User manual

2400 Series SourceMeter
®
User’s Manual SCPI Command Reference 18-31
The above expression defines a vector array that is made up of 10
readings. Since the SourceMeter is programmed to perform 10
source-
measure operations, the calculation will yield one result every 10
SDM cycles. The fourth voltage reading (vector 3) and the 10th volt
-
age reading (vector 9) are used for the calculation.
Now assume that the SourceMeter is configured to perform 20
source-measure operations. Since the vector size is still 10, two 10-
reading arrays will be created. The calculation will now yield two
results, one for each array.
The first result, as before, is based on the fourth and 10th readings of
the first array. The second result is based on the 14th and 20th read
-
ings. These are the fourth (vector 3) and 10th (vector 9) readings of
the second array.
Note that you need complete vector arrays to acquire valid calcula-
tion results. If, in the preceding example, the SourceMeter is
changed to perform 25 source-measure operations, then the third
array will be incomplete (first array is 10 readings, second array is 10
readings, third array is only 5 readings). After the SourceMeter goes
back into idle, the “Insufficient vector data” error message will be dis
-
played, and the third result will be NAN (+9.91e37).
To avoid incomplete vector arrays, make sure the programmed num-
ber of source-measure operations (arm count × trigger count) is a
multiple of the vector array size. In the preceding example, vector
array size is 10. Thus, in order to avoid “Insufficient vector data”
errors, the programmed number of source-measure operations has
to be a multiple of 10 (10, 20, 30, 40, and so on).
The following vector math expression to calculate offset compen-
sated ohms demonstrates proper syntax:
:calc:math ( (volt[1] - volt[0]) / (curr[1] - curr[0]) )
Notes:
1. Use nested parentheses to force math operations that are
imbedded in the calculation (see example in
“Vectored math,”
page 18-30).
2. A calculation expression can be up to 256 characters in length,
including parentheses and white spaces.
3. When using the filter, the measured readings used in the calcu-
lation are filtered - NOT the result of the calculation.
4. For vector math, it is recommended that only the REPEAT filter
be used. For the repeat filter, the calculations use only the fil
-
tered readings of the vector points. If you instead use the MOV-
ING filter, each vector point will reflect the filtered average of all
the previous readings in the vector array.
5. The data format (ASCII or binary) for calculation results is
selected using the :FORMat:DATA? command. (See
“FORMat