AppendixC CommonQuestions
©NationalInstruments Corporation C-3 NI6013/6014 User Manual
Analog Input and Output
Ia mu sing the devicein differential AI mode, and I have connected a
differentialinput signal, but the readings are random and drift rapidly.
Whati s wrong?
Check theg round referenceconnections. The signalm ay be referenced
to a levelthat is considered floating with reference to the device ground
reference. Evenif you are in di fferentialmode, the signal must still be
referenced to the same ground levelas the device reference. You can use
one ofvarious methods to achieve ground reference while maintaining
ah igh common-mode rejection ratio (CMRR). Refer to Chapter 4,
Connecting Signals, for more information.
Ia m using the DACsto generate a waveform, but I discovered with a
digital oscilloscope that therea reglitches on the o utput signal. Is this
normal?
Whenit switches from on evoltage to another, any DAC produces glitches
due to released charges.The largest glitches occur when the most
significantbit (MSB) of the D/A code switches. You can build a lowpass
deglitching filterto remove some of these glitches, depending on the
frequencyand nature of the output signal.
Can I programmaticallyenable channels on the NI 6013/6014 to
acquirein different modes? For example, can I configure ACH0 in
DIFFinput mode and ACH1 in NRSE input mode?
Channels on the NI 6013/6014 canbe enabled to acquire in different
modes,but different pairs of channels are used in different modes. In the
exampleconfiguration given above, ACH0 and ACH8 are configured in
DIFFmod ean dACH1 and AISENSE are configured in NRSE mode.
In this configuration, ACH8is not used in a single-ended configuration.
Toenable multimode scanning in LabVIEW, use the coupling and input
configurationcluster input of the AI Config VI. This input has a one-to-one
correspondencewith the channel array input of the AI Config VI. You must
listal l channels either individually or in groups of channels with the same
inputconfiguration. For example, if you want ACH0 to be differential, and
ACH1and ACH2 to be NRSE, Figure C-1 demonstrates how to program
thisconfiguration in LabVIEW.