PLC input ripples

[heshamzaki]

Dear All,

I would be grateful if someone helped me with this. I am planning to use ABB AC31 PLC. one of the inputs to the PLC will be the output of a single phase full wave rectifier uncontrolled bridge. when using smoothing reservoir capacitor, still the voltage will have some ripples.Are these ripples harmful to the plc? or i shouldn't care that much about them?

If I should totally gt rid of the ripples, how can i do that?

(by the way, the bridge output is inserted to analog input point of the plc)

 

[itsmoked]

The ripple will not be a problem if you are talking a Digital IN. If you are talking an Analog IN it may be a problem.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ScottyUK]

Connect the plc input to the bridge output via a resistor of a couple of k[Ω] or so. Put a relatively small capacitor directly across the PLC input. The small cap will smooth out the ripple and the resistor will decouple it from the main supply. It won't be a perfect representation of the DC level + ripple, but your PLC isn't fast enough to care.


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If we learn from our mistakes I'm getting a great education!

 

[controlsdude]

I know on ab contrologix their is signal conditioning on inputs to look not look unless the signal changes over a predetermined time as configured on card. Siemens though has diagnostic ripple on its input cards, this might be a problem if using these type. This can be disabled Not sure on ABB plc. I would think they would have some scheme similar to above manufacturers, since they always seem to copy off of each other.

 

[heshamzaki]

Thank you guys