The analog inputs have a QuickS
ample option where each conversion is done faster at the
xpense of increased noise. This is enabled by passing a nonzero value for put_config special
options
.6.1 Channel Numbers
ternal analog inputs, plus a few internal channels. The low-
and negative channel for each analog input conversion. With
.3 volts) on the positive input of the ADC. See Section
.6.4 for information about the internal temperature sensor.
g besides 31, the U3 does a differential conversion and
turns a pseudobipolar value. If the negative channel is set to 31, the U3 does a single-ended
l supported by the LabJack driver. When used, the
river will actually pass 30 as the negative channel to the U3, and when the result is returned
to
.6.2 Converting Binary Readings to Voltages
Following are the nominal input voltage ranges for the analog inputs, assuming that DAC1 is not
enabled.
e
channel
LJ_chAIN_RESOLUTION. There is also a LongSettling option where additional settling
time is added between the internal mulitplexer configuration and the analog to digital
conversion. This allows signals with more source impedance, and is enabled by passing a
nonzero value for put_config special channel
LJ_chAIN_SETTLING_TIME. Both of these
are disabled by default.
2
The LabJack U3 has up to 16 ex
level functions specify a positive
the LabJackUD driver, the IOType LJ_ioGET_AIN is used for single-ended channels only, and
thus the negative channel is set to 31. There is an additional IOType called
LJ_ioGET_AIN_DIFF
that allows the user to specify the positive and negative channel.
Positive Channel #
0-7 AIN0-AIN7 (FIO0-FIO7)
8-15 AIN8-AIN15 (EIO0-EIO7)
30 Temp Sensor
31 Vreg
Table 2-4. Positive Channel Numbers
Channel 31 puts the internal Vreg (~3
2
Negative Channel #
0-7 AIN0-AIN7 (FIO0-FIO7)
8-15 AIN8-AIN15 (EIO0-EIO7)
30 Vref
31 Single-Ended
32 Special 0-3.6 (UD Only)
Table 2-5. Negative Channel Numbers
If the negative channel is set to anythin
re
conversion returns a unipolar value. Channel 30 puts the internal voltage reference Vref (~2.44
volts) on the negative input of the ADC.
Channel 32 is a special negative channe
d
the driver adds Vref to the value. This results is a full span on the positive channel of about 0
4.88 volts (versus ground), but since the voltage on any analog input cannot exceed 3.6 volts,
only 75% of the converters range is used and the span is about 0 to 3.6 volts.
2
15
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