MANUAL: 55308
REV: A
ECO: 49582
3
INTRODUCTION
Congratulations on the purchase of a quality PCB
charge mode accelerometer. In order to ensure the
highest level of performance for this product, it is
imperative that you properly familiarize yourself with
the correct mounting and installation techniques
before attempting to operate this device. If, after
reading this manual, you have any additional
questions concerning this sensor or its application,
feel free to call an Application Engineer at 716-684-
0001 or the closest PCB representative.
1.1 Cables in Explosive Atmospheres
The cable lengths (Integral and Cable and Cable
Assemblies) INSTALLED IN AN EXPLOSIVE
ATMOSPHERE IS DEFINED IN THE ATEX, IECEx,
CSA, ETC. APPROVAL CERTIFICATES.
1.2 High Temperature Differential
Charge Output Sensor
Ceramic
or
Single
crystal
shear-structured
accelerometers offer high performance for precision
vibration
measurements
in
high-temperature
environments. The use of ceramic or single crystal
sensing crystals, operating in the shear mode,
reduces erroneous output due to base strain,
thermal transients, and transverse motion.
Charge mode accelerometers output a strong, high-
impedance charge signal directly from their
piezoelectric sensing element. They do not contain
built-in signal conditioning electronics; the signal is
conditioned externally by either a laboratory-style
charge amplifier or in-line charge converter prior to
being analyzed by a readout or recording device.
The absence of built-in electronics permits
operation to elevated temperatures of 500 °F (260
°C) for most models or up to 1300 °F (700 °C) for
special applications.
These accelerometers are ideal for structural
testing, machine monitoring, and vehicular shock,
high temperature machinery and power generation
turbine and other vibration measurement tasks
where high temperatures preclude the use of
accelerometers with built-in microelectronics.
Enclosed is a
Specification Sheet
, which lists the
complete performance characteristics of the
particular accelerometer.
2
CABLING
2.1 General Precautions and
Considerations
2.1.1 Proper Cable Type and Care
Ascertain that you have ordered the correct cable
type. Due to the high-impedance nature of the
output signal generated by charge mode
accelerometers, several important precautionary
measures must be followed. When using soft-line
cable always use special low-noise PCB Series
045 Low-Noise Cable (or equivalent) for
connecting to the input of the differential charge-
output accelerometers. For extremely high
temperature charge mode applications use mineral
insulated (MI) hard-line.
Care and attention to installation is essential, as
the reliability and accuracy of your system is no
better than that of the output cable. Cables and
connectors must be kept clean and dry to maintain
high insulation resistance and low frequency
responce. In the event that the insulation
resistance is compromised, inspect, clean, and
bake cables and connectors to restore insulation
resistance.
2.2 Softline Cable
Special high temperature low-noise, shielded cable
2-wire cable assembly is required with charge
mode sensors for applications up to 500°F to
connect the transducer to the charge amp. When
additional mechanical protection is required a
stainless steel armor can be used.
The shield acts as a Faraday cage to reduce
electrical noise from corrupting the signals, and
minimizes capacitively coupled noise from other
electrical sources.
Standard, two-wire, or coaxial cable, when flexed,
generates a charge between the conductors. This
is referred to as triboelectric noise and cannot be
distinguished from the sensor's charge output.
Low-noise cables have a special graphite lubricant
between the dielectric and the braided shield,
which minimizes the triboelectric effect and
improves the quality of the sensor's charge output
signal.
