V
vaughant
And the importance of being able to read them.
This is a subject that really concerns me with the apprentices where I work and the management staff.
They appear to put no emphasis on what is IMO a fundamental part of electrical control,they seem to prefer getting these lads to either ask someone what the fault is or try guessing first which to me is ludicrous.
I'm not saying I'm perfect (although I have got nice eyes) but I feel I can approach most breakdown situations and given the correct documentation have a damn good chance of saying it's this or that and not just plucking ideas out of the sky that I so often see folk randomly changing components then still looking baffled when it doesn't work.
Of course it's handy to be more lucky than clever but in the real world(or my world at least) luck is a scarce commodity!!!
So,I'm thinking the great folk on here who deal with such instances everyday could maybe contribute some help on this matter with of course pictures and explanations being preferable.
Hopefully this can become some sort of a reference for our good folk who want to get into this relatively untapped field of electrical expertise,after all there's a lot of people out there fitting lights and sockets and as the competition becomes greater in those fields it's my belief that more than a few will look to diversify into the industrial control game.
In my experience our German brothers and sisters do make a damn good diagram but it does require a bit of brain work to see how it all works,again I could be preaching to the converted but I have been amazed by 2 very experienced lads at works inability to even read a basic control diagram,unable to work out where power comes from,not even 100% aware of n/c and n/o switching symbols,fuses,mcb's and forward reverse contactors.
I'll start with this as a basic example.
We had a fault in the week with this motor and I was asked to let the apprentice (3rd year) to lead the way,couldn't get this contactor to kick in.
Sorry for pic quality.
He stands there with the usual teenage blank expression so I tell him to see what we've got.
He starts rambling and tries a few pointless things like checking nothings tripped etc when I ask him what were looking for.
He has no clue.
We want 78K1 to come in to move the motor towards the wall (shuttle car).
Now,from the diagram under 78K1 is in smaller writing 78.1,apprentice has no idea what this means.
This relates to the page in the diagram where I can find what operates 78K1.
So we go to page 78,section 1,just like a map grid reference .
There we find this.
Jeez I'm sorry for the quality,I'm hoping people with better than an old iPhone camera will chip in!!!
Now,it shows a plc output,an n/c contact from 78K2 before we get to 78K1 A1 then through A2 down to 0v.
People who are familiar with this will know that A1/A2 generally relate to the connections of a contactor coil but those new to this can see it's represented by the symbol of a rectangular box,this often has a diagonal line through it.
In british drawn diagrams it's often shown as a circle but the A1/A2 should give it away.
When control voltage is applied to this coil,it should if working correctly energise and in turn pull the contacts in on the contactor allowing three phase out of the bottom of the contactor and off through various wires to the motor windings.
I then got the apprentice to make the next move.
Again after head scratching it meant me talking him through it.
I got him to check for power at the coil,A1 to 0v rail,nothing showing.
I then got him to check from PLC output A88.0 (A or Q are often used as output symbols, I and E as inputs),we had 24v dc.
The next stage was to check what we had at 78K2 terminals 21/22.
This is where experience comes in,often parts are changed with non original manufacturers ones instead which do not always use the same markings.
This was not the case here but if that occurrs again,the diagram can help as it shows us that were looking for an n/c contact on 78K2.
We tested there and found power to terminal 21,but nothing on terminal 22.
A quick power down and switch to continuity on the meter told us the n/c contact was u/s and therefore needed replacing.
This job came to my attention to look at because the previous shift had:
Changed 78K1 contactor
Attached a laptop to the s7 plc to read it
Belled out the motor and found nothing wrong.
Not a diagram in sight.
1/2hr later the machine is working using only simple test procedures and an electrical diagram.
Please feel free to add,again this will I hope be more of an aid too less experienced folk.
I'll get some plc stuff up to look at too as the principals are the same.
This is a subject that really concerns me with the apprentices where I work and the management staff.
They appear to put no emphasis on what is IMO a fundamental part of electrical control,they seem to prefer getting these lads to either ask someone what the fault is or try guessing first which to me is ludicrous.
I'm not saying I'm perfect (although I have got nice eyes) but I feel I can approach most breakdown situations and given the correct documentation have a damn good chance of saying it's this or that and not just plucking ideas out of the sky that I so often see folk randomly changing components then still looking baffled when it doesn't work.
Of course it's handy to be more lucky than clever but in the real world(or my world at least) luck is a scarce commodity!!!
So,I'm thinking the great folk on here who deal with such instances everyday could maybe contribute some help on this matter with of course pictures and explanations being preferable.
Hopefully this can become some sort of a reference for our good folk who want to get into this relatively untapped field of electrical expertise,after all there's a lot of people out there fitting lights and sockets and as the competition becomes greater in those fields it's my belief that more than a few will look to diversify into the industrial control game.
In my experience our German brothers and sisters do make a damn good diagram but it does require a bit of brain work to see how it all works,again I could be preaching to the converted but I have been amazed by 2 very experienced lads at works inability to even read a basic control diagram,unable to work out where power comes from,not even 100% aware of n/c and n/o switching symbols,fuses,mcb's and forward reverse contactors.
I'll start with this as a basic example.
We had a fault in the week with this motor and I was asked to let the apprentice (3rd year) to lead the way,couldn't get this contactor to kick in.
Sorry for pic quality.
He stands there with the usual teenage blank expression so I tell him to see what we've got.
He starts rambling and tries a few pointless things like checking nothings tripped etc when I ask him what were looking for.
He has no clue.
We want 78K1 to come in to move the motor towards the wall (shuttle car).
Now,from the diagram under 78K1 is in smaller writing 78.1,apprentice has no idea what this means.
This relates to the page in the diagram where I can find what operates 78K1.
So we go to page 78,section 1,just like a map grid reference .
There we find this.
Jeez I'm sorry for the quality,I'm hoping people with better than an old iPhone camera will chip in!!!
Now,it shows a plc output,an n/c contact from 78K2 before we get to 78K1 A1 then through A2 down to 0v.
People who are familiar with this will know that A1/A2 generally relate to the connections of a contactor coil but those new to this can see it's represented by the symbol of a rectangular box,this often has a diagonal line through it.
In british drawn diagrams it's often shown as a circle but the A1/A2 should give it away.
When control voltage is applied to this coil,it should if working correctly energise and in turn pull the contacts in on the contactor allowing three phase out of the bottom of the contactor and off through various wires to the motor windings.
I then got the apprentice to make the next move.
Again after head scratching it meant me talking him through it.
I got him to check for power at the coil,A1 to 0v rail,nothing showing.
I then got him to check from PLC output A88.0 (A or Q are often used as output symbols, I and E as inputs),we had 24v dc.
The next stage was to check what we had at 78K2 terminals 21/22.
This is where experience comes in,often parts are changed with non original manufacturers ones instead which do not always use the same markings.
This was not the case here but if that occurrs again,the diagram can help as it shows us that were looking for an n/c contact on 78K2.
We tested there and found power to terminal 21,but nothing on terminal 22.
A quick power down and switch to continuity on the meter told us the n/c contact was u/s and therefore needed replacing.
This job came to my attention to look at because the previous shift had:
Changed 78K1 contactor
Attached a laptop to the s7 plc to read it
Belled out the motor and found nothing wrong.
Not a diagram in sight.
1/2hr later the machine is working using only simple test procedures and an electrical diagram.
Please feel free to add,again this will I hope be more of an aid too less experienced folk.
I'll get some plc stuff up to look at too as the principals are the same.
