Real time without additional hardware and as a system basis

TwinCAT Realtime Extension ensures real time capability

The Windows NT operating system for the PC is not capable of real time operation: it was designed for optimised performance and not for control purposes. Tasks are interrupted by various events, or their calls are delayed. The diagram shows these interruptions in a high-priority, cyclic Windows NT task:

Windows NT is not real time-compatible

Real time without additional hardware and as a system basis 1:
Diagram: Windows NT task is not executed deterministically

Windows NT and Beckhoff Realtime Kernel Extension

As Windows NT is not real time-compatible, the operating system is extended for automation tasks: such a real time extension is the basis for TwinCAT. With a background of more than ten years of experience with PC software solutions for the PLC/NC and more than ten thousand installations under DOS, Beckhoff has developed a proven and independent real time extension for Windows NT as the basis of TwinCAT and has harmonized it with Microsoft as a system partner. In a cyclic mode of operation, 64 tasks are executed with priority control, preemptively and deterministically with a maximum of +/- 15 µs jitter.

TwinCAT is real time-compatible

With this Kernel Extension, TwinCAT has an exact time basis which executes programs with maximum priority, and independently of other processor tasks. To demonstrate this, launching of a TwinCAT task was recorded over a period in order to measure time deviations of the system. During this time, in which 1 million PLC cycles run, the PC is loaded with diverse tasks such as network operation, hard disk access, video display and mouse movements. The diagram shows a rising signal edge, triggered by a task, in an integrating representation that shows the time deviations (jitter). TwinCAT tasks are called up deterministically (timed exactly in 100 % of all cases) with slight fluctuations (jitter) of only a few µs (in this case: +/-12 µs), which are negligible for general applications:

Real time without additional hardware and as a system basis 2:
Diagram: 1 million cycle starts of TwinCAT jitter by around +/- 15 µs

TwinCAT offers a compatible real time basis

The Beckhoff implementation operates without a second operating system thanks to the fact that the real time tasks have been integrated completely in Windows NT:

Automation solutions for practical applications

At the same time, TwinCAT does not focus on the real time implementation. Instead, it represents a complete application solution for the editing, analysis and execution of control programs in real time: no one needs to be an operating system expert to only use real time on a PC. The focus is on practical application in the field of automation.

Open programming Open I/O link Open Windows interfaces

An easy-to-use environment permits: