Fluke PM6690, Service Manual, Page: 106 / 200

Calibration
To maintain the performance of the timer/counter, we recom-
mend that you calibrate the timebase of your instrument every
year, or more often if you require greater timebase accuracy.
If your applications utilize the voltage measurement capabili-
ties of this counter series, you should also calibrate the voltage
ranges with a good calibrator.
Calibration should be performed with traceable references
and instruments at a certified calibration laboratory. Contact
your local service center for information on calibration facili-
ties in your neighborhood.
As both timebase and voltage calibration are closed-case
menu-controlled procedures that require no manual adjust-
ments on the DUT, you can perform the task on your own
without infringing the safety regulations, provided you pos-
sess the required skill and have access to the necessary cali-
bration equipment.
To know the present status of your instrument, test your coun-
ter from time to time. The test can be made according to the in-
formation in Chapter 2, “Performance Check.”
General Principles
The inherent meaning of calibration is to measure and record
the deviation of a parameter from a known reference. Data
from subsequent calibrations under similar ambient condi-
tions form the calibration history, from which you can draw
conclusions regarding aging characteristics.
Consequently calibration does not necessarily include the
next natural step in the procedure, i.e. adjustment in order to
make the instrument meet the original specifications.
The calibration procedure for these instruments also implies
automatic adjustment, so if you want a continuous history re-
cord, you should follow the simple rules of thumb below that
summarize the basics of all calibration, frequency as well as
voltage.
•
Place the instrument in its calibration environment,
preferably at an ambient temperature of +23 ± 2 °C
and power it up.
•
Let the instrument assume its final internal operating
temperature. Allow at least a warm-up period of two
hours before proceeding.
•
Measure the deviation and record the value. Use a ref-
erence source whose uncertainty is at least an order
of magnitude less than that of the DUT.
7-2 General Principles
Model 90 90 90
Option Standard PM6690/_5_ PM6690/_6_
Timebase type UCXO OCXO OCXO
Total uncertainty, for operating
temperature 0°C to 50°C,
@ 2
s
(95 %) confidence interval:
-1 month after calibration
-3 months after calibration
-1 year after calibration
-2 years after calibration
<1.2 x 10
-5
<1.2 x 10
-5
<1.2 x 10
-5
<1.5 x 10
-5
<2 x 10
-8
<4 x 10
-8
<6 x 10
-8
<1.2 x 10
-7
<0.7 x 10
-8
<1.2 x 10
-8
<1.8 x 10
-8
<3.6 x 10
-8
Typical total uncertainty, for oper-
ating temperature 20°C to 26°C,
@ 2
s
(95 %) confidence interval:
-1 month after calibration
-3 months after calibration
-1 year after calibration
-2 years after calibration
<4 x 10
-6
<4 x 10
-6
<7 x 10
-6
<1.2 x 10
-5
<2 x 10
-8
<4 x 10
-8
<6 x 10
-8
<1.2 x 10
-7
<0.7 x 10
-8
<1.2 x 10
-8
<1.7 x 10
-8
<3.5 x 10
-8
For complete specifications see Chapter 8 of the Operators Manual.
Table 7-1
Suitable calibration intervals depend on the total uncertainty of different timebase options and the requirements of your applica-
tion.