Up-to-Third-Order Determination of Time Constants of Models of Avionics Thermocouples in Gas Temperature Control Loop of Automatic Control System of Gas Turbine Engine

Abstract

Ensuring the necessary accuracy of measurement of unsteady temperature of gas in an aircraft gas turbine engine (GTE) is a topical problem. The use of thermocouples in the gas temperature control loop of the automatic control system (ACS) of a GTE is complicated by the need of reducing the thermocouple inertia, which varies significantly in dependence on the GTE operation regimes. The existing methods and means for compensating the inertia of aircraft thermocouples in the gas temperature control loop of the GTE ACS are based solely on the use of a mathematical model of thermocouple in the form of a first-order inertia element. This mathematical description of avionics thermocouples with wire sensors is very approximate. An avionics thermocouple is described more accurately with a second-order mathematical model and in some cases with a third-order one in accordance with OST 1 00334-79 “Temperature Sensors. Dynamic characteristics.” The difficulty with the use of second- and third-order thermocouple models is associated with the need to establish the dependence of all time constants of a selected model on the changing operating regimes of GTE. No such dependencies have been determined yet for practical use. The purpose of this work is to find out the functional dependence of all time constants occurring in mathematical models up to the third-order inclusive on actual operating parameters of GTE. The time constants calculated from the established dependencies can be used for continuous correction of the gas temperature control loop of the GTE ACS to ensure optimal correction of the dynamic characteristics of thermocouples.