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March 12, 2015
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Three Ways To Communicate Between Mobile Devices And PC-Based HMIs


Mobile technology allows instant, on-demand access to production data from anywhere. But users must still select the correct method for establishing communications.

By Jane Alexander, Managing Editor

If your company is like most, it could benefit from communications between your automation systems and mobile devices such as laptops, tablets and smartphones. Many recent technology advances have increased options in this area, making it easier for plant personnel to get the data they need via their preferred (and approved) mobile devices.

For many applications, the PC-based Human Machine Interface (HMI) has emerged as the main gateway between automation-system controllers and operations personnel, according to Jeff Payne of the Automation Controls Group with AutomationDirect.com. These applications run the gamut from control of a single machine to automation of entire plants.

“In a typical setup,” Payne says, “PC-based HMI software is purchased from a supplier and configured by the user to communicate with the automation system controllers, such as PLCs, programmable automation controllers and other intelligent devices. The PC-based HMI provides local operator interface at the plant, but most facilities can benefit from expanded access via remote devices.”

Modern PC-based HMI software is usually provided with a means to establish communications with mobile devices. These communications can generally be two-way, with the PC sending data to the mobile devices, and with the mobile devices sending commands to the PC. Payne explains the three main ways of providing this two-way communication from PC-based HMIs to remote devices: directly from the PC, via onsite IT systems and via the cloud.

1. Direct access

Today’s PCs come with many built-in communication capabilities. When coupled with the latest in PC-based HMI software, a powerful platform is created for managing remote devices. The simplest way to establish communications with these remote devices is through the HMI software’s built-in Web server.

For Web-server communications, the PC-based HMI is connected to the Internet via an Ethernet connection. Users can configure the HMI software to serve pages to the Web, and these pages can be accessed by mobile devices through any Web browser. Once the HMI’s Web server is accessed, the mobile device can be used to view data, and also to send commands to the HMI.

HMI software providers with mobile access capability typically use Apache HTTP and Microsoft Internet Information Services Web servers. These mature Web servers continue to evolve and provide centralized SSL certificate support, IP security and client security mapping to ensure a safe, secure connection.

The HMI software can typically be configured to provide varying levels of access for different users. For example, a plant automation engineer may be given full access to view all Web pages, along with the ability to make changes to automation-system setpoints. Payne says a plant manager may only need to view one or two pages showing key performance indicators such as throughput, energy use and quality parameters. Access is controlled by log-in credentials, giving the HMI software a way to uniquely identify each remote user, and to provide each user with only the required level of access.

The main advantage of this method is its simplicity. Only one PC-to-Internet connection is needed. The Internet becomes the network, so there’s no need to establish and maintain a separate IT network to link the PC-based HMI to the mobile devices. There is also no need to change the graphics when the device size changes.

Payne notes that the relatively new HTML5 standard makes implementing this option easier. With HTML5, the application launches in a mobile-device browser, and automatically resizes the HMI screens to fit the device size. A review of just one smartphone and tablet manufacturer finds over a dozen screen sizes. In the past, when devices were presenting data, some were compatible and some were not. HTML5 overcomes this obstacle when displaying data and Web pages, as most all HMI software packages and mobile devices conform to the HTML5 standard.

Users can start small with just one or two Web pages showing key data which can be accessed by all. Web pages can be added at any time to provide more information. Users can start to discriminate among users so each person or group is only provided with the required level of access.

The main drawback of this approach, Payne acknowledges, is complete dependence on the link from the PC-based HMI to the Internet, as the plant’s Internet service provider becomes the critical link in the data distribution system. There can be security concerns, although modern HMI software provides mechanisms for controlling remote access.


Fig. 1. This PC-based HMI provides local operator interface at a machine, and can also serve Web pages which users can access from any browser on their mobile devices.

A typical case is when a single PC-based HMI is used to provide local operator interface at a machine (Fig. 1). This PC is then connected to the Internet via its Ethernet port, and is configured to serve Web pages to users via the browser-based interface on their mobile devices.


Table I lists pros and cons associated with the direct-access approach, and compares it with onsite IT and the cloud.

2. Onsite IT

Payne says using onsite IT to distribute data from PC-based HMIs to mobile devices provides more power and options than with direct access, but is more expensive and complex. With this option, the PC-based HMI is connected to the plant or company internal IT system through its Ethernet port. In systems with multiple PC-based HMIs, each can be connected to the network. Mobile devices access the PC through the IT network, instead of through the Internet as with direct access.

This option requires an internal IT network to be set up and maintained. Although most plants have such a network for office use, extending the network to the plant isn’t a trivial exercise as it requires close cooperation between the plant’s automation personnel and IT staff.

“The IT staff is likely to see the PC-based HMI as just another node on its network, and treat the PC-based HMI just like it would an office PC,” Payne explains. Among other things, this could mean automatically sending updates and patches to the PC, and remotely rebooting it as required. This is rarely a good idea for a PC-based HMI, he says, as each update or patch must be tested to make sure it doesn’t affect the HMI software and its connections to controllers. Also, reboots must be carefully scheduled so as not to affect production.

“On the other hand,” says Payne, “this method allows plant automation personnel to use existing IT networks along with established remote access practices.” Since most IT departments already have procedures in place for secure remote access, often via VPN, this access can be very tightly controlled to provide a high level of security.

A large manufacturing facility with multiple PC-based HMIs is connected to the plant’s IT network to provide mobile device remote access.

Fig. 2. A large manufacturing facility with multiple PC-based HMIs is connected to the plant’s IT network to provide mobile device remote access.

For mobile-device users, access to the PC-based HMI via the onsite IT network will typically be more complex than with direct access. This is because extra steps will be required to first establish communications with the IT network, and then with the PC-based HMI. Payne describes a typical use as a large manufacturing facility with multiple PC-based HMIs, each connected to the plant’s IT network (Fig. 2). IT would work closely with the plant’s automation staff to provide the required mobile device access.

While the onsite IT option works well in many cases, Payne says it does burden existing IT staff and systems. Moreover, it requires close, ongoing cooperation between IT and a plant’s automation staff—something that may not always be easily achieved. To deal with these and other issues, he says, many plants look to the cloud as a means to establish and maintain communications between their PC-based HMIs and their staff’s mobile devices.

3. The cloud

With this option, the network resides in the cloud instead of with internal IT. Each PC-based HMI is connected via the Internet to a rented network in the cloud. To provide greater reliability, there can be multiple redundant connections from each PC to the cloud, such as through an Internet service provider and a leased communication line.

Network and storage space in the cloud can be rented directly through a provider such as Amazon or Rackspace. This is the lowest-cost option, but requires a degree of IT expertise as the user must interface directly with the cloud company to define needs. Alternately, third-party companies can also provide cloud services to manufacturing and other industrial concerns. These have the required IT expertise to deal with the cloud provider, as well as understand unique manufacturing concerns.

A wide variety of corporate, production and control data can be stored in the cloud and quickly accessed via mobile devices through a Wi-Fi or cellular connection.

Fig. 3. A wide variety of corporate, production and control data can be stored in the cloud and quickly accessed via mobile devices through a Wi-Fi or cellular connection.

In either case, Payne says, mobile users access data through the cloud, requiring only an Internet connection. This connection is typically established through either a Wi-Fi network or through a cellular provider’s 4G network. So if the mobile user can establish an Internet connection, he or she can access data stored in the cloud (Fig. 3).

Storing data in the cloud provides a high level of security given the fact that cloud providers maintain large staffs of IT personnel who are well-versed in security. Still, hackers are continuously trying to breach these high-visibility targets, as breaking through Amazon’s security system is more attractive to the average hacker than accessing a small manufacturing plant’s IT network.

A typical cloud-use case, Payne says, would be a facility or number of facilities owned by one company, all requiring remote access via mobile devices from a widely geographically distributed workforce.

Expanding mobility across industry

While PC shipments have been mostly flat over the past five years, tablet and smartphone sales continue to exhibit strong growth. Payne references a 2013 report by Forbes magazine that more than 56% of all adult Americans had smartphones. That number is projected to reach 70% by 2018. This, he says, plays directly into a more recent trend known as Bring Your Own Device (BYOD), in which plant personnel in some operations use their own smartphones and tablets to access PC-based HMIs. “Once corporate policy catches up,” he observes, “most will be able to use their own devices within the next few years, with HTML5 a key enabling standard.” MT

For more information on these tactics, visit AutomationDirect.com.