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Three Points for Engineers to Pay Attention to in Selecting Industrial Controller
Release Time:2019-08-19 09:53:41    Page views:2273
Most industrial controllers, such as programmable logic controller (PLC) and programmable automation controller (PAC), can handle basic functions such as discrete and analog input/output (I/O) real-time control. In fact, this type of function comes with most controllers. The main concern is the ability to handle the number of I/O points, which is usually easy to determine.

In order to better adapt to the implementation of the Industrial Internet of Things, when choosing industrial controllers, enterprises also need to consider other advanced functions, such as data processing, communication and high-speed control. Understanding how to implement the functions required by the controller and how the new functions will improve the design can help manufacturing enterprises improve efficiency.

Data Processing Function

Modern controllers with advanced tag name programming usually provide various data processing functions, including built-in data recording. Some advanced controllers can also interact with standard databases in enterprise systems, such as enterprise resource planning (ERP) systems.

Recording data directly into USB storage devices connected to controllers is an important function and is usually required in many applications. Controllers with data recorders usually support formatted USB pen drives or mini SD cards, each with a storage space of up to 32GB.

Data records are usually based on events or scheduling. Events are triggered by state changes, such as Boolean data state transitions. Scheduling data records are set to occur periodically, such as every minute, hour, day or month.

The number of tags that can be recorded is usually limited, but at least 50 tag values should be configured for each dispatch or trigger. System errors should also be stored with the time and date of the error or event. Log file names should be configurable or generated automatically according to user preferences.

In addition to recording data locally, some controllers can also communicate with information technology enterprise systems. An example is the OPC server connected to the controller. It allows the server to collect real-time data from the controller of the factory workshop and retrieve, add, delete and update data records in the standard database. This is accomplished by supporting Microsoft Access compatible database, structured query language (SQL) server or open database connection (ODBC) connections.

Some software tools on the market allow users to establish connections between IT enterprise systems and PLC, so that data can be collected from PLC and stored in the database. These servers are usually configurable with little effort, 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 indicators. Controllers that perform actual production tasks can track workshop progress to ensure the optimization of production and manufacturing time. It can also track material consumption. This information can be used to adjust inventory to ensure adequate supplies when needed.

These functions can also be used to track the state of the product from beginning to end by recording production data when producing parts or products. The state of the final product is saved, and the built-in date/time stamp function of the database can be used to meet the quality assurance or audit requirements.

Communication function

Another important feature to consider when choosing an automation controller is communication capability. Multiple Ethernet and serial communication ports should be provided for easy integration with human-machine interface (HMI), motor drivers and other devices (Figure 1).

These high-speed Ethernet ports can also be used in peer-to-peer (P2P) or business system networks. It is also very important to support EtherNet/IP and Modbus TCP/IP Ethernet protocols.

At the same time, 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 can realize simple programming access, connection with high-speed devices such as drivers, and integration with human-machine interface (HMI) for operator monitoring. They also support sending e-mail, scanner/client and adapter/server connections, and other communication functions for remote access.

Remote monitoring applications allow users to connect to the controller using Wi-Fi or cellular network links. By configuring user tags for remote access in the tag database, remote users can monitor local controllers.

In the hardware configuration related to remote access, when remote functions must be enabled, modern controllers should have built-in security and select corresponding tags in the database to enable remote access to them. In addition, for any device that can be accessed from the Internet, it is strongly recommended that firewalls be used to ensure security. Although the remote access function of the controller can and should be configured with password protection, secure and encrypted virtual private network (VPN) connections are a better choice due to Internet security risks (Figure 2).

Another protection function associated with remote controller access is the account and IP address separation configuration, which allows users to upload, download or edit programs given a remote access connection. An account should not allow both remote monitoring and program modification.

Controllers should support remote monitoring applications and include the necessary security. Authorized users should be able to connect smartphones or tablets to controllers via Wi-Fi or cellular connections for remote monitoring.

Other web server functions in the controller allow remote troubleshooting through system tags, error logs and event history, and allow remote users to check data files recorded on the controller's hard disk or mini SD card.

High Speed Control Function

Another important reference feature for choosing modern controllers is the ability to control motion and other high-speed applications. Implementing these functions requires high-speed I/O, powerful processors and the ability to prioritize high-speed tasks.

Although some controllers provide coordination between multiple motion axes, special hardware and built-in controller functions are usually required even for coordinated motion between two axes. Firstly, high-speed output module and high-speed input module are needed. The high-speed output module generates pulses and direction instructions to command the servo driver to control two or more servo motors. These pulses and directional commands can control various applications, such as shear length, stitching and coordinated X-Y axis movement.

The registration function can also be used for mobile commands generated by high-speed output modules. The registration function can trigger multiple internal and external location-based events using the built-in I/O of the module. Through the input of the high-speed input module, the signal from the sensor can trigger the start or stop of the movement, capture the feedback position of the encoder, or turn on/off or pulse output.

Programmable drum switch (PDS) and programmable limit switch (PLS) provide additional high-speed control functions. PDS, such as encoders, can monitor multiple devices at speeds up to 1MHz. These input signals are used to coordinate and control output at rates 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 according to processor load.

When choosing PLC, PAC and other industrial controllers, users need to consider control and I/O requirements beyond basic functions (Figure 3). For many applications, controllers also need to have a wide range of data recording and communication functions, as well as high-speed applications such as coordinated motion control.