National Instruments Corporation SC-207 Series, Руководство пользователя

Страница: 26 / 91

Chapter 2 SC-2070 Board
© National Instruments Corporation 2-9 SC-207X Series User Manual
Connecting Ground-Referenced Signal Sources
A grounded signal source is connected in some way to the building system ground; therefore, the
signal source is already connected to a common ground point with respect to the DAQ board
(assuming the host computer is plugged into the same power system). Nonisolated outputs of
instruments and devices that plug into the building power system fall into this category.
Differential Inputs
If the MIO-16 board is configured for differential inputs, ground-referenced signal sources connected
to the SC-2070 board need no special components added to the SC-2070 board. The SC-2070 board
inputs can be left in the factory-original condition, only with jumpers in the two series positions, E and
F (see Table 2-1). Signal conditioning circuitry, such as filters and attenuators (described in Building
Lowpass Filters, Building Highpass Filters, and Building Attenuators later in this chapter), can be built
in the open component positions.
Single-Ended Inputs
When measuring ground-referenced signals, the external signal supplies its own reference ground point
and the MIO-16 should not supply one. Therefore, configure the MIO-16 board for nonreferenced
single-ended input mode. In this configuration, all of the signal grounds should be tied to AISENSE,
which connects to the negative input of the instrumentation amplifier on the MIO-16 board. The
SC-2070 board inputs can be left in the factory-original condition, with jumpers in the series position
(E or F, depending on the channel). Do not use the open positions that connect the input to AIGND, B
and D (see Table 2-1 and Figure 2-2) in this configuration. Therefore, signal conditioning circuitry
requiring a ground reference should not be built in the open component positions, but must be built in
the custom breadboard area using AISENSE as the ground reference. Referencing the signal to
AIGND can cause inaccurate measurements resulting from an incorrect ground reference.