Wrong output signal of a 1771-OAD

[mulderm]

Hello,

I have using AC 110V Output module's for a PLC/5 system.
Now I have Optocoupler's connected to this Output's.
Problem is that when a Output is Low ("0") the Optocoupler
is activate.
Measuring the Output without a load gives a 70V AC signal when the Output is Low ("0").
How can this happen?
Why is this not 0V ac?
Many other modules have this problem.
Please help me because the Optocoupler's giving a wrong signal
when the Output have a Low signal.

mulderm

 

[msward]

Check out the following :-

http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1771-in024_-en-p.pdf.

The output module has minimum load requirements with capacitor and snibber resistors across the output.


Regards

Mike

 

[mulderm]

Thanks for the information.
I have use a 15K 1W resistor parallel about the Optocoupler.
It works good.

mulderm

 

[artecerv]

There are a number of things I suggest you to check:

1) Type of opto-coupler: PNP or NPN
2) Opto-coupler residual current (that is the flow of current when swithed off).
3) Opto-coupler switched ON “gate” current.
4) Minimum voltage at the “gate” (threshold) before switching off.

I'm assuming that your PLC output module (110V AC) is of the solid-state type (i.e. TRIAC, etc.). If this is the case, you should also check:

a) Outputs residual current.
b) Maximum voltage at which it is still considered switched off (threshold).

I have the sneaky suspicion that your solid-state outputs do not have enough breaking power to switch off the load. This behaviour is typical from inductive loads, which prompt me to ask:

Is your opto-coupler completely “solid-state”?

If I am right, the opto-coupler will damage your PLC outputs (may be it already has).

Regards,

 

[mulderm]

It´s a Weidmuller Optocoupler DK0-115Vuc

mulderm