On its own, this diagram is probably a power plant/process flow diagram with KKS codes attached.
What is clear is that DN50 is the nominal diameter of the pipe, and is a standardized way of expressing the dimensions, where DN is the "nominal diameter", and 50 means that the pipe has a nominal diameter of 50mm or this size (or it may not be 50mm, e.g., 57mm, etc., which is also related to the pressure rating of the pipe). (It may not be 50mm, such as 57mm, etc., which is related to the pressure of the pipeline).
The following is possible:
PDT0001 stands for a specific equipment or device, which should mean a generator transformer differential protection device or similar device, and this code consists of the "PDT" symbol group and the additional identification "0001".
PDIA stands for Circuit Breaker Current Transformer and consists of the symbol group "PD", a common prefix for power generation and distribution equipment, and the symbol "I" for current measurement, with "A" as an additional identifier that may be used to distinguish between different types of circuit breaker current transformers.
FA stands for automatic fire alarm systems, so FA codes are primarily used for fire protection equipment. In the KKS coding system, FA is the symbol for "Fire Detection and Alarm Apparatus" under the symbol group "F." FA usually carries additional identifiers to provide more information about a particular device, such as installation location, function, etc.
The KKS coding system is widely used in power plants to identify, categorize and manage electrical equipment and systems, so as to quickly and accurately identify and locate different equipment and installations for management and maintenance purposes. The unified coding system allows for easy management, maintenance and upgrading of equipment, as well as improved reliability and efficiency.
Because it involves professional design content, the above answer is for reference only and is not to be used as a basis for construction or other behavior.