4
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 Series 3089A
is 0.3 TO 0.6 Sec. yielding a lower -3db frequency of
0.32 Hz, from equation 1.
As rule of thumb, the lower -5% frequency is
three times the -3db frequency or 3 x .16 = 0.64 Hz.
INSTALLATION
(Refer to Outline/Installation drawing 127-
3089A) To install Model 3089A, is necessary to
prepare (or find) a flat mounting area of approximately
1/8 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.
Connect the integral cable to the power unit in
accordance with drawing 127-3089A..
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 to two inches 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.
If the installation is made with a Dytran IEPE
power unit, observe the monitor voltmeter located at
the front panel of each of the power units. If the meter
reads in the mid-scale region, (labeled "Normal"), this
tells you that the cables, accelerometer and power unit
are functioning normally and you should be able to
proceed with the measurement.
Check for shorts in the cables and connectors
if the meter reads in the "Short" region. Check for
open cables or connections if the meter reads in the
"Open" area. In this manner, the meter becomes a
trouble-shooting tool for the measurement system.
HIGH FREQUENCY RESPONSE
All piezoelectric accelerometers are basically
rigid spring mass systems, i.e., second order systems
with essentially zero damping. As a result, these
instruments will exhibit a rising characteristic as the
resonance is approached. A filter incorporated into
Model 3089A compensates for this rise.
The frequency at which the sensitivity may
increases or decrease by 10% is approximately 10000
Hz, the frequency to which the 3089A is calibrated.
CAUTIONS
1) Do not store or use the 3089A above
250°F. To do so can damage the IC amplifier.
2) Do not allow wires to vibrate unrestrained.
This may eventually destroy the wires and could lead
to system inaccuracies.
3) Avoid dropping or striking the
accelerometer, especially against rigid materials such
as concrete and metals. While Model 3089A is
protected against shock induced overloads, the very
high overloads induced by dropping can do permanent
damage to the MOSFET amplifier or to the mechanical
structure of the accelerometer. This type of damage is
not covered by the warranty.
MAINTENANCE AND REPAIR
The welded construction of the Model 3089A
precludes field repair.
Should the mounting surface become
distorted, nicked and otherwise distressed, it can be
redressed by CAREFULLY wiping on a new sheet of
400 grit emery paper on top of a clean surface plate.
We stress "carefully" because if not done properly, this
procedure can do more harm than good. Press the
surface firmly against the paper and draw directly
