HMI | Human Machine Interface | Advanced HMI

 

The Importance of the HMI When Selecting a Process Controller 

 

Tecnologic supplies process controllers with a range of different HMIs including numerical LED displays, text and graphical LCD displays and colour touch screens. So it is important to understand both the features of these different types of HMI, and the benefits of choosing the right one for your application. For an overview of these different types of HMIs, read this article(link to article 2). But what is HMI and why does it matter which type of HMI you choose? Here we focus on explaining why the choice of HMI matters to end users and manufacturers, and how to go about making the right choice.

 

What is HMI?

 

HMI stands for Human Machine Interface and is the means by which a human operator will interact with a process controller. Put very simply, the Human Machine Interface is the process controller’s input/output mechanism for humans. Unless the process being controlled is entirely automated, some form of HMI will be required.

A human will depend on the output of the HMI to provide feedback about the current state of a particular industrial process. This may be as simple as reassuring the human that an automated process is running or has completed correctly, or that specific parameters are operating inside required limits. The HMI output is usually a visual display of some kind (e.g. alphanumeric characters or graphical images) but can also include audible feedback and alarms.

The HMI will also allow a range of inputs by providing interaction controls such as dials, push buttons or, in a more advanced HMI, a touch screen display. These controls allow processes to be started, stopped, adjusted or programmed as necessary.

Process controllers are available with or without a built-in HMI. A built-in HMI means that the HMI is physically integrated with the process controller: the controller’s outputs will already be connected to the display and the input controls will be integrated into a single casing.

Click here to view our range of PLC's with Integrated HMI's

 

Why the Design of the Human Machine Interface Matters

 

Choosing the right HMI can be as important as considering the capabilities of the process controller behind it. The most obvious effect of a particular type of HMI will be on the ease of use of the product. A Human Machine Interface which is easy to understand and gives clear options to end users will produce fewer errors, as well as a more pleasant user experience. A manufacturer which consistently provides an easy to use product will benefit in terms of future orders and recommendations to other customers. A manufacturer whose products may perform very well on a technical level, will find themselves losing business if their end users experience difficulty and frustration when using the product, or if the rate of user error is negatively impacting on a client’s business.

The choice of HMI will also have an impact on the real cost of the product for the end user.

An easier to use HMI means lower training costs. It also potentially means that less skilled personnel will be able to operate the product effectively. In addition, user errors can result in significant losses to a business in terms of time and materials wasted. So while one type of HMI may appear to be significantly cheaper in terms of the component costs, a more advanced HMI may well be more cost-effective when in the longer term.

There are also cost benefits for manufacturers directly. It has been mentioned in other articles that a process controller with integrated HMI already offers manufacturers significant cost benefits in terms of reduced labour costs to integrate controllers with a separate HMI, as well as potentially faster development times. But there are other benefits of choosing a built-in HMI.

Products which are easy to use generate fewer support requests to manufacturers. And advanced HMI’s can reduce product obsolescence and make it easier and cheaper to upgrade or refresh a product range. A powerful PLC with HMI, for example, may well have spare capacity, which can be utilised in the future to add features and capabilities but without changing the hardware components. And if that PLC also has a built-in HMI which allows new screens to be added easily, or existing screens to be refreshed with new graphics or colour schemes, it becomes much cheaper to create a “new” product. Finally, an advanced HMI which can be easily used by a greater range of people offers the possibility of creating products which could have a customer base of many thousands, rather than a handful of very specialised industrial customers. An example of this potential is the HiFri fat-free frying system which uses the Unitronics Vision 570 PLC, and features a built-in advanced HMI, consisting of a 5.7 inch colour touch screen.

 

How to Select the right HMI

 

Given the importance of the Human Machine Interface and the significant variation in type of HMI available, how do you go about choosing the right one for your application?

Correct selection requires analysis both of the back end process control requirements as usual (what I/O’s are needed, required accuracy levels etc), and of the context in which it is to be used. This means defining the user’s task in terms of what information the operator needs at different stages of the process and what user actions are needed at different points of the task.

This will indicate the complexity of the information that needs to be represented at any one time, including the number of items of information, whether they are numerical or text values, and whether a graphical representation would be helpful.

It is also useful to define the expected level of knowledge of a user, which will help define how much contextual information needs to be provided by the display. A highly skilled user who already understands the process can exercise knowledge and memory to make informed decisions about what to do in response to a particular value (e.g. a lab technician monitoring a value relating to an experiment he is running). But a less skilled or novice user will not have this knowledge and must be given contextual information and context-sensitive options in order to prevent errors (e.g. a restaurant employee operating a frying machine).

It is also essential to analyse the type of errors that are possible as a result of incorrect user behaviour, and the consequences of those errors. The more serious the consequences the more it is essential that the choice of HMI should allow the chance of error to be minimised or prevented altogether. A high-risk application is the most likely to require a context-sensitive user interface solution involving an advanced HMI with touch screen.

Once these factors (task complexity, user knowledge and error risk) are clear, it then makes sense to base your choice on the best HMI to meet these user requirements. It is then a relatively straightforward task to check that the PLC behind the HMI has the necessary capabilities to deal with the technical side of the process.

As always, Tecnologic can provide expert advice to help you choose the best process controller for your application. We can discuss your application requirements by phone, or arrange a site visit as necessary. We can also provide candidate models on a sale or return basis, allowing your design team to fully assess both the back end and HMI capabilities.

 

Human Machine Interfaces – Call us today to discuss your requirements on 01252 377 600 or to arrange a site visit.

To see a more detailed overview of the types of HMI supplied by Tecnologic, read this related article:

Types of Human Machine Interface in the Tecnologic Process Controller Range