Data collection device with HART multiplexer

Abstract

The invention relates to a data acquisition device (6), which comprises a multi-channel HART multiplexer (9), whose channels (10) are provided with coupling elements (11) for capacitive coupling with a plurality of HART field devices fed by a current loop. A HART modem (12) is arranged downstream of the multiplexer, and a processor (13) with a field bus interface (14) and controlling the HART communication of the data acquisition device is arranged downstream thereof. In order to quickly and automatically identify changes in the connection configuration of the field devices capacitively coupled to the multiplexer, each channel is connected to a pulse discriminator (15), which detects signal pulses caused by interrupting and / or connecting the loop current on the channel and different from the HART signal, and generates an interrupt signal (18) for the processor when detecting the pulses. The processor is designed to terminate the HART communication running on the relevant channel in response to the interrupt signal and generate a HART command for requesting the identification of the HART field device on the channel.

Description

Technical Field

[0001] The invention relates to a data recording device, which has a HART multiplexer capacitively coupled to a plurality of HART field devices. Background Art

[0002] In facilities in the process industry, for example in the chemical, petrochemical, pharmaceutical, food and other product manufacturing industries, in the context of plant automation, at the field level, decentralized field devices perform predetermined functions and exchange process, facility and / or plant-related information with components of a higher-level control and management system and, if necessary, with each other. Field devices include sensors (measuring transducers) for example for level, flow, pressure and temperature, which transmit information in the form of measured values ​​of process parameters, and actuators, for example valve control drives or position regulators, which receive information in the form of manipulated values ​​in order to influence the process.

[0003] A widely used communication protocol for information transmission is HART (Highway Addressable Remote Transducer), in which the main process value, i.e. the actual measured value or the adjusted value, is transmitted via a current loop (two-wire line) as an analog 4-20 mA current signal, and the other data (HART information) can be modulated at the HART frequency between 1200 Hz and 2200 Hz by frequency shift keying (FSK) and transmitted digitally. The digital HART information can be commands, responses, parameters and variables, for example the temperature measurement value of a field device which operates according to the HART standard and is also referred to as a HART device.

[0004] The HART protocol distinguishes between master devices and slave devices, where HART field devices are usually slave devices that respond to commands from master devices. Typical master devices are decentralized input / output modules of automation systems, handheld operating devices or parameterization PCs (personal computers) with HART modems, which can be temporarily connected to the two-wire line via a point-to-point connection for commissioning and diagnostics of field devices.

[0005] HART-enabled input / output modules of automation systems enable permanent point-to-point connections, but many automation systems cannot directly access HART information. Since it can be very expensive to retrofit conventional input / output modules with HART-compatible I / O cards, HART multiplexers can be used instead, which collect the HART information from multiple HART field devices and provide it to the automation system via a standardized fieldbus interface (EP 0964325A1). In order not to affect the 4-20 mA current signal, the channels of the HART multiplexer are preferably capacitively coupled to different two-wire lines. If (as is usually the case) multiple HART channels are assigned to only one HART modem in order to reduce the complexity of the device technology and the costs associated therewith, the already small transmission capacity is further reduced due to the multiplexing operation.

[0006] During commissioning and startup, the user starts a scan of the field devices connected to the HART multiplexer, where all HART information is cyclically read and the individual field devices are identified (HART command 0: Read transmitter unique identifier). For the reasons mentioned above, this can take several minutes, depending on the number of connected field devices. If a field device is subsequently removed, replaced or a new field device is connected, the scan must be repeated manually, otherwise the automation system has no information about the changes. If the scan is not triggered manually, the automatic detection of the newly connected or replaced device can take several minutes, hours or days, so that the data transmitted during this period does not correspond to the real new configuration. Due to the capacitive coupling to the two-wire line, the loop current cannot be recorded to detect changes in the field device connection configuration.

[0007] The following situations may occur:

[0008] The field device is removed. If no response to HART command 0 is received after a preset time has passed, the automation system recognizes the configuration change only after a few minutes, hours or even days with a new scan. In practice, it is recommended to set the scan period to, for example, one day in order to reduce the communication load and speed up the reading of important HART information, such as reading primary HART variables (PV) for the purpose of secondary process monitoring (condition monitoring).

[0009] Replacement of an existing field device with a new field device. Here too, the automation system only recognizes the change relatively late, when it receives the long address of the new field device in response to HART command 0.

[0010] New field devices are connected to channels of the multiplexer that are not occupied at this time. It is recommended to deactivate unoccupied channels to speed up the overall communication. Therefore, newly connected field devices cannot even be detected for deactivated channels. If unoccupied channels are not deactivated, the recognition of the change will be delayed as in the above case.

[0011] Although users can start a scan themselves after each configuration change, manual intervention is still required afterwards. Summary of the invention

[0012] It is therefore an object of the present invention to quickly and automatically detect changes in the connection configuration of a field device capacitively coupled to a HART multiplexer.

[0013] According to the present invention, this object is achieved by the data collection device of the present invention.

[0014] Therefore, the object of the present invention is a data recording device having:

[0015] A multi-channel HART multiplexer, whose channels are equipped with coupling elements for capacitive coupling with a plurality of HART field devices fed via a current loop;

[0016] a HART modem disposed downstream of the HART multiplexer; and

[0017] A processor is arranged downstream of the HART modem and between the HART modem and the field bus interface, the processor controlling the HART communication of the data collection device,

[0018] in,

[0019] A pulse discriminator is connected to each channel, the pulse discriminator detects signal pulses caused by interrupting and / or making the loop current on the channel and different from the HART signal, and the pulse discriminator generates an interrupt signal for the processor when detected, and

[0020] The processor is designed to terminate the HART communication running on the relevant channel in response to the interrupt signal and to generate a HART command for requesting identification of the HART field device at the channel.

[0021] When a field device is removed or added, the current loop is disconnected or connected. In both cases, the current interruption or the connection of the loop current will generate a voltage spike on the relevant channel of the HART multiplexer after the capacitive coupling. When the HART signal with an amplitude of about 1mA peak-to-peak is modulated onto the loop current, the interruption or connection of the loop current will cause a sudden current change between 4 and 20mA. In addition, HART modulation occurs at a well-defined frequency. Therefore, with the help of a pulse discriminator, the signal pulses on the multiplexer channel caused by interrupting and / or connecting the loop current can be detected. When such an event is detected, the processor (computing unit) will be prompted to terminate any HART communication that may occur on the relevant channel and output a HART command, especially a HART command 0, through the channel. If the field device has been removed, the processor will not receive a response after the preset time has passed. The data collection device then knows that the relevant channel is not occupied, and can then, for example, deactivate the channel and / or report the change of the loop configuration to the superior unit through the fieldbus interface. If the field device is added for the first time or as an exchange for a previous field device, the processor receives an identifier (eg, a long address) of the new field device as a response to the HART command for identification and can report the configuration change to a superordinate unit.

[0022] In order to reliably detect the interruption and / or connection of the loop current, the signal pulses on the channel are identified by an adjustable detection threshold that can also be preset individually for each channel or pulse discriminator. As mentioned above, the sudden change of current caused by interruption and / or connection of the loop current is different from the HART signal in terms of amplitude and frequency. Since interference such as EMC (electromagnetic compatibility) interference or poor electrical contact on the current loop must be taken into account, it is advantageous to perform frequency filtering in the pulse discriminator. For this purpose, each pulse discriminator can each have a frequency filter, which is permeable to frequencies outside the HART frequency range, such as a bandpass filter, and the frequency filter has a (threshold) comparator arranged downstream, and when the filtered signal passing through the frequency filter exceeds the detection threshold (threshold), the comparator generates an interrupt signal for the processor.

[0023] Additionally or alternatively, a software filter can be implemented in the processor of the data collection device, which analyzes the frequency of occurrence of the received interruption signal so as to distinguish the interruption signal caused by interruption and / or connection of the loop current from the interruption signal caused by interference on the current loop. The interruption signal caused by interruption and / or connection of the loop current is only occasional and rarely occurs, while the interruption signal caused by EMC interference or poor contact (false connection) is more frequent and lasts longer. By distinguishing the interruption signal according to possible causes, it is possible to prevent the processor from continuously generating HART commands to request identification of the HART field device in the event of an interruption signal related to a fault, thereby preventing actual HART communication. According to the frequency of occurrence of the interruption signal, filtering can be implemented for all channels of the multiplexer together or for different channels according to different standards that may be preset by the user. In addition, the detection threshold can be advantageously adaptively changed until the frequency of occurrence of the interruption signal depending on the interference is minimized. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The invention will be described below with reference to the accompanying drawings and by way of example.

[0025] Figure 1 An example of a data collection device having a HART multiplexer is shown, which collects HART information from field devices and provides it to an automation system via a standardized interface, and

[0026] Figure 2 A more detailed example of the data collection device according to the present invention is shown. DETAILED DESCRIPTION

[0027] The same reference numerals have the same meaning in the different figures. The figures are purely schematic and do not represent any scale.

[0028] Figure 1 A simplified schematic diagram of a HART field device 1 is shown, which is, for example, a measuring transducer, which is connected to an input / output module 3 of an automation system, not shown here, via a current loop (two-wire line) 2. The input / output module 3 contains a voltage source 4, which provides auxiliary energy for the measuring transducer, wherein the measuring transducer adjusts its current consumption so that the loop current I corresponds to a current measurement value in the range between 4 and 20 mA. As a result, the load 5 arranged in the current loop 2 drops a voltage proportional to the current I and therefore to the measurement value, which is evaluated for indication or further processing purposes. The voltage source 4 can also be arranged in a separate power supply outside the input / output module 3. If the field device 1 is an actuator, the loop current I is adjusted in the input / output module 3.

[0029] In addition to the analog 4-20mA signal, the HART field device 1 can also send and receive digital information (HART information). In order to send the HART information, a digital HART signal with a peak-to-peak value of about 1mA and a HART frequency (a frequency of 1200Hz for binary one and 2200Hz for binary zero) is superimposed on the loop current I. Assuming that the input / output module 3 does not have a HART function, a data acquisition device 6 is provided for this purpose, which extracts HART information from the current loop 2, such as diagnostic data of the field device 1 and transmits it to a higher-level unit, such as an automation system, or as shown here, to an application in a cloud system 8 via a gateway 7. Conversely, HART information, such as commands, are transmitted from the gateway 7 to the HART field device 1 via the data acquisition device 6.

[0030] In order to be able to digitally communicate with multiple, for example up to eight HART field devices 1, the data recording device 6 includes a multiplexer 9 with eight channels 10, wherein each channel 10 is equipped with a coupling element 11 for capacitive coupling to the HART field device 1. The function of the coupling element 11 is to allow only the HART signal to reach the channel 10, while the relatively slowly changing loop current I is away from the multiplexer 9. In the illustrated embodiment, for the sake of clarity, the coupling element 11 connected to the current loop 2 of the HART field device 1 is shown only for one of the channels 10. Since the load 5 is already present in the input / output module 3, the coupling element 11 is connected in parallel with the field device 1. Otherwise, the load 5 can be integrated in the coupling element 11 and then connected in series to the current loop 2.

[0031] Arranged downstream of the HART multiplexer 9 is a HART modem 12 which demodulates the HART signals received in a time-division multiplexed manner from the field device 1 and modulates the HART signals to be transmitted to the field device 1 .

[0032] A processor 13 is arranged downstream of the HART modem 12, which coordinates the HART communication of the data acquisition device 6 and establishes a connection to the gateway 7 via a standardized fieldbus interface 14, such as RS-485, and acts as a protocol converter for converting the HART protocol into a protocol such as a Modbus or Ethernet protocol and vice versa.

[0033] Figure 2A more detailed example of a data acquisition device 6 is shown. A pulse discriminator 15 is connected to each channel 10, which is designed to detect signal pulses caused by interrupting and / or connecting the loop current I on the relevant channel 10 and different from the HART signal. In the embodiment shown, each pulse discriminator 15 includes a frequency filter 16, which is transparent to certain frequencies outside the HART frequencies of 1200 Hz and 2200 Hz. The frequency filter 16 can be a bandpass filter, for example. A comparator 17 is arranged downstream of each frequency filter 16, and when the filtered signal passing through the frequency filter 16 exceeds a detection threshold 19 in the form of a threshold, the comparator generates an interrupt signal 18 for the processor 13 on the output side. The threshold 19 can be set separately for each channel 10, or the same threshold can be set for all channels 10. The processor 13 has an interrupt pin for each interrupt signal 18. In the embodiment shown, the processor 13 generates a respective threshold 19 for each comparator 17. However, the processor 13 can also generate a common threshold 19 for all comparators 17.

[0034] The processor 13 also contains a software filter 20, which for each channel 10 distinguishes interrupt signals that may be caused by interruption and / or switching of the loop current I from interrupt signals that may be caused by interference on the current loop 2, based on the frequency of occurrence of the received interrupt signals 18. In this case, interrupt signals that occur separately subsequently are rarely identified as interrupt signals caused by interruption and / or switching of the loop current I. Interrupt signals that occur frequently and last for a long time are identified as interrupt signals caused by interference on the corresponding current loop 2. Depending on the determined frequency of occurrence, the processor 13 can automatically or under user guidance adaptively adjust the detection threshold 19 until the frequency of occurrence of interrupt signals 18 due to interference is minimized. If, for example during operation, the frequency of occurrence of interrupt signals due to interference exceeds the threshold value, this can be indicated to the user, for example, by an LED 21 or in some other way, or sent as diagnostic information to the gateway 7 for forwarding.

[0035] In the case where an interruption signal caused by an interruption and / or a connection of the loop current I has been identified, if HART communication is currently occurring on the relevant channel 10, the processor 13 first terminates the HART communication. The processor 13 then generates a HART command 0 for the channel 10 so that the field device 1 that may be connected to the channel 10 requests identification. If there is no response within a predetermined time, the processor 13 identifies the corresponding channel 10 as unoccupied. If the channel 10 was not occupied before and a response from the field device 1 is now received, the processor 13 identifies that a new field device has been added. Configuration changes on the channel identified by the processor 13 can be transmitted to the gateway 7 in the form of a "change bit" in the transmission information, and the gateway 7 can therefore read information about configuration changes, such as the address of a newly added field device, from the data collection device 6 with the highest priority.

Claims

1. A data collection device (6), comprising: A multi-channel HART multiplexer (9), wherein the channels (10) of the multi-channel HART multiplexer are equipped with coupling elements (11) for capacitive coupling with a plurality of HART field devices (1) fed via a current loop (2); a HART modem (12) arranged downstream of the HART multiplexer (9); and a processor (13), which is arranged downstream of the HART modem (12) and between the HART modem and the field bus interface (14), and controls the HART communication of the data collection device (6). in, A pulse discriminator (15) is connected to each of the channels (10), the pulse discriminator detecting signal pulses which are caused by interrupting and / or connecting the loop current (I) on the channel (10) and which are different from the HART signal, and the pulse discriminator generates an interrupt signal (18) for the processor (13) when detecting the signal pulses, and The processor (13) is designed to terminate the HART communication running on the relevant channel (10) according to the interrupt signal (18) and generate a HART command for requesting identification of the HART field device at the channel (10).

2. The data collection device (6) according to claim 1, characterized in that: Each of the pulse discriminators (15) is designed to discriminate signal pulses using a settable detection threshold (19).

3. The data collection device (6) according to claim 2, characterized in that: The processor (13) is designed to preset the detection threshold (19) individually for each of the pulse discriminators (15).

4. The data collection device (6) according to claim 2 or 3, characterized in that: Each of the pulse discriminators (15) has a frequency filter (16) that can pass frequencies outside the HART frequency range, and the frequency filter has a comparator (17) arranged downstream, which generates the interrupt signal (18) when the signal passing through the frequency filter (16) exceeds the detection threshold (19).

5. The data collection device (6) according to claim 4, characterized in that: The frequency filter (16) comprises a bandpass filter.

6. The data collection device (6) according to claim 1, characterized in that: The processor (13) contains a software filter (20) which distinguishes, based on the frequency of occurrence of the interrupt signal (18), between interrupt signals caused by interruption and / or switching on the loop current (I) and interrupt signals caused by interference.

7. The data collection device (6) according to claim 2, characterized in that: The processor (13) contains a software filter (20) which distinguishes, based on the frequency of occurrence of the interrupt signal (18), between interrupt signals caused by interruption and / or switching on the loop current (I) and interrupt signals caused by interference.

8. The data collection device (6) according to claim 7, characterized in that: The processor (13) is designed to adaptively adjust a detection threshold (19) in order to minimize the frequency of occurrence of interference-dependent interruption signals (18).

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