Page 14 - Industrial_Technology_EXTRA_May_11th_2020_Classical

SENSORS...

Remote sensing with a precision

instrumentation amplifier

The instrumentation amplifier (IA) is the workhorse of sensing applications. In this
article, Hooman Hashemi of Analog Devices explores some ways to take advantage of
these amplifiers’ balance and excellent DC/low frequency common-mode rejection for
use with resistive transducers when the sensor is separated from the amplifier

hen it comes to sensors, there is impossible to achieve by a traditional op amp, due
little competition for what a to the high degree of external resistor matching
Wheatstone bridge can do. The required.
Wbridge can produce a differential The electronics involved in physical
voltage that predictably changes in response to measurements are often located far from the
changes in a physical parameter – with the side physical parameter under measurement. For
benefit of providing temperature and time drift instance, a strain gage measurement, such as that
immunity. The differential voltage rides atop a large buried under the tarmac at a truck weigh station or
common-mode (CM) voltage. within the structure of a bridge, is unlikely to be
To amplify the small signal from a bridge, an located next to the electronics used to read the
instrumentation amplifier is used. The beauty of an measurement. For example, when dealing with a
IA is that, with little or no loading of the bridge two-wire quarter-bridge strain gage such as Omega
elements, it can sense the differential voltage and Corporation’s SGT-1/350-TY43, placing the sensor
reject the CM voltage to a degree that is next to remotely from the sensing amplifier yields

May 2020 • INDUSTRIAL TECHNOLOGY EXTRA! • p14