MTS Series 793 - Manual (Page 268)

ALC theory
ALC compensates for peak and valley errors by building and continually updating a matrix of amplitude
compensation factors.
The matrix is two-dimensional, with axes mapped to either plus or minus full scale or a subrange of full scale.
Each axis is divided into 16, 32, or 64 equal parts, with each part representing a fraction of the defined range.
The horizontal axis is labeled “To Level” and the vertical axis is labeled “From Level.”
With each pass of the spectrum, the peak/valley errors are calculated, and an estimated compensation factor
is stored in the matrix. Before the command generator generates a new segment, it notes the required “From”
and “To” levels, and refers to the matrix to determine how much to over-program the segment.
The following 5×5 sample matrix is for illustration only. The MultiPurpose TestWare process defines actual
matrixes as either 16Ч16, 32Ч32, or 64×64. An additional diagonal row (not shown here) is added to the
matrix to handle situations where the “From” and “To” levels map to the same cell.
Note:
No compensation is applied if the level remains in the same cell.
Description Callout
When going from 0 to + FS, ALC uses this compensation factor. 1
Calculated Amplitude Compensation Factors 2
In order to run the test as fast as possible, ALC builds a second matrix to store frequency compensation
factors. The command generator uses these factors to maintain the optimum spectrum play-out speed.
Frequency compensation can only be enabled on single-channel tests.
The matrix compensation factors are updated during each pass of the spectrum. Depending on the convergence
rate, it may take a number of cycles before the feedback amplitude tracks the command to within tolerance.
To stop updating the compensation factors when the signals converge, select Hold on the Station Setup
window’s ALC tab. The compensator will continue compensating with the current factors.
268 MTS Series 793 Control Software
Station Setup