acts as a cantilever-beam accelerometer. When the beam is mounted
horizontally, acceleration in the vertical plane creates bending in the beam, due to the inertia of the
mass at the tip of the beam. Strain in the beam creates a piezoelectric response, which may be
detected as a charge or voltage output across the electrodes of the sensor.
The sensor may be used to detect either continuous or impulsive vibration or impacts. For
excitation frequencies below the resonant frequency of the sensor, the device produces a linear
output governed by the “baseline” sensitivity quoted above. The sensitivity at resonance is
significantly higher. Impacts containing high-frequency components will excite the resonance
frequency, as shown in the plot above (response of the MiniSense 100 to a single half-sine impulse
at 100 Hz, of amplitude 0.9 g). The ability of the sensor to detect low frequency motion is strongly
influenced by the external electrical circuit, as described below (see “Electrical Description”).
electrical description
The MiniSense 100
behaves electrically as an “active” capacitor: it may be modelled as a
perfect voltage source (voltage proportional to applied acceleration) in series with the quoted
device capacitance. Any external input or load resistance will form a high-pass filter, with a roll-off
frequency as tabulated above, or calculated from the formula f(c) = 1/(2πRC). The impedance of
the sensor is approximately 650 M ohm at 1 Hz. The active sensor element is electrically shielded,
although care should be taken in the PCB design to keep unshielded traces as short as possible.
Lower Limiting Frequency (-3 dB roll-off)
External R (Ω)
LLF (Hz)
Desired LLF (Hz)
Required R (Ω)
10 M
65
10
65 M
100 M
6.5
1
650 M
1G
0.65
0.1
6.5 G
Electrical Impedance
1E+10
Impedance (ohms)
1E+09
1E+08
1E+07
1E+06
0.1
Magnitude (dB)
10
0
-10
-20
-30
-40
0.1
Low frequency roll-off
1G
100 M
1
10
Frequency (Hz)
100
1
Frequency (Hz)
10
MiniSense 100 Vibration Sensor Rev 1
www.meas-spec.com
3 of 4
05/12/2009
MiniSense 100 Vibration Sensor
off-axis sensitivity
The sensitivity of the Minisense 100 follows a cosine law, when rotated horizontally around its axis,
or vertically around its mid-point. At 90 degrees rotation in either plane, both baseline sensitivity and
sensitivity at resonance are at a minimum. In theory, sensitivity should be zero in this condition. It is
likely that some sensitivity around the resonance frequency will still be observed – but this may be
unpredictable and is likely to be at least -16 dB with reference to the on-axis response. Note that the
sensitivity at 30 degrees rotation is -1.25 dB (87% of on-axis response), at 60 degrees, it falls to -6
dB (50%).
The plots below show the change in sensitivity observed for either:
1) Rotation about major axis of sensing element, or
2) Rotation about mid-point of sensing element.
Off-axis Response
Sensitivity (dB re nominal)
0
-10
-20
-30
-40
-50
0
30
60
90
120
Rotation angle (deg)
150
180
axial
theory
vertical
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.
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