How to select PAC/PLC system for new mining processing plant

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One of the big questions during the development of a new Mining Processing Plant is what kind of Programmable Automation Controller (PAC) or Programmable Logic Controller (PLC) shall be incorporated into the Plant Control System. More specifically, what is the most appropriate brand and what type shall it be.

Almost all brands offer quite similar features. However, there are some differentiators that each brand has that may be put into consideration. The brand selection depends on how the end-user defines the requirements.

From the end-user’s perspective, below are five points that drive the requirements and eventually drive the PAC selection for the mining processing plant.

1. What is the process or equipment that needs automation?

In a Mining Processing Plant, there are many equipment that require a Process Automation or a Control System. Comminution circuit, conveyor lines, rotary kilns, furnaces, converters, leaching circuit, flotation circuit, and other specific equipment depending on the mineral or ore type and the final product. The process flow at each equipment is different thus require different control system as well. However, the control system for each equipment can be broken down into detailed pieces and end up into two types: analog control loops or digital controls. Analog control loops are commonly associated with control valves, electrode positioners, drives, etc. Digital controls are mostly associated with motors, switches, block valves, and other equipment which has only two-states: on or off.

If the analog control loops are significant and take most of the signals, then a high-end PAC is the strongest candidate to be considered. High-end PACs have a larger internal memory and are capable of handling multiple loop controllers (e.g. PID controls). The Modicon M580 ePAC (ethernet Programmable Automation Controller) has several controller models to adapt to various application requirements.

Now what if the analog control loops are significantly present at one area but not the other?

It is not mandatory to have the same type of PAC for the entire plant. End-users may have various types of PACs at their plant, even if it comes from different brands.

However, sometimes there are very specific applications that need specific features of a classic PLC (e.g. processing speed). An example of this application is the thyristor-based voltage regulator in a smelter. The PLC’s purpose is to provide firing function for the thyristor. The PLC for this very specific application typically comes as a package from the OEM/manufacturer and the end-user has limited flexibility to choose their own preference.

2. What is the mission or purpose?

Safety is a very important aspect in the operation of a mining processing plant. Several new processing plants built within the last decade segregate the Business Process Control System (BPCS) and Safety Instrumented System (SIS). The BPCS is to regulate the legacy process while the SIS is specifically to handle the safety-related field instruments. The working principle of SIS and its function is different from the BPCS hence needs a special PAC to be suitable for both applications. The Modicon M580 offers both BPCS and SIS PAC´s.

Both BPCS and SIS may share the same operator interface or Supervisory Control and Data Acquisition (SCADA) system. In case various PAC types and brands are installed in a plant, a SCADA system that can connect to any PAC brand is needed. AVEVA System Platform (previously Wonderware System Platform) is a SCADA platform that can fulfill this need.

3. What is the most cost-effective PAC?

Mineral prices in the global markets are hard to predict. That is one of the reasons why miners need to be more cost efficient. This is another requirement for the PAC selection.

The total life-cycle cost for a PAC includes Capital Expenditure (Capex) and Operational Expenditure (Opex). Cost of material purchasing, installation, maintenance and restoration are among the spending items that end-user considers in defining the specification.

Environmental conditions affect the cost of the system. As an example, a lithium mine needs a PAC system for its brine pumping station. A set of standard PAC systems may work well for the first periods of operation, even without additional environmental protection. However, the PAC’s performance may start to decrease after that because of the corrosive environment around the brine pumping station. As an impact, the production will stop to allow some maintenance activities. In this case, there is a production loss equal to some amount of the financial cost. The production loss might have been mitigated if a PAC system with harsh classification was installed despite its initial higher cost. Harsh classified PLC system will have additional conformal coating and protection against corrosive environments. In some cases, protection against high temperature is also needed.

The Modicon M580 ePAC offers harsh classified systems for the processor, the backplane, the power supply, communication, and IO modules. Protection against extreme temperatures between -25 °C and +70 °C is available as well.

Another source of cost saving comes from spare part rationalization. If various PLC types are compatible and can use the same parts, this means that the end-user can minimize spare stock items in their warehouse. Most of the IO modules, racks, and power supplies of Modicon M580 and M340 are interchangeable, allowing end-user to rationalize the PLC system spare parts better.

4. What is the PAC’s degree of flexibility?

PAC systems connect to various external systems such as SCADA, Historian, field devices, or future applications such as Industrial Internet of Things (IIOT) or machine learning.

Regarding integration with SCADA systems, usually the SCADA and PAC will be programmed independently then will be connected by using Open Platform Communications (OPC) protocols. However, as technology is always evolving so the programming work for both PAC and SCADA can now run simultaneously. EcoStruxure Process Expert (EPE) is a solution from Schneider Electric where PAC and SCADA are programmed simultaneously in a more high-level way.

There are a lot of communication protocols available in the market for connecting field devices to the PAC. However, there are some protocols that are quite popular such as HART, Modbus, Modbus TCP, Ethernet/IP, Profibus, Profinet, CAN bus, IEC61508, etc. The PAC shall be able to communicate using various protocols for easy integration with field devices. Modicon M580 supports major protocols in the industry, including all the protocols mentioned above.

In the era of Industry 4.0, the PAC will play an important role. As a product born in the Industry 3.0, the controller will become the data-hub for some future applications. The applications may run in the internet cloud outside the end-user’s premise. Here, the importance of cybersecurity is very clear. The PAC may be subjected to some cyber-attack trials. The Modicon M580 already has the Achilles Level II Cybersecurity certification.

5. How easy is it to migrate the PAC system?

There is no electronics product that can last forever. Component availability, and technology are only few among other reasons why an electronics product shall be phased-out or obsolete. Therefore, the end-user will have to think early how to migrate the control system in the next two or three decades.

In fact, the end-user may learn from his previous experience. How did the last PAC migration go? What were the most painful things that happened?

One great tip to prepare for a better migration is the rack separation of the PAC processor and it’s IO modules. The local rack will consist only of the power supply, PLC processor, and communication module. All IO modules are installed in remote racks at different cabinets. By having this separation, end-users can first migrate only the processor before the IO modules.

Schneider Electric knows that the migration needs to be as smooth as possible so end-users can keep operating or minimize the delay/stop. The Modicon M580 processor can connect to legacy Quantum Remote IOs. Not only that, the Modicon M580 is compatible with the rack, power supply and IO modules of Modicon M340. In addition to that, the programming control platform is similar thus decrease the re-programming efforts significantly. Therefore, if the end-user wants to modernize then M340 to M580, then it will be less complicated and more cost efficient compared to other PAC systems.

The five points above are considered the main concerns in defining the PAC specification for a new Mining Processing Plant. However, each end-user may have other concerns that are not mentioned in this article. Each end-user has its own uniqueness that is influencing specification of devices for their processing plant.

The Modicon M580 ePAC provides solution to answer all points discussed above. Moreover, Schneider Electric with EcoStruxure Plant provides solutions for a Mining Processing Plant development journey around the world.