Noisy analog voltage on SC-2350

[JBSmo]

My hardware setup is an SC-2350 with an SCC-PWR03 power module. I have an SCC-AI04 module plugged into J1, an SCC-FT01 module plugged into J2, and SCC-ACC01 modules plugged into J3 thru J8.

Using a 12V battery as the power source, I still read 150mV of noise on the +15V and -15V pins of the J18 connector.

Is there something additional I need to do to eliminate this noise, or is this indicative of a hardware problem with either the SC-2350 or one of the modules?

[Alan Armstead]

Bruce,
Are you reading 15V with 150mV noise on top of that?
Since you are powering the SC-2350 with a 12V source, you should not expect great accuracy on the +-15V pins.

-Alan

[JBSmo]

The input power requirements for the SCC-PWR03 power module are 7-42v. 12v should be fine. Since the scope is setup for AC coupling I don't see the DC offset, but the LEDs next to J25 light up.

[<Mike Ross> mross@smpcorp.com]

The noise is only a problem if it obscures signals of interest to you. You don't say what it is you wish to observe so only you know if the noise is too much.

I can tell you that is it very easy to pick up 150mV of noise. You never said if it was just rough random noise or if it has any oscillating or other regular characteristics. What does the noise look like?

Have you got a single point ground? Are you using the appropriate field wiring (differential vs NRSE vs RSE) for the sensors of your system? (See the paper on Field Wiring in the technical resources.) Are all data channels shielded properly or at least twisted?

One excellent way to see if the noise is important (ie, part of the signal or from the environment) is to use
a really good o'scope to check the same signal. I am blessed to have an excellent scope. It is invaluable for sorting out noise prolems.

In my experience that last place to look is the signal conditioning equipment. BTW, I use an SCC-2345 with lots of feedthrough modules and cobbled together input circuitry.

[Alan Armstead]

Bruce,
I have a SCC-2345, with PWR03 and powered it with a 12V source. I see about 15.3V on the +15 pin and about -15.2 on the -15V pin with virtually no AC noise on either pin. Is it possible that you are introducing noise into your system somewhere? Do you see the noise on your J18 pins also?
-Alan