A self-test circuit (100, 200) for testing and verifying proper installation of a sensing emission crystal (110, 211) that is attached to an object, being one of a bearing, a bearing housing and a machine housing, the self-test circuit (100, 200) comprising: a voltage source; a ground (AGND); a controller (102, 202); a pulse waveform input (122, 222); an analyzer (126, 226); and a multiplexer IC (120, 220) having: a voltage input pin provided in signal communication with said ground (AGND), a ground pin provided in signal communication with said ground (AGND), a controller input pin provided in signal communication with said controller (102, 202), a normally open pin provided in signal communication with said pulse waveform input (122, 222), a common pin provided in signal communication with said sensing emission crystal (110, 211); a normally closed pin output in signal communication with said analyzer (126, 226), the self-test circuit being configured such that: said pulse waveform input (122, 222) provides a waveform to said multiplexer IC (120, 220), the controller (102, 202) configures said multiplexer IC (120, 220) into a signal injection configuration in which said waveform is passed to said sensing emission crystal (110, 211), by placing the normally open pin and the common pin in signal communication, the waveform excites said sensing emission crystal (110, 211), the controller (102, 202) configures said multiplexer IC (120, 220) into a signal acquisition configuration in which an output signal emitted from said sensing emission crystal (110, 211) is passed to said analyzer (126, 226), by placing the normally closed pin and the common pin in signal communication; and based on said output signal, the analyzer can detect if the sensing emission crystal is properly attached to or has become detached from the object or is in an open-circuit condition in which the sensing emission crystal is disconnected from analogue acquisition circuitry of the test circuit (100, 200). a voltage source; a ground (AGND); a controller (102, 202); a pulse waveform input (122, 222); an analyzer (126, 226); and a multiplexer IC (120, 220) having: a voltage input pin provided in signal communication with said ground (AGND), a ground pin provided in signal communication with said ground (AGND), a controller input pin provided in signal communication with said controller (102, 202), a normally open pin provided in signal communication with said pulse waveform input (122, 222), a common pin provided in signal communication with said sensing emission crystal (110, 211); a normally closed pin output in signal communication with said analyzer (126, 226), a voltage input pin provided in signal communication with said ground (AGND), a ground pin provided in signal communication with said ground (AGND), a controller input pin provided in signal communication with said controller (102, 202), a normally open pin provided in signal communication with said pulse waveform input (122, 222), a common pin provided in signal communication with said sensing emission crystal (110, 211); a normally closed pin output in signal communication with said analyzer (126, 226), the self-test circuit being configured such that: said pulse waveform input (122, 222) provides a waveform to said multiplexer IC (120, 220), the controller (102, 202) configures said multiplexer IC (120, 220) into a signal injection configuration in which said waveform is passed to said sensing emission crystal (110, 211), by placing the normally open pin and the common pin in signal communication, the waveform excites said sensing emission crystal (110, 211), the controller (102, 202) configures said multiplexer IC (120, 220) into a signal acquisition configuration in which an output signal emitted from said sensing emission crystal (110, 211) is passed to said analyzer (126, 226), by placing the normally closed pin and the common pin in signal communication; and based on said output signal, the analyzer can detect if the sensing emission crystal is properly attached to or has become detached from the object or is in an open-circuit condition in which the sensing emission crystal is disconnected from analogue acquisition circuitry of the test circuit (100, 200). said pulse waveform input (122, 222) provides a waveform to said multiplexer IC (120, 220), the controller (102, 202) configures said multiplexer IC (120, 220) into a signal injection configuration in which said waveform is passed to said sensing emission crystal (110, 211), by placing the normally open pin and the common pin in signal communication, the waveform excites said sensing emission crystal (110, 211), the controller (102, 202) configures said multiplexer IC (120, 220) into a signal acquisition configuration in which an output signal emitted from said sensing emission crystal (110, 211) is passed to said analyzer (126, 226), by placing the normally closed pin and the common pin in signal communication; and based on said output signal, the analyzer can detect if the sensing emission crystal is properly attached to or has become detached from the object or is in an open-circuit condition in which the sensing emission crystal is disconnected from analogue acquisition circuitry of the test circuit (100, 200).