Dryden Flight Research Center's Flight Loads Laboratory (FLL) was constructed in 1964 for use in performing combined mechanical and thermal tests of structural components and complete flight vehicles. The FLL is also used to calibrate and evaluate flight-loads instrumentation under the conditions expected in flight. The required testing is performed by the FLL's data-acquisition and control system (DACS).
A major portion of the FLL's third-generation data-acquisition and control system (DACS III) has been placed in service: This system is being developed in phases through the combined effort of a team composed of both civil-service and contractor personnel. The second-phase version of the system - now fully operational - performs data-acquisition, display, and replay functions, and provides troubleshooting tools. The DACS III provides enhanced capabilities that greatly increase productivity and efficiency.
The DACS III (see figure) consists mostly of a network of computers and workstations linked in a manner to provide maximum flexibility. This system has been designed to prevent obsolescence by use of industry-standard components that can be easily replaced when newer versions are introduced. An extensive use of graphical-user-interface (GUI) techniques simplifies test-setup definitions (test scenarios) as well as test operations and troubleshooting. A minimum time of two to three days was needed to generate a scenario for a typical test by use of the previous DACS. Operators can now generate the same test scenario in two to three hours by use of the DACS III.
The DACS III includes at least one acquisition-and-control processor (ACP) based on the VersaModule Eurocard (VME) and uses WindRiver's Vxworks real-time operating system. An installed Inter Range Instrumentation Group B (IRIG-B) interface card provides time stamping of sampled data. The data-acquisition system can be scaled up to 1,280 channels by using multiple ACPs, and operates at rates that vary from 10 to 160 samples per second.
This system has been designed to function in an environment that includes harsh electrical noise. All analog inputs are fed to the ACP(s) through fiber-optic cables to reduce electromagnetic interference. Each analog input module is an independent analog-to-digital (A/D) converter that generates 16-bit data by the sigma-delta conversion method. All A/D modules feature 1,500-volt isolation and 100 dB of normal-mode rejection at a frequency of 60 Hz.
Each ACP provides local recording of raw data and real-time conversion of engineering units. A key feature of the system is its ability to broadcast engineering-unit-converted data over an Ethernet. These data can be displayed throughout the laboratory on workstations that are equipped with the appropriate display software and attached to the DACS network.
The DACS III includes a data-display system that provides distributed real-time data displays updated at a rate of 5 samples per second. A user can choose several displays that can be overlaid on the same screen. All display parameter entries are driven by a GUI. The following types of displays are available: alphanumeric, x-y plots, vector, bar graph, force-stiffness, and derived parameter. All display engineering workstations are equipped with 21-in. (53-cm) monitors.
Control engineering workstations provide centralized control of test and recording processes for associated ACPs. Calibration functions, troubleshooting, event displays and record control are all available at these stations. The main control workstation performs the same functions as do the control engineering workstations, and offers the additional capability to control any or all of the ACPs.
A recording workstation is dedicated to recording the broadcast data from the ACPs. The recorded information is saved in a format that makes it available, immediately following a test, for evaluation by use of plotting software developed at Dryden Flight Research Center.
The DACS III includes a main computer (not to be confused with the main control computer) that is used for processing raw or engineering-unit-converted data logged during a test run. This computer also serves as the engine for all data-base functions.
One final feature worthy of note is a test-replay option, which enables research engineers to replay portions or all of a test run following a test. The replay can be at the original broadcast speed or slower. Full data-display functions are available during replay. There is also an option to generate displays during replay that were not used during the original test run; this option makes it possible to examine data of interest at a greater level of detail than what was available during the test run.