a previous time, The step of determining the current distance estimate involves the following steps:

• - Determining a last signal strength, which last signal strength corresponds to the signal strength of a last received distance estimate telegram;
• - Determining a last time, which last time corresponds to the time of receipt of the last received distance estimate telegram;
• - Reading the previous distance estimate and the previous time from the memory;
• - Determining a time difference between the last time and the previous time; and
• - determining the current distance estimate as a smoothed estimate, wherein the current distance estimate depends on both the last signal strength and the previous distance estimate such that the contribution of the last signal strength and the previous distance estimate to the current distance estimate are taken into account by means of a smoothing coefficient, which smoothing coefficient depends on the time difference.

In a further development of the previous embodiment, the contribution of the last signal strength and the contribution of the previous distance estimate to the current distance estimate are taken into account by means of the smoothing coefficient such that the greater the time difference, the more the last signal strength and the less the previous distance estimate contribute to the current distance estimate.

wobei in obiger Formel für den Glättungskoeffizienten α (Δt) gilt 0 < α (Δt) < 1, und der Glättungskoeffizient α (Δt) mit wachsender Zeitdifferenz, insb. stetig, größer wird. Auf diese Art wird mit wachsender Zeitdifferenz der vorherige Distanzschätzwert Xid_tj schwächerund mit wachsender Zeitdifferenz wird die zuletzte Signalstärke SP_i stärker gewichtet. Dies entspricht einer sogenannten exponentiellen Glättung mit einem von der Zeitdifferenz abhängigen Glättungskoeffizienten α (Δt)For example, in the simplest case, a weighted average is used, where the current distance estimate Xid _ti is determined depending on the previous distance estimate Xid _tj and the last signal strength SP_i as: $${\text{Xid}}_{\text{ti}}=\mathrm{\alpha }\left(\mathrm{\Delta }\text{t}\right)*\text{SP}\_\text{i}+\left[1-\mathrm{\alpha }\left(\mathrm{\Delta }\text{t}\right)\right]*{\text{Xid}}_{\text{tj}},$$

where in the above formula the smoothing coefficient α (Δt) is 0 < α (Δt) < 1, and the smoothing coefficient α (Δt) increases with increasing time difference, especially steadily. In this way, the previous distance estimate Xid _tj becomes weaker with increasing time difference and the last signal strength SP_i is given greater weight with increasing time difference. This corresponds to a so-called exponential smoothing with a smoothing coefficient α (Δt) that depends on the time difference.

In a further development of the previous embodiment, the smoothing coefficient depends on the time difference in such a way that the time difference is included in the smoothing coefficient only in relation to the limit time interval, in particular as a quotient formed from the time difference divided by the limit time interval.

• - Bestimmen des aktuellen Distanzschätzwerts als die zuletzte Signalstärke, welche zuletzte Signalstärke der Signalstärke eines zuletzt empfangenen Distanzschätzwert-Telegramms entspricht.

In one embodiment of the method, in the event that no previous distance estimate is stored in the memory, the step of determining the current distance estimate comprises the following step:

• - Determining the current distance estimate as the last signal strength, which last signal strength corresponds to the signal strength of a last received distance estimate telegram.

• - Anzeigen des Feldgeräts in einem Anzeigeelement eines durch das mobile Endgerät ausgeführten Bedienprogramms, insb. gleichzeitig zu dem Aktivieren und/oder Ändern der, insb. optischen und/oder akustischen, Anzeige an der Feldgerät-Anzeigeeinheit.

In one embodiment of the method, the mobile terminal is designed to execute at least one operating program with a plurality of display elements and operating functionalities, wherein the field device can be operated by means of the operating program, and wherein at least the following steps are carried out during switching:

• - Displaying the field device in a display element of an operating program executed by the mobile device, in particular simultaneously with activating and/or changing the, in particular optical and/or acoustic, display on the field device display unit.

Such an operating program is published in the form of an app by the applicant under the name "SmartBlue". The app is used to display the display elements on the mobile device. Such display elements are, for example, control surfaces, menu structures and/or buttons via which operating inputs can be made, or graphs which visualize data from the field devices, e.g. measured values or status information. In the case of data glasses as a mobile device, for example, the display elements are displayed in the field of view and the execution of operating functions, e.g. control via gestures, takes place in the field of view. Using the method according to the invention, the respective field device that can be switched using the mobile device is now displayed in the operating program on the basis of the current distance estimate, by means of which a current physical proximity of the field device to the mobile device is identified. This is particularly advantageous if several field devices can be operated via the operating program, all of which are listed in the operating program. In this case, the field device that can be switched via the mobile device is specially displayed in the operating program, e.g. with a colored background.

• - ein erster Datensatz, der erste Datensatz umfassend einen ersten aktuellen Distanzschätzwert und/oder eine erste Signalstäke des ersten mobilen Endgeräts, mit einer zu einem ersten mobilen Endgerät gehörigen ersten Endgerät-Identifikationsinformation und
• - ein zweiter Datensatz, der zweite Datensatz umfassend einen zweiten aktuellen Distanzschätzwert und/oder eine zweite Signalstäke des zweiten mobilen Endgeräts, mit einer zu einem zweiten mobilen Endgerät gehörigen zweiten Endgerät-Identifikationsinformation gespeichert,

wobei sowohl der erste aktuelle Distanzschätzwerts als auch der zweite aktuelle Distanzschätzwert derart in Bezug dem Grenzwert sind, dass das Feldgerät sowohl durch das erste mobile Endgerät als auch durch das zweite mobile Endgerät mittels der drahtlosen Kommunikationsverbindung schaltbar ist,
und wobei das Verfahren den folgenden, vor dem Schalten des Feldgeräts durchzuführenden Schritt umfasst:

• - Auswahl eines der beiden mobilen Endgeräte für das Schalten, auf Basis von zumindest eines der folgenden:
  • - einem Vergleich des ersten aktuellen Distanzschätzwerts mit dem zweiten aktuellen Distanzschätzwert
  • - einem Vergleich der ersten Signalstärke mit der zweiten Signalstärke.

In one embodiment of the method, the memory

• - a first data set, the first data set comprising a first current distance estimate and/or a first signal strength of the first mobile terminal, with a first terminal identification information belonging to a first mobile terminal and
• - a second data set, the second data set comprising a second current distance estimate and/or a second signal strength of the second mobile terminal, stored with a second terminal identification information belonging to a second mobile terminal,

wherein both the first current distance estimate and the second current distance estimate are related to the limit value such that the field device can be switched by both the first mobile terminal and the second mobile terminal by means of the wireless communication connection,
and wherein the method comprises the following step to be performed before switching the field device:

• - Selection of one of the two mobile devices for switching, based on at least one of the following:
  • - a comparison of the first current distance estimate with the second current distance estimate
  • - a comparison of the first signal strength with the second signal strength.

• - ein Feldgerät der Automatisierungstechnik, aufweisend:
  • -- eine programmierbare Rechen-/Steuereinheit und
  • -- eine Feldgerät-Sende/Empfangseinheit, die von der Rechen-/Steuereinheit ansteuerbar ist; und
• - ein mobiles Endgerät aufweisend eine Endgerät-Sende-/Empfangseinheit;

wobei das System dazu ausgestaltet ist, das erfindungsgemäße Verfahren auszuführen.The invention further comprises an automation system comprising:

• - a field device of automation technology, comprising:
  • -- a programmable computing/control unit and
  • -- a field device transmitting/receiving unit that can be controlled by the computing/control unit; and
• - a mobile terminal having a terminal transmitting/receiving unit;

wherein the system is designed to carry out the method according to the invention.

The system includes, mutatis mutandis, all the above-mentioned embodiments of the procedure.

The invention is explained in more detail using the following figures, which are not to scale and in which the same reference symbols designate the same features. If this is required for clarity or if it otherwise seems expedient, reference symbols may be omitted in the figures.

• 1: Eine Ausgestaltung eines erfindungsgemäßen Systems 100;
• 2: Schritte des erfindungsgemäßen Verfahrens in einer Ausgestaltung des erfindungsgemäßen Verfahrens; und
• 3: Schritte des erfindungsgemäßen Verfahrens in einer Ausgestaltung des erfindungsgemäßen Verfahrens.

They show:

• 1 : An embodiment of a system 100 according to the invention;
• 2 : Steps of the method according to the invention in an embodiment of the method according to the invention; and
• 3 : Steps of the method according to the invention in an embodiment of the method according to the invention.

1 shows a system 100 of automation technology in one embodiment of the invention. In the embodiment shown here, this comprises two field devices 1a; 1b, which are installed in the same automation technology process plant, as well as two mobile terminals 2a; 2b. For the sake of clarity, the invention is explained using the system 100 shown here. Without limiting the generality, the system 100 can of course also comprise a large number of field devices 1a, 1b,... and mobile terminals 2a, 2b,... Each of the mobile terminals 2a, 2b and field devices 1a, 1b is equipped with a transmitting/receiving unit, by means of which a communication connection KV can be established. Furthermore, without limiting the generality, the invention is explained here and below in connection with transmitting/receiving units, which are designed to transmit telegrams TG in accordance with the wireless protocol of a Bluetooth standard, e.g. BLE. Of course, the invention also includes all other transmitting/receiving units or wireless protocols known from the prior art for establishing wireless communication connections KV.

For safety reasons, the range of Bluetooth is initially limited for the field devices 1a; 1b by artificially limiting the transmission power below a technically possible transmission power. The field device 1a; 1b periodically sends out telegrams using its field device transmitting/receiving unit 4. The terminal device 2a; 2b periodically listens to the wireless channel of the communication connection KV using the terminal transmitting/receiving unit 5. As soon as the terminal transmitting/receiving unit 5 is activated as in 1 When the field device receives the telegrams TG shown from the field device transmitting/receiving unit 4, it immediately responds with another telegram TG to request more data from the field device 1a, 1b. This step is also known in the state of the art as “advertising and scanning” (here with active scanning), e.g. in Framework of the above-mentioned BLE standard.

Preferably, the further telegram TG which the terminal transmitting/receiving unit 5 sends out as an immediate response to one of the telegrams TG periodically sent out by the field device transmitting/receiving unit 4 as part of the “advertising and scanning” is now used as a distance estimate telegram TGX. Preferably, the mobile terminal 2a; 2b only has to scan for telegrams TG and, upon receipt, immediately respond with the distance estimate telegram TGX. The actual estimation of the physical distance and the determination of a current distance estimate Xid _ti is carried out on the basis of the received distance estimate telegrams TGX by the field device 1a; 1b or its computing/control unit 3 itself. Since many of the operating systems used on common mobile devices 2a; 2b, e.g. Android/iOS, scan in the background by default (e.g. as soon as a display is unlocked), determining the current distance estimate Xid _ti within the scope of the method according to the invention is particularly practical.

In 1 For the sake of simplicity, it is only shown for the first field device 1a and the first mobile terminal 2a how the distance estimate telegram TGX is sent via the communication connection KV from a terminal transmitting/receiving unit 5 of the mobile terminal 2a; 2b and received by the field device transmitting/receiving unit 4. The current distance estimate Xid _ti correlates with a current physical distance between the field device 1a and the mobile terminal and is determined by a computing/control unit 3 of the field device 1a. The field device transmitting/receiving unit 4 of the field device 1a is part of a Bluetooth module 9, which comprises programmable components of the computing/control unit 3 of the field device 1a. The field device 1a comprises a memory 31, in which the quantities determined within the scope of the method according to the invention (see the following figure description for 2 ). If necessary, the computing/control unit 3 comprises a timer as a time recording unit 8 for carrying out the method according to the invention.

The field device 1a is switched by the mobile terminal 2a when it is determined on the basis of the current distance estimate Xid _ti that the mobile terminal 2a is sufficiently close to the field device 1a. This preferably happens automatically when a user carries the mobile terminal 2a and moves it through the process plant.

When the field device 1a is switched, it is, for example, put into an active communication mode in that the transmission power of the field device transmitting/receiving unit 4 is no longer artificially limited, thereby increasing the range of the communication connection KV.

Furthermore, when switching, for example, a field device display unit 6 (here an LED) is made to flash and/or changes color. In this way, it is immediately apparent from the mobile terminal 2a that the field device 1a is located near the mobile terminal 2a.

The mobile terminal 2a is preferably designed to execute an operating program 7 for operating the field devices 1a, 1b,..., for example for running the aforementioned "SmartBlue" app. Using the operating program 7, display elements for operating the field devices 1a, 1b (for example all of the applicant's field devices installed in the process plant) are shown on the mobile terminal 2a. The display elements are shown here by the individual boxes on a display unit of the mobile terminal 2a. Within the scope of the method according to the invention, in one embodiment, the display element that belongs to the field device 1a that is located near the mobile terminal 2a is specially highlighted (box with a solid border). In contrast, the display elements for all other field devices 2b,... are not specially highlighted (box with a hatched border). The highlighting takes place at the same time as the LED field device display unit 6 flashes. In this way, a field device 1a; 1b, e.g. for subsequent operation via the operating program 7, can be very easily identified after it has been switched by the mobile terminal 2a via the communication connection KV.

The exact determination of the current distance estimate Xid _ti is in 2 presented in more detail.

In a first step of the 2 shown design (cf. 1 ) the distance estimate telegram TGX is sent by the terminal transmitting/receiving unit 5 and received by the field device transmitting/receiving unit 4. The subsequent steps illustrate in more detail the concrete determination of the current distance estimate Xid _ti by the computing/control unit 3 of the field device 1a; 1b.

The steps of the method for determining the current distance estimate Xid _ti are at least partially implemented as a computer-aided method using an algorithm in the computing/control unit 3. As already mentioned above, the computing/control unit 3 is, in particular partially, assigned to a module 9 comprising the field device transmitting/receiving unit 4, for example a Bluetooth module - since, for example, a Bluetooth chip (partially) programmable software and/or the computing/control unit 3 is designed as an electronic component of the field device, e.g. a (programmable) microcontroller and/or an FPGA.

In a second step of the 2 In the embodiment shown, the signal strength SP is written into the memory 31 together with a reception time information EZ and an identification information ID specific to the respective mobile terminal 2a; 2b by the computing/control unit 3 and evaluated. The identification information ID is information by means of which the respective mobile terminal 2a; 2b can be clearly identified, for example a so-called MAC address (short for: “media access control”) and/or an IP address. The identification information ID, the reception time information EZ and the signal strength SP are transferred, for example, from a Bluetooth stack of the Bluetooth module. The so-called “Received Signal Strength Indicator” (short: RSSI) of the distance estimate telegrams TGX received by the field device transmitting/receiving unit 4 is used as the signal strength SP. A high RSSI correlates with a small physical distance between the field device 1a,1b and the mobile device 2a,2b.

In a third step of the 2 In the embodiment shown, it is checked whether a data set DS comprising the identification information ID is stored in the memory 31, that is, whether the mobile terminal 2a; 2b is known to the field device 1a; 1b, namely through the (recent) previous receipt of a distance estimate telegram TGX from the respective mobile terminal 2a; 2b.

In the event that no data set DS with the identification information ID is stored in the memory 31 (arrow "n" of the third step) and consequently no previous distance estimate Xid _tj is present in the memory 31, a last signal strength SP_i is determined as the current distance estimate Xid _ti . The last signal strength SP_i corresponds to the signal strength SP of a last received distance estimate telegram TGX.

wobei α (Δt) = α0+ Δt/timeout * (1- α0) ist. Hierbei ist α0 ist ein vorgegebener (d.h. hard-gecodeter) oder vorgebbarer Gewichtungsparameter, der zwischen 0 und 1 liegt. In jedem Fall ist aber Δt immer kleiner als der vorgegebene oder vorgebbare Parameter timeout, da der Speicher regelmäßig geleert wird, dies ist in Zusammenhang mit der nachstehend Beschreibung zu 3 näher erläutert. Daher gilt in jedem Fall 0< Δt/timeout < 1. Aus diesem Grund gilt auch in diesem Bsp. 0 < α (Δt) < 1.In the event that a data set DS with the identification information ID is stored in the memory 31 (arrow "y" of the third step), the current distance estimate Xid _ti is determined in a fourth step, based on both a previous distance estimate Xid _tj and on the basis of the last signal strength SP_i. The previous distance estimate Xid _tj was in turn determined on the basis of a previous distance estimate telegram TGX received at a previous time tj. This is therefore a recursive process. The previous distance estimate Xid _tj and the previous reception time tj (the latter can be determined from the reception time information EZ) are determined from the data set DS read from the memory 31. A time difference Δt between the last time ti and the previous time tj is then determined. Finally, the current distance estimate Xid _ti is determined as a smoothed estimate. The contributions of the last signal strength SP_i and the previous distance estimate Xid _tj to the current distance estimate Xid _ti are taken into account using a smoothing coefficient α (Δt) that depends on the time difference Δt. The larger the time difference Δt, the stronger the last signal strength SP_i contributes and the weaker the previous distance estimate Xid _tj contributes to the current distance estimate Xid _ti . The smoothing coefficient α(Δt) that depends on the time difference Δt is between 0 and 1. For example, the last signal strength SP_i and the previous distance estimate Xid _tj are weighted as follows: $${\text{Xid}}_{\text{ti}}=\mathrm{\alpha }\left(\mathrm{\Delta }\text{t}\right)*\text{SP}\_\text{i}+\left[1-\mathrm{\alpha }\left(\mathrm{\Delta }\text{t}\right)\right]*{\text{Xid}}_{\text{tj}},$$

where α (Δt) = α0+ Δt/timeout * (1- α0). Here, α0 is a given (ie hard-coded) or predefinable weighting parameter that lies between 0 and 1. In any case, Δt is always smaller than the given or predefinable parameter timeout, since the memory is regularly emptied, this is to be explained in connection with the description below. 3 explained in more detail. Therefore, in every case 0< Δt/timeout < 1 applies. For this reason, in this example 0 < α (Δt) < 1 also applies.

After it has been determined, the current distance estimate Xid _ti is written into the memory together with the time information EZ at the time of reception, the identification information ID and, if applicable, the current signal strength SP_i. If applicable, the data record DS in the memory 31 associated with a respective identification information ID is also overwritten as soon as the current distance estimate Xid _ti is re-determined by the field device transmitting/receiving unit 4, triggered by the repeated reception of a distance estimate telegram TGX with the same identification information ID (i.e. from the same mobile terminal 2a; 2b). After the current distance estimate Xid _ti has been re-determined, the previous distance estimate Xid _ti is no longer required. The new, current distance estimate Xid _ti then becomes the previous distance estimate Xid _tj from a time of a renewed, repeated reception of a distance estimate telegram TGX with the same identification information ID.

In a fifth step of the 2 In the embodiment shown, it is checked how the determined current distance estimate Xid _ti relates to a predetermined If the current distance estimate Xid _ti is in relation to the limit value GW in such a way that the distance between the field device 1a; 1b and the mobile terminal 2a; 2b is estimated to be sufficiently small, for example to a value less than 0.5 m, preferably less than 0.2 m, the field device 1a; 1b is switched by means of the mobile terminal 2a; 2b, preferably automatically. This is in the sixth step of the 2 shown configuration (box “s” for switch).

So that the memory 31 does not fill up or can be designed to be sufficiently small, a check is carried out for each data set DS in the memory 31 to determine how a time recorded with a time recording unit 8 behaves in relation to the reception time EZP and the limit time interval timeout. In the event that no new distance estimation telegrams TGX are received by the field device transmitting/receiving unit 4 for a time interval which is longer than a predetermined limit time interval timeout (i.e. with a terminal identification information ID that matches the terminal identification information ID stored in the memory 31), the data set DS associated with the identification information ID is deleted from the memory 31. For example, in the 3 The step shown checks whether the recorded time time minus the reception time EZP is less than the limit time interval timeout: $$\text{time}-\text{EZP}<\text{Timeout}$$

If this is the case, the data record DS is deleted from the memory 31. The specified timeout limit is less than five minutes, in particular less than one minute, and preferably less than half a minute.

If necessary, a global variable "Proxy" that can assume the value "True" (T) or "False" (F) is used to test whether any mobile terminal 2a; 2b is sufficiently close to the field device 1a; 1b. The variable Proxy initially assumes the value Proxy=F, at which the field device 1a; 1b cannot be switched by the mobile terminal 2a; 2b. Proxy=T is only set if the current distance estimate Xid _ti for at least one data set DS in the memory 31 relates to the limit value GW in such a way that the physical distance between the field device 1a; 1b and the mobile terminal 2a; 2b is estimated to be sufficiently small. Otherwise, the variable Proxy=F is set. If there is no mobile terminal 2a; 2b for whose current distance estimate Xid _ti in the memory 31, for example, Xid _ti > GW applies (or Xid _ti < GW, depending on the design of the method), then Proxy=F applies. In this case, the field device 1a; 1b is returned, preferably automatically, to the previous state, so that, for example, the field device 1a; 1b is outside of the active communication mode and the range of the field device transmitting/receiving unit 4 is reduced again and/or the display of the field device display unit 6 is deactivated again and/or no longer switched on. The value of the variable Proxy is constantly re-determined, for example triggered by the receipt of a new distance estimate telegram TGX and/or after the expiry of a time period of a limit time interval timeout (controlled by the time recording unit 8).

For example, the value automatically changes back from T to F if a mobile terminal 2a;2b is no longer sufficiently close to the field device 1a;1b due to a service technician carrying the mobile terminal 2a;2b continuing to walk, so that the data set DS is still present in the memory 31, but the switching condition (either Xid _ti < GW or Xid _ti > GW) is no longer met, or if, for example, the mobile terminal 2a;2b is switched off, so that after the expiry of the limit time interval timeout the data set DS belonging to the mobile terminal 2a;2b is deleted from the memory 31.

reference signs and symbols

100

system

1a, 1b

field devices

2a, 2b

mobile devices

3

computing/control unit

31

memory

4

field device transmitter/receiver unit

5

terminal transmitting/receiving unit

6

field device display unit

7

operating program

8

time recording unit

9

module

KV

communication connection

TG

telegrams

TGX, TGXi

distance estimation telegrams

Xidti„ Xid1ti, Xid2ti

current distance estimates

Xidtj

previous distance estimate

DS

data set

ID

identification information

EZ

reception time information

GW

limit

SP, SP_i

signal strength

Δt

time difference

α(Δt)

smoothing coefficient

time-out

limit time interval

time

time interval

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• DE 10 2020 120 297 A1 [0004]

Claims (15)

Method for establishing a wireless communication connection between a field device (1a; 1b) of automation technology and a mobile terminal (2a; 2b), for switching the field device (1a; 1b) by the mobile terminal (2a; 2b) by means of the wireless communication connection, the method comprising the steps: - providing a field device (1a; 1b) of automation technology, the field device (1a; 1b) having: --a programmable computing/control unit (3) --a field device transmitting/receiving unit (4) which can be controlled by the computing/control unit (3); - Providing a mobile terminal (2a, 2b) with a terminal transmitting/receiving unit (5), wherein the field device transmitting/receiving unit (4) and the terminal transmitting/receiving unit (5) are designed to communicate with one another by means of a wireless communication connection (KV), in particular using a predetermined frequency range, in particular according to a standardized communication protocol; - Transmitting telegrams (TG) from the terminal transmitting/receiving unit (5) to the field device transmitting/receiving unit (4) and/or from the field device transmitting/receiving unit (4) to the terminal transmitting/receiving unit (5) via the wireless communication connection; - Determining a current distance estimate (Xid _ti ) based on the transmitted telegrams (TG,TGX), which current distance estimate (Xid _ti ) correlates with a current physical distance between the field device (1a; 1b) and the mobile terminal (2a; 2b); and - Switching the field device (1a; 1b) based on the current distance estimate (Xid _ti ) procedure according to claim 1 , comprising the steps: - comparing the current distance estimate (Xid _ti ) with a predetermined or predefinable limit value (GW); - In the event that at least the current distance estimate (Xid _ti ) either exceeds or falls below the limit value (GW): switching the field device (1a; 1b). Method according to at least one of the preceding claims, wherein at least one of the following steps is carried out during switching: - Switching the field device (1a; 1b) to an active communication mode in which there is an increased range of the field device transmitting/receiving unit (4) compared to the range of the field device transmitting/receiving unit (4) outside the active communication mode, wherein the range is increased in particular to at least 2 times, preferably at least 10 times, compared to the range of the field device transmitting/receiving unit (4) outside the active communication mode; - Activating and/or changing a display, in particular an optical and/or acoustic display, which is displayed on a field device display unit (6). Method according to at least one of the preceding claims, comprising the steps: - sending a distance estimate telegram (TGX) by the terminal transmitting/receiving unit (5) and receiving the distance estimate telegram (TGX) from the field device transmitting/receiving unit; - determining a signal strength (SP) of the distance estimate telegram (TGX) by the computing/control unit; - determining the current distance estimate (Xid _ti ) based on at least the determined signal strength (SP) of the distance estimate telegram (TGX) by the computing/control unit. procedure according to claim 4 , wherein the distance estimate telegram (TGX) comprises terminal identification information (ID) specific to the mobile terminal (2a; 2b) and/or wherein the field device transmitting/receiving unit determines reception time information (EZ) specific to a time of reception of the distance estimate telegram (TGX) by the field device transmitting/receiving unit, and wherein at least one of the following information is transmitted together with the determined signal strength (SP) from the field device transmitting/receiving unit to the computing/control unit: - the terminal identification information (ID), - the reception time information (EZ). Method according to at least one of the preceding Claims 4 until 5 , wherein a data set comprising at least one of the following: - the signal strength (SP), the terminal identification information (ID), the reception time information, and the current distance estimate (Xid _ti ), is stored in a writable and readable memory (31) of the computing/control unit (3). Method according to at least one of the preceding Claims 4 until 6 , comprising the step: - recurring transmission of distance estimate telegrams (TGX1, ...) by the terminal transmitting/receiving unit (5) and receiving the recurring transmitted distance estimate telegrams (TGX1, ...) from the field device transmitting/receiving unit. Method according to at least one of the preceding Claims 4 until 7 , comprising the step: in the event that for a time interval (time), which time interval (time) is greater than a predetermined Limit time interval (timeout), no distance estimate telegrams (TGX1,...) are received by the field device transmitting/receiving unit (4) which comprise terminal identification information (ID) matching terminal identification information (ID) of a data set (DS) stored in the memory (31): - deleting the data set (DS) from the memory (31), wherein the predetermined limit time interval (timeout) is less than five minutes, in particular less than one minute, and preferably less than half a minute. Method according to at least one of the preceding Claims 4 until 8 , wherein, in the event that a previous distance estimate (Xid _tj ) is stored in the memory (31), which previous distance estimate (Xid _tj ) was determined on the basis of a previous distance estimate telegram received at a previous time (tj), the step of determining the current distance estimate (Xid _ti ) comprises: - determining a last signal strength (SP_i), which last signal strength (SP_i) corresponds to the signal strength (SP) of a last received distance estimate telegram and - determining a last time (ti), which last time (ti) corresponds to the time of receipt of the last received distance estimate telegram; - reading out the previous distance estimate (Xid _tj ) and the previous time (tj) from the memory (31); - determining a time difference (Δt) between the last time (ti) and the previous time (tj); and - determining the current distance estimate (Xid _ti ) as a smoothed estimate, wherein the current distance estimate (Xid _ti ) depends on both the last signal strength (SP_i) and the previous distance estimate (Xid _tj ) such that the contribution of the last signal strength (SP_i) and the previous distance estimate (Xid _tj ) to the current distance estimate (Xid _ti ) are taken into account by means of a smoothing coefficient (α (Δt)), which smoothing coefficient (α (Δt)) depends on the time difference (Δt); procedure according to claim 9 , whereby the contribution of the last signal strength (SP_i) and the contribution of the previous distance estimate (Xid _tj ) to the current distance estimate (Xid _ti ) are taken into account by means of the smoothing coefficient (α (Δt)) such that - the larger the time difference Δt, the more the last signal strength (SP_i) and the less the previous distance estimate (Xid _tj ) contributes to the current distance estimate (Xid _ti ). Method according to at least one of the Claims 9 until 10 , whereby the smoothing coefficient (α(Δt)) depends on the time difference (Δt) in such a way that the time difference (Δt) is included in the smoothing coefficient (α(Δt)) only in relation to the limit time interval (timeout), in particular as a quotient formed from the time difference (Δt) divided by the limit time interval. Method according to at least one of the preceding Claims 4 until 11 , wherein, in the event that no previous distance estimate (Xid _tj ) is stored in the memory (31), the step of determining the current distance estimate (Xid _ti ) comprises: - determining the current distance estimate (Xid _ti ) as the last signal strength (SP_i), which last signal strength (SP_i) corresponds to the signal strength (SP) of a last received distance estimate telegram. Method according to at least one of the preceding claims, wherein the mobile terminal (2a; 2b) is designed to execute at least one operating program (7) with a plurality of display elements and operating functionalities, wherein the field device (1a; 1b) can be operated by means of the operating program (7), wherein at least one of the following steps is carried out during switching: - Displaying the field device (1a; 1b) in a display element of an operating program (7) executed by the mobile terminal (2a; 2b), in particular simultaneously with activating and/or changing the, in particular optical and/or acoustic, display on the field device display unit. Method according to at least one of the preceding claims, wherein in the memory (31) - a first data set, the first data set comprising a first current distance estimate (Xid1 _ti ) and/or a first signal strength (SP1) of the first mobile terminal (2a), with a first terminal identification information (ID1) belonging to a first mobile terminal (2a) and - a second data set, the second data set comprising a second current distance estimate (Xid2 _ti ) and/or a second signal strength (SP2) of the second mobile terminal (2b), with a second terminal identification information (ID2) belonging to a second mobile terminal (2b) is stored, wherein both the first current distance estimate (Xid1 _ti ) and the second current distance estimate (Xid2 _ti ) are in relation to the limit value (GW) such that the field device (1a; 1b) can be accessed by both the first mobile terminal (2a) and the second mobile terminal (2b) by means of the wireless communication connection is switchable, and wherein the method comprises the following steps to be carried out before switching the field device (1a; 1b) Step comprises: - selecting one of the two mobile terminals (2a, 2b) for switching, based on at least one of the following: - a comparison of the first current distance estimate (Xid1 _ti ) with the second current distance estimate (Xid2 _ti ) - a comparison of the first signal strength (SP1) with the second signal strength (SP2). System (100) of automation technology, comprising: - a field device (1a, 1b) of automation technology, having: --a programmable computing/control unit (3) and --a field device transmitting/receiving unit (4) that can be controlled by the computing/control unit (3); and - a mobile terminal (2a; 2b) having a terminal transmitting/receiving unit (5); wherein the system is designed to carry out the method according to at least one of steps 1 to 14.

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