This paper investigates torsional vibration and pulsating noise in a dry screw compressor. The compressor is designed at Gardner Denver (GD) and is oil-free and use for mounting on highway trucks in the dry bulk industry. They are driven using a power take-off (PTO) transmission and gear box on a truck. Torque peak fluctuations and noise measurements are made and their sources are investigated and reported in this work. To accurately predict the torsional response (frequency and relative angular deflection and torque amplitude), the Holzer method is used. It is shown that the first torsional frequency is manifested as sidebands in the gear train meshing frequencies and this can lead to noise. Using measurement data and curve fitting it is deduced that the pulsating noise is a result of amplitude modulation and not frequency modulation. Sensitivity analysis of the drive train identifies the weakest link in the drive train that limits the first torsional frequency to a low value. Tuning options like increasing the stiffness or inertia of the weakest element and shifting the input speed to the right are presented and discussed. Finally, the effect of higher-order torsional modes on inter-lobe clearance distribution of the rotors is investigated.

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Two simple, low-noise audio amplifiers and one low-noise preamplifier for use with intrinsic thermocouples were designed, built, and tested. The amplifiers and the preamplifier have different front end designs. One amplifier uses ultralow-noise operational amplifiers; the other amplifier uses a hybrid component. The preamplifier uses ultralow-noise discrete components. The amplifiers' equivalent noise inputs, at maximum gain, are 4.09 nV and 50 nV; the preamplifier's input is 4.05 nV. Their bandwidths are 15 600 Hz, 550 Hz, and 174 kHz, respectively. The amplifiers' equivalent noise inputs were measured from ~0 to 100 Hz, whereas the preamplifier's equivalent noise input was measured from ~0 to 174 kHz.