National Instruments Corporation SC-207 Series, Руководство пользователя

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SC-2070 Board Chapter 2
SC-207X Series User Manual 2-14 © National Instruments Corporation
Building Attenuators (Voltage Dividers)
Attenuators (voltage dividers) can be connected to the analog inputs of the SC-2070 board when the
inputs from its DAQ board are in differential mode. The SC-2070 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 the custom
breadboard area. Attenuators can be used to reduce a signal that is outside the normal input range of
the DAQ board (
±
10 V maximum).
Warning: The SC-2070 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 DAQ
board. Input voltages greater than 42 V can result in damage to the SC-2070 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 SC-2070 board is shown
in Figure 2-12. 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
V
MIO
= V
SC
* G
where V
SC
is the voltage applied to the screw terminals of the SC-2070. The accuracy of this gain
equation depends on the tolerances of the resistors used.