Abstract: A sensor monitoring system comprises a passive sensor, a monitored transmitter, a repeater, and a central receiver. The system provides easy installation, convenient calibration, and very low maintenance. The sensor and the monitored transmitter are battery powered and, in order the conserve battery power, the sensor and the monitored transmitter receive power only on command from their respective microprocessor.

Abstract: A tank level monitoring and alarm system comprises a passive level switch, a transmitter, a repeater, and a receiver. It provides easy installation, convenient calibration, and very low maintenance. A mechanical level switch for the specific vessel is installed. The contacts of the level switch are connected to the transmitter. When the switch is activated, the transmitter immediately broadcasts an alarm signal to the receiver. A relay output at the receiver is either opened or closed thus activating the alarm or other device attached to it. The relay output may also connect to a control apparatus, such as a signal transmitter to provide for remote operation of such devices as valves.

Abstract: An optical sensor for determining an index of refraction of a substance being monitored includes a light source (20). An optical element (24) having a coupling surface (30) and a measuring surface (26) is arranged such that light directed into the optical element (24) through the coupling surface (30) is partially reflected twice from the measuring surface such that it is directed to and exits through the coupling surface (30). The measuring surface (26) is preferably spherical. An input optical fiber (22) having first and second ends directs light emitted from the light source to the coupling surface of the optical element. The first and second ends of the input optical fiber (22) are optically coupled to the coupling surface (30) of the optical element (24) and the light source, respectively. An output optical fiber (28) has first and second ends and directs light expelled from the coupling surface (30) of the optical element (24) to a photodetector (50).