Traditionally, the worlds of PLC, motion control and control technology on one hand, with measurement technology and laboratory applications on the other, have diverged when it comes to data entry and processing in an industrial environment. Yet divergence always means having to use additional interfaces, which leads to restrictions on efficiency and operating convenience. But why have this separation in the first place? For some time now, PC-based control from Beckhoff has offered sufficient performance reserves to manage both tasks seamlessly, and from the computer to the high-speed EtherCAT fieldbus and the wide range of I/O terminals for measurement in particular.
The reason for the traditional separation of the two data processing worlds is precisely why PC-based control is of such an enormous benefit today: Until just a few years ago, the computing power of control systems was far too limited for handling automation and measurement technology. Thanks to Moore‘s Law and its predicted rapid advancement of PC technology, high-performance automation and sophisticated measurement data processing, as well as functions such as condition monitoring and energy monitoring, can now be united. Taking the step from conventional PLC technology to PC-based control must be accompanied by a corresponding change in thinking, in other words, integration of measurement technology aspects during development and design.
Measurement technology from standard to high-end functionality
This shift in thinking is extremely simple thanks to a unique approach from Beckhoff. Measurement technology is no longer restricted to a ‘black box’ that is difficult to integrate. Rather, it can be implemented directly in a familiar and easily upgraded engineering environment that utilises standard I/O components. The main advantage is in the underlying system structure: The measured data is captured in a simple, cost-effective and optimally scalable manner directly at the machine using measuring terminals and is then transmitted for processing to high-performance industrial PCs via extremely fast EtherCAT communication. All of the software modules, for example PLC, measurement technology and visualisation, are combined on a single platform for the purpose of integrating the two worlds of control and measurement technology.
High-end measurement applications and standard measurement technology tasks are capably covered thanks to a comprehensive range of measurement I/O terminals. The numerous analogue input terminals with standard resolution will suffice for many applications: for example, the KL30xx Bus Terminals as well as EL30xx EtherCAT Terminals with 12 bit resolution record analogue signal voltages in a wide signal range. Standard EL31xx analogue input terminals with 16 bit resolution are already suitable for high-precision control processes. In addition, they also support time-critical applications thanks to the extremely fast A/D conversion time and provide support for EtherCAT distributed clocks.
High-end technology is further supported by terminals with 18 and 24 bit resolution and the corresponding measurement accuracy for standard current and voltage signals. In addition, highly accurate models are available for connecting thermocouples and resistance thermometers as well as versions for especially complex signals, such as performance measurement or condition monitoring based on IEPE acceleration sensors. The EtherCAT Terminals enable the development of technically demanding solutions through the support of XFC technology (eXtreme Fast Control) from Beckhoff and with it, advanced functions like oversampling.
XFC delivers high-speed data acquisition for measured values
XFC technology is based on an optimised control and communication architecture comprising an industrial PC, I/O terminals with extended real-time characteristics and EtherCAT and TwinCAT automation software. I/O response times of under 100 s can be achieved with this finely tuned system. XFC in particular uses functionalities such as distributed clocks, time stamping and oversampling.
The distributed clocks in EtherCAT represent a core XFC technology and are a fundamental component of EtherCAT communications. This is because, in addition to minimum response times, the crucial factors for the control process are deterministic actual value acquisition (i.e. an exact temporal calculation must be possible) and a corresponding deterministic set value output. A deterministic behaviour must therefore be supported by the I/O components, but not in the communication or calculation unit. All EtherCAT devices therefore have their own local clocks that are automatically and synchronised with all other clocks. Different communication runtimes are compensated, so that the maximum deviation between clocks is generally less than 100 nanoseconds and the system time is synchronised with extreme precision.
Time-stamped data types, together with the synchronised distributed clocks, enable the provision of temporal information with significantly higher precision for process data. EtherCAT terminals with time stamp latch the exact system time at which edge changes occur. Digital values can likewise be output at predefined times.
Oversampling data types enable multiple samplings of process data within a single communication cycle and the subsequent collective transfer of all data. The oversampling factor describes the number of samples made within a communication cycle. High sampling rates can be achieved easily, even with moderate communication cycle times. Analogue EtherCAT input terminals with oversampling enable signal conversion up to 100 kHz; in the case of digital input terminals this reaches 1 MHz.
High-precision measured values for sophisticated measurement technology
High resolution analogue input terminals are suitable for recording signals with extremely high precision. Examples include the 2-channel EL3602 input channels with 24 bit resolution for voltage input or the EL3612 for 0-20 mA as well as the 2-channel EL3692 resistance measurement terminal for a measurement range.
The EL3681 EtherCAT terminal is a digital multimeter with 18 bit signal resolution. Currents of up to 10 A can be measured as well as voltages up to 300 VAC/DC. The measurement ranges are switched automatically and the measurement type and range can also be adjusted with EtherCAT if required. Excellent interference immunity is achieved through the design of the EL3681 which features full electrical isolation of the electronic measuring system and dual-slope conversion.
The EL3201-0010 (1-channel) and EL3202-0010 (2-channel) PT100 input terminals for direct connection of resistance sensors enable high-precision temperature measurement. They are extremely precise with a resolution of 0,01°C per digit and are suitable for a temperature range of -200 to 320°C.
Full utilisation of multi-core technology results in lower engineering costs
In particular, it is the new TwinCAT 3 software generation featuring integration in Microsoft Visual Studio that best fulfils the requirements of Scientific Automation – the convergence of automation and measurement technology. The real-time environment is designed in such a way that practically any number of PLCs, safety PLCs and C++ tasks can be performed on the same or different CPU cores. The new TwinCAT 3 Condition Monitoring Library exploits these opportunities in particular: raw data can be sampled with a fast task and processed with a somewhat slower one. This means that measured data will be continuously recorded and can be analysed independently in a second task with numerous algorithms. The individual functional modules of the Condition Monitoring Library store their results in a global transfer tray, i.e. a type of storage table. From here the results can be copied to variables or processed using different algorithms so that an individual measurement and analysis chain can be compiled.
No specific Beckhoff modules or other modifications to the original model are required to create Matlab/Simulink modules. The Matlab and Simulink coders generate C++ code, which is then compiled in a TwinCAT 3 module. Repeated use of the modules is possible through instantiation. The block circuit diagram from Simulink can be displayed directly in TwinCAT and used, for example, to set break points.
TwinCAT Scope enables the graphical representation of all relevant signals from Scientific Automation software. Its viewer component can be used for visualising signals in charts, while the server component logs the data on the corresponding target device. Scope also allows measured values to be read in the microsecond range to the exact cycle and enables visualisation of oversampling values captured by EtherCAT measurement terminals.
For more information contact Kenneth McPherson, Beckhoff Automation, +27 (0)11 795 2898, [email protected], www.beckhoff.co.za
| Tel: | +27 11 795 2898 |
| Email: | [email protected] |
| www: | www.beckhoff.com |
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