DE102016117624A1 - Method for improving the measuring performance of a field device and field device - Google Patents

Abstract

The invention relates to a method for improving the measuring performance of a field device (FG) of process automation, wherein the field device (FG) comprises at least one wireless module (BT) and at least one functional module (M) for detecting a measured variable and wherein the field device (FG) is replaced by a Two-conductor bus (4) is supplied with energy, and wherein depending on environmental parameters, the transmission and / or reception power of the wireless module (BT) is adjusted. The invention further relates to a field device (FG) for carrying out such a method.

Description

The invention relates to a method for improving the measurement performance of a field device of process automation and such a field device.

In process automation technology, field devices are often used to detect and / or influence process variables. A large number of such field devices are manufactured and distributed by the Endress + Hauser Group.

Frequently, field devices are connected to a control center using two-wire technology. In two-wire technology, or else two-wire technology, power is sent to the power supply and communication signals are sent via the same line: a wire for the way out, a wire for the way back. In other words, power and signal use the same line; there is no separate energy supply. This current or the corresponding power must be managed by the field devices and shared among the individual components of the field device. For example, the sensor element for detecting the process variable, the communication with other units and the controller have to get along with the existing power budget.

The elimination of wired data transmission for the connection of a field device in the industrial sector has the potential to reduce costs for cabling, to improve the usability and thus to generate benefits for the user.

There are measuring methods that do not manage without an energy storage in the form of an energy storage capacitor, since the available power is not sufficient for the measurement and energy must first be collected between the measurements. An example of this is a level measurement according to the radar principle. Adding an energy-efficient wireless interface to an appropriate meter requires no additional energy storage in the system if the meter is powered solely by the existing energy storage capacitor. The measurement is in this case performed only when the energy storage capacitor has a sufficient capacity. The duration of the period between the individual measurements then depends on how much power is required by the wireless interface and further functional modules in the system just out of the two-wire current loop. Excess power is stored in the corresponding energy storage capacitor.

The US 7,262,693 for example, discloses the use of a capacitor to latch the power from the bus to then provide it to a wireless module.

Depending on the power consumption of the measuring function, however, an exact simultaneous operation of the measurement and radio transmission is often not possible. Then it is e.g. required to perform the measurement alternately to the radio transmission in order to continue to get along without energy storage in the system.

As mentioned, however, both functions (radio transmission and measurement) can often not be operated simultaneously because then a synchronization of the various units is necessary so that the power balance of the entire device can be maintained or it is often necessary to give priority to one of the functions in terms of energy consumption ,

If, for example, priority is given to the radio module, this is at the expense of the measuring performance. If more energy is consumed by the wireless function, less energy is available for the measurement function and thus can be measured less frequently or less intensively, which ultimately leads to a reduction in measurement performance and thus to restrictions for the user.

The invention has for its object to ensure a sufficiently high accuracy of a field device.

The object is achieved by a method wherein the field device comprises at least one wireless module and at least one functional module for detecting a measured variable and wherein the field device is supplied with energy by a two-conductor bus, and adapted depending on environmental parameters, the transmitting and / or receiving power of the wireless module becomes.

Preferably, with decreasing transmission and reception power of the wireless module, the measurement performance of the field device is increased by changing operating parameters, and vice versa.

In one advantageous refinement, the operating parameters are the measurement rate, measurement power, resolution, mathematical operations, clock rate of participating computation units, activation of additional evaluation units, compensation units, etc. In general, the operating parameters are operations and settings that increase energy consumption Improvement of measuring accuracy and measuring speed require.

In a further preferred development, the connection quality between the field device and a receiver is measured, and the transmission and / or reception power is reduced to a defined minimum, so that the required measurement performance is still maintained. As a result, the consumed power of the wireless module is reduced and thus more energy is available to the functional module.

In an advantageous embodiment, the connection quality determined by the ambient conditions is measured by the field device and / or the receiver by means of the measurement of the Received Signal Strength Indicator (RSSI) and / or the packet error rate.

In this case, in a preferred embodiment, the distance from field device to receiver can be determined at least qualitatively on the basis of this measurement.

In an advantageous embodiment, the operation of the wireless module and the functional module is controlled so that the wireless module energy priority over the functional module has priority.

It is particularly advantageous that no synchronization takes place between the wireless module and the functional module.

The environmental parameters are preferably at least one of the parameters: distance between the field device and a receiver, atmospheric attenuation / absorption, attenuation / absorption by persons and objects in the vicinity of the field device and / or the receiver, and / or reflections and cancellation by superimpositions of radio waves, electromagnetic interference fields / waves, other sparking systems in the environment and weather phenomena which affect the connection quality.

The object is likewise achieved by a field device which is set up to carry out a method described above.

The invention will be explained in more detail with reference to the following figure. The 1 shows a field device in which the method according to the invention is applied.

1 shows field devices FG of process automation technology. More specifically, two field devices FG1 and FG2 are depicted, these being sensors. The sensor is a pH, redox potential, ISFET, conductivity, turbidity or oxygen sensor. Further possible sensors are flow sensors according to the principles of Coriolis, magnetic induction, vortex and ultrasound. Further possible sensors are sensors for measuring the fill level according to the principles of guided and free-radar radar and ultrasound, also for detecting a limit level, which can also be used to detect the limit level and capacitive methods. The sensor comprises a sensor element as a function module M of the field device FG. Also, the sensor element part of the electronic circuit 2 be, see below.

Shown is a pH sensor on the left and a fill level sensor on the right according to the radar principle. The field device FG determines a measured variable of a medium 1 , in the example in a cup as shown on the left. However, other containers such as pipes, basins (as shown on the right side), container, boiler, pipe, pipe or similar. possible.

The field device FG communicates with a control station, for example directly with a control system 5 or with an intermediate transmitter. Also, the transmitter may be part of the field device, such as in the case of the level sensor. The communication to the control system 5 via a two-conductor bus 4 , for example via HART, PROFIBUS PA or FOUNDATION Fieldbus. It is also possible the interface 6 Additionally or alternatively, the bus can be designed as a wireless interface, for example according to the WirelessHART standard (not shown), whereby a connection is made directly to a control system via WirelessHART via a gateway. In addition, a 4..20 mA interface is optionally or additionally provided in the case of the HART protocol (not shown). If communication takes place additionally or alternatively to a transmitter instead of directly to the control system 5 , either the above-mentioned bus systems (HART, PROFIBUS PA or FOUNDATION Fieldbus) can be used for communication or, for example, a proprietary protocol, for example of the "Memosens" type is used. Corresponding field devices as described above are distributed by the applicant.

As mentioned, there is an interface at the bus end of the field device FG 6 to connect to the two-way bus 4 intended. Shown is a wired variant for connection to the bus by means of the interface 6 , the interface 6 is designed, for example, as a galvanically isolating, in particular as an inductive interface. This is shown with the pH sensor. the interface 6 then consists of two parts with a first part on the field device side and a second part on the bus side. These can be coupled together by means of a mechanical plug connection. It will be over the interface 6 Data (bidirectional) and energy (unidirectional, ie in the direction of the control station 5 sent to field device FG). Alternatively, an appropriate cable with or without galvanic isolation is used. Possible versions include a cable with an M12 or 7/8 "plug. This is shown for example in the level measuring device according to the radar principle.

The field device FG further comprises an electronic circuit 2 comprising a wireless module BT for wireless communication 3 , This wireless communication 3 does not serve the connection to the Zweileiterbus 4 ,

The wireless module BT is designed as a Bluetooth module. In particular, the Bluetooth module complies with the protocol stack Low Energy as "Bluetooth Low Energy" (also known as BTLE, BLE, or Bluetooth Smart). Optionally, the wireless module BT comprises a corresponding circuit or components. The field device FG thus satisfies at least the standard "Bluetooth 4.0".

The communication 3 takes place from the field device FG to a higher-level unit H here or receiver. This is not shown to scale. The higher-level unit H is, for example, a mobile unit such as a mobile phone, a tablet, a notebook, or the like. Alternatively, the higher-level unit H can also be designed as a non-portable device, such as a computer. Alternatively, the higher-level unit H is a display with a corresponding interface.

In order to ensure a sufficiently high measurement accuracy of the field device FG, depending on the connection quality, the transmission and reception power of the wireless module BT is reduced to a defined minimum. As a result, the consumed power of the wireless module is reduced, and thus more energy is available to the functional module M. The chipsets available today for the BT wireless module allow adjustment and measurement of various parameters. It may even be possible to put the chip BT in a "whisper mode" to further save energy.

The inventive method provides to reduce the transmission and reception power of the wireless module so as to increase the measurement performance of the field device by changing operating parameters. The operating parameters are, for example, the measurement rate, measurement accuracy, resolution, mathematical operations, etc. In this case, the transmission and / or reception power of the wireless module BT is adjusted as a function of ambient parameters. At least one of the parameters distance between field device FG and a receiver H, atmospheric damping / absorption, damping / absorption by persons and objects in the vicinity of the field device FG and / or the receiver H, and / or reflections and cancellation by Superimpositions of radio waves, electromagnetic interference fields / waves, other sparking systems in the environment and weather phenomena that affect the quality of the connection are understood.

To determine the link quality determined by the environmental conditions, two independent measurements are made either by the field device FG, the receiver H, or both. On the one hand, the measurement of the Received Signal Strength Indicator (RSSI) should be mentioned. The RSSI is the received broadband power in the frequency channel, including thermal noise and noise generated in the receiver itself. Also, the power components from all other sources, for example, neighboring neighboring cells and adjacent channel interference, are included in the measurement. Second, this is the measurement of the packet error rate, i. how many packets per time unit arrive undisturbed at the receiver. Or in other words, it checks how many repetitions were necessary to transmit the packets / time unit. In order to determine the packet error rate by the field device FG, a feedback of the respective remote station H is necessary. If the measurement is located at the receiver H, an adjustment between transmitter FG and receiver H is necessary only for acyclic data transmission.

Based on these two measurements, it is possible to approximate the distance between the measuring device and the evaluation unit.

The wireless module BT always transmits with the lowest possible power and thus provides the measuring function with the greatest possible power component from the overall budget of the two-wire interface 4 to disposal. Thus, the measurement performance is increased, for example, by increasing the measurement rate, measurement accuracy, further calculation such as averaging, clock rate of participating computing units, activation of additional evaluation, compensation units, etc. In general, it is operations and settings, the increased energy consumption to improve the accuracy and measurement speed require.

A synchronization of the wireless module BT with the function module M does not take place. In the optimal case, this is not necessary either, since sufficient power is available for both.

As an additional aspect, it should be mentioned that the security is increased if the field device does not transmit FG with maximum possible power, but with minimum required power, since then the " Action radius "of the field device FG with the radio transmission is limited.

LIST OF REFERENCE NUMBERS

1

 Container with medium to be measured

2

 Electronic switch

3

 wireless connection

4

 two-wire bus

5

 control Unit

6

 interface

BT

 wireless module

C

 Energy storage capacitor

FG

 field device

H

 Parent unit

M

 function module

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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 assumes no liability for any errors or omissions.

Cited patent literature

• US 7262693 [0006]

Claims (10)

Method for improving the measuring performance of a field device (FG) of process automation, wherein the field device (FG) comprises at least one wireless module (BT) and at least one function module (M) for detecting a measured variable and wherein the field device (FG) is controlled by a two-wire bus (FG) 4 ) is supplied with energy, and wherein depending on environmental parameters, the transmission and / or reception power of the wireless module (BT) is adjusted. The method of claim 1, wherein with decreasing transmission and reception power of the wireless module (BT), the measurement performance of the field device (FG) by changing operating parameters, is increased, and vice versa. Method according to claim 2, wherein the operating parameters are the measuring rate, measuring power, resolution, mathematical operations, clock rate of participating computing units, activation of additional evaluation units, compensation units, etc. Method according to at least one of claims 1 to 3, wherein the connection quality between the field device (FG) and a receiver (H) is measured, and wherein the transmitting and / or receiving power is reduced to a defined minimum, so that the required measurement performance just barely is complied with. Method according to claim 4, wherein the connection quality determined by the ambient conditions is measured by the field device (12) and / or the receiver (12) by means of the received signal strength indicator (RSSI) measurement and / or the packet error rate. Method according to claim 5, wherein at least qualitatively the distance from field device (FG) to receiver (H) is determined on the basis of the measurement. Method according to at least one of claims 1 to 6, wherein the operation of the wireless module (BT) and the functional module (M) is controlled so that the wireless module (BT) energy priority over the function module (M) has priority. Method according to at least one of claims 1 to 7, wherein no synchronization takes place between the wireless module (BT) and the functional module (M). Method according to at least one of claims 1 to 8, wherein the environmental parameters are at least one of the following parameters: distance between field device (FG) and a receiver (H), atmospheric attenuation / absorption, attenuation / absorption by persons and objects in the field Field device (FG) and / or receiver (H) environment, and / or reflections and radio wave superimpositions, electromagnetic interference fields / waves, other surrounding sparking systems, and weather phenomena affecting link quality. Field device (FG) for process automation, which is adapted to carry out the method according to at least one of the preceding claims.

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