National Instruments AT-MIO-16X - Manual (Page 48)

Chapter 2 Configuration and Installation
AT-MIO-16X User Manual 2-26 © National Instruments Corporation
resistors. For example, if two 100-k
Ω
bias resistors are used, there
could be as much as 200
µ
V of input offset voltage (0.66 LSB at a gain
of 1, bipolar range).
Single-Ended Connection Considerations
Single-ended connections are those in which all AT-MIO-16X analog
input signals are referenced to one common ground. The input signals
are tied to the positive (+) input of the PGIA, and their common ground
point is tied to the negative (–) input of the PGIA.
When the AT-MIO-16X is configured for single-ended input, up to
16 analog input channels are available. Single-ended input connections
can be used when all input signals meet the following criteria:
• Input signals are high level (greater than 1 V).
• Leads connecting the signals to the AT-MIO-16X are less than
15 ft.
• All input signals share a common-reference signal (at the source)
or are floating.
DIFF input connections are recommended for greater signal integrity if
any of the preceding criteria are not met.
The AT-MIO-16X can be software-configured for two different
types of single-ended connections: RSE configuration and NRSE
configuration. The RSE configuration is used for floating signal
sources; in this case, the AT-MIO-16X provides the reference ground
point for the external signal. The NRSE input configuration is used for
ground-referenced signal sources; in this case, the external signal
supplies its own reference ground point and the AT-MIO-16X should
not supply one.
If using the AT-MIO-16X with a 50-pin I/O connector in single-ended
configurations, more electrostatic and magnetic noise couples into the
signal connections than in differential configurations. Moreover, the
amount of coupling varies among channels, especially if a ribbon cable
is used. The coupling is the result of differences in the signal path.
Magnetic coupling is proportional to the area between the two signal
conductors. Electrical coupling is a function of how much the electric
field differs between the two conductors. If AI GND is used as the
signal reference, Channels 0 and 8 are the quietest and Channels 7 and
15 are the noisiest. AI GND is on pins 1 and 2, which are very close to
pins 3 and 4, which are Channels 0 and 1. On the other hand, Channels 7