Software Control of a High Speed, Modular Signal Conditioner and PCM Encoder System

Abstract

The increasing channel capacity and complexity of flight test data acquisition systems have made the problems of physical distribution of the system throughout the test aircraft and determining the system configuration a very time consuming and costly portion of the flight test process. These problems are complicated because the new aircraft, irrespective of size, have more complex systems and less space is available to install the classical data acquisition and recording system. The solution to the installation problem is to have a highly modular system that can be configured as either a distributed system with remote multiplexing and a PCM Central Controller, or with the same multiplexed hardware as a stand-alone or master/slave system where the functional power and complexity afforded by the PCM Central Controller are not required. The solution to the configuration control problem is to have a 'hands-off' data acquisition system with all variables of the signal conditioning and PCM encoding functions under software control. In one concept, this includes functions such as instrumentation amplifier gains and offsets, presample filter knee selection, a common gain programmable amplifier with programmable offsets, and randomly addressable multiplexers with a PCM Central Controller that can store multiple data cycle maps. With all of the variable functions of the system under software control, system configuration can be determined automatically during pre- and post-flight test from a portable ground test set that produces a hardcopy printout of the system configuration. This system concept is being augmented by increasing sampling rate capability up to 500k sps for processing vibration/acoustic data. Fiber optical communications are available between the PCM Central Controller and the remote signal conditioners and multiplexers to provide immunity from extremely high common mode plateaus between subsystem elements located in different parts of a composite materials airframe. This next generation data system is being developed for general purpose flight and ground test applications.