Determinism of ASI

Evaluation of the Determinism of the Actuator Sensor Interface (ASI) on Programmable Logic Controller (PLC), Personal Computer (PC) and Real Time Operating Systems (RTOS)


The basic aims of the research is to determine if a similar level of determinism can be achieved using a PC based control as can be achieved with the current architectures of Networks for I/O, PLC for control and PC for visualisation.

The Research Team

Dr. Brendan McCormack Principal Researcher Department of Engineering, IT, Sligo. Mr. Fergal Henry Joint Researcher Department of Engineering, IT, Sligo. Mr. Shane Loughlin Research Student Department of Engineering, IT Sligo.


A typical PLC implementation of a ASI architecture has been demonstrated in many applications to be deterministic, and has the following characteristics.

  • Nodes what are “intelligent” and require to pass a lot of data use the Profibus DP network.
  • The simpler the devices at the Actuator/Sensor level as the AS-Interface network.
  • The 2 networks are joined using a Profibus DP/ASI Gateway.
  • The Control Software runs on a Programmable Logic Controller (PLC)
  • The Visualisation Software runs on a PC.

Recent developments have made the following advances possible;

  • A PC be connected directly to the AS-Interface Network using an ASI Master Card
  • The ASI Master Card suppliers provide an OLE for Process Control (OPC) Server for these Cards
  • The OPC Server makes all of the data on the AS-Interface Network available to OPC Clients such as Visual Basic, Visual C++, etc
  • But there is one major hurdle. We cannot be sure that it is deterministic. There are 5 major areas where this design could fail.
  • The AS-Interface Network and its Master Card.
  • Ethenet.
  • The OPC Server.
  • The PC Hardware.
  • The PC Operating System.
  • The Control and Visualisation Software.

Project Details

To gain an appreciation of the relevant literature and hence acquire a mastery of the principles and theory of:

  • Determinism.
  • AS-Interface Networks.
  • PLC Systems.
  • Profibus DP.
  • Ethernet.
  • PC Based Operating Systems.
  • Real Time Kernels.

To bench mark the determinism by a PLC implementation of an ASI Network.

To compare the determinism achieved by a PC implementation of an ASI Netork (with or without a RTOS Kernel).

  • Literature Survey using Library, CD Rom, online searches and Internet.
  • Design & construct a typical PLC implementation of an ASI Network.
  • Simulate an artificial loading of the PLC Central Processing Unit (CPU).
  • Generate benchmark results.
  • Design and construct a typical PC implementation of a ASI Network.
  • Simulate an artificial loading of the PC using PC loading simulator.
  • Labview, VB, C++ application capable of doing the following :-
  • Measure and log the signals on the AS-Interface Network.
  • Use simulation to generate artificial loading of the PCs Memory, Hard Disk, CPU etc.
  • Measure the PC response time.
  • Analysis and interpretation of results.
  • Compare and contrast the different methods.
  • Identify advantages and disadvantages.