Drawing Number: 21091
ECO: 52570
Revision: B
OPERATION MANUAL FOR
HELIUM BLEED WATER-COOLED
PRESSURE SENSORS
123 Series
2
inlet tube. Use at least a 50 psi source of clean water
for cooling.
For charge-mode models, connect 4 ft. cable to
charge amplifier and switch to "LONG" time constant
position and check for drift.
Clean cable connections with Tryclor
or equivalent
solvent to restore insulation resistance.
It is good practice to depress ground button (or place
switch in "GND" position) on the charge amplifier
while attaching input cables to the amplifier. This
will prevent spurious charges which may accumulate
on sensors and cables from blowing out the input
circuitry of the charge amplifier.
Since the charge output sensors are susceptible to
decreased insulation resistance, use care to keep cable
connections clean by use of shrink tubing wherever
possible.
The ICP
®
Series Sensors use low-output impedance
probes (ICP
) and will not require the insulation
resistance cautions previously described for the
charge-mode models.
Connect the sensor cable to the appropriate ICP
power unit and check the front panel monitor meter to
check cable connections and internal amplifier.
Consult Guide G-0001B, "General Guide to ICP
Instrumentation" for installation and usage hints for
ICP
instruments.
4.0
OPERATION
4.1
CHARGE OUTPUT MODEL
For the charge-mode, it is only necessary to select the
proper range on the charge amplifier and proceed
with the measurement.
The probe sensitivity is approximately 1.0 pC/psi.
(The exact sensitivity is given on the calibration
certificate supplied with each instrument.)
Sensor connection for ICP
®
operation
EXAMPLE: The dynamic pressure expected is 500
psi and the desired output voltage for this pressure is
1 volt.
Simply set the range switch of the charge amplifier to
500 units per volt and dial the standardization pot to
the exact sensor sensitivity at 500 psi (from
calibration graph).
The system will then yield exactly 1 volt for 500 psi
of input pressure (dynamic).
4.2
TIME CONSTANT
During in-place calibration static methods (dead
weight tester) may be used in a drift-free system by
placing the charge amplifier in "LONG TC" position.
However, during actual use, the TC mode switch
should be in "SHORT" position for two reasons.
Often times, the dynamic pressure being measured
exists superimposed upon a higher static level. The
short TC position will allow the effect of this static