  We describe the on-line algorithms developed to probe Lumped Element Kinetic
Inductance Detectors (LEKID) in this paper. LEKIDs are millimeter wavelength
detectors for astronomy. LEKID arrays are currently operated in different
instruments as: NIKA2 at the IRAM telescope in Spain, KISS at the Teide
Observatory telescope in Tenerife, and CONCERTO at the APEX 12-meter telescope
in Chile. LEKIDs are superconducting microwave resonators able to detect the
incoming light at millimeter wavelengths and they are well adapted for
frequency multiplexing (currently up to 360 pixels on a single microwave
guide). Nevertheless, their use for astronomical observations requires specific
readout and acquisition systems both to deal with the instrumental and
multiplexing complexity, and to adapt to the observational requirements (e.g.
fast sampling rate, background variations, on-line calibration, photometric
accuracy, etc). This paper presents the different steps of treatment from
identifying the resonance frequency of each LEKID to the continuous automatic
control of drifting LEKID resonance frequencies induced by background
variations.
