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Operator interface (OI) or human-machine interface (HMI) is a means for the operator to monitor and control machinery and processes.
Although initially designed as a replacement for push buttons, in the 1980s operator interface matured into a more compact, manageable and flexible way for plant personnel to interact with plant processes.
They have evolved into much more than simple monitoring and can include, for example, web serving, email, trending and smartphone support.
By helping plant-floor personnel make faster, better decisions and take decisive actions, OI devices can generate benefits such as:
Also, as OI devices have got smarter, they've been able to offload OI-related tasks for PLCs and other control devices by performing calculations and logical comparison, tracking alarms, generating printed summaries and completing additional tasks that might otherwise burden the PLC, network or other control devices.
Hardware, also referred to as the OI, is the online unit or operator station that displays insight into the machine functionality. OI hardware includes:
PC-based software is used to configure and transfer applications to and from the OI. OI software includes:
Proprietary design features both hardware and software that is unique to the brand or OI. The software will only run on the designed hardware, and hardware will only run the software package.
Proprietary units typically have the advantage of lower pricing because they are designed for a dedicated OI.
Open platform design features unique software, which typically runs on a Windows-based personal computer platform.
Open designs are typically based on an Intel-architecture PC, which allows for use of off-the-shelf hardware and software to extend the capabilities of the OI. Today's open systems are typically more expensive than proprietary designs.
Operator input methodology gives operators the ability to input data using technology that is suited to their environment, as well as the type and complexity of information they must enter.
Some examples of techniques that allow data to be entered into the system include touchscreens and keypads.
Resistive
Capacitive
Infrared
The software development environment allows a user to create screen images and then link the images to data available in a programmable logic controller (PLC).
The images are often built from tools such as icons, templates or symbols. Users can create their images or import customised bitmaps and JPGs.
Development environment: This is the programming software tool to develop OI screens.
Run time: This is the application running on the OI that was developed in the programming software tool.
An interface provides a medium for the transfer of data. Interfaces to PLCs, networks or other plant automation employ serial transfer of data.
Serial transfer of data involves one sender and at least one or more listeners. Once the connection is made, the data is transferred as a string of bits (1 s and 0 s).
Early PLCs used the Bell System of serial data transfer to incorporate the RS-232 interface into their hardware platform.
As the need for the transfer of serial data continued to grow, new interfaces were developed to enable communication over greater distances and finally to allow multiple senders and listeners to occupy the same physical wire. For example, RS-485, RS-422, wireless and Ethernet.
When selecting operator interfaces for an application, make sure to ask the following questions.
