Selecting Digital Output Module

2) 24 VDC Output Module with Interposing Relay after Output Module

I always recommend isolating your I/O with a relay anyway.

Guest,

Both are frequently used. My choice would depend on a number of factors:

• Availability of DC for controlling the contactors in the MCC.
• Speed of response--AC has an inherently slower response than DC.
• Ability to isolate the DC from higher-voltage AC signals.
• Number of operations expected during the life of the equipment (solid-state devices are much more long-lived).

I would always design in certain components:

• Surge suppression to eliminate or trap the voltage spikes from the contactor and relay coils so they do not damage the output module--diodes backwards for DC outputs and RC networks for AC outputs. Do this for relays or solid-state outputs.
• Separate wireways as needed to conductors with different voltages apart.
• Isolating relays being mandatory for certain types of loads such as horns or buzzers.
• Hard-wired emergency stop circuits and wiring the power for the outputs through the master control relay.

--JMM

Thanks for all the Info.

Regards

Jose