Page 6 - Metroid Mag - November 2016_Neat2

6 METROID MAG

UTILISING THE

FULL POTENTIAL OF

HMI TOUCHSCREENS

There's an increasing trend among packaged equipment manufacturers to include
a HMI touch screen as part of the electrical control system. Touch screens are intu-
itive to use and look great, and can be set up with some very intelligent and useful
features. Let's take a look at what can be done with a HMI.

Process overview
A HMI will generally display a graphical represen-
tation of the process flow on one or more screens,
displaying the current status of all equipment in-
cluding motors, valves and instruments - just like a
P&ID. The displayed objects can be programmed
to change colour to signify different statuses, for
example red for faulted and green for running, and
key process variables such as flow, pressure and
level can be displayed in real time.

Trend graphs
A touch screen HMI can visually demonstrate how
process variables change over a period of time.
For example, in a water treatment system the op-
erator could bring up a trending display of the in-
fluent turbidity and pH, pressures on either side
of a filter, or the effluent turbidity. Trends can be
very useful for adjusting PID control loops, as they
show clearly how the system responds to changes
in the process.

Data-logging
HMI's can be configured to log any number of pro-
cess variables, and store the logs either in the in-
ternal memory or to a USB stick or SD card. These
logs can be viewed on the screen as a trend graph
as previously described, or the raw data viewed on
a computer using a spreadsheet application such
as Excel.