15 Human Machine Interface
Introduction
Communications between processor and HMI (human machine interface) is an important subject as well as constructing an operator interface. The chapter includes procedures for attaching computers as HMI devices to the CompactLogix processor from A-B and the Siemens 1200 processor. Graphic control packages used are A-B’s RSView ME and Siemens’ WinCC. Other packages exist and were not excluded based on their capabilities. The ones used are among the more common and popular ones used today.
The following HMI panels communicating to PLC processors will be discussed in this chapter followed by a lab that can show advantages and disadvantages of each.
Fig. 15-1 HMI Graphic Control Packages
In each case, the emphasis is on getting a simple application operational and then expanding from that, remembering the analogy of the kite flying with a simple string over Niagara River. Later, the more difficult applications are discussed but only after a single button is programmed from the HMI and communicates successfully to the PLC.
Historical Panel Design
The design of an operator panel requires much coordination with the programming of the PLC and the design of the machine being controlled. Before the computer-designed systems, there were individual component systems that were hard-wired to the control devices inside the panel.
Fig. 15-2 A Simple Control Panel with Push Buttons and Switches with Indicator Lights
Fig. 15-3 This Printer is used for alarms for a process. Each alarm was recorded at the time of occurrence and printed as a single line of data to be analyzed by a process engineer or controls engineer.
Fig. 15-4 This panel shows many discrete devices as well as mimic panels showing process lines. Meters show levels or flows of various devices. Alarms are shown in grids of illuminated push buttons.
Fig. 15-5 Alarm panels were designed with discrete panels that lit or blinked with each alarm. Buttons were used to acknowledge each alarm point.
Fig. 15-6 Data was collected with recording devices similar to the above. Multiple points were individually recorded and studied.
Fig. 15-7 A handheld thermocouple readout device with paper recording output
Fig. 15-8 Several discrete controller devices for process control. Each device is capable of solving a single or multiple loops of process data executing a PID formula and controlling the output of the control loop.
Fig. 15-9 Whatever the appearance of the outside of the panel, the inside many times looks similar to the panel shown at left. It is too easy for the panel to look like this after a short time even though the original plan showed a neat design with well-organized wiring layout. This is not just a rare bad example.
Fig. 15-10 The picture below is of a panel designed in 1980 for a chemical batching system. It should be seen as what ‘was’ and not as what today should be a good design. It cost approximately $100K then and was a divider between the operator room and