Producing off-line programs for programmable logic controller equipment
Overview
This standard identifies the competences you need to produce, load and prove programs on programmable logic controller (PLC) equipment, in accordance with approved procedures. You will be required to produce the control programs using a remote computer, saving the prepared program on the computer and downloading it into the PLC from the computer. You will need to check the program using single block run and program edit facilities. You will also be required to adjust the PLC program, following proving/editing procedures to achieve the control specification. You must ensure that any edited programs are saved, safely and correctly.
Your responsibilities will require you to comply with organisational policy and procedures for producing, loading and proving PLC programs, and to report any problems with these activities that you cannot personally resolve, or are outside your permitted authority, to the relevant people. You will be expected to work with a minimum of supervision, taking personal responsibility for your own actions and for the quality and accuracy of the work that you carry out.
Your underpinning knowledge will provide a good understanding of your work, and will provide an informed approach to applying programming techniques and procedures to PLC control equipment. You will understand the PLC sensors and actuators used in the process, and their application, and will know about the programming, editing and proving process, in adequate depth to provide a sound basis for carrying out the activities, correcting faults and ensuring that the PLC is set up and performing to the required specification.
You will understand the safety precautions required when working on the PLC and associated equipment. You will be required to demonstrate safe working practices throughout, and will understand the responsibility you owe to yourself and others in the workplace.
Performance criteria
You must be able to:
- work safely at all times, complying with health and safety legislation and other relevant regulations, directives and guidelines
- produce computer control programs that contain all the relevant and necessary data for the engineering activity to be carried out
- produce the control programmes in the appropriate formats
- make sure that codes and other references used in the programs are applicable to the type of controller used
- pass on the programs to the appropriate people, within agreed timescales
- save and back up the program detail, and store securely in accordance with organisational requirements
- undertake changes to program details, within agreed control procedures
Knowledge and Understanding
You need to know and understand:
- the specific safety precautions to be taken when working with computer systems (to include safety guidance relating to the use of visual display unit (VDU), equipment and workstation environment, repetitive strain injury (RSI); the dangers of trailing leads and cables; how to spot faulty or dangerous electrical leads, plugs and connections)
- how to return the work area to a safe and useable condition (such as cleaning down work surfaces; putting media, manuals and unwanted items of equipment into safe storage; leaving the work area in a safe and tidy condition)
- the basic set-up and operation of the computer system, and any peripheral devices that are used
- the correct start-up and shutdown procedures to be used for the computer system
- how to access the specific programming software, and the use of manuals and related documents to solve problems and aid the efficient programming of PLCs
- the importance of protecting the computer system from viruses, and the implications if the correct procedure is not followed
- how to power up, log on and activate the computer system and programming software correctly
- how to deal with system problems (such as error messages received, peripherals which do not respond as expected)
- the checks to be carried out to ensure that peripheral devices are connected correctly
- the correct procedure to shut down the operating and programming system
- how to create and structure directories and files correctly (such as importing, copying, transferring, exporting, deleting, backing up and saving files)
- the different types of storage media that can be used to save program files on
- the offline programming methods used in PLCs (such as linear, structured, ladder, statement lists, logic function blocks)
- the common PLC numbering systems (such as binary, octal, decimal, hexadecimal, binary coded decimal (BCD))
- the different programming codes used to identify factors (such as safety interlocks/guards and sensor inputs, actuator and other outputs, process management and auxiliary functions)
- the main PLC types that are available, and the importance of understanding that a different PLC may use completely different codes for similar functions
- the information and data required in order to produce complete and accurate PLC programs
- how to extract and interpret general and technical data and information from different sources (such as drawings, computer models, symbols and conventions, BS or ISO standards) in order to produce the PLC program for process control
- the factors to be taken into account when producing PLC programs (including, the type of PLC (fixed I/O, unitary, modular, rack mounted) and its control capabilities, safety, the product/environment being controlled by the process)
- how to produce effective and efficient programmes to avoid unnecessary operations (including the use of macro programs and canned cycles, to reduce program size)
- how to faulty find the PLC program using software features (such as syntax checking, simulation, forcing inputs/outputs on/off, monitor test)
- the methods and procedures used to check that the completed program will control the required parameters safely, accurately and efficiently
- how to save the completed programs in the appropriate format, and the need to store programs safely and correctly
- how to back up completed or edited programs, and the implications if this is not carried out effectively
- the problems that can occur with the downloading and running of the PLC program, and how these can be overcome
the correct procedure to be followed before the program is released to the end user
the extent of your own responsibility, and whom you should report to if you have problems that you cannot resolve
Scope/range
Ensure that you apply all of the following checks and practices during the PLC programming activities:
- check that all the computer equipment is correctly connected, and is in a safe, tested and usable condition (such as cables undamaged, correctly connected, safely routed)
- power up the equipment and activate the programming software
- set up the computer system to produce programs
- ensure that the correct process input/output and control data to produce programs is obtained and checked for currency and validity
- identify and deal with problems (such as information based and/or technical)
Prepare, load and prove programs for one of the following types of programmable logic controller:
- fixed I/O or unitary
- modular
- rack mount
Produce control programs for a PLC with inputs/outputs from six of the following:
- proximity sensors
- safety devices
- optical guard curtains
- barcode scanners
- limit switches
- pressure switches
- optical sensors
- timer switches
- liquid flow switches
- colour sensors
- temperature sensors
- air flow switches
- external counters
- control panel switches
- footswitches
- liquid level sensors
- analogue to digital converters
- hydraulic actuators/valves
- pneumatic actuators/valves
- other types of actuators
Develop programs which use nine of the following, as applicable to the type of controller:
- ladder and logic diagrams
- function diagrams
- statement lists
- communication protocols (such as RS232, IEE 488, RS 422, 20mA)
- advanced functions (such as less than, greater than, binary to BCD, calculations, PID control)
- high level language (such as BASIC, 'C')
- Boolean algebra
- graphical programming language
- networking methods and standards
- appropriate letter address codes
- all necessary positional information
- preparatory commands and process management/auxiliary functions
- repetitive programs (sub-routines, canned cycles, labels)
- switch/actuator positions
- sensor information
- failsafe positions (where appropriate)
Prove the programmable logic controller program, using six of the following:
- single block run
- data input facilities
- program save/store facilities
- full dry run
- search facilities
- graphic displays
- program override controls
- edit facilities
- syntax checks
Carry out all of the following on completion of the programming activity:
- check and review program formats and content
- edit programs using the correct procedure (where appropriate)
- check that programs have the correct identification name and reference
- ensure that programs are saved and stored safely and correctly, in the correct format
- ensure that programs have been checked and approved before forwarding to the end user
- create a separate back-up copy of the program, in case of file corruption or accidental deletion