When an HMI project requires more functionality than that offered by self-contained touchscreen units, the next step is to use an industrial PC-based system. The PC can be a traditional keyboard and mouse if the environment allows, or an integrated computer/touchscreen with varying degrees of environmental protection.
The PC offers many advantages over a simple, single-purpose operator terminal. Large and often expandable amounts of RAM and very fast graphic processing are an advantage over a purpose-designed and -built HMI graphic panel. Advantages include:
- PC operating system and the available tools to ease networking
- drivers for most any printer and other peripheral devices
- database connection software
- file-sharing capabilities
- remote operations.
Include historian software, and the operators can take a process back in time from a few hours to a few years to help to identify problems, performance and changing tolerances.
Most major automation manufacturers offer HMI runtime software that has the same look and feel of the smaller interfaces. The development software is similar or, in most cases, the same software used for the smaller HMIs. This lowers development costs and can keep the look and feel of graphical interfaces consistent throughout the plant. Manufacturers often team up with system integrators that are officially sponsored and promoted.
The prices of the major software packages vary a great deal. Some software packages are available with an unrestricted number of tags, such as a variable or I/O point, that can be accessed. Other manufacturers have several levels and several prices for the total number of tags that can be defined. In addition to the HMI software, other packages can be purchased and added to the HMI to seamlessly integrate other aspects of factory control and monitoring. Historians, asset management, SCADA, communication gateways, batch control and many other products may be added to the project.
It’s very helpful and efficient when using an HMI package from the same manufacturer, and the tag names can be imported directly from the PLC logic. I personally always felt that importing the tag comments would save me the time of typing the error messages twice.
Because major automation manufacturers need to reach the widest prospective audience, the HMI packages available must try to offer every option and every widget to everyone. These software packages often become large and unwieldy with simple functions hidden in multi-level menu systems. Does a designer actually need four different ways to change the color of some HMI screen text? An engineer from an integration company or a maintenance person at a plant who only uses the programming software occasionally may find it difficult to find all the attributes associated with one single HMI screen element.
In my experience, major automation manufacturers view their software offerings in one of three ways. First, some manufacturers consider their software to be a product to sell. There is little differentiation between the marketing of the software and the marketing of a PLC CPU or a proximity sensor. Software costs money to create and should contribute to the profitability of the company. This software is typically costly. It may have many features that have been included by request from the manufacturer’s largest customers.
A second general view is that the automation software is a sales tool to assist selling the hardware. This software is typically less costly and can be more user-friendly. When software bugs are found, they are usually fixed quite rapidly.
A third view is that the manufacturer realizes its competition has programming software, so it must have something also. This software is typically low-cost and low-quality.
Another source for HMI software is from third-party companies. These companies don’t build hardware, only software. Some have been around for decades; others are fairly young. Because the company focus is limited to producing software only, these third-party offerings are often more innovative than what may be available from the automation manufacturers. They often are quicker to adopt new trends in the industry. In addition to displaying information and providing control functions for the main processors in a system, the software may also communicate with multiple IIoT devices, display Web pages on tablets or phones and offer features such as statistical analyses or built-in database functions.
Third-party software will have drivers to communicate with multiple brands of control systems. Some packages allow the programmer to use native addressing for display and control objects.
Linus Torvalds released the Linux kernel in 1991 under an open-source license. This allowed programmers to change and add code to the basic operation system and had a profound effect on the open-source community. The community has grown quite large with participants located around the world. Most any type of software now has an open-source counterpart. Some of the software is quite good. Other software, not so much. HMI and soft PLC software have not escaped the open-source movement. Several packages can be downloaded from the Internet. These packages are usually a set of tools or a framework on which a programmer can build a project.
The three biggest advantages when using open source are the price (free or close to it), the programmer’s ability to modify and extend the code in any way required and having the final project being a smaller, more efficient product. The programming skill needed to create an application is somewhat higher than what is required using off-the-shelf development packages.
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