Intelligent sensors used in jet engines?

Answer 1

By Grant Patterson and Mike Bennett The installation of a jet engine for testing in an altitude test cell requires electronic and mechanical connections to the engineer. Presently, to configure the test facility to acquire measured data, operators need to route aerodynamic pressure lines (up to 600) and electrical cable through patch panels to pressure scanners, power supply and signal conditioners, analog-to-digital (A/D) systems, and acquisition systems for processing, display, recording, analysis, and data transmission. The process is manpower intensive in setup and configuration control. Using smart sensors with calibration information gives operators the chance to reduce the number of connections for measured data to one or a few wires. Because the measurement information stores with the sensor, it reduces the probability of configuring the instrumentation system incorrectly. A process called snap-in/snap-out (SISO) describes the use of smart sensors to reduce test facility/engineer instrumentation setup time, reduce costs of setup and configuration management, and eliminate the present front-end data acquisition components and their associated maintenance costs. SISO's goal is to work with the Arnold Engineering Development Center (AEDC), a large aerodynamic and propulsion test facility operated by the U.S. Air Force, to reduce the time required to prepare the instrumentation system to support a turbine engine test. The AEDC supports simulated altitude and sea-level testing of large and small turbine and rocket engines and the aerodynamic testing of full-scale aircraft components and subscale models. The center provides test facilities for the U.S. government and commercial customers. The SISO process will replace and eliminate many of today's processes in the setup of test instrumentation and data acquisition systems. It will reduce the number of connection points at the engine test facility interface, reduce and simplify the test facility instrumentation infrastructure, and simplify the process for entering the measurement requirements necessary to configure the data acquisition system. The initiative uses smart sensor characteristics in individual sensors and measurement scanners to realize these setup improvements. The object of SISO is to remove the infrastructure of power supply and amplifier signal conditioners, the rack-mounted pressure scanners, and the A/D systems and replace them with smart sensors located on the engine stand. Before testing a jet engine in a test cell, operators terminate aerodynamic pressure lines and electrical lines from measurement points and transducers mounted on the engine. They route the pressures through the mating panels to the pressure scanning system located outside the test cell-sometimes up to 600 measurements. Problems with this type of measurement include leaks at the panel interfaces and at the pressure scanner interface. Sometimes operators need to recalibrate the pressure scanner system during the test. They might also terminate individual pressure transducer measurements. They need pressure transducers (for wet and dry measurement) for applications close to the measurement point on the engine and in facility systems for the desired frequency response. These terminations must accommodate the measurement connection and power supply and excitation connection. Transducer electrical terminations occur through panels that route the transducer inputs and outputs to the power supply and amplifier circuitry. Managing the instrumentation and data acquisition system configuration is crucial to producing data with correct parameter name, scan rate, and range. The setup of the system is tedious, time-consuming, and manpower intensive, with the setup data passing through multiple lists, creating many sources for error in the configuration. Smart sensors can improve the setup process and reduce setup costs. The infrastructure associated with temperature measurement includes universal temperatures reference units, the interconnect wiring, interconnect panels, and the A/D system. The costs of replacing this infrastructure are comparable to the costs of a smart sensor system designed to perform the same function as the temperature measurement systems. But temperature measurements acquired via smart sensors should have better measurement uncertainty than traditional systems. The advantages of implementing SISO are associated with infrastructure maintenance and test costs, which come from labor and material needed to maintain the system and labor to set up the system for test. SISO will also eliminate infrastructure associated with measuring pressure from close-coupled transducers on the engine, including data conditioning amplifiers and power supplies and interconnect wiring and panels. This type of signal conditioning is designed to be some distance from the sensor and requires expensive, high-quality instrumentation to meet the required measurement uncertainty. IT Grant Patterson is an engineering specialist, Aeropropulsion Programs Department, Jacobs Sverdr