HMI and Panel PC: selection, PLC connection and screen design
The operator panel is the face of the machine: the right touch technology, the right connection and a readable screen design directly reduce downtime and operator error.
4 questions answered
Basics
Commissioning
Basics
01
Should I choose a resistive or a capacitive touch screen?
A resistive screen works by pressure: it is reliable with gloves, with a stylus and in oily or dusty conditions, which makes it a safe choice for shop-floor machines. A capacitive screen works by the finger's electrical effect: brighter, multi-touch and more fluid, but it may not work with thick gloves. The HMI-R9 family is resistive; the VO Panel PC and the QT teach pendant are capacitive.
An HMI panel is built to run the operator screen: it boots fast, needs no upkeep and works alongside the PLC. A Panel PC is a full computer, chosen when you need to run SCADA, data collection, custom software or a software-based controller. The VO Panel PC runs Windows 10; the QT teach pendant runs Qt6 on Ubuntu.
How do I design an HMI screen that operators do not get wrong?
Keep colour for what needs attention: show normal conditions plainly in greys and alarms and abnormal states in bright colour. Give each screen one job, make dangerous commands ask for confirmation, and always print values with their units. This approach is the basis of the ISA-101 standard for high-performance HMIs.
Alarm list: time, source, description and what the operator should do
The HMI and the PLC usually talk over Ethernet. In a CODESYS-based system a CODESYS-compatible panel such as the HMI-R9 accesses the PLC variables directly, so tags do not have to be defined twice. Plan the IP addresses of the panel and the PLC on the same subnet, and keep the machine network separate from the office network.