Chapter 5 Adding Components forSpecial 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 R2 (10 kΩ is recommended).
2. Use Equation 5-12 to calculate the value for R1. Base the R1 calculation
on the following values:
•Maximum Vin you expect from the transducer
•Maximum voltage (<10VDC) 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)
Veri fy th at R1 and R2 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 Figure5 -20.