Drawing Number: 21091
ECO: 52570
Revision: B
OPERATION MANUAL FOR
HELIUM BLEED WATER-COOLED
PRESSURE SENSORS
123 Series
1
1.0
INTRODUCTION
The series of sensors described in this guide is
designed to measure dynamic pressures in intense
thermal environments typified by rocket engine
combustion chambers.
These sensors feature acceleration-compensated
piezoelectric pressure probes mounted in
a helium
bleed adaptor with water cooling.
The helium gas, applied from a 1500 psi source, is
metered by a built-in orifice and flows around the
probe body and out the passage of the adaptor head of
the probe diaphragm. The helium gas flowing out the
passage protects the sensor diaphragm from the hot
gasses as well as increasing the natural frequency of
the passage by a factor of approximately three to one.
2.0
DESCRIPTION
The charge-mode models contain a one pC/psi
pressure probe (sensor) and is designed to be used
with electrostatic charge amplifiers.
The ICP
®
Models contain built-in impedance
converter electronics circuits which convert the high-
impedance voltage from the quartz crystal to a low-
impedance voltage signal that can be fed directly into
most common indicating or recording instruments.
The 123 Series sensors contain a 10 micro helium
filter contained in a fitting threaded onto the helium
input tube. The purpose of this filter is to prevent
particles in the helium supply from plugging the
metering orifice.
The outer body of this series is 17-4 PH hardened
stainless steel and features a ceramic-coated tip for
protection against erosion by hot gasses when the
sensor is flush-mounted directly in combustion
chambers.
The probes in all models are electrically ground
isolated from the outer housing.
NOTE: The sensor probe in this series is factory
installed at a precise depth in the outer body. Do not
attempt removal of this probe. Contact the factory
should any questions or problems arise concerning
the sensor probe.
123 Series: Water- Cooled & Helium Bleed
Rocket Motor, ICP
®
and Charge Sensors
3.0
INSTALLATION
Prepare mounting port in accordance with
instructions on the installation drawing
Inspect the mounting port for burrs and tool marks at
the seal surface.
Use recommended mounting torque when installing
sensors. Do not over torque as damage to seal
surface could result.
NOTE: When attaching helium supply hose, do not
torque hose fitting through helium tube on sensor.
Back up fitting with wrench on 3/8 hex on helium
hose fitting. (Refer to note 3 on installation drawing.)
Especially in the presence of high vibration, support
helium supply tubes by clamping to rigid surfaces
with adequate strain relief loop to avoid stressing
helium tube on sensor.
Follow the same procedures and apply similar
precautions when installing the water supply and
drain hoses. Either water tube may be used as the
