The Human Machine Interface (HMI) is the way in which a person communicates with a software application or hardware device, specifically an AC drive. The goals are mutually beneficial for both man and the drive. It enables the user to effectively operate and control the drive (and the machine it runs), and it allows the drive to provide feedback simultaneously that helps the user to make decisions that will have a positive effect on his/her process.
Varying from a basic LED status indicator to sophisticated software tools, the interfaces allow the user to efficiently control, monitor and diagnose issues with the machine (drive) and its applications or devices.
Here are the five most frequently applied HMIs:
LEDs
These are the most basic forms of HMI. Typically there are LED indicators that show, for example, that the power is on and the device is operating, a warning is present or to indicate an alarm. Users can quickly see when action needs to be taken. This fast, visual indication is also an important benefit in other settings. Take, LED rear brake lamps, for example. According to research by Hewlett Packard, LEDs illuminate 200 milliseconds faster than incandescent bulbs. This means a faster braking distance response time for following vehicles of about a full car length at a speed of approximately 100 km/h which significantly reduces rear-end accidents.
Numerical and alphanumerical panels
These devices provide an easy way to control a drive, to monitor its actual status and to commission it.
Input and output terminals
Dedicated input and output control terminals are available in order to build an interface between a programmable logic controller (PLC) and the drive. Input control signals (start/stop, coast or reverse) ensure that the user has functions to control the drive according to the needs of the application. To control the drive and to get feedback signals from the application, analog input signals (0–10V or 0(4)–20 mA) can be used. Feedback signals from the drive to the PLC are digital or relay outputs which can be configured to indicate status like ‘motor running’ or ‘alarm’. Analog output signals from the drive can also be configured to monitor, for instance, the actual load conditions.
Fieldbus
Using a standardized fieldbus interface between the PLC and the drive helps with commissioning and with control and monitoring of the application.
Software tools
Integration of the drive control into PC software gives the user full system configuration and control. With software tools, it is possible to monitor the entire system more effectively for faster diagnosis and better preventive maintenance.
Modern software tools can be used as follows:
- for planning a new communication network offline; software tools contain a complete database with supported drive products
- for online commissioning of drives
- for easy replacement of drives in the event of failure
- for easy expansion of the network with more drives
- for backup of parameter settings of drives in a communication network
- as software supports fieldbus protocol, this eliminates the need for an extra communication network
HMIs are a vital component of today’s drives business. A good interface lets the user interact with the software or hardware in a natural and intuitive way. It should make everything clear through a combination of language and visual elements. And it should save you time and money by making you more efficient and making your processes more productive.
This article was first published on the Vacon Blog.
