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 comes with most controllers, and the focus is primarily on the capability of the number of I/O points that can be handled, which is usually easy to determine.
In order to better accommodate the implementation of the Industrial Internet of Things, when shopping for industrial controllers, companies need to consider other advanced features such as data processing, communication, and high-speed control. Understanding how to implement the features needed in a controller and how new features will improve the design can help manufacturing companies improve efficiency.
Data Processing Functionality
Modern controllers with advanced markup name programming often offer a variety of data processing features, 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.
Logging data directly into a USB storage device attached to the controller is an important feature and is often a requirement in many applications. Controllers with data logger capabilities typically support formatted USB pen drives or mini SD cards with up to 32GB of storage each.
Data logging is usually based on events or scheduling. Events are triggered by state changes, such as Boolean-type data state transitions. Scheduled data logging is set to occur at regular intervals, e.g., every minute, every hour, every day, or every month.
The number of tokens that can be logged is usually limited, but at least 50 token values should be configured for each dispatch or triggered piece. System errors should also be stored along with the time and date the error or event occurred. Log file names should be configurable or automatically generated based on user preferences.
In addition to logging data locally, some controllers can communicate with IT enterprise systems. An OPC server connected to the controller is an example. The server is allowed to collect real-time data from controllers on the plant floor and retrieve, add, delete and update data records in a standard database. This is accomplished by supporting connections to Microsoft Access compatible databases, Structured Query Language (SQL) servers, or Open Database Connectivity (ODBC).
Some software tools on the market allow the user to establish a connection between the IT enterprise system and the PLC so that data can be collected from the PLC and stored in a database. The configuration effort for these servers is usually minimal and users can configure them to collect only the data needed for their processes.
These database functions provide practical applications for tracking material movement and production metrics. A controller that performs actual production tasks can track factory floor progress to ensure optimization of manufacturing time. It can also track material consumption. This information can be used to adjust inventory to ensure that materials are in sufficient supply when needed.
By recording production data as parts or products are manufactured, these features can also be used to track the status of a product from start to finish. Saving the status of the final product, the database's built-in date/time stamp feature can be used to fulfill quality assurance or auditing requirements.
Communication Features
Another important feature to consider when selecting an automation controller is communication capabilities. Multiple Ethernet and serial communication ports should be available for easy integration with human machine interfaces (HMIs), motor drives, and other devices.
These high-speed Ethernet ports can also be used for peer-to-peer (P2P) or business system networks. Support for EtherNet/IP and ModbusTCP/IP Ethernet protocols is also important.
At the same time, the controller should provide other communication ports for USB in/USB out, mini-USB, mini-SD, remote I/O, RS-232 and RS-485 connections.
These connections, allow for simple programming access, connection to high-speed devices such as drives, and integration with the operator's supervisory human-machine interface (HMI). They also support sending e-mail, scanner/client and adapter/server connections, and other communication functions for remote access.
Remote monitoring applications that allow 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, where remote functionality must be enabled, modern controllers should have built-in security and the corresponding tag in the database should be selected to enable remote access to it. In addition, as is true for any device that can be accessed from the Internet, it is highly recommended that a firewall be used for security. Although the remote access feature of the controller can and should be configured with password protection, a secure and encrypted Virtual Private Network (VPN) connection is a better option due to the Internet security risks!
Another protective feature associated with remote controller access is the account and IP address separation configuration, which allows a user to upload, download, or edit a program for a given remote access connection. An account should not allow both remote monitoring and program modification.
The controller should support remote monitoring of applications and include the necessary security. Authorized users shall be able to connect a smartphone or tablet to the controller for remote monitoring via a Wi-Fi or cellular connection.
Additional web server functionality in the controller may allow remote troubleshooting of problems via system tags, error logs, and event history, and allow remote users to inspect data files logged to the controller's hard disk or mini-SD card.
High-Speed Control Features
Another important reference feature for selecting a modern controller is the 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 axes of motion, coordinated motion between even two axes usually requires special hardware and built-in controller features. First, high-speed output modules and high-speed input modules are required. The high-speed output module generates pulse and direction commands to command the servo drive to control two or more servo motors. These pulse and direction commands can control a variety of applications such as cut-to-length, stitching, and coordinated x-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. Via inputs from the High Speed Input Module, signals from sensors can trigger the start or stop of movement, capture encoder feedback position, or turn on/off or pulse outputs.
Programmable Drum Switches (PDS) and Programmable Limit Switches (PLS), provide additional high-speed control capabilities. pDS, such as encoders, are capable of monitoring and controlling multiple devices at rates of up to 1 MHz. These input signals are used to coordinate and control outputs at a rate of tens of thousands of times per second. This type of hardware configuration provides precise and accurate motion control independent of controller scan time, which can vary depending on 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. Since this function typically operates with high-speed inputs, it is completely independent of processor load and associated scan times, thus providing accurate and repeatable timing for high-speed applications.
When selecting PLCs, PACs and other industrial controllers, users need to consider control and I/O requirements that go beyond basic functionality. For many applications, controllers also need to have extensive data logging and communication capabilities, as well as control for high-speed applications such as coordinated motion.