IO191 Usage Notes
IO191 Usage Notes — Usage information about the
ADC Sample Rate
The IO191 I/O module can be configured to use up to eight single-ended input
channels or four pairs of channels. The sample rate, therefore, depends on the
number of channels selected. For four-channel pairs (Differential mode), the maximum
sample rate is 250 kSPS. For eight channels (Single-ended), the maximum sample rate
is 31.25 kSPS for each channel.
Programmable Input Range
The IO191 uses the ADAS3022 which incorporates a programmable gain instrumentation
amplifier with seven selectable ranges (±0.64 V, ±1.28 V, ±2.56 V,
±5.12 V, ±10.24 V, ±20.48 V and, ±24.576 V), enabling the use of
almost any direct sensor interface. The input range settings are specified in terms
of the maximum absolute differential input voltage across a pair of inputs (for
example, Ch 1+ to Ch 1−). Note that because the IO191 can use any input type, such
as differential or single-ended, setting the mode is important to make full use of
the input span available.
These usage notes provide some examples of setting the mode in differential to be
able to use ±20.48 V or ±24.576 V. Note that the ADAS3022 always
calculates the difference between the Ch # + and Ch # − signals.
Example: Differential signals with a Nonzero DC
When a 12 V p-p signal with a 3 V dc level-shift is connected to one channel (Ch x
+) and the dc ground sense of the signal is connected to Ch x−, the input range
configuration is set to a ±20.48 V or ±24.576 V range because the maximum
differential voltage across the inputs is 12 V p-p and only half the codes available
for the transfer function are used.
Example: Antiphase signals with a zero
With a pair of 20.48 V p-p differential antiphase signals in zero-common mode,
when the input range configuration is set to ±20.48 V or ±24.576 V, the
maximum differential voltage across the inputs is ±20.48 V.