Computer machine interface unit

The first set of case studies illustrates errors due to the inadequate design of the human-machine interface (HMI). The HMI is the boundary across which information is transmitted between the process and the plant worker. In the context of process control, the HMI may consist of analog displays such as chart records and dials, or modem video display unit (VDU) based control systems. Besides display elements, the HMI also includes controls such as buttons and switches, or devices such as trackballs in the case of computer controlled systems. The concept of the HMI can also be extended to include all means of conveying information to the worker, including the labeling of control equipment components and chemical containers. Further discussion regarding the HMI is provided in Chapter 2. This section contains examples of deficiencies in the display of process information, in various forms of labeling, and the use of inappropriate instrumentation scales. 

The central computer is called the master terminal unit, or MTU. The MTU has two main functions to periodically obtain data from RTUs/PLCs and to control remote devices through the operator station. The operator interfaces with the MTU using software called human machine interface (HMI). The remote computer is called the program logic controller (PLC) or remote terminal unit (RTU). The RTU activates a relay (or switch) that turns mechanical equipment on and off. The RTU also collects data from sensors. Sensors perform measurement, and actuators perform control. 

They controlled this highly automated aromatics plant by supervising the process from a Central Control Room (CCR) equipped with visual display units (so-called computer screens) as the human-machine interface. The five shifts of operators, at that time, had been working for about 16 years (approximately 5 million man hours) without a single Lost-Time Injury case, which meant an excellent safety performance according to that, standard. 

The main items of the trainbome sub-system are European Vital Computer assembled with 17 different LRUs Odometry sub-system (including radar and accelerometer as LRUs) Driver Machine Interface (DMI) sub-system (consisting of ERTMS DMI and Voice DMI as LRUs) Cab Radio (consisting of Data rack. Voice rack, and Antenna Coupling Unit as LRUs) GSM-R/GPS antenna GSM-R/Amlog antenna Train Recorder Unit (TRU) Eurobahse antenna, etc. 

However, the codes were pretty machine-dependent and certainly could not be used as black boxes. In these respects the codes were no better (and no worse) than any others available in the United States and elsewhere. Computational chemistry codes became portable in a routine way only in the 1980s, when also their operation became transparent to users, with the widespread use of free-format input, made interactive on an interface with suitable graphics. In fact, free-format input was actually a feature of the ATMOL suite, and so it was rather ahead of its time. 

If machine and man are to be matched to form an integral working unit, close attention must be paid to the area of contact between th - the display and control interface -to reconcile their fundamentally different characteristics. In human-computer interaction, WYSIWYG (what you see is what you get) user interfaces are very good... 

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