Microwave oscillator as a sensor of electrophysical flow parameters

New results of the authors in the development of microwave self-excited oscillating sensors of high-temperature technological processes, mainly processes of burning, are presented. As in the majority of microwave-diagnostic devices, the sensor reacts to the flame permittivity. The main disturbance actions, created by control process and causing measurement error, have been described. Temperature error has been researched in detail. The research on a physics-mathematical relation is similar to self-excited oscillator frequency instability analysis, and the means of error reduction coincide with stabilization methods. Nonuniform sensor heating forms thermal flows and complicated temperature field. Quantitative dependence of frequency instability from temperature and electrophysics, thermophysics and constructive self-excited oscillator parameters has been established by electric and thermal processes comparative analysis. Analysis has been carried out in two modes: quasi-static (the start of the process being controlled) and dynamic (nominal process run under the perturbation actions). In the first one-relational frequency drift is notably high (to 10^-3), in the second-two-four orders lower in the perturbation frequencies range ν>10^-2 Hz. Two original technical solutions have been suggested along with a traditional stabilizing measures