is deflected by direct contact, the device acts as
a flexible "switch", and the generated output is
sufficient to trigger MOSFET or CMOS stages
directly. If the assembly is supported by its
contacts and left to vibrate "in free space" (with
the inertia of the clamped/free beam creating
bending stress), the device will behave as an
accelerometer or vibration sensor. Adding mass,
or altering the free length of the element by
clamping, can change the resonant frequency
and sensitivity of the sensor to suit specific
applications. Multi-axis response can be
achieved by positioning the mass off center. The
LDTM-028K is a vibration sensor where the
sensing element comprises a cantilever beam
loaded by an additional mass to offer high
sensitivity at low frequencies.
dimensions
FEATURES
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Solder Tab Connection
Both No Mass & With Mass Version
Withstands High Impact
Operating Temperature: 0ºC to 85ºC
Storage Temperature: -40ºC to 85
ºC
Higher Temperature Version up to 125
ºC
available on a Custom Basis
APPLICATIONS
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Vibration Sensing in Washing Machine
Low Power Wakeup Switch
Low Cost Vibration Sensing
Car Alarms
Body Movement
Security Systems
LDT0-028K Piezo Vibration Rev 1
www.meas-spec.com
1of 4
10/13/2008
LDT with Crimps Vibration Sensor/Switch
examples of properties
Four different experiments serve to illustrate the various properties of this simple but versatile component.
Experiment #1
LDT0 as Vibration Sensor
- with
the crimped contacts pushed through a
printed-circuit board, the LDT0 was
soldered carefully in place to anchor the
sensor. A charge amplifier was used to
detect the output signal as vibration from
a shaker table was applied (using a
charge amplifier allows a very long
measurement time constant and thus
allows the "open-circuit" voltage
response to be calculated). Small
masses (approximately 0.26g
increments) were then added to the tip of
the sensor, and the measurement
repeated. Results are shown in Table 1
and the overlaid plots in Fig. 1. Without
adding mass, the LDT0 shows a
resonance around 180 Hz. Adding mass
to the tip reduces the resonance
frequency and increases "baseline"
sensitivity.
TABLE 1: LDT0 as Vibration Sensor (see Fig 1)
Added Mass
0
1
2
3
Baseline
Sensitivity
50 mV/g
200 mV/g
400 mV/g
800 mV/g
Sensitivity at
Resonance
1.4 V/g
4 V/g
8 V/g
16 V/g
Resonant
Frequency
180 Hz
90 Hz
60 Hz
40 Hz
+3 Db
Frequency
90 Hz
45 Hz
30 Hz
20 Hz
Experiment #2
LDT0 as Flexible Switch
- using a charge
amplifier to obtain "open-circuit" voltage sensitivity,
the output was measured for controlled tip
deflections applied to the sensor (supported by its
crimped contacts as described above). 2 mm
deflection was sufficient to generate about 7 V.
Voltages above 70V could be generated by
bending the tip of the sensor through 90° (see
Table 2, Fig. 2).
LDT0-028K Piezo Vibration Rev 1
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2 of 4
10/13/2008
LDT with Crimps Vibration Sensor/Switch
examples of Properties (continued)
TABLE 2: LDT0 as Flexible Switch (see Fig 2)
Tip Deflection
2 mm
5 mm
10 mm
max (90Ε)
Charge Output
3.4 nC
7.2 nC
10 - 12 nC
> 30 nC
o/c Voltage Output
7V
15 V
20 - 25 V
> 70 V
Experiment #3
LDT0 Electrical Frequency Response
-
when the source capacitance of around 480 pF is
connected to a resistive input load, a high-pass
filter characteristic results. Using an electronic
noise source to generate broad-band signals, the
effect of various load resistances was measured
and the -3 dB point of the R-C filter determined
(see Table 3, Fig. 3).
TABLE 3: LDT0 Electrical Frequency Response
(see Fig 3)
(480 pF source capacitance)
Load Resistance
1 Megohm
10 Megohm
100 Megohm
-3 db Frequency
330 Hz
33 Hz
3.3 Hz
LDT0-028K Piezo Vibration Rev 1
www.meas-spec.com
3 of 4
10/13/2008
LDT with Crimps Vibration Sensor/Switch
Experiment #4
LDT0 Clamped at Different Lengths
-
using simple clamping fixture, the vibration
sensitivity was measured (as in (1) above) as
the clamp was moved to allow different "free"
lengths to vibrate. The sensor may be "tuned"
to suit specific frequency response
requirements (see Table 4, Fig. 4).
TABLE 4: LDT0 Clamped at Different Lengths (See Fig. 4)
Length Beyond
Clamp
20 mm (no clamp)
16 mm
11 mm
7 mm
Resonant
Frequency
180 Hz
250 Hz
500 Hz
1000 Hz
Settling Time
(5 cyc)
28 msec
20 msec
10 msec
5 msec
The information in this sheet has been carefully reviewed and is believed to be accurate; however, no responsibility is assumed for inaccuracies. Furthermore, this information does not
convey to the purchaser of such devices any license under the patent rights to the manufacturer. Measurement Specialties, Inc. reserves the right to make changes without further notice
to any product herein. Measurement Specialties, Inc. makes no warranty, representation or guarantee regarding the suitability of its product for any particular purpose, nor does
Measurement Specialties, Inc. assume any liability arising out of the application or use of any product or circuit and specifically disclaims any and all liability, including without limitation
consequential or incidental damages. Typical parameters can and do vary in different applications. All operating parameters must be validated for each customer application by
customer’s technical experts. Measurement Specialties, Inc. does not convey any license under its patent rights nor the rights of others.
