Drawing Number: 21114
Revision: NR
OPERATION MANUAL FOR
ICP
HIGH PRESSURE SENSOR
Series 108B
3
For air at room temperature, (EQ. 1) becomes:
L
3300
f
r
(EQ. 2)
Where: L = Passage Length (in.)
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
(u Sec)
.050
66
5
.100
33
10
.200
16.5
20
.50
6.6
50
1.0
3.3
100
Actual resonant frequencies measured in practice may
differ slightly from the chart values 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 .010
”
clearance ahead of the diaphragm as shown
in previous figure.
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 the 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.
Flash temperature effects are usually longer term and
will show up as baseline shift long after the event to
be measured has passed.
For flush mount installations, a silicone rubber
coating approximately .010
”
thick can be effective.
General Electric RTV type 106 silicone rubber is
recommended. Follow manufacturer
’
s instructions to
apply. It is best to recess the diaphragm .010
”
for this
type of protection.
3.6
INSTALLING CABLES
It is convenient, though not necessary, to use co-axial
cable such as PCB Model 002A to connect sensor to
power unit.
Cable need not be low-noise treated and in fact, if it is
desired to use lighter, more flexible cable, 070A09
solder connector adaptors may be used to employ
twisted pair or other types of two-wire cable.
3.7
CIRCUIT CONNECTIONS
Figures 5a and 5b show two typical circuit
connections normally used with the 108B Series to
connect to the power units.
