Chapter 3 Signal Conditioning Application Examples
BNC-2090 User Manual
3-8
National Instruments Corporation
the closest standard value) in its capacitor position, E. The closest
standard 5% tolerance resistors are 6.2 k
Ω
. The closest standard 1%
resistors are 6.34 k
Ω
. Figure 3-6 shows both the schematic and the
component placement for a 50 kHz highpass filter placed on differential
input channel 1. If the input signal source is floating, you must place a
bias return resistor in the B position (R4 in this case).
Note:
Highpass filters generally exhibit poorer common-mode rejection
characteristics than lowpass filters because capacitors are in the series
input paths. Capacitors have poorer tolerances than resistors, and
matching the input impedances is crucial for good common-mode
rejection.
The BNC-2090 open component locations do not facilitate RC highpass
filters with the MIO board configured for single-ended inputs. Therefore,
if the MIO board is configured for single-ended inputs, you must build
highpass filters external to the BNC-2090.
Figure 3-6.
Highpass Filter on Differential Channel 1
Building Attenuators (Voltage Dividers)
Attenuators or voltage dividers allow voltage measurements larger than
the maximum input range of MIO boards. For example, voltage signals
in the
±
20 V range can be measured by building a 2:1 voltage divider
circuit.
You can connect attenuators to the analog inputs of the BNC-2090
when the inputs from its DAQ board are in DIFF mode. The BNC-2090
open component positions do not facilitate voltage dividers with the
MIO board configured for single-ended input signals. Therefore, if you
configure the MIO board for single-ended inputs, you must build
To Input
Mux
J2
R22 = .001
µ
f(D)
R21 = .001
µ
f(C)
+
-
C2 = 6.34 k
Ω
(E)
