HMI Design is integral to building HMI screens that are both intuitive and easy to operate. HMI design has become vital for any new controls or automation installation.
HMI come in many different sizes. The larger screens allow for more detailed designs and functions. It is important to select a screen size that is appropriate for the system.
Never migrate a HMI from a larger screen to a smaller screen. Smaller screens usually have less RAM leading to slow response times.
TAG functionality will also be reduced. It is better to redesign new screens for the smaller HMI. Most HMI are now Touch Screen.
However, a few manufacturers still produce HMI with physical buttons. It must be remembered that any HMI with physical buttons will not be suitable for a future HMI upgrade to a Touch Screen system.
Choose a HMI that matches your communication protocol. HMI are available with multiple options including RS232, EtherNet, PROFIBUS, ControlNet, DeviceNet etc..
Failure to select the correct communication option will result in extra PLC programming and slow response times. Ensure the engineering design is completed for the entire system before selecting a HMI.
The price of a HMI will increase along with the number of inputs available. Ensure you have enough inputs for your system.
A typical HMI can use from 2 to 10 screens. Minimum requirements are usually :-
1: Overview or Home Screen. This screen is used to see the overall status of the process or area controlled by the HMI.
2: Control or Settings Screen. This screen is usually password protected and used to change parameters in the system.
3: Area Screen: This can give a more detailed view than the Overview screen of certain process important areas. You may have many areas to examine therefore you would have multiple area screens. Area1, Area2, Area3 etc.. Obviously the screen names will be changed to meaningful names used in the project/process.
4: Pop-Up Screens: These are usually selected by clicking on a valve or motor on the HMI and will give detailed status information on the selected item.
This type of design is usually referred to as a Shallow HMI Design.
Deep Design systems are based on top level screen access priorities. As the operator uses the screens selected to go deeper into the process this design prevents the operator from navigating to a different area unless starting again from the main page. This design usually has more screens and detail than a shallow system and is typically used in more complex systems. The different areas accessed from the HOME screen can also be password protected in order to safeguard the integrity of the system.
There are certain design principles used in a navigation menu. There are a lot of poor designs that do not take into account the end result and functionality.
The navigation buttons should be at least 2cm x 1.5cm on a Touch Screen system. Smaller buttons can be used on mouse & keyboard system.
The buttons should be in a neutral colour, for example, blue or green with different shades used for active/inactive. The current screen should be visible to the user as active.
Any screens that are not accessible or password protected can be visible but greyed out to indicate they cannot be used. The navigation bar is usually located on the bottom of the screen with the status at the top.
This has been shown to be the most intuitive layout for operators.
The display can be simple or complex but must provide the operator with the required information while not confusing with a vast amount of unnecessary information. A complex system with a large amount of tags must be broken down into sub-systems using a shallow or deep design method.
HMI design is an art and a skill. The final design must be easy to operate, navigate, efficient and specific to the system. The engineer needs to consider hardware and software options that are suitable for the project.
