Multiplexing (aka MUXING) is a method of serial transmission of multiple signals over a shared medium. In the process all signals are apparently transmitted simultaneously. Strictly speaking, however, they are transmitted “one-by-one” as it were, in alternation in time slices. The shared transmission channel is divided into time slices. A time slice is allocated to each signal. To transmit, a multiplexer (MUX) sends one signal after the other to the transmission link, each for the duration of one time slice. At the other end of the link a demultiplexer (DEMUX) synchronously sends the transmitted signals to the associated recipients. A complete multiplex cycle consists of the sum of all time slices. A defining variable in multiplexing is the multiplexing rate. It corresponds to the inverse of the cycle time and is an expression of the number of signal channels that can be transmitted per time unit (usually per second). The particular advantages the multiplexing method offers include the reduction of hardware costs (fewer measurement channels and less cable), the reduction of space requirements (multiple probes can be run with one instrument, thinner cable), considerable time savings (with multifrequency examination or the use of array probes), and the prevention of interference or crosstalk between the channels.
On the other hand there are disadvantages: Under certain conditions seamless scanning cannot be guaranteed anymore at high testing speeds (at multiplexing rates that are too low); also poorer signal quality (signal-noise ratio), because at increasing multiplexing rates less and less data points per time slice are available.
In eddy current testing one differentiates between the following types of multiplexing: Parameter-multiplexing (e.g. as multifrequency examination) and probe multiplexing (switching over to multiple probes or running array probes).
