Chapter 5
Adding Components for Special Functions
©
National Instruments Corporation
5-17
SCB-68 Shielded Connector Block User Manual
Figure 5-18.
Current-to-Voltage Electrical Circuit
The application software must linearly convert voltage back to current.
Equation 5-8 demonstrates this conversion, where the resistor is the
denominator and
V
in
is the input voltage into the DAQ device:
(5-8)
Selecting a Resistor
For best results when measuring current, you should choose a resistor that
has the following characteristics:
•
Low wattage of approximately 1/8 W
•
Precision of at least 5%
•
Temperature stability
•
Tolerance of 5%
•
232
Ω
(suggested)
•
AXL package (suggested)
•
Carbon or metal film (suggested)
If you use the resistor described above, you can convert a 20 mA current to
4.64 V by setting the device range to either (–5 to +5 V) or (0 to 5 V).
I
R
Transducer
Input
V
m
+
–
+
–
I
V
m
R
------
=
