8
4 POWERING
4.1 Installation
Before connecting the low-noise cable from the accelerometer to the charge amplifier, be sure to ground both
the charge amplifier and the cable. This ensures that an excessive static charge that may have accumulated
across the accelerometer or cable is harmlessly discharged. Failure to observe this precaution can result in
the destruction of the input FET of certain amplifiers.
Connect the transducer to the input of a PCB differential 422 series or equivalent charge amp using low noise
cable.
Note:
For optimum noise performance, the cable length between the sensor and the 422 should be
minimized.
Connect the output of the 422 to any ICP ® signal conditioner using standard cable. Finally, the output of the
signal conditioner may then be connected to an oscilloscope or other monitoring device. This output will be an
AC signal (see
specification
for actual frequency response) with a DC bias. Many PCB signal conditioners
remove the bias via an AC coupling circuit.
4.2 Operation
Once each element is connected, allow a few minutes for the system to thermally stabilize. Place the switch on
the charge amplifier in the OPERATE position and proceed with the measurement.
It is often convenient to normalize the accelerometer and charge amplifier system to a precise sensitivity, such
as 10.0 or 100.0 mV/g for ease of data analysis. This is accomplished with most PCB laboratory charge
amplifiers and some miniature in-line units as well.
For fixed sensitivity in-line charge converters, such as the PCB Series 422, the system sensitivity (mV/g) is
determined as the product of the charge amplifier sensitivity (mV/pC) and the charge sensitivity of the
accelerometer (pC/g).
Note:
When using charge-amplified systems, the noise floor of the system is dependent on the input
capacitance to the charge amplifier. Since the cable adds to the capacitance and to minimize the noise
threshold, keep the cable length between the accelerometer and the charge amplifier to a minimum. Cable
length does not affect the system sensitivity of charge-amplified systems.
Since charge amplifier operation varies, please contact the respective signal conditioner manufacturer or check
the product manual for additional information.
Summary of Contents for EX619A11
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