Understand data communications media and networks used with modern programmable
Task #1
“describe the importance of health and safety when working with programmable controlled equipment” [P5]
Describe the importance of health and safety when working with programmable controlled equipment. A range of ‘what if’ scenarios for various applications could be used to cover the full requirements of the unit content.
An instrumented control system is an electrical, electronic, or programmable electronic system (E/E/PES) which may perform some or all of the following functions:
Monitoring, recording and logging of plant status and process parameters;
Provision of operator information regarding the plant status and process parameters;
Provision of operator controls to affect changes to the plant status;
Automatic process control and batch/sequence control during start-up, normal operation, shutdown, and disturbance. i.e. control within normal operating limits;
Detection of onset of hazard and automatic hazard termination (i.e. control within safe operating limits), or mitigation;
Prevention of automatic or manual control actions which might initiate a hazard. (http://www.hse.gov.uk/comah/sragtech/techmeascontsyst.htm)
The safety of machinery affects all of us in everyday life, machines are part of our lives and safety is dependent on the machines being safe for us to use at all time. This type of safety systems are widely applied in verity of sectors from manufacturing plants to coal mining facilities to ensure the safety of the workforce.
These safety programmable control systems are that part of the control system of machine that prevents hazardous conditions from occurring. It can be separate dedicated system or it may be integrated part of standard machine.
For example, consider a machine with an overspeed detection and protection system in which failure of the system could lead to injury in the event of the machine exceeding its maximum speed.
So in the example given above a sensor be placed next to actuator that rotates with the appropriate machine actuator. This sensor will constantly be sending the speed of the machine to a safety control system that has set parameters, if crossed will either alarm or cut the power automatically to the machine. This would prevent hazard of the rotatery blade being flown off and causing serice injury to operator or the machine.
The example cell uses light curtains to control product access in and out of the hazardous area. Each light curtain is muted by a pair of photoelectric sensors. A solenoid interlocking door switch keeps operators from opening a guard door unless access has been granted by the PLC. An e-stop and two push button modules complete this simple setup. The network addresses are listed next to the hardware components. (http://www.plantengineering.com/home/single-article/networked-safety-in-three-steps/1fad4a008f.html)
Task #2
“explain how one example of each of the three types of communication media would be selected for a specific programmable controller application.” [P6]
You need to explain how one example of each of the three types of communication media (cable e.g twisted pairs, coaxial, fibre-optic, shielded/unshielded, categories, operational lengths, connector eg Bayone-Neill-Concelman (BNC), registered jack (RJ-45), straight tip
(ST), universal serial bus (USB) type A and type B; opto-isolator e.g photodiode, phototransistor, thyristors, triacs)) would be selected for a specific programmable controller application. The key point here is for learners to recognize the media, understand how each one is selected, describe the main features and consider aspects such as frequency ranges and the technology to which they are being applied.
The transmission medium is the physical path between transmitter and receiver in a communications network. The media that have been used in local networks include twisted-pair wire,
