Chapter 5
Adding Components for Special Functions
SCB-68 Shielded Connector Block User Manual
5-20
ni.com
Selecting Components
To set up the resistors, complete the following steps:
1.
Select the value for
R
2
(10 k
Ω
is recommended).
2.
Use Equation 5-12 to calculate the value for
R
1
. Base the
R
1
calculation
on the following values:
•
Maximum
V
in
you expect from the transducer
•
Maximum voltage (<10 V
DC
) that you want to input to the DAQ
device
Accuracy Considerations
For best results when attenuating voltage, you should choose a resistor that
has the following characteristics:
•
Low wattage of approximately 1/8 W
•
Precision of at least 5%
•
Temperature stable
•
Tolerance of 5%
•
AXL package (suggested)
•
Carbon or metal film (suggested)
Verify that
R
1
and
R
2
drift together with respect to temperature; otherwise,
the system may consistently read incorrect values.
Adding Components
You an build a two- or three-resistor circuit for attenuating voltages at the
single-ended inputs, differential inputs, analog outputs, and digital inputs
of the SCB-68.
Single-Ended Input Attenuators
To build a two-resistor circuit for attenuating voltages at the single-ended
inputs of the SCB-68, refer to Figure 5-20.
