1756-OF8 Current Mode

[hmiman 1]

Hi,

I had a problem where what was thought to be a loop powered current to pressure converter was not starting up during commissioning. It appears now that it requires a separate 24V supply.

During fault finding I did notice that the voltage at the output of the 1756-OF8 channel was at 20.2V @ 20mA output. I could not find the specification in the 1756-UM009D-EN-P manual.

This led me to wonder if this is in fact normal and needs to be considered in future loop powered applications. Other loop powered control valves in the plant seem happy at 20V out of a 1756-OF8.

Do we only get 20V in 4-20mA mode?

Thanks,

Deon

[kaiser_will 65]

The specifications for this output module, page 186, note an output voltage range of +/- 10V.  

http://literature.rockwellautomation.com/idc/groups/literature/documents/td/1756-td002_-en-e.pdf

[hmiman 1]

Hi Kaiser,

Thanks for the link. The spec of +/- 10V is not applicable in my situation as we use current output.

The table does state a drive capability of 0-750 Ohm. That answers my question.

Thanks,

Deon