Dytran 3049D, 3049D1 Operating Manual

OG3049D.DOC
6/9/06

3049D

Dynamic Transducers and Systems

21592 Marilla St. • Chatsworth, CA 91311 • Phone [phone]
www.dytran.com • e-mail: [e-mail]

OPERATING GUIDE

MODEL 3049D, 3049D1

HIGH SENSITIVITY MINIATURE LOW PROFILE

CHARGE MODE ACCELEROMETER,

HERMETICALLY SEALED, GROUND ISOLATED

NOTE:

Model 3049D features very low mass and hermetically sealed
construction. Hermeticity is obtained by all-welded construction
and glass-to-metal sealed connector. Electrical connection is via
a top mounted 10-32 coaxial connector. 3049D has integral 10­32 stud mount, 3049D1 is adhesive mount. Performance
characteristics are identical.

This guide contains:

3049D1

1) Operating instructions, Model 3049D.

2) Specifications, Model 3049D

3) Outline/installation drawing, 127-3049D

4) General Guide to Charge Mode Accelerometers.

SPECIFICATIONS MODEL 3049D, 3049D1
SPECIFICATION VALUE UNITS
PHYSICAL

WEIGHT, 3049D 3.2 grams
WEIGHT, 3049D1 3.0 grams
SIZE, HEX X HEIGHT .39 (10mm) X .54 inches
MOUNTING, 3049D 10-32 integral stud
MOUNTING, 3049D1 adhesive mount
CONNECTOR, TOP MOUNTED 10-32 coaxial
MATERIAL, HOUSING AND CONNECTOR Titanium alloy

PERFORMANCE

SENSITIVITY, NOM.[1] 5.8 pC/g
FREQUENCY RANGE, ± 5% to 8k Hz
RESONANT FREQUENCY, NOM. 40 kHz
LINEARITY [2] ± 1% % F.S.
TRANSVERSE SENSITIVITY, MAX. 5 %
STRAIN SENSITIVITY .03 g/µε @250µε

ENVIRONMENTAL

MAXIMUM VIBRATION/SHOCK 1000/2000 ±g pk
TEMPERATURE RANGE -100 to +350 °F
SEAL, HERMETIC glass-to-metal and TIG welded
COEFFICIENT OF THERMAL SENSITIVITY .06 %/°F

ELECTRICAL

CAPACITANCE, NOM. 650 pF
OUTPUT SIGNAL POLARITY positive
FOR ACCELERATION TOWARD TOP
CASE GROUNDING signal ground is isolated from
mounting surface

[1] Measured at 100 Hz, 1 g rms per ISA RP 37.2.
[2] Measured using zero-based best straight-line method, % of F.S. or any lesser range.

2

OPERATING INSTRUCTIONS, MODEL 3049D

MINIATURE CHARGE MODE ACCELEROMETER

INTRODUCTION

The Dytran Model 3049D accelerometer is a
miniature low-profile piezoceramic shear, charge
mode, hermetically sealed instrument, designed to
measure high frequency shock and vibration at high
temperatures. Its small size and mass (only 3 grams)
makes it ideal for measurement of very small test
objects where space is at a premium. Model 3049D
has an integral 10-32 mounting stud, while Model
3049D1 is designed for adhesive mounting.

The self-generating ring shear mode seismic
element, utilizing piezoceramic crystalline material,
converts input acceleration (vibration and shock) to an
analogous charge signal. This signal is connected to a
miniature hermetically sealed 10-32 coaxial connector
mounted vertical to the centerline of the instrument.

Simple in-line charge amplifiers such as
Dytran’s Model series 4705A or 4751B may be used to
convert the signal from the 3049D to IEPE operation.
Laboratory charge amplifiers may also be used to
amplify and/or standardize the signal.

Model 3049D features hermetic sealed
construction for normal operation in moist and dirty
environments. The nominal sensitivity of Model 3049D
is 5.8 pC/g.

DESCRIPTION

Model 3049D is a low-profile instrument with a
10 mm hex housing and a 10-32 electrical connector
mounted vertically atop the housing on the center line
of the unit.

The seismic mass, made from a very dense
tungsten alloy, is bonded around the piezoceramic
shear mode crystal. This means there is insignificant
relative motion between mass, crystals and base
keeping the non- linearity low and the natural
frequency high.

The force from acceleration (vibration or
shock) acting upon the mounting base, is transferred
to the seismic mass through the crystal, stressing the
crystal in shear mode and producing an electrostatic

charge proportional to the input acceleration. This
signal is connected to the axial 10-32 coaxial
connector, integral to the housing.

SIGNAL POLARITY

The output polarity of Model 3049D is positive­going in response to acceleration toward the top of the
instrument. Bear in mind however that Dytran charge
amplifiers are inverting amplifiers and the resultant
signal will be inverted, i.e., will be negative-going with
acceleration toward the top of the instrument, if used
with such an amplifier.

INSTALLATION

(Refer to Outline/Installation drawing 127­3049D)

To install Model 3049D or Model 3049D1
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 3049D1,
clean the mounting surface 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.

NOTE: It is important to keep the bond line as thin

as possible, consistent with a secure installation, for
best high frequency response.

To install the stud mounted 3049D, drill and
tap a 10-32 mounting hole with enough thread depth

3

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 3049D to the mating surface with 15 to 20
lb-inches 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 6013AXX
(10-32 to 10-32) or 6019AXX (10-32 to BNC) to the
accelerometer snugging up the threaded lock ring
tightly by hand.

NOTE: Since this is a charge mode instrument, only

low-noise treated coaxial cable must be used to
connect this instrument to its charge amplifier. Both
cables that we recommend are low-noise treated.

NOTE: Do not use pliers or vise grips on the knurled

lock ring. This could damage the connector of the
3049D 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.

Connect the other end of the cable to the input
of the charge amplifier and switch the power on.

THE CHARGE AMPLIFIER

Model 3049D is a piezoceramic instrument
and as such, it is usually used with an AC-coupled
charge amplifier rather than a direct-coupled
electrostatic charge amplifier such as those designed
for use with quartz sensors. Because of the reduced
insulation resistance of piezoceramic materials, direct
coupled charge amplifiers may drift when the 3049D is
connected to the input unless there is a provision for
AC coupling at the input or reduced time constant
such as featured in Dytran laboratory charge
amplifiers.

For this reason, it is best to use one of the in­line series of amplifiers such as the 4705A, 4751B or a
true vibration type laboratory charge amplifier which is
AC coupled or has provision for piezoceramic sensor
inputs. These amplifiers convert to 3049D to 2-wire
IEPE operation. Again, remember that all of Dytran’s
charge amplifiers are inverting amplifiers which will
result in a reversal of the signal polarity of the 3149C.

HIGH FREQUENCY RESPONSE

All piezoelectric accelerometers are basically
rigid spring mass systems, i.e., second order
mechanical systems with essentially zero damping. As
a result, these instruments will exhibit a rising
characteristic as the resonant frequency is
approached. Some charge amplifier feature low-pass
filtering to compensate for this characteristic.

The upper frequency at which the sensitivity
may increase or decrease by 15% is approximately
10,000 Hz, the frequency to which the 3049D is
calibrated. The accelerometer is usable above this
frequency but to use it above 10,000 Hz, it must be
calibrated at the specific frequencies of intended use
because sensitivity deviations will increase drastically
as you exceed this high frequency calibration limit.
Consult the factory for special calibrations required
above 10,000 Hz.

4

CAUTIONS

1) Do not store or use the 3049D above
400°F. This could compromise the integrity of the
piezoelectric crystals and result in modified sensitivity.

2) Do not allow cables to vibrate unrestrained.
This will eventually destroy the cable and could lead to
system inaccuracies.

3) Avoid dropping or striking the
accelerometer, especially against rigid materials such
as concrete and metals. This type of damage is not
covered by the warranty.

MAINTENANCE AND REPAIR

The welded construction of the Model 3049D
precludes field repair.

Should the mounting surface become
distorted, nicked and otherwise distressed, so as to
make operation suspect, return the instrument to the
factory for repair. We can re-lap the mounting surface
to restore the flatness to original specifications.

Should the electrical connector become
contaminated with moisture, oil, grease, etc., the entire
instrument may be immersed in degreasing solvents to
remove the contaminants. After degreasing, place the
instrument in a +200°F to +300°F oven for one hour to
remove all traces of the solvent.

Should a problem be encountered with the
operation of the instrument, contact the factory for
trouble shooting advice. Often our service engineers
may point out something which may have been
overlooked and which may save the expense and time
of returning the 3049D to the factory.

If the instrument must be returned, the service
department will issue you a Returned Materials
Authorization (RMA) number to aid in tracking the
repair through the system. Do not send the instrument
back without first obtaining an RMA number. At this
time you will be advised of the preferred shipping
method.

A short note describing the problem, included
with the returned instrument, will aid in trouble
shooting at the factory and will be appreciated.

We will not proceed with a non-warranty repair
without first calling to notify you of the expected
charges. There is no charge for evaluation of the unit.

5