Which instrument function symbols and graphics from the P&ID diagram should be displayed on the HMI?

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This post was last edited by yunrun on 2019-10-19 at 14:30. P&ID is short for Piping and instrumentation diagram; it is an important input document for engineers when designing HMI systems. What do the instrument function labels and graphic symbols on a P&ID diagram mean? Which instrument function symbols and graphics from the P&ID diagram should be displayed on the HMI? It will be explained in detail in this post. The graphic symbols for the installation locations of instruments refer to two standards: one is ISA (International Automation Society)’s “ISA-5.1 Instrumentation Symbols and Identification”, and the other is the domestic industry standard “HG/T 20505-2014 Functional Indicators and Graphic Symbols for Process Measurement and Control Instruments”. Regarding the installation locations of instruments, both ISA-5.1 and HG/T 20505-2104 classify them into four categories, as shown in A/B/C/D of the figure below. ISA-5.1 provides a more detailed explanation, while HG/T 20505-2014 offers a more straightforward one. Industrial automation has reached a very high level, with features such as centralized control, fieldbuses, and wireless instruments; it is highly informational and intelligent. As a result, definitions like those for panel-mounted installations and installations behind panels have become somewhat outdated. Changhui Instruments believes that the boundaries are not so clear, but for better understanding, this article still classifies and explains them by category. http://yunrun.com.cn/upload/201909/25/201909252255575390.png http://yunrun.com.cn/upload/201909/25/201909252256135063.png The left image in the following pictures shows a section related to the motor, extracted from a standard P&ID diagram; the right image shows that same section with colors added for differentiation. http://yunrun.com.cn/upload/201909/25/201909252305568838.png ◆ The graphic symbols in the yellow area represent the devices on-site; there is a start/stop control knob and two status indicator lights. ◆The graphic symbols within the blue area represent the signals entering the central DCS; there is one run/stop signal and two status signals. ◆The graphic symbols in the red area can be understood, according to the ISA standard, as the shutdown function of a safety PLC. Which instrument function symbols and graphics from the P&ID diagram should be displayed on the HMI? yunrun.com.cn/tech/2718.html The field devices shown in the P&ID diagram are illustrated in the image on the right. The operator controls the operation and start of the motor using a knob, and there are operation and stop indicator lights on site. http://yunrun.com.cn/upload/201909/25/201909252306412447.png The DCS portion shown in the P&ID is the part that the HMI is meant to display to operators. The operation and start of the motor are controlled via the start and stop buttons on the HMI in the control room; meanwhile, the motor’s status is displayed directly on the motor itself, eliminating the need for two separate indicator lights. Finally, let’s talk about the emergency stop in the red area: ◆ Under normal conditions, the emergency stop DO is green; since there is no logical trigger from the safety PLC, it always outputs a value of 1. This causes the panel relay to engage, ensuring that the motor always has power supply. In this way, the motor can be started and stopped both at the site and via the central HMI. ◆In case of an emergency, such as the operator pressing the emergency stop button, or abnormal levels or pressures at the site triggering the relevant logic, the DO output will become 0, the power supply to the control panel will be cut off, and the motor will stop immediately. At this point, it is impossible to start the motor either from the site or from the central HMI, as there is no power available. Only when the emergency situation is resolved and the DO outputs a value of 1 again can the motor be operated again. Author: TOP T