TE CONNECTIVITY SENSORS / WHITE PAPER
Predictive Maintenance with Vibration Sensors
PAGE 6
Long-Term Stability with Minimum Drift
The long-term stability of PE sensors is well known with over 30 years field installations. Piezo-electric crystals are
inherently stable and have shown to have excellent stability over time. The long-term drift parameters will also
depend on the crystal formulation used so an actual value would be difficult to present. Quartz has the best
long-term stability of any PE accelerometer but it is rarely used in condition monitoring applications due to limited
output and cost. PZT (Lead-Zirconate-Titanate) crystals are the most common crystals used in PE accelerometers
and are increasingly becoming the choice of crystal for most applications.
Variable Capacitance MEMS accelerometers also have wide specification limits for long-term drift depending on the
MEMS design structure. A bulk micromachined MEMS sensor will have the best long-term drift but will also be
significantly more expensive and typically only used in inertial applications. For condition monitoring, MEMS vendors
are offering a surface micromachined VC MEMS sensors which are much less expensive but the end user will sacrifice
measurement resolution and long-term stability. The MEMS structure of surface micromachined designs are less
stable than the bulk micromachined MEMS sensors.
Operating Temperature Range
The operating temperature range of PE and VC MEMS accelerometers are comparable and both are suitable
for the typical environment of condition monitoring applications which would span from -40°C to +125°C.
In certain extreme installations a higher temperature range sensor may be required where a charge mode
piezo-electric sensor would be the recommended choice. Charge mode PE accelerometers which do
not include the onboard charge converter circuit, can be used to temperatures exceeding+700°C.
Packaging Options and Ease of Installation
For embedded condition monitoring installations of smaller machinery, the size and mounting options can become an
important factor in choosing an accelerometer. Larger machinery typically used an externally TO-5 stud mounted
accelerometer but for machinery with smaller bearings and rotating shafts, it will be necessary to use an embedded
or miniature accelerometer.
Most VC MEMS accelerometers are offered in a SMT mount package which is ideal for high volume PCBA
assembly. The VC MEMS sensors are also offered in very small packages which enables more packaging options.
PE accelerometers come in various configurations. The SMT mount version are available, similar to VC MEMS,
but the size of the SMT package is typically larger than VC MEMS designs. PE accelerometers are also offered
in rugged TO-5 can packages with a stainless-steel housing. These designs allow for direct mounting to bearing
housings or embedded installations. The pictures below illustrate some options offered for PE sensors.
ACCELEROMETER MOUNTING OPTIONS
805M1 SINGLE AXIS
TO-5 ACCELEROMETER
820M1 SINGLE AXIS
SMT ACCELEROMETER
830M1 TRIAXIAL SMT
ACCELEROMETER
