Most industrial controllers, such as programmable logic controllers (PLCs ) and programmable automation controllers (PACs), can handle basic functions, such as real-time control of discrete and analog input/output (I/O) connections. In fact, this type of functionality is built into most controllers, and the main focus is on the number of I/O points that can be handled, which is usually easy to determine.
To better adapt to the implementation of the Industrial Internet of Things (IIoT), companies also need to consider other advanced functions when selecting industrial controllers, such as data processing, communication, and high-speed control. Understanding how to implement the required functions of a controller and how new functions will improve the design can help manufacturing companies increase efficiency.
Data processing function
Modern controllers with advanced tag name programming typically offer a variety of data processing capabilities, including built-in data logging. Some advanced controllers can also interact with standard databases in enterprise-level systems, such as Enterprise Resource Planning (ERP) systems.
The ability to directly log data to a USB storage device connected to the controller is an important feature and is often a requirement in many applications. Controllers with data logging capabilities typically support formatted USB pen drives or mini SD cards, each with up to 32GB of storage.
Data logging is typically based on events or schedules. Events are triggered by state changes, such as boolean data state transitions. Scheduled data logging is set to occur periodically, such as every minute, hour, day, or month.
The number of loggable tags is typically limited, but at least 50 tag values should be configured for each scheduled or triggered event. System errors should also be stored along with the time and date of the error or event. Log filenames should be configurable or automatically generated based on user preferences.
In addition to recording data locally, some controllers can also communicate with IT enterprise systems. An OPC server connected to the controller is one example. This allows the server to collect real-time data from controllers on the factory floor and retrieve, add, delete, and update data records in a standard database. This is accomplished through connections that support databases compatible with Microsoft Access, Structured Query Language (SQL) servers, or Open Database Connectivity (ODBC).
Some software tools on the market allow users to establish connections between IT enterprise systems and PLCs, enabling them to collect data from the PLCs and store it in a database. These servers typically require minimal configuration effort, and users can configure them to collect only the data needed for their processes.
These database functionalities provide practical applications for tracking material movement and production metrics. Controllers executing actual production tasks can track factory floor progress to ensure optimization of manufacturing time. They can also track material consumption. This information can be used to adjust inventory to ensure adequate material supply when needed.
These features can also be used to track the state of a product from start to finish by recording production data as parts or products are manufactured. The database's built-in date/time stamp functionality, which saves the final product's status, can be used to meet quality assurance or audit requirements.
Communication function
Another important characteristic to consider when selecting an automation controller is its communication capabilities. Multiple Ethernet and serial communication ports should be provided for easy integration with human-machine interfaces (HMIs), motor drives, and other devices (Figure 1).
Figure 1: Productivity depends on data collection. The controller's communication and data processing capabilities can connect to many different devices. Image source: AutomationDirect
These high-speed Ethernet ports can also be used for point-to-point (P2P) or business system networks. Support for EtherNet/IP and Modbus TCP/IP Ethernet protocols is also very important.
Additionally, the controller should provide other communication ports for USB input/USB output, mini-USB, mini-SD, remote I/O, RS-232, and RS-485 connections.
These connections enable easy programmable access, connectivity to high-speed devices such as drives , and integration with human-machine interfaces (HMIs) for operator monitoring. They also support email sending, scanner/client and adapter/server connections, and other communication functions for remote access.
The remote monitoring application allows users to connect to the controller using a Wi-Fi or cellular network link. Remote users can monitor the local controller by configuring user tags for remote access within the tag database.
In hardware configurations related to remote access, modern controllers should have built-in security and select the corresponding tag from the database to enable remote access to the device where remote functionality must be enabled. Furthermore, for any device accessible from the internet, firewall security is strongly recommended. While remote access functionality of the controller can and should be password protected, a secure and encrypted Virtual Private Network (VPN) connection is a better option due to internet security risks (Figure 2).
Figure 2: Obtaining remote data from the controller. Some modern controllers have up to seven built-in communication ports, providing critical functionality for connecting factory floors and enterprise-level business networks.
Another protection feature related to remote controller access is the separation of account and IP address configuration, which allows users to upload, download, or edit programs within a given remote access connection. An account should not simultaneously allow remote monitoring and program modification.
The controller should support remote monitoring applications and include necessary security features. Authorized users should be able to connect their smartphones or tablets to the controller for remote monitoring via Wi-Fi or cellular connectivity.
Other web server functions in the controller allow for remote troubleshooting of problems via system tags, error logs, and event history, and allow remote users to inspect data files recorded to the controller's hard drive or mini SD card.
High-speed control function
Another important feature to consider when selecting a modern controller is its ability to control motion and other high-speed applications. Performing these functions requires high-speed I/O, as well as a powerful processor and the ability to prioritize high-speed tasks.
While some controllers offer coordination between multiple motion axes, even coordinated motion between two axes typically requires specialized hardware and built-in controller functionality. First, high-speed output and high-speed input modules are needed. The high-speed output module generates pulse and direction commands to instruct servo drives to control two or more servo motors. These pulse and direction commands can control a variety of applications, such as cutting lengths, stitching, and coordinated X and Y axis movement.
The registration function can also be used for movement commands generated by the high-speed output module. The registration function can use the module's built-in I/O to trigger multiple internal and external position-based events. Signals from sensors, received via the high-speed input module, can trigger the start or stop of movement, capture encoder feedback position, or turn on/off or pulse output.
Programmable drum switches (PDS) and programmable limit switches (PLS) provide additional high-speed control capabilities. PDS, like encoders, can monitor multiple devices at rates up to 1 MHz. These input signals are used to coordinate and control the output at a rate of tens of thousands of times per second. This type of hardware configuration provides precise and accurate motion control, independent of the controller scan time, which can vary depending on the processor load.
The PLS instruction works similarly to a mechanical rotary cam with limit switches, but the virtual shape of the cam can be controlled in real time. Because this function typically runs alongside high-speed inputs, it is completely independent of processor load and associated scan time, thus providing accurate and repeatable timing for high-speed applications.
Figure 3: Controller functionality is constantly expanding. Data processing, communication, and high-speed control capabilities should be considered during the selection process to improve the design.
When selecting PLCs, PACs, and other industrial controllers, users need to consider control and I/O requirements beyond basic functions (Figure 3). For many applications, the controller also needs extensive data logging and communication capabilities, as well as control for high-speed applications such as coordinated motion.
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