Design and Operation
17
3.2 Signal Generation
To achieve the specified quality of the output signals, the generation of sine
signals of high quality is necessary. The requirement for 6 fixed-phase
coupled signals suggests a digital implementation.
In the CMC 156 the quality of the signals is achieved due to the use of a
modern and powerful signal processor.
The implemented algorithm linearly interpolates between the basic values of
any signal table according to the following equation:
S[i+x]=S[i]+x*{S[i+1]-S[i]}
S[i] .......... basic table value i
x ............. fractional component of the table pointer
The table may be processed with any real step width. The output of sine
signals uses the internal sine table which has 256 basic entries. The
frequency resolution is 2.33 μHz, and the phase resolution is < 50 μ degrees.
16k words are available per channel in the signal table for transient signals. By
means of interpolation, the signals are always output at 10k-samples/s, even if
the basic value table contains less samples/s, as is common in fault
recordings.
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