DJB Instruments

Instrumentation - CA/04/V

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Transducer Interface Converts • Acceleration to Velocity • Input Range 1/100pC/g O/Ps 100mV/g & 1V/mm.sec. (max)

1/100pC/g normalising charge amplifier input section precedes noise limiting 10Hz 4 pole high pass filter and single integrator. Integrator converts periodic acceleration above the filter corner frequency to velocity. Integrator gain is controlled over 50dB dynamic range by 6 position switch.

Charge Amplifier

Provides wideband 100mV/g acceleration proportional output when normalised, transducer sensitivity range 1/100pC/g, by means of ten-turn dial and x1, x10 multiplier.
Output is independent of transducer lead capacitance. CAL input terminal allows injection of test signal, 1mV ≡ 1pC.

High Pass Filter

Noise level alter integration, hence the realisable signal threshold, is proportional to fmin -n, where fmin is the high pass filter corner frequency and n is a function of the noise type, being 1/2 for that predominating in FET input stage charge amplifiers at low frequencies (<100Hz).

Spurious signals also emanate from the transducer and its cable resultant upon environmental factors, and these may be considered as introducing additional f-n noise components, subject to high pass filter constraint. HP filter corner frequency is thus the determinant of threshold velocity level.

Integrator/Range Amplifier

Converts acceleration input to velocity output levels of 1-316mm/sec/volt in six 10dB increments. Integrator bandwidth is controlled by the HP filter integrator frequency response constraints and ultimately background noise. Peak limiting input of around 120g pk. equates to a velocity-frequency product (v x f) of 2 x 105mm/sec2 , thus absolute constraints may be readily calculated.