These devices or programs are vital for smooth machine or process operation.
HMI – Human Machine Interface
HMIs are the computer displays that an operator uses to interface with the process or machine. They send and receive tag data to/from the controller via a built-in driver or an OPC server such as Kepware. Sometimes, a touchscreen is preferable. Other times, a desktop PC is fine.
HMIs can provide control and monitoring of equipment, alarms, diagnostics, etc. An example would be the Rockwell FactoryTalk View ME (Machine Edition) or the Siemens WinCC Basic.
SCADA – Supervisory Control and Data Acquisition
SCADA combines an HMI with any combination of the following:
- Multiple HMIs
- Server/client architecture
- Server contains all the graphics, communicates to equipment, and serves it up to clients
- Client looks to server for updated graphics and data.
- Data Historians and historical trends
- Reporting § Batch operation
- Networks including Ethernet, Fiber optic, field bus
- Server Redundancy
Examples include the Rockwell FactoryTalk View SE (Site Edition), and the ICONICS Genesis64. SCADA shares a lot of functionality available with a DCS (Distributed Control System), such as Siemens PCS7.
Things to Consider:
The graphics on the display need to be functional; aesthetics are secondary. There are a lot of features out there that don’t always help the operator, such as 3D graphics and cool animations. We typically build our graphics to look like a P&ID (Piping & Instrument Diagram), if available. Some are opposed to this, but in our experience, the operator can quickly find devices on the screen because he/she is familiar with the layout of the process.
The colors, fonts, and animations need to MEAN something to the operator. Therefore, we use them sparingly and only when the operator’s attention needs to be grabbed (interlocks, alarms, etc.). This can mean a sparing use of color on normal displays.
An operator should be able to quickly find what he/she is looking for on the screen. Therefore, we crowd the display. We use reusable block icons (valve, pump symbols) and faceplates to make things visually simple. Most software packages allow you to use icons and graphics more than once, so you’re not doing the same thing over and over. To do this, just copy, paste, and change the tag link (hopefully in just one place).
This also is nice for the end user if they need to add something after the system has been commissioned.
Eliminate nuisance alarms!
The worst and most dangerous alarm log is the one that has been dismissed as a nag. Any log that has too many alarms that just aren't that alarming is a serious problem. Our rule is that if something happens during normal operation, it’s not an alarm.
We use colors to indicate the severity of the alarm, such as red for an interlocking condition and yellow for a warning.
With the exception of high speed machine control, data presented on screens doesn’t need to be updated very quickly. Analog values (pressures, temperatures, etc.) can be updated every second, and discrete values (level switches, motor and valve feedback, etc.) every 500 miliseconds. That is usually plenty fast.
This also keeps the data server from getting overwhelmed with requests.
Where are you storing your valuable tag data? Does the EPA require you to report certain values on a 15 minute cycle? Consider backing this up to a Historian with RAID hard drives for data loss prevention.
Is your HMI in a harsh environment? Consider installing an HMI client on an Industrial PC (IPC) that can be easily swapped out and replaced. Your data will still be on the server, which should be in a clean, controlled environment.
Choose Cross Company
The effectiveness of our HMI/SCADA design has been proven over 23 years of integration. We have used most of the available HMI’s and SCADA packages including:
- Siemens PCS7, WinCC (Advanced and Basic)
- Rockwell FactoryTalk View SE and ME (as well as legacy software like RSView32)
- ICONICS Genesis (64, 32)
- iFix o Wonderware
- Trihedral's SCADA Software