National Instruments SCB-68 - Manual (Page 62)

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
------ =