can not read 115vac

[jtm]

I am using a scxi-1000 4 slot chasis, a scxi 1600, a scxi-1120 with a scxi-1327. I am using Signal Express to monitor these signals.

I tested this tool a few weeks ago on multiple 125vdc  and -5,+5 voltages and it worked well. I now have it hooked up to multiple 115vac signals and 30 vdc signals.

I know my jumpers are set right because I can read the 30vdc signals, and they are set the same as when I was reading the 125vdc signals. I put a meter right at the 1327 and am reading 115vac on the terminals.

It only shows noise when I test the signals. I have tried two different 1327 modules and 1120 modules.

My external wires are hooked up to 115vac and ground as my reference. My meter reads the 115vac when hooked up to the signal and ground as a reference.

I can not figure out why I can not read the 115vac signals.

What am I missing?

[Brooks_C]

Hello jtm,

If I had to guess I would say that your filters are probably set to the 4Hz bandwidth which is the factory default on the SCXI-1120.  Please see page 2-12 of the SCXI-1120/D Manual to find the correct setting for an AC signal.

I hope this helps, and if not feel free to post back.

Have a great night!

[jtm]

If I set the bandwith to 10khz will that interfere with the DC readings. In other words will I have to switch back to 4khz to read a DC signal?

I hope to get back to this next week and test your suggestion. Thanks!!

[Brooks_C]

Hello jtm,

The 4 Hz and 10 kHz filters are low pass so technically speaking the answer is no; you can read DC signals with either setting.  However, the 4 Hz filter is provided to filter out noise above 4 Hz when measuring DC signals.  If you don't have much noise in your system it may not be necessary to change the jumpers back to the 4 Hz filter setting, but in most cases your measurement would benefit from doing so.  That being said, these filters are set on a channel by channel basis so you can always configure your channels to measure both AC and DC at the same time if that is what you were asking.

Cheers,

[jtm]

Thank for all your help.