How to improve your system from PLC to PAC

2022-09-21
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From PLC to PAC: how to improve your system

in the past decades, programmable logic controller (PLC) has been widely used in the field of automation, and in the foreseeable future, PLC will continue to flourish. The design of PLC for discrete control has actually become a dominant tool of great significance in the industrial field

however, with the increasing complexity of industrial machines and plant systems, PLC has been difficult and impossible to complete all automation tasks. Now the automation system has gone beyond the functional scope of PLC, so engineers in the field of industrial machinery must integrate more and more advanced i/o, processing and control strategies in the automation system

the new programmable automation controller (PAC) hardware system is such an extraordinary PLC system expansion scheme, which can be easily integrated into the PLC system, add more advanced functions to industrial machines, and improve the efficiency of machines

1. Demand: how to improve the efficiency of the machine, promote 39 industrial energy-saving technologies, 119 industrial energy-saving equipment and 80 consumer household appliances "energy efficiency star" product rate

how to improve the efficiency of the machine? Let's take a look at how integrated industrial systems (I2S) does it. I2S is greatly improved on the existing PLC system. This is a private original equipment manufacturer from the United States. For decades, it has been committed to manufacturing first-class rolling equipment and control systems for iron and non-ferrous metal industries around the world. Its strong technical background in this field makes it a leader in the industry

i2s also used PLC to automate and control the rolling equipment of production for a long time. In recent years, they have been trying to update the rolling equipment control system to improve efficiency and quality. In order to improve the efficiency and quality of steel-making equipment, they mainly improved their gamma measurement system in order to control the metal thickness more accurately

for several years, gamma measurement system has been a landmark product in the I2S product family, and it is still widely popular, but many hardware and software features of the system have become obsolete. In order to update the system and improve its machine, I2S company needs a scheme with more accurate analog input resolution to connect the gamma measurement sensor and advanced signal processing, so as to obtain analog signals from the sensor and realize highly accurate thickness measurement, which is then used by PLC in the control system of rolling machine

2. Gamma meter technology

the gamma meter uses "americium" as the constant emission source, which is located in the lower part of the "C" frame assembly. At the top of the structure is a receiver and preamplifier. When passing through the space between the transmitting source and the receiver, the metal belt will absorb part of the radiation, and the amount of absorption depends on its thickness and density. The remaining part is measured by the receiver and converted into belt thickness measurement

the first step of implementing the transformation: Test of existing equipment

in order to save time and cost, I2S first tries to carry out advanced analog measurement and processing in the existing PLC system. However, the analog i/o and signal processing of PLC cannot achieve the required accuracy. I2S company should ensure that the control system running in PLC will not be reduced due to the increase of additional i/o and processing

therefore, they need a system that can obtain analog signals from gamma sensors and process them to calculate accurate thickness measurements, and can insert this thickness measurement into the PLC control system. However, the PLC used is not suitable for high-performance processing and high-speed analog i/o

step 2: if the existing equipment can't work, try other methods

after realizing that PLC can't provide the i/o and processing required to connect the gamma measurement sensor, I2S turned to PAC technology. It selects compactrio PAC of national instruments to provide additional functions necessary to improve the quality of rolling machines. Compactri/o is a resettable embedded system, which not only combines the advantages and reliability of traditional PLC, but also provides more advanced i/o and processing. All PACS of national instruments can be programmed through its LabVIEW graphic programming tool, so it is easy to program and configure

step 3: add advanced i/o

compactrio has an embedded field programmable gate array (FPGA) chip and real-time processor, which can be programmed through the built-in LabVIEW function block. In addition, it also has more than 30 analog and digital i/o modules, with built-in signal conditioning (anti aliasing, isolation, ADC, DAC, etc.), high-speed timing (analog i/o speed up to 800KHz, digital i/o speed up to 30 MHz) and high resolution (24B ADC), which can be connected with any industrial sensor or trigger

Figure 1 compactri/o architecture

i2s uses compactrio analog input module to connect gamma level thickness sensor to provide high-speed timing and resolution required for accurate measurement. Since each i/o module is directly connected to FPGA, engineers can use LabVIEW FPGA to easily customize the analog i/o rate of compactrio

step 4: add advanced processing

after obtaining the analog data from the gamma sensor, compactrio uses the built-in NI LabVIEW real-time floating-point function block to process the data in the real-time processor and convert it into accurate thickness measurement

labview's real-time function block performs deterministic advanced logarithmic processing on the data (as shown in equations 1 and 2 below) to calculate thickness measurements. Because LabVIEW real time has built-in calculation and analysis functions, PAC can easily perform this operation

equation 1:log I = (log I0) y/μ = (y/μ) Log i0

equation 2: y/μ = Log I0/log I = log (i0-i)

compactrio system performs all i/o and signal processing in FPGA and real-time processor, and transmits high-precision thickness measurement to the connected PLC, without reducing the speed of the existing PLC control system. With the help of compactrio's performance, I2S engineers can add this custom measurement and analysis function to gamma level sensors without sacrificing the control speed of the rolling machine

Step 5: integrate PAC

each rolling machine is equipped with three compactrio systems forming networks. These three systems are intelligent nodes that can communicate using an industry standard modbus/tcp, tcp/ip or UDP protocol. Two of these systems are connected to gamma level sensors and perform analog input measurement and advanced processing to calculate accurate thickness measurements

Figure 2 typical system topology

in today's society, ompactrio system obtains the thickness value from the other two systems, converts it into analog output measurement value, and inputs it to the PLC that is controlling the rolling machine. All three systems are interconnected via Ethernet connections and use a UDP Ethernet information protocol to transmit thickness measurement calculations. There are three basic methods to connect PAC to the existing PLC architecture:

1 Basic analog and digital i/o. Analog/digital signals can be output from PAC to PLC. This is the most basic way to integrate PAC into PLC. I2S company uses this method to transfer the processed data from compactrio PAC to the PLC running the rolling machine control system

2. Industrial network. Most PAC products support industrial protocols such as DeviceNet, PROFIBUS, CANopen, and Ethernet based protocols such as tcp/ip, UDP, and Modbus tcp/ip. This makes engineers have many network options when connecting PAC to PLC. I2S company uses Ethernet protocol to transmit data between compactrio PAC and connect PAC and PLC to the HMI forming the network

3. OPC connectivity PAC can also be used as OPC client or server, and send and receive network data to PLC or other PACS through OPC tag. OPC standard provides a set of standard processes, so that the automation systems of different manufacturers can be easily connected

the processed data will be transmitted between compactrio systems interconnected via Ethernet at an interval of less than 20 milliseconds. The acquisition, processing and transmission speed of compactrio measurement values are very fast. Therefore, the process of inputting accurate thickness measurement values into the PLC control system will not reduce the speed of the whole system at all

i2s company can easily connect the system to the Allen Bradley PLC forming the network through the compactrio system based on LAN and 10/100 Mbps Ethernet interface, and connect it to the human machine interface (HMI) system using a standard tcp/ip protocol. All the instruments in the rolling machine are connected by the craftsman through Ethernet, so there is no need to transmit analog signals over a long distance in a noisy environment

3. Summary

in the next few years, PLC will continue to be used in the field of automation. However, with the improvement of machines and the need to improve automation efficiency, PLC is no longer omnipotent. PAC technology provides a good supplement to PLC, adding high-performance i/o and processing that traditional PLC cannot provide. There are many ways to connect PAC to the existing PLC architecture, so engineers will be able to easily improve their PLC based automation system. (end)

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