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Ratiometric and Non-ratiometric sensors interface with A/D

Discussion in 'Electronic Design' started by [email protected], Jan 14, 2005.

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  1. Guest

    Wondering what is the best way to interface both ratiometric (absolute)
    and non-ratiometric (relative) sensors to a single a/d ( an A/D with,
    say, a 8 channel mux,internal ref, external ref option)

    I think the most obvious is
    1) Disable the internal reference, connect the ratiometric excitation
    power to the external a/d reference pins (so the ratiometric sensor
    outputs track with the a/d reference). For the non-ratiometric sensor
    inputs read the internal reference and use that to calibrate the
    non-ratiometric (absolute) readings.

    or maybe,

    2) Enable the internal reference so you can correctly read the
    non-ratiometric reading without calibration, for the ratiometric
    sensor, read its excitation power with a spare channel and use that to
    calibrate the ratiometric readings.

    and perhaps you can do this

    3)Power the ratiometric sensor (they only require 1 mA) with an
    external precision reference and also connect that reference to the
    external a/d reference pins. No calibration needed for either.
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