Grewe, R. Arnold, M. Brauch, A. Dutine, M. Jürgensen, L.E. Pietralla, N. Schließmann, F. Schneider, D. JACoW Publishing Geneva, Switzerland 2673-5504 978-3-95450-234-9 10.18429/JACoW-SRF2023-MOPMB008 English 70-74 cavity linac SRF coupling resonance Contribution to a conference proceedings 2023 2023-09 https://doi.org/10.18429/JACoW-SRF2023-MOPMB008 https://jacow.org/srf2023/papers/mopmb008.pdf The Superconducting Darmstadt Linear Accelerator (S-DALINAC) is a thrice recirculating electron accelerator wich can be operated in a multi-turn energy recovery mode*. The design parameters for kinetic energy and beam current are up to 130 MeV and up to 20 uA respectively. The injector consists of a six-cell capture cavity and two 20-cell srf cavities. The main linac consists of eight 20-cell cavities. The cavities are operated at a temperature of 2 K with a frequency of 2.9972(1) GHz. Monitoring of the srf cavities is important for the overall performance of the accelerator. A key parameter for the rating of the srf cavity performance is the intrinsic quality factor Q. At the S-DALINAC it is measured for selected cavities during the yearly maintenance procedures. The unique design of the rf input coupler allows for a wide tuning range for the input coupling strength. This makes in-situ quality factor measurements using the decay time measurement method** possible. The contribution illustrates the principal design of the input couplers and the benefits it yields for Q measurements. Recent results including the progression of the quality factors over time will be presented.