National Instruments AT-MIO-64F-5, User Manual

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Configuration and Installation Chapter 2
AT-MIO-64F-5 User Manual 2-8 © National Instruments Corporation
With this input configuration, the AT-MIO-64F-5 can measure up to 64 different analog input
signals. This configuration is selected via software. See the configuration memory register and
Table 4-9 in Chapter 4,
Register Map and Descriptions , for additional information. The results
of this configuration are as follows:
¥ AI SENSE is tied into the negative (-) input of the PGIA.
¥ Multiplexer outputs are tied together into the positive (+) input of the PGIA.
¥ Multiplexer control is configured to control up to 64 input channels.
Note: The NRSE input mode is the only mode in which the AI SENSE signal from the I/O
connector is used as an input. In all other modes, AI SENSE is programmed to be unused
or driven with the board analog input ground.
Considerations for using the NRSE input configuration are discussed in the Signal Connections
section later in this chapter. Figure 2-10 shows a schematic diagram of this configuration.
Input Polarity and Input Range
The AT-MIO-64F-5 has two polaritiesÐunipolar input and bipolar input. Unipolar input means
that the input voltage range is between 0 and V
ref
where V
ref
is a positive reference voltage.
Bipolar input means that the input voltage range is between -V
ref
/2 and +V
ref
.2/ The
AT-MIO-64F-5 has a unipolar input range of 10 V, and a bipolar input range of 10 V (±5 V).
Polarity and range settings are programmed on a per channel basis through the configuration
memory register.
Considerations for Selecting Input Ranges
Input polarity and range selection depend on the expected input range of the incoming signal. A
large input range can accommodate a large signal variation but worsens the voltage resolution.
Choosing a smaller input range improves the voltage resolution but may result in the input signal
going out of range. For best results, the input range should be matched as closely as possible to
the expected range of the input signal. For example, if the input signal is certain not to be
negative (below 0 V), a unipolar input is best. However, if the signal is negative, inaccurate
readings will occur if unipolar input polarity is used.
The software-programmable gain on the AT-MIO-64F-5 increases its overall flexibility by
matching the input signal ranges to those that the AT-MIO-64F-5 ADC can accommodate. The
AT-MIO-64F-5 board has gains of 0.5, 1, 2, 5, 10, 20, 50, and 100 and is suited for a wide
variety of signal levels. With the proper gain setting, the full resolution of the ADC can be used
to measure the input signal. Table 2-4 shows the overall input range and precision according to
the input range configuration and gain used.