The SRL1 is the extension for the SPL-D2 and SPL-D3 display units and the SPL3, SPL3TS, SPL5 and SPL6 limiters. Coupled to one of the SPL series limiters or the display unit allows you to connect a warning light and cut the power supply when exceeded. Coupled to the SPL-D2 or SPL-D3 it is also possible to adjust the settings via the SPL-D2 and SPL-D3 software as delay and penalty.