Tham khảo tài liệu 'harris' shock and vibration handbook part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CALIBRATION OF PICKUPS in order to reduce the effect of measurement noise curve fitting may be used to estimate the step value. Equation shows how the sensitivity of the reference force transducer is related to the other parameters of the system. Sr SrfM - M gM g where Sr acceleration sensitivity of the reference force transducer in mV ms 2 Srf force sensitivity of the reference force transducer in mV N M total mass on the force transducer in kg eg output of the force transducer in mV g acceleration of free fall due to gravity in ms 2 Note that eg is numerically equal to Sr expressed in mV g. Step 2. Measure the voltage ratio et er. Remove the reference force transducer reference mass and the pickup being calibrated from the drop-test fixture then mount them on the vibration exciter as shown in Fig. . By measuring the transfer function et er . the ratio of the voltage output of the signal conditioner from the test pickup to the voltage output of the signal conditioner from the reference force transducer shown in Fig. the frequency response of the test pickup can be FIGURE System configuration for frequency response calibration by measuring acceleration-to-force ratio. measured over to 100 000 Hz depending upon frequency range of the vibration exciter and signal-to-noise ratio of the system. For use at low frequencies the discharge time constant of the reference force transducer should be ten times greater than that of the test pickup. Step 3. Calculate the sensitivity St of the test pickup. If the reference force transducer and the test pickup are linear the acceleration sensitivity of the test pickup St expressed in the same units as Sr can be calculated from Eq. . If either velocity or displacement sensitivity of the test pickup is required it can be obtained by dividing the acceleration sensitivity by 2 f or 2 f 2 respectively. CENTRIFUGE CALIBRATOR A centrifuge provides a convenient means of applying constant acceleration
