5
Referring to Figure 1, the feedback resistor Rf
in conjunction with shunt capacitance Cf, forms a first
order high-pass filter which sets the low frequency
response of the accelerometer in accordance with the
following equation:
.16
f-3db = ------------------ (eq.1)
RC
where:
f-3db = lower -3db frequency (Hz)
R = resistance value R (Ohms)
C = total shunt capacitance C (Farads)
RC = discharge time constant TC (Seconds)
Equation 1 above, defines the frequency at
which the accelerometer sensitivity will be 3db down
when compared to the reference sensitivity measured
at 100 Hz.
The discharge time constant for all Models is
0.5 seconds, yielding a lower -3db frequency of 0.3
Hz, from equation 1.
As rule of thumb, the lower -5% frequency is
three times the -3db frequency or 1 Hz.
INSTALLATION
(Refer to Outline/Installation drawing 127-
3049E) To install Model 3049E series accelerometers,
it is necessary to prepare (or find) a flat mounting area
of approximately 0.5 inch diameter. Ideally, the
mounting surface should be flat to .001 in. TIR. The
flat mounting surface ensures intimate contact
between accelerometer base and mounting surface for
best high frequency transmissibility, thus accuracy.
To install the adhesive mounted 3049E1 or
3049E3, clean the mounting surfaces with solvent if
necessary to remove all traces of oils and other
impurities including burrs or any matter which could
preclude intimate contact between mating surfaces.
Apply a light coating of cynoacrylate adhesive
(or other type of suitable adhesive) to either mounting
surface, position the accelerometer in the desired
cable orientation and press the accelerometer firmly
onto the mounting surface and hold for several
seconds.
To install the stud mounted 3049E or 3049E2
accelerometers, drill and tap a 10-32 mounting hole
with enough thread depth to accommodate the integral
stud. Clean the area to remove all traces of machining
chips, burrs, etc. Spread a light coating of silicone
grease, or other lubricant, on either of the mating
surfaces and thread the accelerometer/stud
combination into the tapped hole by hand, until the
accelerometer base seats against the mounting
surface. Check to see that the mating surfaces are
meeting properly, i.e., that they are meeting flush and
that there is not an angle formed between the two
surfaces indicating that they are not co-planar. If this
condition is observed, torquing the accelerometer
down will strain the base causing possible poor
frequency response and even erroneous reference
sensitivity. Inspect the perpendicularity of the tapped
hole. If the hand tight meeting between the two
surfaces is satisfactory, torque the 3049E or 3049E2
accelerometer to the mating surface with 15 to 20 lb-
inch of torque, preferably measuring the torque with a
torque wrench torquing on the hex surface only.
Proper torque will ensure the best high
frequency performance from the instrument as well as
repeatability of sensitivity when mounting and
remounting. Excessive torque could damage the
ground isolation base.
Connect the cable (typically Models 6010AXX
or 6011AXX) to the accelerometer snugging up the
threaded lock ring tightly by hand.
NOTE:
Do not use a pliers or vise grips on the
knurled lock ring. This could damage the
connector of the 3049E Series and/or the
cable connector.
To avoid stressing the cables which could lead
to early failure, especially under larger excursions of
the test object, it is good practice to tie the cable down
to a fixed surface near the mounting area at a point
approximately one inch from the accelerometer.
If there is excessive motion between the
accelerometer and the nearest tie point, allow a strain
loop of cable to let relative motion occur without
stressing the cable.
Содержание 3049E Series
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