noise spike in scope

[ChandranNextech]

Hi,

For the first time I am using NI scope USB-5132. I programmed the scope to edge trigger mode. I noticed that the scope is triggering unnecessarily. When I noticed there are spike noise in the scope. I have attached the program and the picture of the noise. 

But when I use the SCOPE program provided by NI, I don't see the noise. Photo attached too.

Is there anything wrong in my program?

TQ [Chandran]

[Aalenox]

Oddly enough, I spent all day trying to hunt down noise that looked almost identical to what you posted. It ended up (I think) being one of the accelerators.  I don't see any problem with your program at all, and I'd be inclined to believe that it isn't showing up on the NI because the sample rate is too slow, the voltage range too large, or some combination of both.

If I were you, the first thing I'd do is verify whether or not the noise is real. Hook up a fast scope to your signal, or unhook your signal completely to see whether or not that removes the noise. It will give you a starting spot anyway... 🙂

[JÞB]

But when I use the SCOPE program provided by NI, I don't see the noise. Photo attached too

---

you are tricking yourself.  your graph is displating a full 1 second of data while only a very short time is displayed in the scope SFP picture. 

The noise looks to be about 5Hz (on a strain guage right?) so I would look for a biological cause first.  Someone walking around and causing vibrations, a elevator running, fingers tapping on the desk.... that sort of issue.

[ChandranNextech]

If you say my program is OK, than the noise must be real. Let me confirm this with other scope.

TQ [Chandran]

[AB@17]

Is there any possibility of noise due to impedance mismatch

[ChandranNextech]

I am not sure, but I will check on that as well.

TQ [Chandran]

[Aalenox]

"Is there any possibility of noise due to impedance mismatch"

That doesn't really look like an impedance mismatch. Those usually show up in the form of ringing on real signals, not as background blips of noise.

[johnsold]

I agree that this looks like a real noise.  It only occurs six times per second in the example shown in the original post.  I do not know what trigger options are available in NI Scope, but see if you can set it to trigger at about 0.1 V. Then it should only trigger when the noise is present. The duration of the noise appears to be a few milliseconds so you may need to change the sweep speed also.

Lynn