29. Human Machine Interfaces - HMIs
• These allow control systems to be much more interactive than before.
• The basic purpose of an HMI is to allow easy graphical interface with a process.
• These devices have been known by a number of names,
• These allow an operator to use simple displays to determine machine condition and make simple settings.
allow the operator to start and stop cycles
• These devices allow certain advantages such as,
color coding allows for easy identification (eg. red for trouble)
pictures/icons allow fast recognition
use of pictures eases problems of illiteracy
screen can be changed to allow different levels of information and access
• The general implementation steps are,
1. Layout screens on PC based software.
2. Download the screens to the HMI unit.
4. Read and write to the HMI using PLC memory locations to get input and update screens.
• To control the HMI from a PLC the user inputs set bits in the PLC memory, and other bits in the PLC memory can be set to turn on/off items on the HMI screen.
• The common trend is to adopt a user interface which often have,
A pointer device (such as a mouse)
Support for multiple windows, which run programs simultaneously
Windows can be moved, scaled, moved forward/back, etc.
• The current demands on user interfaces are,
ability to interrupt processes
deal with many processes simultaneously
• To design an HMI interface, the first step is to identify,
1. Who needs what information?
2. How do they expect to see it presented?
3. When does information need to be presented?
4. Do the operators have any special needs?
6. What choices should the operator have?
• Design an HMI for a press controller. The two will be connected by a Devicenet network.