NI 6009 unstable reading signal

[zybear]

Hello, everyone:

Thanks for your time and attention on my question.

I confronted a problem with NI 6009 card when i tried to aquire some analog signals, the signal should be stable e.g. 2 V, and it was proofed with Keithly 2100 Multimeter, the reading signal always stayed around 1.97~1.98, but with NI 6009 the result varied from1.8 to 2.1, and i can not get a stable signal at all, it is so strange. Does anyone have the similar experience or some ideas for this problem?

thanks in advance.

YU

[MarcoMauri]

Just a couple of hints:

1) Have you checked the signal with a scope? (the multimeter can filter out the noise)

2) If on the scope you see a 'perfect' 1.97~1.98 V signal, then check the cabling of the NI 6009 (grounding, etc.)

Regards,

Marco

[zybear]

Hi, Marco

Thanks for your reply.

After checking of multimeter's user manual, there is no filter for DC signal.

and the connection for NI 6009 seems quite simple, 2 cables for difference Voltage measurement.

So i do not konw what caused this problem.

Regards

YU

[sebster]

Hi,

try using a pure DC input from a 1.5V battery, or two in series, and see if you get a stable reading.

And it's definitely worth checking your original signal with a scope. The multimeter won't capture any spikes in the signal because it's not quick enough whereas the NI-6009 will.

Regards,

Sebster

[ben64]

The digital filter is enable by default in the 2100. If you set the averaging to 10 for the measurement with the USB-6009 you should get a result similar to the 2100 reading.

Ben64

Digital filter

Definition

The Model 2100 uses an averaging digital filter to yield a reading from 2 to 100 past measurement

readings (past measurement readings are stored in stack memory). You can select one of two

modes of digital filter operation:

The moving average filter puts the specified number of reading conversions in a first-in, first-out

order. The very first measurement reading simply fills up the stack. To yield a reading for display,

the filter produces an average of the stacked measurement readings every time a new

measurement reading is available, replacing the oldest reading in the stack. In the

Average

average to produce a reading for display. It then flushes the stack and starts over with an empty

stack. Consequently, the repeating digital filter yields one reading for display every specified

number of measurement readings.

The digital filter is not available for diode, continuity, frequency, and period measurements.

Moving Average mode or Repeating Average mode.Repeatingmode, the multimeter waits for the measurement reading stack to fill up, then take an

Default

The digital filter is enabled, is in Moving Average mode, and is set to use the last 10 readings by

default.

[zybear]

thanks so much for the replies, i will do some test again with your advices.

regards

yu