PLC

The 4-20mA current loop is a widely used standard in industrial control and instrumentation systems, primarily for transmitting analog signals over long distances. It is valued for its simplicity, reliability, and immunity to electrical noise. However, one of the most frequent questions engineers and technicians encounter is: How far can a 4-20mA signal be transmitted? […]

In process industries such as petrochemicals, oil & gas, and power plants, shut-off valves (SDVs) are critical components of safety and process control systems. They are often controlled by Distributed Control Systems (DCS) or, in safety-critical applications, by Safety Instrumented Systems (SIS). A common question during system design or plant operation is:“Can shut-off valves in

In the field of process safety and instrumented system design, one common question often surfaces: “If a safety function has an achieved SIL (SILa) of SIL0, do we still need to retain that SIL rating in the interlock logic?” At first glance, the answer may seem obvious—SIL0 means “no required safety integrity,” so we can

RS-485 is a widely used serial communication standard known for its robustness, simplicity, and effectiveness over long distances. However, when it comes to speed, RS-485 has a clear upper limit—10 Mbps under ideal conditions—and most practical applications run well below that. But why is it so difficult to push RS-485 beyond 10 Mbps? Let’s break

Oscilloscopes are essential tools in electronics for visualizing electrical signals. One key feature that users often need to understand is the difference between DC coupling and AC coupling. These modes control how the oscilloscope processes the input signal, either displaying all components of the signal or focusing specifically on its alternating current (AC) parts. In

In the evolving world of industrial automation, Model Predictive Control (MPC) is often positioned as the future of process control—boasting advanced features like constraint handling, multi-variable coordination, and performance optimization. But will MPC replace the time-tested PID (Proportional-Integral-Derivative) controller, which has dominated the industry for nearly a century? From a conservative engineering perspective, the answer

This article examines whether Safety Instrumented Systems (SIS) are required for Level-3 major hazard sources involving liquefied gases. The analysis is based on Chinese regulations, industry standards, and risk assessment methodologies. We explore key conditions under which SIS becomes necessary, especially for hazardous chemicals such as LNG, LPG, and liquid ammonia. 1. Regulatory and Standard-Based

1. General Principles for I/O Allocation 1.1 Redundancy Principle To comply with the single-fault tolerance requirement, redundant devices should be assigned to different controllers or I/O modules to ensure that failure in one does not affect the entire system. 1.2 Power Isolation Principle DO points may have different power sources (e.g., 24VDC or 220VAC, powered

1. Introduction In process industries, liquid level is a typical integrating process variable, representing the physical balance of inflows and outflows in a vessel. Due to its integrating nature, level control loops often exhibit a unique set of challenges when applying conventional PID tuning methods—especially regarding the integral time. One of the most common issues

In industrial automation, Programmable Logic Controllers (PLCs) are the backbone of reliable and repeatable control systems. But one common question from engineers and end users alike is: Can a PLC function without an HMI (Human-Machine Interface) or SCADA (Supervisory Control and Data Acquisition) system? The short answer is yes — a PLC can absolutely run