Wow, you are really trying to budget for mA loads?  That's pretty extreme (if you ask me).

Use the TIA Select Tool to estimate the power supply requirements for a given module.  If you are trying to figure out how to get the right circuit overload protection, use a Siemens circuit protection module with variable overload settings meant for this type of thing.

Or, you can pretty much ignore it and add 20% safety margin to loads that exceed 0.5A.

john_c_k

Hi,

I apologize if this a duplicate post at all. I did check through the forum, but did not see what I was looking for.

I have a question about power requirements for signal modules. I used a AI module for S7-1200 for an example. Attached is an example for calculating the 24 VDC current requirements for one SM 1231 AI 4 x 16 bit (6ES7231-5ND32-0XB0). The L+ for the module in this case would be supplied from a 24VDC power supply external from the CPU.

I was just wondering if anyone familiar with this could look through and make sure I am understanding this correctly?

The attachment has more details, but basic summary below:

Say for example you have an SM 1231 AI 4 x 16 bit (6ES7231-5ND32-0XB0) in use with a S7-1200 cpu (1214C for example). You want to use the AI signal module to take an AI from:

- Three 2-wire 4-20mA transmitters

- One 4-wire 4-20mA transmitter

The data sheet lists "Current consumption, typ." as 65mA. This is current that is expected to be drawn through L+ continuously just to supply additional power to electronics for the signal module to function (this does not include power used from the backplane)?

So the breakdown of required 24VDC mA for the module (supplied through L+ from an external power supply) would be:

- 65mA for the AI signal module to function

- ~20mA for each 2-wire 4-20mA transmitter (~60mA total)

- 0mA for the one 4-wire 4-20mA transmitter

So the total required 24VDC mA for the module (supplied through L+ from an external power supply) would be approximately 125 mA.

Thanks!