Section 6
OM6530-C1-00
19 November, 2019
6-12
6.4.
CALIBRATION THEORY
After each resistance reading the integration time is converted to a resistance. The conversion
from time to resistance is achieved using the formula:
V
test
x T
integration
Resistance =
___________________________
- R
protection
2 x C
integrator
x T
integrator
Where: Resistance is the value of the unknown resistor
V
test
is the test voltage from the 6530 source
T
integration
is the time for the integration
C
integrator
is the value of the integrator capacitor
T
integrator
is the threshold of the integrator
R
protection
is the value of the protection resistor.
The nominal values of each of the components in the equation are known except for the
unknown resistance. The variances from the nominal values are determined during the
calibration process using Sofcal utilities. The 6530 system software calls up the nominal value of
each component and corrects each by use of the respective calibration coefficient before
computing the resistance value.
6.4.1.
Rprotection COEFFICIENT
The value of the protection resistor is measured by the instrument during calibration
using a short circuit connection between the source and input connectors of the 6530 and
is stored in the instruments Non-Volatile memory.
6.4.2.
Vtest COEFFICIENTS
The variance of the test voltage from its nominal value is determined during calibration
by selecting each possible output voltage and measuring its absolute value with a
precision voltmeter. The variance of the output voltage from its nominal value is
computed in Parts Per Million (ppm) and entered into the instruments Non-Volatile
memory either from the front panel or through one of the bus interfaces (RS-232C or
GPIB). It should be noted that there are (14) fourteen different coefficients computed,
and stored in the instrument, one for each voltage of each polarity.
