Sigma Control L is an advanced Control Unit for use with small size gas detection systems. It controls all the devices connected and integrates them to create a single Sigma Gas system. Sigma Control L Unit reads the status of detectors connected to the system. This information is presented on the display and the built-in Visual System Indicator. Based on gas concentration measured and other special statuses (e.g. failures), it controls outputs for visual and acoustic indicators as well as for dual outputs. Control Unit reads the status of dual input and depending on its status, controls system operation (enables or disables outputs). During operation, the unit runs cyclic self-diagnostic procedures used to detect any damage to Sigma Control L Unit and detectors. In addition, it is possible to control the NC valve.