reduction of outputs

[ramcr]

any experienced people please explain the circuit for reducing the outputs used in PLC . for example a single output should be used to energise two lamps which indicates complementary function

[Sleepy Wombat]

Have the output energise an external relay with a change over contact.

[ramcr]

Thanks for your reply sir but the output circuit i asked is without using a relay.

[Eric Nelson]

See my answer to JD's "10 outputs from 7" challenge in THIS POST. That should give you an idea about how you can get by with minimal outputs.

And it uses none of those 'annoying' relays!...

beerchug

-Eric

[Antipathy]

Eric

I just looked at your post on the JD thread and I'm not sure it works!

How, for example, could you have lamps 1 & 4 on without lamps 2 & 3 also being on?

As far as I can see it would only work if exclusive (only one at a time) lamps were required; in which case you could extend the logic to make 12 from 7 (3 x 4) or 16 from 8 (4 x 4).

Anthony

[Eric Nelson]

Originally posted by Antipathy
As far as I can see it would only work if exclusive (only one at a time) lamps were required

That's correct!...

If you notice, JD's 'challenge' was "10 individual lights with 7 outputs".

I just thought ramcr might glean some knowledge by looking at it...

beerchug

-Eric

[rsdoran]

. for example a single output should be used to energise two lamps which indicates complementary function

Did I read this wrong? Is there more to it then what I see stated?

If by complemetary you mean 2 devices work at same time?, then the answer is obvious...wire them parallel. This assumes the plc output is capable of the power needed to drive the 2 devices.

There are creative ways using relays to make different multiple devices work from different outputs...but WHY do it? Just add more I/O or a larger plc.

[Eric Nelson]

Complementary: Of words so related that each is the negation of the other; "`male' and `female' are complementary terms"

I think this is the definition ramcr meant. IOW, one lamp to indicate the output is ON, and the other to indicate the output is OFF. Most, if not all of us, would use a SPDT relay to do this, but ramcr has some 'no relays' rule to follow...

beerchug

-Eric

[rsdoran]

I see what you mean but the statement doesnt follow that logic..I think he meant it in another fashion which may also apply...ie Supplying mutual needs or offsetting mutual lacks.

If that is the case then what I stated should be correct, his statement was:

a single output should be used to energise two lamps

I am getting better at reading the details.

[Steve Bailey]

I would look for a contact output module with form C contacts.

[Antipathy]

Eric said:

JD's 'challenge' was "10 individual lights with 7 outputs"

I really need to read things more carefully...

Ron said:

but WHY do it? Just add more I/O or a larger plc

Some of us don't always have the luxury of this option!

The reason I got excited when I first saw Erics post is that I am frequently burdened with the problem of customers wanting extras on the agency machines we sell. These machines are low budget imports usually with just enough I/O for their standard operation and no room for expansion. In fact usually basic non-expandible PLC's are used!

Anthony

[jvdcande]

Anthony,

that's what you get when customers want extra's on low budget machines: problems. In my experience it's the one or the other: low budget or extra's, never both.

ramcr,

from your post I think you're looking for a circuit where two lightbulbs are connected in series between the power rails with the center connected to the PLC output. Unfortunately, most PLC's have open collector outputs, so you can't use this solution.

I have seen this circuit a lot in the old days when we were using discrete logic (eg. 7400 family) where some functions had totempole outputs. In that case this is indeed a simple way to indicate both the ON and the OFF-states.

Kind regards,