Isotron® IEPE-type voltage mode accelerometers features an integral electronic impedance converter eliminating the need for an external charge amplifier. An IEPE accelerometer has a fixed amplitude range. A typical charge-mode accelerometer will have an operating temperature range of –55°C to 288°C. Special-purpose accelerometers are available for extreme environments as low as –269°C to as high as 760°C. Special radiation-hardened charge-mode accelerometers are available for use in a nuclear environment. For low-level shock measurements, a general-purpose accelerometer will usually do the job. The accelerometer will need a linear range of at least 500 g and a shock survivability rating of 500 g. An IEPE type is usually preferred because they are less susceptible to producing erroneous. For far-field shock measurements, a special shear-mode accelerometer with a built-in electronic filter is often adequate. These are usually lightweight IEPE types with solder connections. The electronic filter attenuates the resonance frequency of the accelerometer to prevent overloading of the DA equipment.
IEPE accelerometers can drive long cables with minimal distortion and noise pick-up. Isotron® electronics are compatible with industry standard IEPE current sources built into most industry standard data acquisition systems.
The sensing element of Piezoelectric accelerometers is a piezoelectric material that can be either natural quartz crystals or man-made polycrystalline ceramics. The basic principle of Piezoelectric Effect is an inherent or induced property of these crystals. As the crystal undergoes stress due to applied force during acceleration, negative and positive ions will accumulate onto the opposed surfaces of the crystal.
The amount of accumulated charge is directly proportional to the applied force when the applied acceleration can be calculated according to Newtons’ law of motion F=mA.
A proof mass is bonded to the crystal and an electrical charge is generated when a force is imposed upon the crystal during acceleration and this output is relative to the applied force. The piezoelectric element is connected to the Sensor output via a pair of electrodes.
The sensing element is housed in a suitable sensor body to withstand the environmental conditions of the particular application. One side of the piezoelectric material is connected to a rigid post at the sensor base. A seismic mass is attached to the other side. Due to the piezoelectric effect a charge output proportional to the applied force is generated and the charge output signal is proportional to the acceleration of the mass. Over a wide frequency range both sensor base and seismic mass have the same acceleration magnitude so that the sensor measures the acceleration of the testing object.
Piezoelectric accelerometers cannot measure constant acceleration because they are inherently AC coupled, however, they are typically the most versatile and economic choice for measuring fast transient and periodic acceleration wherever shock or vibration is of interests.
Meggitt piezoelectric accelerometers are charge mode accelerometers that requires use of an external charge amplifier, allowing for reliable operation over wider temperature and amplitude ranges. Piezoelectric accelerometers are ideal choices for acceleration, shock and vibration measurements, due to their wide frequency range, easy installation, and multiple options in shapes, weights, size, and sensitivities. Special purpose piezoelectric accelerometers are also available for flight test, extreme low- and high-temperatures and radiation environments.
Meggit Endevco® has successfully designed and manufactured shock accelerometers with built-in mechanical filter. This piezoelectric accelerometer features both an input mechanical filter and an electronic low-pass filter for sensor isolation and maximum bandwidth. Based on a well-established piezoelectric shock sensor, this accelerometer features a captive mechanical filter arrangement. Compared to the model of an external filter, this unique design provides mechanical isolation to the sensor (m) from all sides. High frequency energy, in the sensitive and transverse directions, is filtered by the isolation material, leaving the sensing element with only the pass-band signals. In addition, the transducer’s external housing keeps the entire assembly together in case of excessive shock input.
- Extremely wide dynamic range, low output noise
- Suitable for shock and vibration measurement
- Excellent linearity over dynamic range
- Acceleration signal can be integrated to provide velocity and displacement
- Wide frequency range
- Compact, non-contact design
- Highly sensitive
- Self-generating – no external power required
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