A doubt with auxiliary contact addressing in plc

svk · Oct 18, 2013

Hello members,
I have written a code for following program but my only doubt is about addressing of auxiliary contacts that are used for indication (whether i use binary addressing or real output addressing)

3 motors M1, M2, M3, have their own start and stop push button. only one motor has to run at any point of time, motor running indication shall be available. auxiliary contact are used for indication.

pls members help me out , thanx in advance.

balash · Oct 18, 2013

i don't know waht you want exactly.
do M1 and M2 use aux contact as running status and M3 as ready to run?
if that's the case then, if controlled from vfd you have output drive ready.
if not i guess you would have to look for all precondition (not overload tripped, not MCCB tripped, voltage on...

svk · Oct 18, 2013

@ balash thanx for reply.
my doubt is about auxiliary indication addressing, pls check the above code, and tell me whether i use binary addresing (B3:0/0) or output addressing(0:2.0/0) as i have already written in example.

rdrast · Oct 18, 2013

svk said:
@ balash thanx for reply.
my doubt is about auxiliary indication addressing, pls check the above code, and tell me whether i use binary addresing (B3:0/0) or output addressing(0:2.0/0) as i have already written in example.

Neither.
You use the Auxiliary Contact from the (respective) starter.
Wire the aux contacts back to the PLC as inputs.

And for the record, your output file and your B3 file are both examples of 'binary addressing' as you call it.

svk · Oct 18, 2013

@rdrast ,but sir then how to assign motor running indication using auxiliary contacts?

iant · Oct 18, 2013

Rdast is saying to separate your Indication output
use the Aux input I:0/? to OP O:2/1 as one rung

as far as using B3
normally I would do "control" via B3 (Bin) area
then separately send it to he Op/s
- not good for extremely large programs
- you can have an output section - good for fault finding
add up the Pro's and Con's

svk · Oct 18, 2013

@ iant , sir is this code correct?

is this new code correct?

balash · Oct 18, 2013

what they are trying to say to you is that you do not use motor running indication based on plc coil, rather you physically wire aux contact on motor starter to PLC B3 input and use that input as motor running status. except if you want to indicate that plc command to start is active...

iant · Oct 18, 2013

it will work but it is the virtually the same as the program you have written
RDAST is referring to the hard wiring method.
the Output O:... goes to a contactor 'M1'
'M1' has contacts that 'Power' the motor
AND
an Axillary contact on the same 'M1'
this is usually a low current contact.

That contact can be wired to a PLC input I:......
you the use that input to run the indicator output O:....

the result
when the motor is told to start the contactor energizes
the Aux. contact then closes
the input I:.. turns ON
the Indicator Output then turns ON.

this is a confirmation circuit that all is OK
it is more common when you want to be sure the motor is actually being told to run.

svk · Oct 18, 2013

@ iant

sir is this code correct?

iant · Oct 18, 2013

there is nothing wrong with any of the code you have written.
the I/O list per motor is not what Rdrast was talking about.
Your layout per motor
- Ip = start
- Ip = Stop
- Op = Motor contactor
- Op = Motor indicator

We are suggesting one additional input
- Ip = Motor contactor contact

This is not needed but optional

svk · Oct 18, 2013

Thank u all .
@ iant , Thank u sir for ur consistent help and support.

balash · Oct 18, 2013

svk
your code will work but it is not a good solution. besides you don't need additional Q set in parallel with motor cause you can read the respective motor coil status anyway.

but if someone disconnect power to motor starter coil, plc will set its output coil, your B3 will be on, but motor won't start. THAT is the difference

aux contacts are meant to show state of starter, i.e hardware, NOT your program logic.

set run indication in plc program rather than wire it in cabinet is just bad engineering

iant · Oct 18, 2013

Hey balash.
Before plc,s or electronics it was the only way

Don't knock the old buggers like me.

pino2003fr · Oct 18, 2013

unless you want to use it as feedback

A doubt with auxiliary contact addressing in plc

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