Extended Low Frequency (ELF) Accelerometer
Dytran Instruments new series 7705A accelerometers, are a new generation of sensors that combine two technologies, which until now have only been used separately.
Also referred to as the E.L.F. (Extended Low Frequency), the accelerometer contains both a piezoelectric and a variable capacitance element with respective filtering, whose outputs are electrically superimposed over one another.
The Dytran series 7705A feature a hybrid design, combining the most desirable features of piezoelectric sensors and variable capacitance accelerometers, which result in a flat frequency response from 0 to 10,000 Hz. The main principle of operation of the Dytran series 7705A is the instrumentation amplifier at the output buffer. The positive input is provided by the variable capacitance element and the negative input is provided by the piezoelectric element.
Both the variable capacitance element and the piezoelectric element are filtered appropriately (low pass single pole and high pass single pole, respectively) to provide the corner frequency of both filters precisely matched at approximately 30 Hz. Both signals are also out of phase as they enter the instrumentation buffer.
Accelerometers are powered through the power pin with a 5-28 VDC power and require 7-9 mA of current. Designed in a hermetically sealed, titanium housing, the series 7705A incorporates a 10-32 tapped mounting hole and a 4-pin M4.5 x 0.35 radial connector. Currently there are three models available, offering 20, 40 or 200g ranges, and typical applications would include flight testing, Health & Usage Monitoring Systems (HUMS), and ride quality.
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