In the past, programmable logic controller (PLC) addresses were register based. The data is stored in registers with addresses such as mw210, b3:6 / 2, n7:50, or db5. Dbx50.2. They’re not very intuitive, are they?
These addresses can be assigned a “symbol” or shortcut to make them easier to program or find, but these symbol names are usually limited by length. Symbols are not saved in the PLC; It is stored in the programming computer and software.
Descriptions can also be assigned to addresses, but they are also stored only in the software. They provide additional information about addresses and their functions, but are still not searchable.
With the emergence of label based PLC system, the address becomes more descriptive, and the register based address is hidden and invisible. Label names have different rules according to different brands or platforms of PLC. They can be 40 or more characters in length and can use alphanumeric characters. Some platforms allow spaces, while others require underscores.
Tags that can be downloaded
The tag is actually downloaded into the PLC. They can also be organized alphabetically or numerically in the label database, which makes naming conventions important. Because so many characters can be used, tag names can be very descriptive and contain a lot of information. At the same time, long signatures with too many abbreviations can be difficult to read.
Common functions or terms such as automode, autocycle, fault, or cyclestop are common in the industry and do not require much additional information. The system or machine may be divided into areas or stations and labeled zone2, cell15 or station003. These labels may require more documents or instructions.
User defined data type (UDT) makes labels more complex because it allows “point” connection, such as “vfdrive2100. Actualspeed”. Nested UDTs allow the use of the above tags.
Large companies, machine manufacturers and system integrators usually prepare a template for programming, which gives how to name labels. Many common tags have been created in the template program, while other tag names can be automatically generated through spreadsheet. Different companies use different rules, but the purpose is the same: to make the program more readable and easier to troubleshoot.
Label naming rules are mainly divided into two parts: factory automation and process control labels. In automobile and other manufacturing industries, equipment is usually named by its function and location. Generally, they also include the reference numbers of the pages and lines where the equipment is located in the electrical drawing. For example, “palletpushcyl_extpx_4120”. The label consists of components (pallet push rod cylinder), equipment and its position (extended proximity switch) and the position in the electrical drawing.
Factory automation label abbreviation
Factory automation equipment is usually represented by the following abbreviations:
Photoelectric sensor: PE, PEC, per
Proximity switch / Hall sensor: Px, PRX
Limit switch: LS
Main control relay: MCR
Buttons: Pb, HPB (HMI)
Solenoid valve: SV
Control relay: Cr, K
Motor starter: ms
The second rule comes from the process control industry, such as petroleum or chemical processing. Their technicians use process and instrument diagrams (P & IDs). Isa supports these coding guidelines, but may vary from company to company.
These drawings assign device numbers to components such as tanks or slides and assign loop numbers to different control components, such as instruments and sensors.
Since the equipment name is controlled, the label name in the process industry only contains the P & ID number, rather than the more descriptive method used in factory automation. These names are completely different from the label names used in discrete manufacturing.
For example, the flow transmitter may be named 20-ft-1982-a, where the area code is 20, FT is the type of sensor, 1982 is the loop number, and a indicates at least one additional redundant device. Since labels cannot start with a number on many platforms, the order of characters may change or letters may be appended before the unit number. For example, the label of the above device may be ft_ 20_ 1982a or D20_ FT_ 1982A。 Such labels may not be as descriptive as those used in discrete manufacturing, but the description of “flow transmitter a in device 20” can be added.
Abbreviation of process control label
Process control equipment may use the following label names:
Flow transmitter: ft
Valve: HV, FV
Limit switch: LSL (low), LSH (high)
Loop control: FIC, PIC
Button / switch: HS, his
Photoelectric eye, proximity switch: ZS
Motor starter: M
Pressure transmitter: Pt, pit.
When creating tag names, the first thing to remember is to treat technicians or maintenance personnel as customers. Helping others find and understand code is the primary responsibility of programmers.
5 label and address naming suggestions
The naming rules of equipment or device label names are very important to help understand and speed up troubleshooting. When deciding on a label name template or rule, you need to consider the following five suggestions:
1. Make the name describe the function of the label as much as possible. Use standardized terms and abbreviations that are easy for technicians to understand. If necessary, add a description.
2. Labels are displayed in alphabetical and numerical order. For the same function or area, using labels starting with the same letter / number is very important for organizational order.
3. If necessary, use underline or uppercase letters to make the label more readable.
4. If the software platform allows the use of local labels, assign all labels to a specific assembly or program before copying it to the reuse program. This can save a lot of time.
5. Create labels using spreadsheets. This is much easier than manually typing labels in the database. Tags make it easier to add and copy data. The PLC platform allows easy export / import of labels. This also ensures that programmers use the same labels as electrical and mechanical designers.