Using Non-Referenced Single-Ended (Nrse) Connections For Floating Signal Sources - National Instruments NI 6221 User Manual

Using Non-Referenced Single-Ended (NRSE) Connections for Floating
Signal Sources
© National Instruments Corporation
1 MΩ). In this case, connect the negative input directly to AI GND. If the
source has high output impedance, balance the signal path as previously
described using the same value resistor on both the positive and negative
inputs; be aware that there is some gain error from loading down the source,
as shown in Figure 4-7.
AC Coupled
Floating
Signal
Source
Figure 4-7. Differential Connections for AC Coupled Floating Sources
It is important to connect the negative lead of a floating signals source to
AI GND (either directly or through a resistor). Otherwise the source may
float out of the valid input range of the NI-PGIA and the DAQ device
returns erroneous data.
Figure 4-8 shows a floating source connected to the DAQ device in NRSE
mode.
Floating
Signal
Source
Figure 4-8. NRSE Connections for Floating Signal Sources
All of the bias resistor configurations discussed in the
Connections for Floating Signal Sources
resistors as well. Replace AI– with AI SENSE in Figures 4-4, 4-5, 4-6,
and 4-7 for configurations with zero to two bias resistors. The noise
AC Coupling
+
V
s
–
with Balanced Bias Resistors
+
V
s
–
R
section apply to the NRSE bias
4-19
Chapter 4 Analog Input
AI+
AI–
AI SENSE
AI GND
AI
AI SENSE
AI GND
Using Differential
M Series User Manual