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NI myDAQ User Guide and Specifications
14
ni.com
Figure 9.
Differential Connections for Floating Signal Sources with Two Resistors
Both positive and negative analog input lines require a DC path to ground
in order for the instrumentation amplifier to work. If the source is
AC coupled (capacitively coupled), a resistor is needed between the
positive input and AGND. If the source has low impedance, choose a
resistor that is large enough not to significantly load the source but small
enough not to produce significant input offset voltage as a result of input
bias current (typically 100 k
to 1 M
). In this case, connect the negative
input directly to AGND. 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.
NI myDAQ DMM Fuse Replacement
NI myDAQ has a fuse to protect the device from overcurrent through
HI (A) current measurement input on the DMM. If the DMM soft front
panel (SFP) always reads 0 A current, the cause may be a blown fuse.
Testing Your Fuse
To test for a blown fuse, complete the following steps.
1.
Using a banana cable, connect the HI (V) and HI (A) DMM terminals.
2.
Launch the NI ELVISmx Digital Multimeter (DMM) Soft Front Panel
instrument from the NI ELVISmx Instrument Launcher, located at
Start»All Programs»National Instruments»NI ELVISmx for
NI ELVIS & NI myDAQ»NI ELVISmx Instrument Launcher
.
3.
Select the
Resistance
mode.
4.
Set the Range to
200
.
5.
Click
Run
.
6.
If the fuse is blown, the display will show
+Over
, indicating a
disconnected circuit path. Replace the fuse and complete the procedure
again.
+
–
+
–
AI+
AGND
Sign
a
l So
u
rce
R
s
o
u
rce
>100
Ω
AI–