What is sensor output power for?

The best use for the 24VDC Sensor Output is for accepting digital inputs aux contacts from relays and contactors.  Attempting to power even a couple prox switches can exceed the available current capacity of the 24VDC Sensor Output supply -read last part from @qwazee's prior post above.

I tend to not wire that to anything - except for what has been suggested, AC powered S7-1200's to sense aux contact dig inputs.

It also works well for switches (without a light).

Basically, if it is a dry contact, it can be a good solution if it saves installing a separate 24VDC supply.  That's a rather rare exception for most projects, but if it's a small desktop prototyping project where you have a starter kit AC powered s7-1200, it's great for powering the dig input simulator switches.

Yuliya1106

Hello guys,

You helped me a lot and I continue learning PLC. I am trying to build my electrical diagram and I am a little bit confused. What is the "24 VDC sensor out" input used for? Is it just to power my sensors? Thank you!

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Split fromLearning plc.

NOTE: the digital inputs must be simple inputs, like switches (limit, pressure, level, selector, temperature...), pushbuttons, and other devices which do not require external power to operate.

For proximity switches, you typically need an external supply, so those would not be appropriate for PLC powered DIs.

C-3PO

Thanks to quazee and 0_Einstein, I have reviewed System Manuals (one old from 2009 and the newest from year 2022, both have the same data) about this issue.

For 1211 and 1212, declared Output current rating (max.) is 300 mA, and for 1214 is 400 mA. Because Logic 1 signal (min.) is 15 VDC at 2.5 mA, that means that more than hundred DI can be powered with this output.

Of course, that is an approximate calculation, because the length of cables (wires) impacts the current capacity. Although typical cable (0.8 mm) have a resistance around 100 Ω/km, you must carefully  account it.

So, generally, few DI wouldn't make a problem.