Teledyne LeCroy X-STREAM OSCILLOSCOPES Remote Control - Manual (Page 63)

C H A P T E R F O U R : Understanding and Managing Waveforms
WM-RCM-E Rev D ISSUED: February 2005
57
INTERPRET VERTICAL DATA
Knowing now how to decipher the data, you may wish to convert it to the appropriate measured values. The
vertical reading for each data point depends on the vertical gain and the vertical offset given in the descriptor.
For acquisition waveforms, this corresponds to the volts/div and voltage offset selected after conversion for
the data representation being used. The template tells us that the vertical gain and offset can be found at Bytes
156 and 160 and that they are stored as floating point numbers in the IEEE 32
- bit format. An ASCII string
giving the vertical unit is to be found in VERTUNIT, Byte 196. The vertical value is given by the relationship:
value = VERTICAL_GAIN x data - VERTICAL_OFFSET, where:
VERTICAL_GAIN 2.44141e-07 from the floating point number 3483 126f at Byte 156
VERTICAL_OFFSET 0.00054 from the floating point number 3A0D 8EC9 at Byte 160
VERTICAL_UNIT V = volts from the string 5600 ... at Byte 196
Therefore:
since data[4] = FA00 = 64000 from the hexadecimal word FA00 at byte 373. Overflows the maximum. 16
bit value of 32767, so must be a negative value. Using the two’s complement conversion
64000-2 16 = -1536
value[4] = -0.000915 V as stated in the inspect command
If the computer or the software available is not able to understand the IEEE floating point values, use the
description in the template.
The data values in a waveform may not all correspond to measured points. FIRST_VALID_PNT and
LAST_VALID_PNT give the necessary information. The descriptor also records the SPARSING_FACTOR,
the FIRST_POINT, and the SEGMENT_INDEX to aid interpretation if the options of the
WAVEFORM_SETUP command have been used.
For sequence acquisitions, the data values for each segment are given in their normal order and the segments
are read out one after the other. The important descriptor parameters are the WAVE_ARRAY_COUNT and
the SUBARRAY_COUNT, giving the total number of points and the number of segments.
For waveforms such as the extrema and the complex FFT there will be two arrays (one after the other) for the
two of the result.