Manual

HAPTER

OUR

Understanding and Managing Waveforms

WM-RCM-E Rev D ISSUED: February 2005

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

= -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.