Selecting components, Adding components, Selecting components -11 adding components -11 – National Instruments SCB-68 User Manual

Page 56

Chapter 5

Adding Components for Special Functions

5-11

SCB-68 Shielded Connector Block User Manual

Use Equation 5-3 to design a lowpass filter for a simple resistor and
capacitor circuit, where the values of the resistor and capacitor alone
determine f

. In this equation, G is the DC gain and s represents the

frequency domain.

Selecting Components

To determine the value of the components in the circuit, fix R (10 k

Ω is

reasonable) and isolate C from Equation 5-3 as follows:

(5-4)

The cut-off frequency in Equation 5-4 is f

For best results, 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%

•

AXL package (suggested)

•

Carbon or metal film (suggested)

Choose a capacitor that has the following suggested characteristics:

•

AXL or RDL package

•

Tolerance of 20%

•

Maximum voltage of at least 25 V

Adding Components

Using the circuit shown in Figure 5-11, you can use a two-component
circuit to build a simple RC filter with analog input, analog output, or
digital input. You can build a single-ended analog input RC filter with pads
F and B for one channel and pads G and D for the next channel. You can
build a differential analog input RC filter with pads F and E.

For TRIG1, you can use pads R1 and RC1. For AO, you can use R2 and
RC2 for DAC1OUT, and you can use R3 and RC3 for DAC0OUT.

πRf

---------------