Chapter 3
BNC-2081 Board
© National Instruments Corporation
3-13
BNC-208X Series User Manual
A two-resistor circuit for attenuating voltages at the single-ended inputs of the BNC-2081 board is
shown in Figure 3-11. The figure also shows the placement of the resistors on the open component
positions for Channel 1. The gain,
G
, of this attenuator is given by the following formula:
G =
R
D
(R
C
+ R
D
)
(Formula
3-3)
Therefore, the input to the Lab board (V
Lab
) is as follows:
V
Lab
= V
SC *
G
where V
SC
is the voltage applied to the BNC connectors of the BNC-2081 board. The accuracy of this
gain equation depends on the tolerances of the resistors used. The input impedence of the channel with
the voltage attenuator is R
C
+ R
D
. This should be kept sufficiently high to avoid any loading effect on
the voltage you are measuring.
AIGND
(Case)
Channel 1
(Center)
BNC Connector
R4
R5
R6
R14
10-k
Ω
Resistor
Channel 1
(Center)
To
Input
Multiplexer
Input Schematic for
ACH1
BNC Connector
+
AIGND
A
B
C
D
C
D
R14 = 10 k
Ω
ACH1
AIGND
(Case)
Figure 3-11. Attenuator for Use with BNC-2081 Board Inputs
