Downloaded from https://www.everyspec.com ADS-79D-HDBK In trend analyses, parameters are monitored and examined for shifts over time or in comparison with reference levels. Both accuracy and repeatability are important in selecting the parameters to be measured. Greater measurement repeatability is desired to separate performance shifts from the data scatter. Parameters typically measured in a condition monitoring system include 36 :
Table G-VI Parameter representing thrust or power setting Low pressure rotor speed Engine pressure ratio Engine pressure ratio Table G-VII Engine trending parameters Exhaust Gas Temperature (EGT) Power Turbine Inlet Temperature (PTIT) Interturbine Temperature (ITT) Mass fuel flow Rotor speeds Table G-VIII Accessory load parameters Bleed status Power extraction Anti-icing condition The general guidance on sensor requirements provided in Appendix E – Vibration Based Diagnostics is equally applicable to sensors used in engine monitoring systems. This guidance covers sensor characteristics including: sensitivity, dynamic range, linearity, drift, and bandwidth.
Additional requirements for engine monitoring system sensors are provided below. To the extent possible, engine monitoring systems should use signals already available for other purposes such as engine control, cockpit control and display, or crash data recording. Further, the sensors should be calibrated in the range where data acquisition is most likely to be required. Modern turbine engines make extensive use of full authority digital electronic control systems (FADEC) to obtain optimal engine performance. These systems include a number of sensors that are robust, well-placed, and monitored for proper functionality with built-in tests.
Many of these engine control signals are categorized as ―flight critical‖. As such, due consideration should be given to sharing these signals for CBM purposes. Many parameters can be shared safely with EMS/EMHS devices over the aircraft data bus. However, where data latencies impact the ability of CBM algorithms to function properly, it may be necessary to tie into the analog sensor outputs directly. This is sometimes the case 36 SAE AIR 1873 Guide to Engine Monitoring Systems for Aircraft Gas Turbine Engines, pg. 5.
123 Table G-IX Mechanical parameters Oil quality Fuel Filter Health Oil Level/Consumption Fuel Pressure Oil Filter Health Vibration Oil Pressure Control positions Fuel contamination