Many (if not to say the vast majority) machines are controlled by a dedicated computer called a programmable logic controller (PLC). The roots of this trend can be traced back to the late 1960s, when machines and assembly lines became increasingly complex, as did the corresponding control systems. The hard-wired relay-based control system at the time was inflexible and prone to errors. Maintenance is more like a nightmare. The sheer number of relays and wiring required does not make life easier for engineers. Mechanisms like relays are more prone to wear than well-designed electronics. In order to optimize the control system of its assembly line for better reliability and maintenance, General Motors entered into a contract with PFAFF to design an electronic alternative for control systems based on different hard-wired relays. The first PLC was born. It is called MODICON-084 and is today considered the ancestor of all PLC systems. Thanks to its flexibility, simplicity and better cost structure, this revolutionary technology is quickly being applied across the industry.
In the years that followed, the PLC's form factor became smaller and smaller, and programming became easier. More and more PLC manufacturers have emerged and set standards for programming and function settings. Today, the infrastructure and capabilities of large PLC systems have virtually all the problems of automation and process control.
The main advantage of PLC-based control systems is their flexibility and simplicity, which now motivate machine users to optimize their workflow. Changing the software can increase the speed of the machine or reduce the cycle time of the production process. time is money! However, the result is that the machine wears out faster. They can even be dangerous because when the waiting time between the two is too short, the two processing steps may conflict. Changing hardware can also be appealing. Suppose our machine function happens at a specific time - if the process step requires additional cooling, why don't we have a fan connected to the digital output that controls this function? This is really not a problem as long as we don't violate the specified parameters of the output. But what happens if we do violate the parameters and cause the machine to become damaged or age faster? Although the machine manufacturer may block unauthorized access to the main functions of the software, it is difficult to block access to the screw terminals of the PLC I/O module.
Once the hardware patch is removed again, proof may not be possible. Machine manufacturers may be blamed for damage to the output modules or even the mechanical components of the machine, although this is not their fault. What can they do to get at least such tampering instructions? Since we live in the electronic age, there should be an electronic solution.
The 8-channel 1A/Ch high-side driver (TIDA-00183) for the programmable logic controller reference design records the output current and compares it to the stored reference in real time. Each 1A output has the function of measuring the output current. Various loads have a specific current mode when turned on. For example, a typical bulb starts to start at a current 10 times higher than the average current during operation. The soft start current is used at the beginning of the relay and then its operating level is increased. The motor initially has a high current peak, but then drops to a level corresponding to its mechanical load.
How can manufacturers use this current recording function to protect the machine when the machine is damaged and perform some forensics work? The control PLC knows when it switches the load on and off. The designer of the machine knows which type of load is required for which output. These two pieces of information, together with current sensing, enable the PLC to verify the connected load in real time. Alternatively, the machine can record the current mode of all connected loads during the machine end test before shipment and store the mode for subsequent reference and verification. This verification not only makes the unauthorized modifications visible, but also the effects of aging and defective loads. In many cases, the machine can inform the operator early that the machine will malfunction or has been modified by unauthorized personnel.
The current sense function demonstrated in TIDA-00183 can perform even more tasks. It enables the application of soft fuses, a software configuration protection solution tailored to the connection load. In addition, load balancing can be achieved; if one output requires more current than the 1A output quota, but several other outputs require less current, the PLC can adjust the current limit accordingly, provided that the current sum remains below the current limit. . These features can help achieve functional and diagnostic levels that did not exist before.
other information
Find out more about terminal device solutions for PLCs .
Download the Programmable Logic Controller (PLC) Solution Guide .
View TI's overview of factory automation for reference design libraries and product solutions.
SHAOXING COLORBEE PLASTIC CO.,LTD , https://www.colorbeephoto.com