Drawing Number: 21113
Revision: A
OPERATION MANUAL FOR
ICP
®
HIGH PRESSURE SENSORS
Series 108 & 109
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 (
sec)
.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
It is convenient, though not necessary, to use coaxial
cable, such as PCB 002 Series, to connect the
transducer to the power unit. Cable need not be low-
noise treated.
If the use of lighter, more flexible cable is desired,
PCB Model 070B09 solder connector adaptors may
be used to employ twisted pair or other types of two-
wire cable.