Drawing Number: 21102
Revision: A
OPERATION MANUAL FOR
3
Series 138
The steel wire can have a weight attached to it to
submerge the entire assembly. Tape or attach the
coaxial cable loosely to the steel wire at ~one foot
intervals. Attach a monofilament line (~50 lb. test) to
the end of a steel wire braid, and let it hang down past
the end of the sensor.
Attach a three to five lb. weight to the end of the
monofilament
and
tape
the
sensor
to
the
monofilament.
Another method of mounting the sensor is to tape the
sensor to the surface of a structure. (The pressure
measured when mounted to the surface of a structure
will be twice the free field pressure since the pressure
wave reflected off the surface adds to the pressure
wave initially striking the sensor.)
For applications in which the 138 is immersed only a
few feet into a liquid, and the blast may be in very
close proximity to the sensor, a steel pipe can be
placed around the cable and sensor so that only the
tourmaline sensing element is exposed to the blast.
Since the static pressure is not high, a standard micro
cable with 10-32 coax connector can be used with
heat shrink tubing to seal the cable/connector.
3.0
OPERATION
It is necessary only to supply the sensor with a 2 to 20
mA constant current at +20 to +30 VDC through a
current-regulating diode or equivalent circuit.
Most PCB signal conditioners have an adjustable
current feature allowing a choice of input currents
from 2 to 20 mA.
In general, for best resolution, choose the lower
current ranges, and for driving long cables (to several
thousand feet) use the higher current, up to 20 mA
maximum. Line-impedance matching may be
necessary to produce flat-frequency response over
long (hundreds or thousands of feet) cables.
Switch power on and observe reading of bias
monitoring voltmeter on front panel of the signal
conditioner.
If indicator is in green section of indicator panel, the
IC amplifier is producing proper bias (+8 to 14
VDC), cable connections are normal and the system
is ready to operate.
If the needle moves to the red area of the fault
monitor meter, output is zero and a short is indicated.
Short could be located in amplifier, cable connectors,
or power unit.
If the pointer moves into the yellow area of the fault
monitor meter, an open circuit is indicated with full
power supply voltage. An open circuit could be the
result of a faulty amplifier, an open cable or open
connectors.
Allow the sensor to stabilize for about one minute. A
signal drift may occur when cable is connected to the
readout instrument.
This drift occurs during charging of the coupling
capacitor in the power unit. The signal will stabilize
in several minutes.
4.0
CALIBRATION
Series 138 are calibrated dynamically using a drop
weight tester. For best accuracy, use the calibration
certificate supplied. Factory recalibration is available
for a nominal charge.
5.0
POLARITY
This sensor series produces a positive-going output
voltage for increasing pressure input. See the
specification sheet for polarity of the sensor.
6.0
LOW-FREQUENCY RESPONSE
The low-frequency response of an ICP
®
system is
determined by:
l.) The discharge time constant of the sensors.
2.) If AC-coupled at the power unit, the
coupling time constant.
Содержание ICP 138A50
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