instrumentation
IN-FLIGHT PRESSURE
MEASUREMENT
As engineering and development look to expand the
capabilities of aircraft, the need for specialized
instrumentation presents new challenges to pressure
measurement device manufacturers
// MICHAEL GRIMM
Multi-channel pressure measurement
devices have become a dominant
choice for flight test instrumentation
- the integration of Ethernet connectivity
coupled with an engineering unit data
stream of all channels has simultaneously
simplified pressure testing and system
requirements. Yet, where environmental
considerations are concerned, certain
instrumentation still lacks the ability to be
subjected to harsh test environments. To
further complicate processes, flight
testing requires ruggedized equipment
that is often located in areas where space
is limited.
Environmental conditions such as high
vibration, shock, temperature and
humidity require that instrumentation
devices provide accurate data in conditions
that push the limits of flight testing.
Historically, pressure measurement devices
have been designed around piezoresistive
pressure sensors. These sensors are known
to be robust, simple, and stable in nature.
Still, temperature can be a challenge to
these devices’ sensors. For instance, while a
flight test may start on a runway at 60°C
with little to no vibration, conditions can
rapidly evolve into temperatures of -40°C
with severe turbulence.
CONFORMING TO
To help pressure measurement
instrumentation conform to
these types of testing
conditions, modules
can be mounted into
ruggedized enclosures. These
enclosures, often referred to as
Thermal Control Units, allow for the
installation of self-controlled heating
elements. The combination of the
enclosure and heating provides protection
from high vibration elements and will help
regulate the internal temperature of the
pressure measurement device, keeping it
within the typical calibrated temperature
range. Not only will this solution prevent
complications like condensation and
moisture from damaging the internal
sensors, but it will also help provide
consistent and accurate data.
Although Thermal Control Units may
help maintain constant module
temperature, piezoresistive sensors are not
immune to temperature fluctuations - as
temperatures change, the characteristics of
sensors may fluctuate in response.
Therefore, the incorporation of “quick-zero
offset calibrations” is required for the most
138 SHOWCASE \\ AEROSPACETESTINGINTERNATIONAL.COM
1 // Oldest flying Boeing, a
1928 Model 40C, flying
beside a Boeing 787
2 // Scanivalve MPS4264/
EPx 64 channel Ethernet
Intelligent Pressure
Scanner and Thermal
Control Unit
TESTING CONDITIONS
accurate data possible. Quick-zero offset
correction, in most pressure measurement
devices, requires the operation of an
internal valve system to switch the state of
the device to a “Calibration” mode.
Calibration mode typically shorts all
channels within the device to a single port,
which is often tied to a static or reference
port. Devices typically require a pneumatic
control pressure to change the valve state
to read this single reference pressure across
all channels.
Several factors in flight testing may
limit the use of a pneumatic pressure
source that can supply constant control
pressures needed to perform any valve
operation and necessary quick-zero
corrections. Compressors often do not
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