Assignment Help!

Hi Guys,

I am new to this forum and I need help with my assignment for PLC class.
Here is the tasks I need to complete;

Task 2 Examine the inputs to a PLC and state the switching voltages that may be used. Using diagrams and manufactures data investigate five input sensor that may be used on the production line.

Task 3 Examine the outputs from a PLC and state the output voltages that may be used. Using diagrams and manufactures data investigate five output actuators that may be used on the production line.

Task 4 The PLC has to store and execute a PLC programme. Produce a diagram of the internal architecture of the PLC and explain the function of each section including CPU, ALU, Flags, Registers, ROM, RAM, Buses

thanks for taking the time to look guys and I really appreciated any help you guys can give me

Ah the British HNC course. Do they no longer ask about unitary, modular and rack-mount PLCs or was that Task 1?
My suggestion is to read your course material. Failing that, there used to be a website called freestudy.uk or something like it that had the all the answers.

yes that was task one I managed to complete that. just struggling with the other tasks haha! I will check the website out, thanks.

most PLC have 24 volt inputs, now find a datasheet and the voltages for minimum and maximum.
do this for 5 types of inputcards, (analog/digital)
task 3 same for output cards, this can be AC and DC or even analog cards like 4-20 mA.

daniel25891 said:

Task 4 The PLC has to store and execute a PLC programme.

Click to expand...

It's been many years since I heard a computer or PLC program being called a programme !!

I thought that's what you paid too much money for when you went to a concert.....

daniel25891 said:

Task 4 The PLC has to store and execute a PLC programme. Produce a diagram of the internal architecture of the PLC and explain the function of each section including CPU, ALU, Flags, Registers, ROM, RAM, Buses

Click to expand...

Ignore the first sentence, it has absolutely no relevance to the task. It is a statement of fact... every PLC has to store a program and execute it.

As for the second part, IMHO they introducing terms that are not PLC specific.

An "ALU" (Arithmetic Logic Unit) is a term usually attached to the microprocessor embedded in the hardware, and is generally hidden from you in the PLC world, because PLCs work with predefined "instructions". The ALU is a "machine-level" artifact that produces results that are interpreted by the PLC instruction that is executed. Each PLC will have an "instruction set", and each instruction may affect its arithmetic Flags in some way, as determined by inbuilt code that is executed when an instruction is executed.

For PLCs, "Registers" are simply places to store data. Each PLC manufacturer will have different methods for this. Some use "data-tables", some use a proper "tag database", some use predefined memory areas that you index into. Either way, "registers" is a generic term used to address the data you want to examine or manipulate.

ROM is the acronym for "Read Only Memory", In its purest form it is memory space that can NEVER, EVER be modified, and its usage in PLC terms is rare. Some manufacturers will put the PLC Operating System in ROM, meaning that you will have to replace the PLC controller to upgrade.

Most manufacturers however, will allow upgrades, either by using...

EPROM (Erasable Programmable Read Only Memory) technology. You have to "cook" these chips under UV light to erase them, then re-write them.

EEPROM E^2PROM (Electrically Erasable Programmable Read Only Memory). These can be programmed/reprogrammed at will using the correct hardware/software/protocol.

RAM is the acronym for "Random Access Memory". In its purest form it is memory space that is volatile. requiring continuous refresh to retain its contents. The majority of PC memory is RAM, turn the power off, the contents are lost.

A variant of RAM is NVRAM, the NV standing for "Non-Volatile" - this is also known today as "Flash-RAM", it is a crossover from EEPROM to RAM, different technologies, but very similar result. Your SIM card in your phone is almost certainly Flash-RAM.

I hope I got basics covered, no doubt there'll be many replies