HMI stands for Human Machine Interface. While the acronym HMI is not restricted to industrial machines and production plants, it is a well recognised term in this environment to describe screen based devices, usually LCD touch screens which enable users to see the status of a machine, enter set-points for the machine, and respond to alarms. A HMI touch screen works in concert with a controller device such as a programmable logic controllers (PLC).
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
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.