Analog break out problem.

[Al Skierkiewicz]

Gary,
If as I suspect the 22 ufd cap, C10 is missing, then the regulator can and likely will oscillate. The addition of your 10 ufd then is merely returning some of the needed capacitance to the output. You will need to keep the noise filtering in Labview. There are two noise problems you are dealing with, the noise normally found in the sensors you are using, and that generated by a defect in the power supply. The reason I am concerned is that adding caps to anything except motor leads is not allowed in the rules. Repairs to electrical components are allowed so I would want you to get this right so you have no problems in inspection in a few weeks.
This is assuming that your load is less than the 500 ma the power supply is capable of providing.

[EricVanWyk]

Originally Posted by Al Skierkiewicz

Gary,
If as I suspect the 22 ufd cap, C10 is missing, then the regulator can and likely will oscillate.

I agree.

Originally Posted by Al Skierkiewicz

The reason I am concerned is that adding caps to anything except motor leads is not allowed in the rules. Repairs to electrical components are allowed so I would want you to get this right so you have no problems in inspection in a few weeks.

My understanding of the rules differs from yours on this point. I believe the added capacitor would fall under the "custom electronics" category and therefore be legal (R62). R63 explicitly allows the motor filter caps because custom electronics are explicitly illegal on the power-path.


Gdeaver -

This is going to sound weird, but be sure to use a crappy capacitor for this. Using a high quality, low-ESR cap can make this specific power supply either squeal or throb.

[Alan Anderson]

Originally Posted by EricVanWyk

My understanding of the rules differs from yours on this point. I believe the added capacitor would fall under the "custom electronics" category and therefore be legal (R62). R63 explicitly allows the motor filter caps because custom electronics are explicitly illegal on the power-path.

Right. The capacitor in question is not on the 12 volt power input, but on the "input pins" of the Analog Breakout. That's a legal place for a custom circuit to connect.

[Al Skierkiewicz]

Guys,
You can call it a custom circuit but my experience tells me that the GDC doesn't see it that way. I can make an excellent case for it being a field repair on a damaged electrical device, however. (which is now legal) I should have mentioned that although it is rare, these types of caps do occasionally show up open in the field.