Fluke 1595A - Manual (Page 117)

107
Calibration
RESISTANCE CALIBRATION (F4)
To properly calibrate a Super-Thermometer internal resistor, the expanded uncertainty (k = 2) of the standard
resistor should be no greater than 25% of the 95% confidence level, 1-Year Absolute Resistance Accuracy
specifications. Its resistance should be approximately the same as that of the internal reference resistor being
calibrated, which will result in the least measurement noise and best test uncertainty. The standard resistor may
be connected to any one of the four front-panel measurement channels.
To set up the resistance calibration, the user must configure the following fields displayed in the Resistance
Calibration screen:
RESISTOR - specifies the internal reference resistor to be measured
CHANNEL - is the front channel input to which the standard resistor is connected.
STANDARD RESISTANCE - is the calibrated resistance value of the standard resistor.
The START (F1) function key begins the resistance calibration. As the test proceeds, the screen indicates the
status of the process. The user may press the CANCEL (F5) function key or EXIT key to cancel the test.
The resistance calibration uses the sensing current for which the resistor’s Absolute Resistance Uncertainty
is specified. During the resistance calibration the digital filter is disabled and the timing is set to the Precision
settings so that results will be consistent and accurate. Normal temperature measurement and data recording is
suspended. Settings are automatically restored after the test. The reported measurement is the mean of a series
of samples of the resistance acquired over a period of about 1 min.
When the measurement is completed, the screen shows the results, which includes the following:
MEASUREMENT - is the measured resistance of the standard resistor. This may be compared to the calibrat-
ed resistance of the standard resistor to provide an indication of the accuracy of the internal reference resistor.
ABSOLUTE ERROR - is the difference between the measurement and the Standard Resistance value, pre-
sented in ohms.
RELATIVE ERROR - is the difference between the measurement and the Standard Resistance value, divided
by the Standard Resistance and multiplied by a factor of one million to produce a value in parts per million
(ppm).
STANDARD ERROR - is the standard deviation of the samples comprising the measurement, divided by
the square root of the number of samples. This provides an estimate of the standard uncertainty of the mea-
surement mean due to measurement noise. It does not include uncertainty of the calibrated resistance of the
standard resistor.
TIME - is the time at which the test ended, taken from the system clock. It is in 24 hour format.
DATE - is the date on which the test ended, taken from the system clock. It is in the format specified by the
Date Format setting in the User Settings screen.
Tolerances for the reported error, which are required for assessing pass or fail conditions, may be found in the
Absolute Resistance Uncertainty section of the Specifications section.
The results of the resistance calibration may be written to a file on a USB memory device using the WRITE
FILE (F1) function key as explained below.
The calibration parameter associated with the calibrated internal reference resistor may be adjusted to improve
the accuracy of the resistor using the ADJUST RESISTOR (F2) function key as explained below.
9.5.1 WRITE FILE (F1)
The Write File function allows the user to write the results of the resistance calibration to a file on the USB
memory device.
The user may change the file name by pressing the ENTER key and using the Alpha-Numeric Interface. Once
the file name is set, and after the USB memory device is inserted into the front USB port, the user presses the
CONTINUE function key to proceed to write the file. The file is stored in a folder named “\159x\test”. If the
file already exists, the new test results are added to the file.