PCB Piezotronics EX619A11, Инструкция по установке и эксплуатации

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5.5 Other Precautions
Always remember to keep the OPR-GND switch on the charge amplifier in the GND position while connecting
or disconnecting sensors, cable, or capacitor to the input connector. Stray or accumulated electrostatic
charges may build to the point that they may saturate or even damage the input circuitry of the charge
amplifier.
Operate the charge amplifier in the SHORT time constant while the sensor is subject to elevated or changing
temperatures.
If it is not necessary to procure data during the transition from room temperature to operating temperature,
place the OPR-GND switch in the GND position to keep spurious, thermally generated charges grounded.
It is prudent to momentarily switch to the GND position even during the measurement period to ensure that
excess charges do not accumulate at the input of the charge amplifier.
6 ACCELEROMETER CALIBRATION
Accelerometer calibration provides, with a definable degree of accuracy, the necessary link between the
physical quantity being measured and the electrical signal generated by the sensor. In addition, other useful
information concerning operational limits, physical parameters, electrical characteristics, or environmental
influences may also be determined. Without this link, analyzing data becomes a nearly impossible task. PCB
provides a calibration record that documents the exact characteristics of each sensor. (The type and amount
of data varies depending on the sensor type, contractual regulations, and other special requirements.)
Under normal operating conditions, piezoelectric sensors are extremely stable, and their calibrated
performance characteristics do not change over time. However, harsh environments or other unusual
conditions that cause the sensor to experience dynamic phenomena outside of its specified operating range
may temporarily or permanently affect the sensor. This change manifests itself in a variety of ways, including a
shift of the sensor resonance due to a cracked crystal, or a temporary loss of low-frequency measuring
capability due to a drop in insulation resistance.
For these reasons, it is recommended that a recalibration cycle be established for each accelerometer. This
schedule is unique and is based on a variety of factors, such as extent of use, environmental conditions,
accuracy requirements, trend information obtained from previous calibration records, contractual regulations,
frequency of “cross-checking” against other equipment, manufacturer recommendation, and any risk
associated with incorrect readings. International standards, such as ISO 10012-1, provide insight and
suggested methods for determining recalibration intervals for most measuring equipment. With the above
informa
tion in mind and under “normal” circumstances, PCB conservatively suggests a 12- to 24-month
recalibration cycle for most piezoelectric accelerometers.
Note: It is good measurement practice to verify the performance of each accelerometer with a Handheld
Shaker or other calibration device before and after each measurement. The PCB Model 394C06 Handheld
Shaker operates at a fixed frequency and known amplitude (1.0 g) to provide a quick check of sensor
sensitivity.
6.1.1 SENSOR RECALIBRATION
Accelerometer recal
ibration services are typically performed by PCB’s internal metrology laboratory. (Other
international and private laboratories are also available.) The PCB laboratory is certified to ISO 9001,
accredited by A2LA to ISO 17025, complies with ISO 10012-1 (and former MIL-STD-45662A), and uses
equipment directly traceable to N.I.S.T. This assures an accurate calibration of relevant specifications.
In addition, many companies choose to purchase the equipment necessary to perform the recalibration
procedure themselves. While this may result in both a savings of time and money, it has also been attributed