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Types of Human Machine Interface in the Tecnologic Process Controller Range
Tecnologic supplies a range of process controllers with a variety of type of HMI (Human Machine Interface). The choice of controller for a particular application will depend a great deal on the technical capabilities of the processor e.g. accuracy, reliability, number of processes that can be controlled, and so on. But the features of the associated HMI can also be critical in determining the overall efficiency of the process or processes that are to be controlled. Here we overview the different types of Human Machine Interface available from the Tecnologic process controller range. The types of HMI available fall into three main categories, largely determined by display technology. These are LED, LCD and touch screen HMIs.
Process Controllers with LED Displays
LED (Light Emitting Diode) displays have been around the longest and are a very mature technology. LED displays typically involve bar shaped LEDs arranged and illuminated to form numeric characters. The size and colour of the LEDs can vary – typical colours are red, green and blue.
The image below shows the TT34 Timer which has a 4 character numeric display, with additional LED indicators showing specific status information.
This type of LED display is specifically designed to display numeric, rather than alphabetic characters, and so this type of Human Machine Interface will usually be employed in a situation where it is sufficient to show a single numerical value, or possibly a choice from a small number of numerical values. A typical application might be to show the current temperature within a process (e.g. thermostats and thermistors). Other applications including timing and counting. Where alphabetic text is required, this type of display will typically employ a status light, with a fixed text label next to it on the casing.
In terms of inputs, the simplicity of the display is reflected in the input options, usually consisting of a few buttons. These can either be physical push buttons, or touch sensitive buttons.
The main advantage of an LED HMI is its simplicity. It is especially suited to a situation in which a key value needs to be prominently and permanently displayed. Some process controllers have multiple value LED displays, such as the one used on the K39 PID controller:
Process Controllers with LCD Displays
LCD (Liquid Crystal Display) screens allow a far greater resolution, allowing alphabetic text characters and other graphical shapes to be rendered accurately. This in turn increases the quantity and range of information that can be displayed. LCD displays are of two main types: text displays and graphic displays.
LCD character displays usually have between 1 and 4 lines of text, similar to those seen on early models of DAB radios. The number of characters which can be shown per line will vary, but is typically between 8 and 40 characters. For instance, the Jazz Series Micro PLC (below) has a 2 line display of 16 characters.
The complexity of the information which can be displayed is mirrored by the input controls. A phone type keypad allows both numeric and text input to be entered, while additional keys offer navigation around a menu system.
This type of Human Machine Interface can support complex processes involving multiple PID loops and is suitable for simple to medium control tasks.
LCD graphic displays offer a quantum step up in terms of the sophistication of information that can be displayed. Even a small graphic LCD display can show a high level of detail about a process, showing multiple items of information at the same time.
For instance, the Unitronics Vision 130 PLC (below) incorporates a relatively small LCDdisplay, taking up about the same space as a 4 line LCD text display.
It has a similar number of input controls to the text display model: alphanumeric keypad, navigation keys, and a small number of additional function keys.
But, this type of display is capable of displaying graphical symbols relating directly to the process, in addition to relevant values represented in alphanumeric form. This combination of qualitative and quantitative information allows a user to instantly assess the current state of a process, and then to inspect exact values as needed.
Again the complexity of the display mirrors the complexity of the PLC behind it. This PLC can control up to 24 independent PID loops and is suitable for medium complexity tasks.
PLCs with Integrated Touch Screen HMI
As the power and complexity of a process controller increases, so the ability of the HMI torepresent that complexity needs to increase also. Our touch screen PLC’s provide the necessary screen size, colour capability and resolution necessary to display information relating to multiple processes in way which is both easy to understand and attractive. For instance, the Vision 1210 is our largest PLC with integrated touch screen HMI.
But the value of a touch screen HMI goes far beyond the ability to represent complex information easily. A touch screen HMI allows the screen to become both output and input device. This makes it possible to have virtual on-screen controls which are context sensitive. In other words, only valid options at any given stage of the process are displayed. This clearly reduces the reliance on the user’s memory and previous experience, and it can greatly reduce user error.
A greater amount of effort is required to define the user interface screens, specifying task sequences, designing and producing graphics, and so on. But in the case of the Unitronics range, a great deal of assistance is provided in the form of image libraries, free software tools and ongoing support.
In addition, the cost of designing and implementing the user interface is offset by a number of other savings including the potential for reduced support costs and the ability to quickly upgrade products without incurring additional hardware or retooling costs.
To find out more about the importance of choosing the right HMI, the benefits for product users and manufacturers, and how to get advice on PLC selection, read our related article:
The Importance of the HMI When Selecting a Process Controller