Choosing the optimum mounting arrangement will significantly
improve the accuracy.
For best performance, particularly
at high frequencies, the accelerometer base and the test object should
have clean, flat, smooth, unscratched and burr-free surfaces.
A scratched accelerometer base can be applied to a lapping
plate for restoration of flatness. If lapping is not possible, other
machining processes such as grinding, spot facing, milling, turning,
etc., can produce acceptably flat mounting surfaces.
It is also important to provide a stiff mechanical connection
between the sensor and the source of vibration. Sheet metal or plastic
parts and other thin and flexible components are unsuited for
Figure 15: Typical reasons of coupling errors
Errors due to unwanted sensor vibrations can be reduced by symmetric
mounting. The weight of the sensor including all mounting components
should be low compared to the weight of the test object. As a
rule the sensor should not weigh more than 10 % of the test object.
Misalignment of the sensor axis and the measuring directions should be
kept as low as possible, particularly if transverse vibration of high
magnitude occurs. When using screw mounting, make sure that the screw
is not longer than the threaded hole. The must be no gap under the
The following mounting methods are recommended for accelerometers:
Figure 16: Mounting methods for accelerometers
Figure 17 compares the typical high frequency performance of
some mounting methods as a result of added mass and reduced mounting
a: probe model 001; b: insulating flange; c: magnetic clamp; d:
adhesive; e: stud bolt
Figure 17: Resonance frequencies of different mounting methods
Metra accelerometers may have the mounting thread sizes: M3,
M5, M8 and M10.
Many transducers are available with an accessory kit (ordering
option "/01") containing all suitable mounting parts.
The following table shows the available mounting accessories from Metra:
022 (M3 to M5)
044 (M5 to M8)
045 (M5 to 10-32)
046 (M5 to ¼"-28)
- For best performance.
- For permanent mounting. Mounting pads
- Tapped hole in test object required.
- A thin layer of silicon grease between mating
surfaces aids in the fidelity of vibration transmission.
- Recommended torque: 1 Nm.
- Make sure that the mounting stud is not too long
resulting in a gap between sensor and test object
106 (2 x M3)
006 (2 x M5)
206 (2 x M8)
- Avoid ground loops.
- Limited performance at high frequencies.
- Model 006 not suited for temperatures above 100 °C.
129 (M3, small)
329 (M3, large
- Adhesive attachment using cyanoacrylate, epoxy glue
or dental cement.
- For applications where drilling is not allowed or
- Models 029, 129 and 329 provide isolation against
108 (M3, small)
308 (M3, large)
408 (M4 tap)
008 (M5, large))
708 (M5, small)
208 (M8, small)
508 (M8, large)
- For rapid mounting with limited high frequency
- Ferromagnetic object with smooth and flat surface
- If not available, weld or epoxy a steel mounting pad
to the test surface.
- Important: Don’t drop the magnet onto the test object
to protect the sensor from shock acceleration. Gently slide the sensor
with the magnet to the place.
- Do not use magnets for seismic accelerometers (risk
- Use small magnets for small sensors.
|Triaxial mounting cubes
- For triaxial measurements with three uniaxial
- For the attachment of accelerometers with M3 thread
on curved surfaces
- For estimating and trending measurements above 5 Hz
and below 1000 Hz.
- Attach the accelerometer via the M5 thread.
- Press onto the test object perpendicularly.
- Drilling a countersink will increase repeatability.
|Adhesive wax / bee wax
- For quick mounting of light sensors at room
temperature and low acceleration.
- Soften the wax with the fingers. Apply thinly onto
the test surface. Press sensor onto it the wax.
- Avoid introduction of force via the cable into the
- To be screwed onto the test object together with the
Proceed to chapter Accelerometer