A Rotor Mounted Data Acquisition System

Abstract

Research and development testing of rotating machinery has always been limited in the number of measurements because slip ring assemblies have a limited number of conductors available for signals to pass from rotating to non rotating sections. Such testing has been impeded because relatively long wires are needed to pass low level analog signals. Because of the line resistance and capacitance and their susceptibility to stray fields, much effort is dedicated to the investigation of line loss and protection from EMI. The solution in recent years is to use current drivers or to digitize these signals as close to the transducers as possible or to employ painstaking procedures for correction of data in software. At NASA's Ames Research Center, recent research requirements have approached the limit of practical slip ring assemblies. Line lengths needed for wind tunnel tests can be 300 feet. The solution provides for an increase of channels by an order of magnitude, improved data quality, elimination of all efforts to correct data for line loss, a simple and quick installation, real time monitoring with extensive graphics capability and a manageable method for data storage. The system is called the Rotor Mounted Data Acquisition System (RMDAS) and has been acquired through a U.S. Government contract with Aydin Vector Division in Newtown, Pennsylvania. This is a high density, high speed, signal conditioning and multiplexing system which mounts on the rotating hub of full scale rotorcraft and transmits PCM, NRZ-L bit streams to a fixed end data system. The system is 512 channel capable at 20 KSPS/channel when configured for maximum channel capacity. The channel sampling capability for a single channel or for a group of channels is 177 KSPS. The individual channel sample rate can be changed by reprogramming the number of channels per segment. Various other configurations exist but always with an aggregate rate of 17 Mbps, including overhead words, per serial bit stream. This system utilizes 12-bit digitizers to provide high accuracy over the operating temperature range.