National Instruments BNC-208 Series, Руководство пользователя

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BNC-2080 Board Chapter 2
BNC-208X Series User Manual 2-20 © National Instruments Corporation
Building Attenuators (Voltage Dividers)
Attenuators can be connected to the analog inputs of the BNC-2080 board when the inputs from its
data acquisition board are in DIFF mode. The BNC-2080 board open component positions do not
facilitate voltage dividers with the MIO-16 board configured for single-ended inputs. Therefore, if
the MIO-16 board is configured for single-ended inputs, attenuators must be built on a separate
breadboard. Attenuators can be used to reduce a signal that is outside the normal input range of the
data acquisition board (
± 10 V maximum).
Warning
: The BNC-2080 board is not designed for any input voltages greater than 42 V, even
if a user-installed voltage divider reduces the voltage to within the input range of the
data acquisition board. Input voltages greater than 42 V can result in damage to the
BNC-2080 board, any and all boards connected to it, and the host computer.
Overvoltage can also cause an electric shock hazard for the operator. National
Instruments is
not
liable for damage or injury resulting from such misuse.
A three-resistor circuit for attenuating voltages at the differential inputs of the BNC-2080 board is
shown in Figure 2-16. The figure also shows the placement of the resistors on the open
component positions for differential Channel 1. The gain
G
of this attenuator is given by the
following formula:
G =
R
G
(R
E
+ R
F
+ R
G
)
(Formula 2-3)
Therefore, the input to the MIO-16 board (V
MIO
) is as follows:
V
MIO
= V
SC
* G
where V
SC
is the voltage applied to the BNC connectors of the BNC-2080. The accuracy of this
gain equation depends on the tolerances of the resistors used.
Note:
Due to space constraints, when a resistor is to be inserted in position
G
(capacitor
position) it must be inserted vertically before bending the other lead to the board.