DetachFixClose

XFC | eXtreme Fast Control Technology

The fast control solution XFC is based on an optimised control and communication architecture. With XFC it is possible to realise I/O response times < 100 μs.0 μs.

XFC technology information

The new class of control performance

With XFC technology (eXtreme Fast Control Technology) in 2008 Beckhoff presented an ultra fast control solution: XFC is based on optimized control and communication architectures comprising an advanced Industrial PC, ultra-fast I/O terminals with extended real-time characteristics, the EtherCAT high-speed Ethernet system, and the TwinCAT automation software. With XFC it is possible to achieve I/O response times < 100 μs.

XFC represents a control technology that enables very fast and highly deterministic responses. It includes all hardware and software components involved in control applications: optimized input and output components that can detect signals with high accuracy or initiate tasks; EtherCAT as very fast communication network; high-performance Industrial PCs; and TwinCAT, the automation software that links all system components.

Not long ago, control cycle times around 10 to 20 ms were normal. The communications interface was free-running, with corresponding inaccuracy of the determinism associated with responses to process signals. The increased availability of high-performance Industrial PC controllers enabled a reduction in cycle times down to 1–2 ms, i.e. by about a factor of 10. Many special control loops could thus be moved to the central machine controller, resulting in cost savings and greater flexibility in the application of intelligent algorithms.

XFC offers a further reduction of response times by a factor of 10, and enables cycle times of 100 μs, without having to give up central intelligence and associated high-performance algorithms. XFC also includes additional technologies that not only improve cycle times, but also temporal accuracy and resolution.

Users benefit from entirely new options for enhancing the quality of their machines and reducing response times. Measuring tasks such as preventive maintenance measures, monitoring of idle times or documentation of parts quality can simply be integrated in the machine control without additional, costly special devices.

In a practical automation solution, not everything has to be extremely fast and accurate – many tasks can still be handled with “normal” solutions. XFC technology is therefore fully compatible with existing solutions and can be used simultaneously with the same hardware and software.

XFC technologies

In a normal, discrete control loop, actual value acquisition occurs at a certain time (input component), the result is transferred to the control system (communication component), the response is calculated (control component), the result is communicated to the set value output module (output component) and issued to the process (controlled system).

The crucial factors for the control process are: minimum response time, deterministic actual value acquisition (i.e. exact temporal calculation must be possible), and corresponding deterministic set value output. At what point in time the communication and calculation occurs in the meantime is irrelevant, as long as the results are available in the output unit in time for the next output, i.e. temporal precision is required in the I/O components, but not in the communication or the calculation unit.

The distributed EtherCAT clocks therefore represent a basic XFC technology and are a general component of EtherCAT communication. All EtherCAT devices have their own local clocks, which are automatically and continuously synchronized with all other clocks via the EtherCAT communication. Different communication runtimes are compensated, so that the maximum deviation between all clocks is generally less than 100 ns. The current time of the distributed clocks is therefore also referred to as system time, because it is always available across the whole system.

Process data is usually transferred in its respective data format (e.g. one bit for a digital value or one word for an analog value). The temporal relevance of the process record is therefore inherent in the communication cycle during which the record is transferred. However, this also means that the temporal resolution and accuracy is limited to the communication cycle.

Timestamped data types contain a timestamp in addition to their user data. This timestamp – naturally expressed in the ubiquitous system time – enables provision of temporal information with significantly higher precision for the process record. Timestamps can be used for inputs (e.g. to identify the time that an event occurred) and outputs (e.g. timing of a response). This way, it is possible to determine, for example, the precise point in time when an output is to be switched. The switching task is executed independently of the bus cycle.

While timestamp terminals can execute one switching task or switching event per bus cycle, multi-timestamp terminals can execute up to 32 switching tasks or switching events per cycle.

Process data is usually transferred exactly once per communication cycle. Conversely, the temporal resolution of a process record directly depends on the communication cycle time. Higher temporal resolution is only possible through a reduction in cycle time – with associated practical limits.

Oversampling data types enable multiple sampling of a process record within a communication cycle and subsequent (inputs) or prior (outputs) transfer of all data contained in an array. The oversampling factor describes the number of samples within a communication cycle and is therefore a multiple of one. Sampling rates of 200 kHz can easily be achieved, even with moderate communication cycle times.

Triggering of the sampling within the I/O components is controlled by the local clock (or the global system time), which enables associated temporal relationships between distributed signals across the whole network.

Very fast physical responses require suitably short control cycle times in the associated control system. A response can only take place once the control system has detected and processed an event.

The traditional approach for achieving cycle times in the 100 μs range relies on special separate controllers with their own, directly controlled I/Os. This approach has clear disadvantages, because the separate controller has only very limited information about the overall system and therefore cannot make higher-level decisions. Reparameterization options (e.g. for new workpieces) are also limited. Another significant disadvantage is the fixed I/O configuration, which generally cannot be expanded.

XFC performance data

  • 100 μs (min. 50 μs)
  • new performance class for PLC application: control loops with 100 μs

  • from 85 μs
  • Deterministic synchronized input and output signal conversion leads to low process timing jitter.
  • Process timing jitter is independent of communication and CPU jitter.

  • multiple signal conversion in one control cycle
  • hard time synchronization through distributed clocks
  • for digital input/output signals
  • for analog input/output signals
  • support of analog I/O EtherCAT Terminals
    • up to 100 kHz signal conversion
    • down to 10 μs time resolution
  • support of digital I/O EtherCAT Terminals
    • up to 1 MHz
    • up to 1 μs time resolution
  • application
    • fast signal monitoring
    • fast function generator output
    • signal sampling independent of cycle time
    • fast loop control

  • extremely precise time measurement for digital single shot events per cycle: resolution 1 ns, internal sampling 10 ns, accuracy with distributed clocks << 1 µs (+ input delay)
  • exact time measurement of rising or falling edges of distributed digital inputs
  • exact timing of distributed output signals, independent of control cycle
  • absolute distributed clocks time with 64 bit resolution, easy time handling over > 580 years

  • precise time measurement of up to 32 events per cycle: resolution 1 ns, internal sampling 10…40 µs dependent on configuration
  • exact time measurement of rising or falling edges of distributed digital inputs
  • exact timing of distributed output signals, independent of control cycle
  • distributed clocks time with 32 bit resolution, sufficient for actions in a ±4-second time frame

  • distributed absolute system synchronization for CPU, I/O and drive devices
  • internal sampling: 10 ns
  • distributed clock precision: << 1 µs

XFC components

Implementation of the XFC technologies described above requires full support for all hardware and software components involved in the control system, including fast, deterministic communication and I/O and control hardware. A significant part of XFC are the software components responsible for fast processing of the control algorithms and optimized configuration of the overall system.

Beckhoff offers a special XFC product range based primarily on four categories: EtherCAT as fieldbus, EtherCAT Terminals as I/O system, IPCs as hardware platform, and TwinCAT as higher-level software. All components are based on open standards, which means that any engineer or programmer can develop very fast control solutions with high performance based on standard components (i.e. without special hardware).


The EtherCAT I/O system provides a wide range with more than 200 different signal terminals. Standard EtherCAT Terminals already offer full support for XFC technology. Synchronization of the I/O conversion with the communication or – more precisely– with the distributed clocks is already standard in EtherCAT and is therefore supported by all terminals. Further developed XFC terminals offer additional special features that make them particularly suitable for fast or high-precision applications:

  • digital EtherCAT Terminals with very short TON/TOFF times, or analog terminals with particularly short conversion times
  • EtherCAT Terminals and EtherCAT Box modules with timestamp latching at the exact system time at which digital or analog events occur. Output of digital or analog values can occur at exactly predefined times.
  • Terminals with oversampling enable actual value acquisition or set value output with significantly higher resolution than the communication cycle time.

Oversampling

  • time synchronization across the system through distributed clocks
  • jitter < 1 μs

   
EL1262
type 3, oversampling
2-channel digital input 24 V DC
EL2262
oversampling
2-channel digital output 24 V DC
EL3742
differential input, 16 bit, oversampling
2-channel analog input 0…20 mA
EL3702
differential input, 16 bit, oversampling
2-channel analog input -10 V…+10 V
EL4732
16 bit, oversampling
2-channel analog output -10 V…+10 V
EL4712
16 bit, oversampling
2-channel analog output 0…20 mA

Timestamp

  • system accuracy 1 μs

Synchronized responses can be realized with timestamp input and output terminals; in the past, precision of < 1 μs was impossible with bus systems. The new XFC technology replaces hardware wiring.

   
EL1252
type 3, timestamp
2-channel digital input 24 V DC
EL2252
timestamp
2-channel digital output 24 V DC
EP1258-0001
8 x M8, 2-channel timestamp
8-channel digital input 24 V DC with 2-channel timestamp
EP1258-0002
4 x M12, 2-channel timestamp
8-channel digital input 24 V DC with 2-channel timestamp

Fast I/O

  • input delay TON/TOFF 1 μs
With the EL1202 and EL2202 XFC terminals, delays in the terminal hardware are reduced down to < 1 μs and therefore become negligible. Input and output data are for warded with maximum speed.

   
EL1202
type 3
2-channel digital input 24 V DC
EL2252
timestamp
2-channel digital output 24 V DC

With high communication speed and usable data rates EtherCAT offers the basic prerequisites for XFC. However, speed is not everything. The option of using the bus to exchange several independent process images arranged according to the control application enables parallel application of XFC and standard control technology. The central control system is relieved of time-consuming copying and mapping tasks and can fully utilize the available computing power for the control algorithms.

The distributed EtherCAT clocks that form the temporal backbone of the XFC technologies are available in all communication devices without significant additional effort.

The crucial point of XFC is the option of integrating all I/O components directly in the EtherCAT communication, so that no subordinate communication systems (sub bus) are required. In many XFC terminals the AD or DA converter is connected directly to the EtherCAT chip, so that delays are avoided.

Central control technology can be particularly advantageous if it can run faster and more powerful control algorithms than would be the case with many distributed small controllers. Modern Industrial PCs offer significantly more processing power and memory at lower cost than the sum of a large number of small controllers.

The latest general PC technology innovations can also be used to good effect for control technology. Fast multi-core processors are ideal for running the operator interface of the machine in parallel with the control tasks. Large caches available with modern CPUs are ideal for XFC technology, because fast algorithms run in the cache and can therefore be processed even faster.

An important factor for short XFC cycle times is the fact that the CPU is not burdened with complex process data copying tasks needed by traditional fieldbuses with their DPRAM-based central boards. EtherCAT process data communication can be handled entirely by the integrated Ethernet controller (NIC with bus master DMA).

TwinCAT as high-performance automation suite fully supports the XFC technologies while retaining all the familiar features. The real-time implementation of TwinCAT supports different tasks with different cycle times. Modern Industrial PCs can achieve cycle times of 100 μs or less without problem. Several (different) fieldbuses can be mixed. The associated allocations and communication cycles are optimized according to the fieldbus capabilities.

The EtherCAT implementation in TwinCAT makes full use of the communication system and enables application of several independent time levels. It uses distributed clocks. Different time levels enable coexistence of XFC and normal control tasks in the same system, without the XFC requirements becoming a “bottleneck”.

An option specially designed for XFC enables inputs to be read during independent communication calls and outputs to be sent directly after the calculation. Due to the speed offered by EtherCAT the inputs are read and processed “just” before the start of the control tasks, followed by immediate distribution of the outputs with a second fieldbus cycle. The resulting response times are faster than the fieldbus cycle time in some cases.

Special TwinCAT extensions facilitate handling of the new XFC data types (timestamp and oversampling). PLC blocks enable simple analysis and calculation of the timestamps. The TwinCAT scope can display the data picked up via oversampling according to the allocated oversampling factor and enables precise data analyses.

Product overview

EL1202 | 2-channel digital input terminal 24 V DC, TON/TOFF 1 µs

EL1202

The EL1202 digital input terminal acquires the binary 24 V control signals from the process level and transmits them, in an electrically isolated form, to the higher-level automation unit. The EtherCAT Terminal contains two channels whose signal state is indicated by LEDs.

EL1252 | 2-channel digital input terminal with timestamping

EL1252

The EL1252 digital input terminal acquires the fast binary 24 V control signals from the process level and transmits them, in an electrically isolated form, to the controller. The EtherCAT Terminal contains two channels whose signal state is indicated by LEDs. The signals are furnished with a time stamp that identifies the time of the last edge change with a resolution of 1 ns. With this XFC technology, signal characteristics can be traced exactly in time and correlated with the distributed clocks system-wide. With this technology, machine-wide parallel hardware wiring of digital inputs or encoder signals for synchronization purposes is often no longer required. In conjunction with the EL2252 EtherCAT Terminal (digital output terminal with time stamp), the EL1252 enables responses with equidistant time intervals, largely independent of the bus cycle time.

EL1262 | 2-channel digital input terminal with oversampling

EL1262

The EL1262 digital input terminal acquires the fast binary 24 V control signals from the process level and transmits them, in an electrically isolated form, to the controller. The EtherCAT Terminal has two channels that indicate their signal state via light emitting diodes. The signals are sampled with a configurable, integer multiple (oversampling factor: n) of the bus cycle time (n microcycles per bus cycle). For each microcycle, the EtherCAT Terminal generates a process data block that is transferred collectively during the next bus cycle. The timebase of the terminal can be synchronized precisely with other EtherCAT devices via distributed clocks. This XFC procedure enables the temporal resolution of the digital input signals to be increased to n times the bus cycle time.

M8

EP1258-0001

The EP1258-0001 EtherCAT Box with digital inputs acquires the fast binary control signals from the process level and transmits them, in an electrically isolated form, to the controller. The signals are furnished with a timestamp that identifies the time of the last edge change with a resolution of 1 ns. This technology enables signals to be traced exactly over time and synchronised with the distributed clocks across the system. With this technology, machine-wide parallel hardware wiring of digital inputs or encoder signals for synchronisation purposes is often no longer required. In this way, the EP1258 enables responses with equidistant time intervals, largely independent of the bus cycle time.

M12

EP1258-0002

The EP1258-0002 EtherCAT Box with digital inputs acquires the fast binary control signals from the process level and transmits them, in an electrically isolated form, to the controller. The signals are furnished with a timestamp that identifies the time of the last edge change with a resolution of 1 ns. This technology enables signals to be traced exactly over time and synchronised with the distributed clocks across the system. With this technology, machine-wide parallel hardware wiring of digital inputs or encoder signals for synchronisation purposes is often no longer required. In this way, the EP1258 enables responses with equidistant time intervals, largely independent of the bus cycle time.

EL2202 | 2-channel digital output terminal 24 V DC, TON/TOFF 1 µs, push-pull outputs, tri-state

EL2202

The EL2202 digital output terminal connects the binary control signals from the automation device on to the actuators at the process level with electrical isolation. This terminal benefits from very small output delay and is therefore suitable for signals requiring particularly fast output. The EtherCAT Terminal supports distributed clocks, i.e. output data can be monitored synchronously with other data from terminals with distributed clock support, if the user switches to terminal version EL2202-0100 (see documentation). The system-wide DC accuracy is << 1 μs. The EtherCAT Terminal has a push-pull output that can be actively switched to 24 V, 0 V or high-impedance. The EL2202 contains two channels. LEDs indicate the signal state of each channel.

EL2252 | 2-channel digital output terminal with timestamp, tri-state

EL2252

The EL2252 digital output terminal connects the binary control output signals at the process level with electrical isolation. The outputs of the EtherCAT Terminal are switched with high precision to match the transferred timestamp, which has a resolution of 10 ns. This technology enables output switching times to be specified precisely across the system. The distributed clocks are used for reference. In conjunction with the EL1252 (digital input terminal with time stamp), the EL2252 enables responses with equidistant time intervals, largely independent of the bus cycle time. Each output can be switched to high resistance individually.

EL2262 | 2-channel digital output terminal with oversampling

EL2262

The EL2262 digital output terminal connects the binary control output signals at the process level with electrical isolation. The outputs are controlled with an adjustable integral multiple (oversampling factor: n) of the bus cycle time (n microcycles per bus cycle). For each micro-cycle, the EtherCAT Terminal receives a process data block that is output consecutively. The timebase of the terminal can be synchronized precisely with other EtherCAT devices via distributed clocks. An output pattern with a significantly higher pulse sequence than the bus cycle time is thus output precisely with the system-wide timebase. This procedure enables the temporal resolution of the digital output signals to be increased to n times the bus cycle time. The maximum output rate is 1 Msamples/s.

EL3742 | 2-channel analog input terminal 0…20 mA, differential input, with oversampling

EL3742

The EL3742 analog input terminal handles signals in the range between 0 and 20 mA. The voltage is digitised to a resolution of 16 bits, and is transmitted, electrically isolated, to the controller. The input channels of the EtherCAT Terminal have differential inputs and possess a common, internal ground potential. The signals are oversampled with an adjustable, integer multiple (oversampling factor: n) of the bus cycle time (n microcycles per bus cycle). For each microcycle, the EtherCAT Terminal generates a process data block that is collected and transferred during the next bus cycle. The time base of the terminal can be synchronised precisely with other EtherCAT devices via distributed clocks. This procedure enables the temporal resolution of the analog input signals to be increased to n times the bus cycle time. In conjunction with the EL47xx (analog output terminal with oversampling), responses with equidistant time intervals, e.g. in the event of a threshold value being exceeded, become possible. The distributed clocks function enables several EL3742 devices to be synchronised in almost any configuration. The maximum sampling rate per channel is 100 ksamples/s (100,000 samples/s).

EL3702 | 2-channel analog input terminal -10…+10 V with oversampling

EL3702

The EL3702 analog input terminal handles signals in the range between -10 and +10 V. The voltage is digitised to a resolution of 16 bits, and is transmitted, electrically isolated, to the controller. The signals are oversampled with an adjustable, integer multiple (oversampling factor: n) of the bus cycle time (n microcycles per bus cycle). For each microcycle, the EtherCAT Terminal generates a process data block that is transferred collectively during the next bus cycle. The time base of the terminal can be synchronised precisely with other EtherCAT devices via distributed clocks. This procedure enables the temporal resolution of the analog input signals to be increased to n times the bus cycle time. In conjunction with the EL47xx (analog output terminal with oversampling), responses with equidistant time intervals, e.g. in the event of a threshold value being exceeded, become possible.

EL4732 | 2-channel analog output terminal -10…+10 V with oversampling

EL4732

The EL4732 analog output terminal generates signals in the range between -10 V and +10 V. The voltage is supplied to the process level with a resolution of 16 bits and is electrically isolated. The output channels have a common ground potential. The outputs are oversampled with an adjustable, integer multiple (oversampling factor: n) of the bus cycle time (n microcycles per bus cycle). For each microcycle, the EtherCAT Terminal receives a process data block that is output consecutively. The time base of the terminal can be synchronised precisely with other EtherCAT devices via distributed clocks. This procedure enables the temporal resolution of the analog output signals to be increased to n times the bus cycle time. In conjunction with the EL37xx (analog input terminal with oversampling), responses with equidistant time intervals, e.g. in the event of a threshold value being exceeded, become possible. The EL4732 device can output a maximum of 100,000 values (100 ksamples/s) per channel and second.

EL4712 | 2-channel analog output terminal 0…20 mA with oversampling

EL4712

The EL4712 analog output terminal generates output signals in the range between 0 and 20 mA. The voltage is supplied to the process level with a resolution of 16 bits and is electrically isolated. The output channels have a common ground potential. The outputs are sampled with an adjustable, integer multiple (oversampling factor: n) of the bus cycle time (n microcycles per bus cycle). For each microcycle, the EtherCAT Terminal receives a process data block that is output consecutively. The time base of the terminal can be synchronised precisely with other EtherCAT devices via distributed clocks. This procedure enables the temporal resolution of the analog output signals to be increased to n times the bus cycle time. In conjunction with the EL37xx (analog input terminal with oversampling), responses with equidistant time intervals, e.g. in the event of a threshold value being exceeded, become possible. The EL4712 device can output a maximum of 100,000 values (100 ksamples/s) per channel and second.