Before the advent of HMI touch screens the user would install individual devices in a control panel such as switches, indicator lights, potentiometers and thumb wheel switches. This was a much more labour intensive solution as holes had to be drilled in the panel, the devices had to be installed and wires had to be pulled to each individual device. Thereafter if any modifications were required it was back to making more holes and pulling more wires.
By comparison a modern HMI requires a single cut-out in the panal and a communications cable to the controller. The functionality the user needs access to is configured using a Windows based application supplied with the HMI.
HMI screens typically have their own operating system. Because they have been developed for the singular purpose of being a machine interface device they do not need all the extra complexity and baggage which comes with a PC based operating system. In addition HMI screens use solid state memory and commonly purchased memory such as compact flash (CF) cards for memory expansion and data storage.
When the first economically priced HMI screens hit the market in the early 90's the physical communications between the HMI and a PLC was via an RS232 or RS422/485 communications port. In recent years there has been a dramatic growth in Ethernet a as medium for industrial communications. This can be attributed to Ethernets speed, flexibility and ubiquity. Current HMI screens therefore can communicate over, serial, Ethernet and fieldbus type links such as DeviceNet, Profibus and CC-Link.
The availability of Ethernet communications has enabled such developments as FTP servers now being embedded in HMI screens to facilitate remote program download and data transfer.
For information about our Human Machine Interface solutions, please visit our HMI Products page.
