In the 1950s, the first mini computers were developed for use in industrial environments. These have evolved drastically in the decades that followed and the rise of the Internet of Things (IoT) means that more interconnected devices in plants can now be monitored. Here, Adrian Swindells, a director of industrial computing specialist Distec Ltd, explains why human machine interfaces (HMIs) offer a more flexible alternative to supervisory control and data acquisition (SCADA) systems in most applications
SCADA software is typically used in large plants with complex production setups. Plant managers use the software to monitor the state of the production line, including variables such as temperature, speed or pressure. Alarms will sound if these variables fall outside pre-determined limits, a critical safety measure for proportional-integral-derivative (PID) intensive applications such as temperature control in a furnace.
In large plants it is not unusual to generate millions of points of data from sensors every day. Here, SCADA systems can collect the data centrally and provide historian database access to trends and forecasts.
However, processing all this data can be demanding and requires servers, industrial PCs, a network of PLCs, data hosting and effective data security systems. Although this is manageable for many end users, original equipment manufacturers (OEMs) often struggle to accommodate this due to the high capital costs.
A decade ago, many businesses purchased SCADA software, despite the high costs, because HMIs were simply not adequate for effective plant management at the time. We have come a long way in the last decade and HMIs now offer a flexible alternative to SCADA systems for many OEMs.
HMIs are controller operator panels, which offer smart reporting and can relay management information. They display a graphics based visualisation of the control and monitoring system. HMIs are now single, plug-and-play, units. Plant managers no longer to need to install a separate monitor connected to an industrial PC running an operating system (OS) that needs to be configured each time it is connected to a different line.
HMIs are also available pre-loaded for engineers to install them quickly, whereas SCADA systems take a long time to configure. They are also a relatively closed system, meaning that there are limited data security concerns.
HMIs are becoming powerful enough to programme, visualise and manipulate data, meaning smaller businesses can benefit from the flexibility and response times of using HMIs. For example, while HMIs and SCADA systems are complex, HMIs are more user friendly than SCADA. This means that for companies with limited resources, staff can use the HMIs and monitor the system much more easily, with less training.
If plant managers decide to replace their SCADA software with HMIs, there are a few considerations. While companies may wish to save money by using HMIs rather than SCADA software, they must be mindful of hidden costs associated with some HMIs. Companies such as Red Lion Controls offer the programming software for its HMIs as a free download from their website and also offer regular updates for free. This means that the software can be used over a long period of time and will not require regular costly updates.
HMIs now offer web serving and data logging and allow data to be shared remotely or through expandable storage. However, many HMI manufacturers offer these features as additional upgrades. If managers wish to use these features as an alternative to SCADA software, they should consider choosing a HMI with these features built in.
Another important factor to consider when choosing a HMI is integration into legacy systems. Not all HMIs are compatible with all proprietary communication protocols.
Larger plants often use either the PROFIBUS or the DeviceNet protocol and many HMIs are only compatible with one protocol or the other. However, discerning customers can purchase HMIs from Red Lion Controls, which are compatible with both protocols. This means that the HMIs can link to over 300 PLCs and OEMs can use the HMIs in the end user’s plant.
Plant managers should also consider using controllers to convert analogue stations so that they can be monitored by HMI panels. The controllers monitor the device and relay the signals back to the HMI panels, without requiring additional panel space or a separate programming package.
For added flexibility, many OEMs are looking to wireless 4G cellular modules. OEMs can use a plug-in 4G module to monitor systems and make changes to the device remotely, without the need to send an engineer out to the plant, which may be a long distance away.
HMI panels now offer a much better range of features than they did previously. While SCADA software still has its place in large plants, OEMs can use HMIs to monitor PLCs and production lines. However, they should be careful in their choice of HMI to ensure that all of the necessary features are included and that the device effectively delivers their requirements when working with end users. Plant managers interested in learning more about industrial automation and networking can attend the Smart Factory Day on March 28, 2017 at the De Vere Cranage Estate in Cheshire to ensure that they can get the best results for their plant.