15.9 Summary
Various methods of analog and digital signal conditioning to correct for nonlinear
characteristics in sensors, temperature effects, and offset zero were discussed. Methods
of correction include logarithmic amplifiers, impedance matching amplifiers,
and bias adjustment in linear conditioning, and lookup tables and equations in digital
conditioning. The conditioning of the various types of sensors was considered,
together with their amplification and the signal transmission mode. Both pneumatic
and electrical transmissions were considered, as well as the span adjustment of the
signal. When using electrical transmission, voltage, current, or digital modes can be
used, and their relative merits were discussed. Digital transmission is preferred, due
to lower power requirements, greater integrity of transmission, higher speed, minimized
noise, and increased direct interfacing with the controller. Digital signal
transmission standards, as well as the use of Fieldbus, to reduce cost and the load on
the controller, were discussed.
Wireless transmission falls into two categories: short range, such as Bluetooth
and Zigbee; and long range, in which telemetry signals can be transmitted using
pulse modulation techniques to minimize power requirement in battery operated
equipment