Chapter3 HardwareOverview
NI6013/6014 User Man ual 3-4 ni.com
Settling times can also increase when scanning high-impedance signals
becauseof a phenomenon called charge injection, where the AI multiplexer
injectsa small amount of charge into each signal source when that source
is selected. If the impedance of the source is not lowenough, the effect of
thecharge—a voltage error—does not decay by the time the ADC samples
thesignal. For this reason, keep source impedances under 1 kΩtoperform
high-speedscanning.
Dueto the previously described limitations of settling times resultin g from
these conditions, multiple-channel scanning is not recommended unless
sampling rates are lowenough or it is necessary to sam ple severalsignals
asnearly simultaneously as possible. The data is much more accurate and
channel-to-channelindependent if you acquire data from each channel
independently (for example, 100 points from channel 0, then 100 points
from channel 1, then 100 points from channel 2, and so on.)
Analog Output♦NI 6014 only
The NI 6014 supplies two channels of 16-bit AOvoltage at the I/O
connector.Each device has a fixed bipolar output range of ±10 V. Data
writtento the D/A converter (DAC) is interpreted in two’s complement
format, where for a number xexpressedinbase2withndigits to the left
oft he radix point, the (base 2) number is 2n–x.
Analog Output Glitch
In normal operation,a DAC output glitches whenever it is updated with
an ew value. The glitch energydiffers from code to code and appears as
distortion in the frequency spectrum.
Digital I/OThe NI 6013/6014 contains eight lines of digital I/O (DIO<0..7>) for
general-purposeuse. You can individually software-configure each line for
either input or output. At system startup and reset, the DIO ports are all
high-impedance.
The hardwareup /downcontrol for general-purpose co unters0 and 1 are
connected onboard to DIO6 and DIO7, respectively.Thus, you can use
DIO6 and DIO7 toc ontrol the general-purpose counters. The up/down