SCCAI-03 oscillations

[Hwy-Star]

Has anyone had oscillations problems with SCC-AI03?  I am running an SCC2345 with 3 modules in it.  A TC01 and 2 AI03's.  The AI's are used in NRSE mode with only one channel being used on each module.  The negative input is grounded.  After a few minutes the unused channel(s) go into oscillation.  Right now thew only thing I hace hooked up to the channels (being used) is an EDC voltage standard.  The unused channels have no connections to the inputs.

[AnalogKid2DigitalMan]

Inputs with high input impedance tend to do this when not connected to anything, they may oscillate, pick up ambient EMI, or saturate to their input rails. Tie them to ground and they shoul dsettle at zero.

-AK2DM

[Hwy-Star]

Thanks for the reply. As it turns out, it wasn't the AI-03 that was oscillating.  I had a power supply issue that was fouling up the +15V rail. 

Maybe you can answer another question about the AI modules.  The manual says an AI-XX requires 13.67 mA from each 15V rail and 130mA from the 5V rail.  What does it use the 5V for?  Both the input amps are +/-15V rails and I don't see any digital signals on the connector.

[_kb]

Hi Hwy-Star,

The 5V power line is used as a reference for the input offset voltage required by the input amps.

[Hwy-Star]

What type of reference uses 130+ mA?

[_kb]

Remember that the manual we're looking at covers a series of SCC analog input modules, some of which do utilize the 5V line for more than referencing.  Keep in mind, also, that the spec is a maximum current draw.

[Hwy-Star]

Since the title of this thread is SCC-AI03, you can assume that is the module I am asking about.  Does this module use 130mA from the 5V rail?  If so, what does it use it for?

[_kb]

All of my previous posts were written under that assumption -- the 5V line is used as a reference source in the SCC-AI03.  Off the top of my head, I cannot say for sure how much current the amps require, but I seriously doubt it's anywhere near 130mA -- likely much less.

[Hwy-Star]

Right out of the SCC-AI user's guide.  Page 10.

Power Requirement
Analog power .........................................410 mW max
+15 V...............................................13.67 mA max
–15 V...............................................13.67 mA max
Digital power (+5 V) ..............................650 mW max
130 mA max

[_kb]

Right.  The module will never need to pull more than 130mA through the +5V power rail.  These values are conservative limits.  A much smaller current is drawn through typical operation of the AI03.