Drawing Number: 21110
Revision: B
OPERATION MANUAL FOR
QUARTZ PRESSURE SENSOR
Series 118 & 119
3
The natural frequency and approximate fastest
pressure step rise time for various length passages is
shown in the following chart. (Medium, air at 25
C).
PASSAGE
LENGTH
(in)
PASSAGE
RESONANCE
(kHz)
APPROX.
FASTEST
PULSE RISE
TIME (uSec)
.050
66
5
.100
33
10
.200
16.5
20
.50
6.6
50
1.0
3.3
100
Passage Resonance vs. Passage Length
Actual resonant frequencies measured in practice may
differ slightly from the chart values. These
differences are due to variations in the velocity of
propagation of sound in air caused by changes in
temperature and pressure of the air in the passage.
For best matching of passage to diaphragm, maintain
the 0.010 inch (0.254 mm) clearance ahead of the
diaphragm, as shown in the Recessed Mount figure
on the previous page.
3.4
FLUSH MOUNT
In the flush mount installation, there is no reduced
area passage from the sensor diaphragm to the test
chamber; rather the sensor diaphragm is mounted
flush with (or slightly recessed from) the inside
surface of the test chamber.
Use this type of installation only if space or rise time
considerations preclude the use of recessed
installation.
In severe pyrotechnic environments, sensor life may
be severely limited with flush installation.
3.5
FLASH TEMPERATURE
EFFECTS
The ceramic coating on the diaphragm of these
sensors should render the flash thermal effect
insignificant in most cases, especially when recessed
mounted.
However, if more protection from flash thermal
effects is required with the recessed mount, the
passage can be filled with silicone grease (DC-4 or
equivalent). Several layers of black vinyl electrical
tape directly on the diaphragm have proven effective
in many cases as well.
Flash temperature effects are usually longer term and
will show up as a baseline shift long after the event to
be measured has passed.
For flush mount installations, a silicone rubber
coating approximately 0.010 inch thick can be
effective; GE RTV type 106 is recommended, and is
available from PCB as Model 065A67. Follow
manufacturer’s instructions to apply. It is best to
recess the diaphragm 0.010 inch for this type of
protection.
3.6
INSTALLING CABLES
Use only low-noise treated coaxial cable, such as
PCB 003 Series, to connect the sensor to the charge
amplifier, in-line voltage amplifier, or other high
input impedance readout instrument. To protect the
high impedance connection against moisture and
contamination, shrink tubing or other equivalent
connection protection is recommended. See the
following page for typical circuit connections.
Excessive cable motion can generate noise and
shorten cable life. For this reason, it is important to
support sensor cables by tying them to rigid structures
with adequate strain relief loops.
4.0
CALIBRATION
PCB 118 & 119 Series sensors are supplied with a
calibration
certification
from
the
factory.
Recalibration services are provided at the factory for
a nominal fee.
Several charge amplifiers are specially designed for
use with ceramic accelerometers measuring higher
frequencies. In general, this type of charge amplifier
is not suitable for calibration of quartz pressure
sensors by quasi-static means.
Do not attempt to use a charge amplifier which has
less than a 5000 second time constant in the “long
time constant” mode.
Following thermal stabilization of the sensor, use a
high pressure pump with dial reference sensor or a
dead weight tester to apply pressure in desired
increments to full scale. Release pressure after taking
the reading and before proceeding to the next higher
pressure level.
A calibration graph can be plotted using output
voltage vs. input pressure to determine sensitivity and
linearity.
