From industrial panel PCs, to open-platform graphic operator interface terminals (OITs), to microOITs, to human-machine interfaces (HMIs), there are many choices of interactive display technologies for manufacturing and process control. It can be a challenge to decipher the right product for the right application — even for the more technically minded individual, let alone the business owner who simply wants his process automated. The best way to get a handle on these products is to categorize them and then describe each group.
Alpha Numeric OITs
Let’s start with the most basic display interface terminal — the alphanumeric OIT. Often called microOITs, these operator interfaces have been around for years and are simply a combination of a monochrome display (with room for 40 to 80 characters) combined with a programmable key-pad containing function keys (usually 12 to 24 of them). The display on these units simply provides the visual feedback for the function performed.
MicroOITs are prevalent everywhere, from the temperature thermostat in your house, to the programmable key-code entry lock on your garage door, to the keypad entries on a gas pump. The higher quality units come with rugged metal enclosures, as well as a wide range of controller drivers. And those with a Class I Division II rating will perform well even in extreme ranges of temperature (one popular brand will function in temps ranging from -10 to 65 oC).
The display on a microOIT consists of either a backlit LCD (Liquid Crystal Display) or a VFD (Vacuum Fluorescent Display). Choose the VFD microOIT when you need a light-emitting display for low-light environments and those situations where crisp, high-contrast readability is in order. Be mindful, though, that VFD displays are not well suited for extremely bright conditions (especially sunlight).
Conversely, the liquid crystal display is more appropriate for normal lighting conditions, but with a backlight they can still be viewed in the dark — just not to the degree of the VFD. Just be mindful that your choice should hinge upon the prevalent lighting condition.
HMI or Graphic OITs
Today, when most people think of an HMI they think of a touchscreen control panel — a display that utilizes proprietary configuration software that allows you to create an interactive touchscreen application that can communicate with a controller, another HMI, or an industrial computer/panel PC. The configuration process involves loading the software onto a PC and then creating your application. Then the application is generally downloaded via serial, USB, or Ethernet cable to your HMI.
HMIs range in size from tiny 3" screens all the way to 15" (and larger), and they can be utilized as a data collection terminal, a data display terminal, a touchscreen control panel for OEM applications, and as a plant floor industrial terminal. HMIs are used either singularly or networked in all locations of the control /automation process.
Recently, HMIs have undergone some impressive technological advances like high-resolution widescreen displays with hundreds of thousands of pixels; the ability to display up to 65,000 bright, crisp colors; the ability to create HMI applications in either landscape or portrait mode (you can orient your HMI with the short side up); and the ability to play gif animations and even play video (on the faster models).
With these new advances, you can create applications on your touchscreen display that will have the visual cues that relate directly to the operation. And standard technical functionality includes things like data entry, data logging, data sampling, process monitoring, recipes, bar graphs, meters, trends, alarms, switches, etc. that all allow you to engage and control your process.
It is important to remember that the limitation of the HMI/graphic OIT is that it only runs the proprietary configurations software. Unlike a PC, it will not run other software like Windows®-based applications.