National-instruments SCB-68 Manual de usuario descargar pdf (Pagina 62)

Chapter 5 Adding Components for Special Functions

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

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).

Transducer

Input

–

------=

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National-instruments SCB-68 Manual de usuario Pagina 62