Peaks/Noise on Square wave (PWM) signal

[A-T-R]

Hi there,

I have to acquire a PWM signal from a certain sensor. For that, I use the cDAQ-9147 chassis + NI 9229 AI module.

Unfortunately, I see a lot of noise at the edges of the signal...but those peaks are not existant outside of the cDAQ device! I verified that by connecting two different oscilloscopes (TEK TDS 210 and TEK TDS 3052B) and one additional DAQ board (NI PCI-6229 + CB 68LPR) in parallel! If there were such noise outside the chassis, all the measurement devices should see it.

What's wrong with those cDAQ devices?

Please look at the pictures below:

PCI-6229

PCI-6229

cDAQ-9174 + NI 9229

cDAQ-9174 + NI 9229

TEK TDS 210   +   TDS 3052B

BTW: I also posted this question here

[Duffy2007 · Accepted solution]

Hi A:T:R,

the 9229 Modul has a sigma delta amplifier with an antialising filter onboard.

The modul is to aquire dynamic singnals. In your situation the sigma delta amplifer

need some time to engage and the signals before the PWM go down could come

from the internal oversampling from the card. The 6229 only has a nomal amplifier

onboard. You can use the 9215 to see the same results like with the 6229.

Please let me know, if this helps to understand the functionality of the 9229.

[A-T-R]

Hi Alex,

thanks for your help so far!

The problem is, I need both the higher input voltages AND the simultaneous sampling of the 9229 module! I have to acquire a signal from an automotive sensor, which have to be tested at voltages between 8-16 VDC, and it's output has to be set in exact relation to another analog signal of a position sensor!

Do you have another suggestion, which setup alternatively should be used?

I also need the USB solution for easily connecting a Laptop to the whole test rig, which is transportable! I can't use a PXI chassis with some DAQ board, because that's way too expensive (and not to forget in this particular case: of much higher weight!), and also much more complicated to handle (for the customer)...

Any help is appreciated!

Regards

Achim

[Duffy2007]

Hi Achim,

i didn´t no a module for your specifications either the measure up to 16V and they have a sigma delta or

the only can measure up to 10V.