The automation control system PAC and PLC are widely used in industrial automation, and which one is better or worse? The following article analyzes the characteristics from several aspects such as cost, advanced functions, external structure, controller, I/O, and software. In systems that monitor machine operation, real-time data collection from analog or digital I/O channels is required to effectively detect fault conditions. The automation control system PAC and PLC are widely used in industrial automation, and which one is better or worse? The following article analyzes the characteristics from several aspects such as cost, advanced functions, external structure, controller, I/O, and software.
1. Cost - Which is more economical
Adopting a single controller saves costs. It has a single controller and chassis that can be used to process digital and analog I/O, with motion, visual functions, and modular instruments, so there is no need to spend money on purchasing multiple controllers. Therefore, if a control system needs to have multiple functions, such as vision or modular instruments, then using PAC will be the most economical choice.
2. Advanced features of multifunctional real-time control
Advanced Control for Process Control Optimization
Due to the high cost of energy or materials, engineers often need to optimize PID control algorithms for process control to minimize waste. These algorithms often use control design techniques such as fuzzy logic or neural networks to minimize the stability time of process control. The PID control algorithm that traditional PLCs can achieve has not been optimized for specific process control. If advanced control algorithms are used, not only do they require powerful floating-point processors, but they also occupy a large amount of memory. However, using the PAC platform can meet the requirements of process control optimization.
Real time analysis of monitoring
In systems that monitor machine operation, real-time data collection from analog or digital I/O channels is required to effectively detect fault conditions. It may require complex tasks such as real-time order tracking and vibration analysis to effectively detect the condition of the machine. However, for these applications, the efficient platform of PAC can be used for real-time analysis work.
Control system, database, and network connection
By utilizing real-time data from within the factory building, operators can make decisions based on the information obtained in the control room. However, it is difficult to make the control system capable of outputting on-site data. Enterprise systems generally use standard JDBC, ADO, and XML to obtain data from automated systems. PLC can only communicate through standard OPC, which means adding a PC to use OPC to obtain data and transmit it to the enterprise using standards such as JDBC (Open Data Warehouse Interconnection), ADO (Data Automation Design), and XML (Extensible Description Language). In order to effectively transmit on-site data to the ERP system, the control system must be able to communicate directly with external databases, and based on this, PAC can be fully used to complete these tasks.
Encrypting data through network transmission
When connecting the control system to the database and network, security issues need to be considered. For security reasons, many vendors choose not to connect their automation systems to enterprise databases, but for most vendors, the benefits of connectivity far outweigh security concerns. Although PLC can be locked to prevent others from intruding into the factory's network, it is not suitable for preventing hacker intrusion because PLC sends non encrypted packets through Ethernet. PAC can encrypt data when transmitting it over the network. Although this is not currently the first factor to consider, it will be the main reason for adopting PAC in distributed systems within the factory in the future.
Deterministic application of multiple speeds and cycles
PLC can only operate at a fixed speed, and it is not designed to handle independently at different cycle rates. But nowadays, complex control systems often require deterministic applications of multiple rates, which require multiple loops, each running at a different rate. This requires parallel processing, and only operating systems running on PAC have such characteristics.
3. Flexible and sturdy structure
Suitable for factory environment
A common reason for choosing a PLC is that it can work normally in the factory environment. However, the vast majority of PLCs are installed in directional boxes. However, in such an environment, the additional cooling device, sturdy outer surface, and enhanced impact and vibration resistance of the PXI platform make the system have the same reliability as the PLC. Strong extension function
Engineers are eager to use flexible automation systems to meet constantly evolving requirements, so they need control systems that are modular, flexible, and scalable. Due to the limitations of I/O, PLC systems can only have scalability in digital and motion aspects, while PAC not only has the scalability of PLC, but you can also add visual, modular instruments, or high-speed analog I/O to the system. Multiple PCs can also be used through Ethernet and the number of PCs can be increased or decreased as needed.
Easy to update or replace modules
For on-site engineers, minimizing downtime is crucial. When updating or replacing I/O modules in the control system, it is necessary to minimize the workload of replacing or adding modules to the greatest extent possible. The modular characteristics of PAC meet this requirement.
4. Controller
RAM with Pentium 4 processor and G byte capacity
Due to the use of existing hardware to build PAC based systems, the PAC controller can use a Pentium 4 processor and has G bytes of RAM, which can meet the requirements of high-speed processors and large memory capacity for monitoring the high-speed status of machines.
Information storage function
PAC can record data according to specified time, method, and data format. What is the use of information if it cannot be saved and viewed? Traditionally, PLC lacks the function of data recording. Digital I/O can provide a voltage of 24V, a driving current of up to 500mA, and optical isolation
Traditionally, the digital I/O of PLC platforms can only provide standard voltage driving current for industrial sensors and actuators. However, new digital I/O modules such as the N1651x series can provide a voltage of 24V, a driving current of up to 500mA, and optical isolation. It also features features a watchdog timer, programmable power start state, input filters for improving safety and reliability, and a cost of only $5 per channel.
Analog input speed can reach up to 200M per second
At present, some PLCs also have analog I/O modules, but their programming is very complex and not suitable for high-resolution and large data applications. The analog input rate provided by PAC can reach up to 200M per second and has a resolution of 24 bits. This is mainly due to the fast speed of PCI bus technology, so PC based platforms can be used to provide analog I/O.
Up to 8-axis motion mode
Software plays a major role in various platforms, especially when you need to move above two axis modes. The motion controller on the PXI platform can provide up to 8-axis motion modes, and the system can be easily configured using the NI motion assistant.
Visual applications
The data transmission rate is the biggest obstacle to providing visual functionality on the PLC platform. At present, analog, digital, and FireWire cameras for visual applications can be used on the PXI platform for automatic monitoring of parts and inspection of drug packaging. Multiple visual algorithms can be integrated into the control program, such as pattern matching, optical character recognition, color matching, specification and color detection.
Provide interconnection through various industrial fieldbuses
Similar to PLC, PAC can provide interconnection through various industrial fieldbuses, such as FoundationFietdbus, DeviceNet, CAN, Modbus, Ethernet, Profibus, serial port, etc. PAC can not only serve as the main control device for distributed I/O modules, but can also be added as a slave device to existing systems.
5. Software
Real time operating system
Real time operating systems (RTOS) such as RTLinux, PharlapETS, QNX, and VxWorks can be used on the PAC platform. Generally speaking, programming real-time systems is difficult, but using software like LabVIEWRT can change the way engineers develop real-time systems. Engineers can now download programs developed on Windows to real-time transport platforms, such as PXl controllers. Image display of HMI (Human Machine Interface)
Especially in mixed and process control industries, most control systems require a human-machine interface that can connect to the control system. An HMI (Human Machine Interface) consists of a touch screen, which can include an embedded controller or not. Due to the consideration of using the same controller for I/O in PAC based systems, there is no need to add additional embedded controllers to achieve HMI image display.
Easy development environment
Although traditional ladder logic programming is very suitable for digital I/O programming, it is very cumbersome for programming methods that handle analog I/O, motion, or vision. PAC can write control programs in general-purpose languages, providing you with great flexibility. These general-purpose languages include C, C, VisuaIBasic, LabVIEW, and even traditional ladder logic.
From the above, it can be seen that there is a difference in functionality between PAC and PLC, as PAC can perform more advanced tasks;
Real time vibration analysis, image processing, motion control, and CAN;
Execute PID control with automatic adjustment or PID control with adjustable gain. Fuzzy logic;
Use built-in web server, FTP server, and email function for communication.
Due to PAC, you can add the necessary PC functions for advanced control, real-time analysis or connection to enterprise databases, while maintaining the reliability of PLC. If you not only need to integrate digital I/O and motion control, or need faster computer processing power, PAC may be a very good choice. Therefore, in addition to PLC control, today's engineers consider PAC as the best choice as it is occupying the field of automation, and the concept of PAC will play an important role in today's and future factory automation.