[en] We developed sensors and instrumentation dedicated to detection and location of thermal quenches in SRF cavities via 2nd sound events in HeII. We studied 2 types of Quench Detectors (QD): 1) Oscillating Super leak Transducer (OST), 2) LOw REsponse Time resIstive Thermometers (LORETIT). The QD were characterized in He II bath (Temperature T₀ = 1.6 K- T_λ. The SRF cavity quench is experimentally simulated using resistors of different sizes and geometries. High pulsed heat flux q_P (q_P < 2MW/m2) were applied to these heaters and the dynamic response of QD were investigated as function of several parameters (T₀, q_P, distance to heater). The OST were used for locating quench on different SRF cavities resonating at 2 frequencies f₀ (f₀ =88 MHz or f₀ =352 MHz). The quench dynamics and critical size of normal resistive area leading to quench were investigated. Furthermore, a Second Sound Resonator (SSR) equipped with a pair of OST at each extremity (2nd sound generator (G) and detector (D)), a low thermal capacity heater (G) and a LORETIT (D), was successfully operated in the resonating and in the pulsed mode. The measured 1st sound and 2nd sound spectra were compared theoretical results and a good agreement is obtained. (paper)