Operating method, electronic ballast and system for resonant operation of high pressure lamps in the longitudinal mode

DETAILED DESCRIPTION What is claimed is: 1.
An operating method for acoustic resonant operation of a metal halide lamp using a radio frequency carrier frequency which is frequency-modulated (FM) by means of a sweep signal and which is amplitude-modulated (AM) at the same time, with a fundamental frequency first of all being set for the AM signal, which is derived from an i.
sup.
th, preferably the second, longitudinal resonance, wherein at least the following steps are carried out successively after starting of the lamp and after waiting for a stabilization time: a) Preparation step: during this step, a first resonance of the impedance value (Z) of the lamp, that is to say (ZEXT 1), is first of all determined theoretically or experimentally during this step with a very low AM level (AMI) of 5 to 15% in such a way that a large frequency interval is covered for (f(AM)) which will certainly include an extreme; a frequency point (FM1) associated with (ZEXT 1) is used to define a measurement interval (MI) which has a width of 8 to 25 kHz with cut-off points (ST) (upper cut-off frequency) and (SM) (lower cut-off frequency), and in which (FM1) is arranged such that (FM1) is located at approximately 55 to 80%, preferably 60 to 70%, of the interval between (SM) and (ST), where (FM1) must always be closer to (ST); b) Step 1: the measurement interval (MI) is passed through during this step; a family of characteristics is thus determined which is obtained by passing through different AM levels, which are changed in steps, in a maximum range (AMI)=5 to 45%, in particular 10 to 40%, with the measurement interval (MI) in each case always being passed through from top to bottom, that is to say from (SM) to (ST); c) Step 2: determination derived from the family of characteristics, of an optimum AM level (AMI)=(AMopt) by comparison of a change in the lamp impedance as a function of the frequency for various AM levels; determination of a maximum of a change in the lamp impedance for an associated value of (AMI) equal to (AMmd); definition of (AMopt) by the rule (AMopt)=(AMmd)+(W) where (W)=3 to 10%; d) Step 3: search for a frequency (FMmin) associated with (AMopt); e) Step 4: definition of the operating frequency (FMopt) by passing through a frequency interval (OPT) between (FMmin) and a value which is 20% of (FM2) away in the interval between (FMmin) and a lower frequency end point (FM2)