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IO191 Usage Notes

IO191 Usage Notes — Usage information about the I/O module

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 offset

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 common

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.