For detecting and processing a physiological variable, a signal transmitter has devices for processing, using, and/or providing signals, which are generated from measurement values of the physiological variable. In accordance with a sequence control approach, the measurement values are acquired from the detection of electromagnetic waves of different wavelengths. Before the signals are detected, the electromagnetic waves pass through the medium to be examined or are reflected by this medium. For at least a certain percentage of the overall signal quantity, at least two measurement values detected close together in time are used for each generated signal. The signal transmitter is suitable for use in a control circuit, which is designed with an actuator to influence the physiological variable detected instrumentally by the signal transmitter.