Specifications

Chapter 4 41
Preparing for Accurate Measurement
Performing Calibration
4. Preparing for Accurate
Measurement
LOAD standard: 25 to 100 W
OPEN standard: 100 W or higher
NOTE When you validate the R
dc
measurement results returned by the :DATA:RCAD{1-3}?
command, you should use the absolute value for the following reasons.
When you measure the SHORT standard, whose resistance is extremely low (nearly zero)
and susceptible to disturbance during measurement, the command may return a small
negative R
dc
value. On the other hand, when you measure the OPEN standard, whose
conductance is extremely low (nearly zero) and susceptible to disturbance during
measurement, the command may return a large negative R
dc
value (an inverse to a negative
small conductance value).
The measurement data of the respective standards used for calculating the calibration
coefficients for impedance measurement are stored in the calibration data array (see
“Calibration Data Arrays” on page 80). You can retrieve this data with the following
command:
• :DATA:CAD{1-8}? on page 259
Note that the command shown above returns raw RF measurement data. Unlike DC
measurement, you cannot simply compare the raw RF measurement data with the standard
values to detect operational errors that may have occurred when measuring the calibration
data.
Saving or recalling calibrated state (retrieving or writing calibration
coefficients)
You can retrieve the calibration coefficients and save them to a file. Later, you can retrieve
the calibration coefficients from the file and load them into the 4287A to restore the
calibrated state at the time you saved the file.
The calibration coefficients for impedance measurement are stored in the calibration
coefficient array (see “Calibration Coefficient Arrays” on page 80). To read or write the
calibration coefficient array, use the following command:
• :DATA:CCO{1-6} on page 260
To read or write the calibration coefficients for R
dc
measurement, use the following
command:
• :DATA:RCCO{1-3} on page 265
NOTE When setting calibration coefficients, note the following:
• To ensure that the instrument will provide correct measurement results, you must
configure the instrument to use the same measurement points (point setup table
settings) as when you obtained measurement data for calibration and then set all the
coefficients.
• You must turn on the calibration functions before you set the calibration coefficients.
To do so, follow the steps shown in “Measuring data for calculating calibration
coefficients and turning on calibration function” on page 38 before setting the
calibration coefficients. This procedure includes only measuring tentative data and
does not require you to connect the standard before issuing the data measurement
command.