Help

speds02 · Apr 7, 2012

Hi im new to the forum and to PLCs. I am currently studying to a HNC at college and have a assignment I cant get my head around and was wondering if you could give me a few pointers.

The purpose of the assignment is to produce a report using the specifications below if a manager gave you a budget and the go ahead.

PLC power supply 240v at 50 Hz
No. of relay outputs 24 max rating 1mA each
No. of transistor, triac or thyristor outputs , 0
No. of contact closure inputs , 20
No. of three line proximity devices , 1
No. of analogue inputs , 1 0-10v dc
0 analogue outputs
interface with Rs232c or similar
memory 2k
scan time better than 50ms

has to be IP67 protected with external ambient temp 110'c

close to a high voltage source of magnetic interference and one output drives a contactor to switch a motor of 240v 20A , suggest contactor type and plc be able to control coil directly

I know there are probably lots of similar threads but i have done hours or searching and not done alot of work....

the output max of 1mA seems to be odd as 2A seems to be the norm and protecting to IP67 in a cooled enclosure so operating temp range is met..... HELP PLEASE

Thanks speds02

pmac10 · Apr 7, 2012

hnc assignments seemed to have changed a little recently,
anyhow, a siemens s200 cpu226 ac/dc/rly with i/o expansion module should fit the bill, (should!, check!), as for output rating, if i'm reading that correctly, a 2Amp rating should be about 2000 times able to handle your 1mA spec.

OkiePC · Apr 7, 2012

Yes, some of the specifications seem to be "inverted" or just unclear:
1) "No. of relay outputs 24 max rating 1mA each"
Should that be
"No. of relay outputs 24 max, with a minimum rating of 1mA each"? PLC relay outputs always have a much higher rating than 1mA.

2) "No. of contact closure inputs , 20" I never heard of a contact closure input. Output yes, but a contact closure input is lacking a voltage specification. You may have the freedom to choose your own input voltage for use with dry contacts provided by the devices...In any case it is unclear.

3) "No. of three line proximity devices , 1" AC or DC? What voltage?

4) "has to be IP67 protected with external ambient temp 110'c" "has to be IP67 protected with external ambient temp 110'c" I think these are clues that you need a rated enclosure and sufficient cooling.

This sounds like an exercise that is designed to give you practice with clarifying specifications. In the real world it is pretty common for someone to provide specifications with a mistake or two or ask for something unrealistic. Maybe that is the purpose of the exercise?

iant · Apr 7, 2012

you need to examine what the specifications mean.
the idea behind this assignment is not for us to do the work for you.

Choose a supplier - Schneider may be the easiest to use as they cover a vast range of components.
The PLC that pmac10 mentioned will do fine.
the 24v relays stated to you have a current of 1 mA that is their coil's current draw.
@ 100 degreec C water boils, so at or above 110 deg, C it evaporates into steam. Check that - as it is an abnormal ambient temperature any where on this planet.

the motor contactor - all the details are their

IP67 rating - find out what that means - yes I do Know

speds02 · Apr 7, 2012

WOW thanks for replies!! V. helpful.

pmac10- haha how has HNC changed only in first year and nearing exams , so they re building coursework up :S thanks for siemens suggestion , seems good, i will look into it more. I was considering the micrologix 1200 by allan bradley as i did a previous assignment but was stumped by the 1mA rating ....and still am actually!!!!

okiePC - i was taking it as 24 relay outputs with a max rating of 1mA but looking at relay specs it seemed to be 2A ??? this is why i am confused...

2) i think contact closure inputs are just digital inputs either sensor or switch

3) just specifies three line proximity device , 1 . theres no AC/DC .... just needs some internet time from me i think

and again just more research and sourcing for the enclosure.

It does sound like my tutor ,

defo wants limitations, extra suggestions etc.

iant - i agree that the work is for me just got my mind boggled

and needed a few pointers from more experienced PLC users as i have never used them till this course. so your help is much appreciated.

thanks for schneider suggestion- i saw the also produce the enclosures....

IP67 - dust may not enter and permanently submerged in water up to 1m

I hadnt considered that at 110 it would be steam, thats another consideration

this also why IP67 rating ???

The light bulb is starting to appear........

Again thanks for your input, MASSIVE help....

L D[AR2P#0.0] · Apr 7, 2012

speds02 said:
The purpose of the assignment is to produce a report using the specifications below if a manager gave you a budget and the go ahead.

What does your report have to contain ?

speds02 · Apr 7, 2012

Assignment to include - suitable PLC, detailed advice and consideration on environmental protection, installation and maintenance , meanings and calculations of MTBF,MTTR and MT including costings etc also explanations of optocouplers , buses , fault finding aids ....LOTs hahaha

L D[AR2P#0.0] · Apr 7, 2012

Couldn't resist this picture.

That is one mother of an assignment. Still, when your year has done it next years intake will be able to copy it

L D[AR2P#0.0] · Apr 7, 2012

speds02 said:
I was considering the micrologix 1200 by allan bradley as i did a previous assignment but was stumped by the 1mA rating ....and still am actually!!!!

Are you reading the 2k memory in the spec as a minimum or as a mandatory set amount for the plc you have to select ?

speds02 · Apr 7, 2012

its just required memory 2k so taking it as min, more room for modification and expansion ????

Nice pic BTW never been to the museum...

pmac10 · Apr 7, 2012

speds02 said:
WOW thanks for replies!! V. helpful.

pmac10- haha how has HNC changed only in first year and nearing exams , so they re building coursework up :S thanks for siemens suggestion , seems good, i will look into it more. I was considering the micrologix 1200 by allan bradley as i did a previous assignment but was stumped by the 1mA rating ....and still am actually!!!!

if you want specifics, its changed from a level 5 to a level 4 qualification which is unfortunate for you, in one sense, but as your struggling with this question, perhaps not,
does your college use a certain type of plc? when i did this hnc the college used Mitsubishi fxon or something, so they expect your research answer to be a Mitsubishi fx?? plc,then you had to write a program for an acid bath mixer with analogue sampling etc

iant · Apr 7, 2012

110deg C Ambient Temperature would be standing next to a high temp furnace like blast furnace or billets of steel.
Most system designs would have the PLC panel remotely mounted in a more suitable temperature.
"Ambient" is the normal temperature - not the maximum temperature
so it would be fun trying to fault trace the PLC program or replace components.
Buy a space suit

KalleOlsen · Apr 8, 2012

iant said:
110deg C Ambient Temperature would be standing next to a high temp furnace like blast furnace or billets of steel.
Most system designs would have the PLC panel remotely mounted in a more suitable temperature.
"Ambient" is the normal temperature - not the maximum temperature
so it would be fun trying to fault trace the PLC program or replace components.

Buy a space suit

Or hire this heat-resistant commissioning crew from Finland:

http://oslopuls.aftenposten.no/film/article488796.ece

dahnuguy · Apr 8, 2012

much of these specs are a bit vague or misleading or maybe misinterpreted.

a few things I see:

a 3 wire sensor is any of many sensors that has a pos and neg voltage supply on 2 wires and then the return signal on the 3rd.

Such as a prox switch. So it boils down to a single digital input.

And the requirement that the PLC directly control the motor contactor can not be controlled with a 1mA PLC digital output.

Look at what outputs are available for the PLC, then look at the ratings of each. Some output types are better suited to switching higher current.

This assignment is the second step of designing a control system.

I would call the first step determining what is required to run the process.

Then second would be hardware selection.

This is very relevant and you should focus on understanding all the details, not just flying through to get the right answer.

( I am not saying you ARE flying through to get the right answer, just cautioning against that)

iant · Apr 8, 2012

yuck Kalle now my mind is full of that picture yuck

Help

speds02

Member

pmac10

Member

OkiePC

Lifetime Supporting Member

iant

Lifetime Supporting Member + Moderator

speds02

Member

L D[AR2P#0.0]

Lifetime Supporting Member

speds02

Member

L D[AR2P#0.0]

Lifetime Supporting Member

L D[AR2P#0.0]

Lifetime Supporting Member

speds02

Member

pmac10

Member

iant

Lifetime Supporting Member + Moderator

KalleOlsen

Member

dahnuguy

Member

iant

Lifetime Supporting Member + Moderator

Similar Topics