To work well on the production floor, a human machine interface (HMI) must provide a reliable and responsive operator interface sturdy enough for industrial applications. To do this, it must perform certain functions simultaneously without locking out the operator (or simply locking up).
First, the HMI must take operator input and pass it to the machine controller as quickly as possible. In other words, when an operator hits a "Stop" button, the machine needs to stop. The HMI can't just sit there because it's busy doing other things it thinks are more important.
The HMI also needs to update the display with data from the machine as quickly as possible. The faster it can update, the better the user experience. Along with this, log data needs to be logged. Alarms need to alarm. Panels need to switch. Recipes need to be downloaded, scripts need to be run, and reports need to be generated.
Three main measures of HMI performance
Lots of factors affect an HMI, but here are the three main measures of performance:
- Initial startup time: how long it takes an operator to power on an HMI and start "interfacing" with a machine. It includes the time it takes to boot the operating system, start the HMI, load and display the first panel(s), and connect to the machine(s) and get initial data.
- Panel switching time: the time it takes to bring up a new panel once the system is already running.
- Real-time update rate: a measure of how quickly the HMI reads and writes data.
Although you can improve an HMI's performance with hardware upgrades (like adding a faster CPU, more memory, and/or a faster hard drive), it's always possible to overload an HMI with more work than it can handle at one particular moment. Good HMIs handle this in the smartest way possible.
What makes for a smart HMI?
Consider what happens when an HMI shows a single core processor maxing out at 100 percent of available cycles. This isn't a problem when the interface remains responsive to user input. For example, InteractX, a Windows-based HMI, remains responsive by making use of the available CPU time. Unlike other interfaces, InteractX doesn't just spin cycles uselessly while waiting on user input. Instead, it might do background tasks or speed up the graphic update.
Moreover, when the HMI does become overloaded, InteractX slows down the screen redraw rates. That way, it doesn't spend all of its time redrawing the screen instead of responding to the operator.
In this series, we offer tips on tweaking performance by discussing how InteractX handles data updates and explaining the panel caching options. As a pioneer in the HMI industry, Parker understands the needs of automation users and translates those needs into innovative product solutions.
Article contributed by Brent Meranda and originally published in the ParkerMotion blog January 2012.
Image: © Paha_l Dreamstime.com - Control Panel Of Machine For Cooking Photo