Topic
HMI & SCADA
Operator interfaces that work under pressure: ISA-101 design, screen hierarchy, colour, alarm rationalisation and flood prevention, and where SCADA starts.
8 articles
Free HMI software: what you can use, and on what terms
Free HMI software comes in three kinds. Open-source packages such as FUXA (MIT) and Rapid SCADA (Apache 2.0) may be used for paid work. Panel makers' editors such as Weintek EasyBuilder Pro are free but only build projects for their own panels. Ignition Maker Edition is free for personal, non-commercial use only. Read the terms before drawing the first screen.
8 min readISA-101: the grey screen that finds faults faster
ISA-101 describes an operator display where the normal state is low contrast greyscale and colour is reserved for abnormal conditions. Equipment is drawn flat and schematic rather than photorealistic, numbers are shown with context rather than alone, and the screen hierarchy runs from overview to detail. The result is that anything coloured on the screen is by definition something wrong, which is found without being searched for.
8 min readAlarm rationalisation: how to cut a list nobody reads
Alarm rationalisation is the process of deciding, one condition at a time, whether it should be an alarm at all, and if so what priority, what the operator should do about it, and how long they have. ISA-18.2 asks for it to be documented in a master alarm database. Anything with no operator action is not an alarm; it is an event, and moving those out is usually where most of the reduction comes from.
8 min readAlarm floods: why one fault produces two hundred alarms
A flood happens when one root cause trips many correlated alarms at once, typically after a trip or a power dip. The four tools are suppression by design, where a downstream alarm is disabled while the upstream unit is off; state based alarming, where limits change with operating mode; delays and deadbands to remove transients; and shelving, which lets an operator silence a known nuisance temporarily and automatically returns it.
7 min readHow many HMI screens, and what goes on each
Four levels: a process overview with no navigation needed, unit control screens where the operator works, detail screens for diagnosis, and support screens for trends and documentation. Navigation should reach any level 2 screen in one action from anywhere. A screen earns its place if it answers a question the operator actually asks; screens built per piece of equipment rather than per task are how a plant ends up with fifty nobody uses.
6 min readHMI colour: what each one should mean, and how many you need
Reserve a small palette for alarm priority and use it for nothing else. Equipment state is better shown by shape, fill or label than by colour. Avoid red for running and green for stopped, a convention inherited from electrical panels that conflicts with the alarm palette. Around eight percent of men have a colour vision deficiency, so no state should be indicated by colour alone.
6 min readChoosing an HMI panel size before you draw anything
Pick the panel before drawing, because a fixed resolution graphic does not scale to a smaller screen, it is cut off. Common sizes run from 4 inch at 480 by 272 up to 21 inch at 1920 by 1080, and the useful number is the resolution rather than the diagonal. Viewing distance decides minimum text size, which decides how much fits, which decides the size long before aesthetics do.
6 min readSCADA or HMI: what the words actually distinguish
An HMI is the operator interface to one machine or unit, usually a panel mounted on it. SCADA is a system for supervising and acquiring data from many distributed units, with a server, a historian and multiple clients. The distinction is scope and architecture rather than software: the same package often builds both, and the useful questions are how many machines, how far apart, and does the data need to outlive the shift.
6 min read