Computer-based digital data acquisition systems
(DAs) are used to measure physical variables such as pressure, temperature,
force, and flow. With such systems, the input measure is first converted
to an electrical parameter such as resistance, voltage or current
using a sensor which is external to the data acquisition system
where it is conditioned and converted to a digital word that is
equivalent to the analog signal. The digital word is then transmitted
to a computer where conversion to engineering units and analysis/display
functions are performed.
Digital DAs used today are primarily multi-channel
systems. That is, up to N sensors are connected to a single DAs
where they time share common equipment. These measurement systems
are referred to as multiplexed data acquisition systems. Depending
on the extent of the shared equipment, multiplexed DAs are categorized
as amplifier-per-channel systems or low-level multiplexed systems.