Page 6 from 12
Figure 3. Cable Extension
Using an HP 16048E (4m)
impedance value. However, when the DUT's impedance value is very low
or very high, it is recommended to use a standard DUT of 100½ or 1k½,
whose value isn't close to the impedance of the DUT.
When a low or high impedance standard DUT is used, the reference value
(described later) of the standard DUT cannot be obtained accurately, and it
may cause the abnormal measurement results, not the true value
of the DUT.
(3) Referencing the standard DUT
To perform the OPEN/SHORT/LOAD correction, it is necessary to measure
the standard DUT for a reference value (known value) beforehand. When
measuring it, it is important to use a high accuracy instrument and to set
its measurement conditions (such as integration time or averaging time) so
that it can measure as accurately as possible. To minimize the measure-
ment error, the standard DUT should be measured using a direct-
connected test fixture after performing the OPEN/SHORT correction.
Measurement condition of impedance measurement instruments
when performing the OPEN/SHORT/LOAD correction
Impedance measurement equipment with the OPEN/SHORT/LOAD correc-
tion function will automatically set the measurement condition (such as
integration time or averaging time) so that it can perform error correction
with highest accuracy.
If performing the OPEN/SHORT/LOAD correction for instruments not
equipped with the OPEN/SHORT/LOAD correction function using an exter-
nal controller, the measurement conditions should be set to measure cor-
rection data as accurately as possible.
Example of actual OPEN/SHORT/LOAD correction
Figure 3 shows the measurement example to extend the HP 4285A's
measurement terminal using 16048E(4m cable). In this case, it is necessary
to perform the OPEN/SHORT/LOAD correction since the HP 4285A cannot
compensate the 4m extension cable with its cable length correction func-
tion. Figure 4 shows the comparison of measurement error between 100pF
capacitor measurement with the OPEN/SHORT correction and that with 4.
Page 7 from 12
Figure 4. Comparison
Between OPEN/SHORT Correction
and OPEN/SHORT/LOAD Correction
OPEN/SHORT/LOAD correction with an external controller
The OPEN/SHORT/LOAD correction can be accomplished with simple key
operation when using an impedance measurement instruments equipped
with the OPEN/SHORT/LOAD correction function. When using instruments
not equipped with the OPEN/SHORT/LOAD correction function, it is possi-
ble to perform the OPEN/SHORT/LOAD correction by executing the correc-
tion calculation with an external controller. But this method has the
following tradeoff problems as the comparison with the correction of a
measurement instrument alone.
n Complicated operation
n Slow measurement speed due to data transfer time
Figure 5 shows an example program to execute the OPEN/SHORT/LOAD
correction for capacitor measurement using the HP 4194A Impedance Ana-
lyzer. In this program, the measurement is performed at one frequency
point with a manual trigger mode.
Line 130-190 setting measurement condition.
Line 210-270 Measuring impedance of OPEN condition in G-B mode.
Line 300-330 Measuring impedance of SHORT condition in R-X mode.
Line 350-610 Measuring impedance of the standard DUT after inputting
Cs-D or Cp-D value of valued standard DUT.
Line 660-690 selecting DUT mode(Cs-D or Cp-D),
Line 710-10l0 Executing correction calculation after measuring
impedance of DUT, then displaying the result.
the OPEN/SHORT/LOAD correction. A 47pF capacitor is used as a stan-
dard DUT. This measurement result shows the error cannot be minimized
sufficiently with the OPEN/SHORT correction, but can be compensated
with an OPEN/SHORT/LOAD correction as shown by the plot.
Page 8 from 12
This application note shows the principle of the OPEN/SHORT/LOAD
correction and some points to be considered in the execution. With the
proper OPEN/SHORT/LOAD correction, measurement comes
higher in accuracy.
"Reference" Impedance measurement handbook (5091-3000)
Page 9 from 12
Figure 5. Sample Program for HP 4194A OPEN/SHORT/LOAD Correction
Page 10 from 12