Specifications

Sensors
Pressure sensors and weigh scales (force sensing)
60 Maxim Industrial Solutions
Overview
The need to detect and measure
pressure and weight is a very
common requirement for modern
industrial control and system moni-
toring. Pressure measurement is
especially important, as it is also used
indirectly to measure flow, altitude,
and other properties. Pressure- and
weight-measurement devices can
be regarded as “force sensors,” since
force is the property that affects the
transducers’ outputs. The applica-
tions for force sensors are vast and
range from vacuum gauges, to heavy
machinery weigh scales, industrial
hydraulic equipment, and manifold
absolute pressure (MAP) sensors for
internal-combustion engines. Each
application has its own diverse needs
for precision, accuracy, and cost.
Although there are several methods
and technologies for measuring
pressure and weight (force sensing),
the most commonly used measure-
ment element is the strain gauge.
The two most common types of
strain gauges are the metal-foil type
used in a variety of weight/pressure
sensors and the semiconductor-
based piezoresistive transducers,
widely used to measure pressure.
Compared to metal-foil-type trans-
ducers, piezoresistive transducers are
more sensitive with better linearity,
but have large temperature depen-
dence and large initial offsets.
In principle, all strain gauges react
to an applied force by varying a
resistance value. Therefore, in the
presence of electrical excitation they
effectively convert a pressure or
weight to an electrical signal. Usually,
one, two, or four of these active
resistive elements (strain gauges)
are arranged in a Wheatstone bridge
configuration (sometimes called a
Pressure sensors and weigh scales (force sensing)
EXCITATION
μC
TRANSDUCER /
BRIDGE
AFE FILTER ADC DIGITAL DOMAIN
ADC
Reference
DAC
OP AMPS
REF
TEMP
SENSORS
PGA
IA
FILTERS
REFERENCE
LEVEL
TRANSLATOR
ISOLATION
ADC
OP AMPS
DIGITAL
POTENTIOMETERS
PRECISION
RESISTORS
INTEGRATED SIGNAL CONDITIONER
= MAXIM SOLUTION
Block diagram of the signal chain in a force-sense application. For a list of Maxim’s recommended pressure-sensor solutions, please go to: www.maxim-ic.com/psi.