Fluke PM6690, Service Manual, Page: 107 / 200

•
Start the calibration & adjustment procedure and fol-
low the instructions.
•
Measure the deviation and record the value.
•
Check that the parameter meets its specification.
The Calibration Submenu
When used for the first time, this submenu can be activated
from the
USER OPT
menu after first entering the fixed pass-
word 62951413. All calibrations that can be performed manu-
ally are controlled from here. Internal delays can be compen-
sated for as well as aging of the timebase and voltage refer-
ences. All calibration procedures are performed without hav-
ing to remove the instrument cover. In this way it is easier to
keep the calibration environment as close to the operating en-
vironment as possible. No special tools are necessary, and live
parts are not exposed to the operator, who is guided through
the procedures by instructions on the instrument display. The
whole concept is known as
Closed-Case Calibration .
NOTE: The timer/counter must have been switched on for at
least one hour before you start any calibration.
When the instrument leaves the factory, the calibration data is
stored as
factory calibration that cannot be changed by the
user.
There is one active set of calibration data. It can be a user set
or the factory set. If a user set is active and a new user calibra-
tion procedure is initiated, then the older set of data is stored to
make it possible to return to the earlier calibration status.
Password Protection ON/OFF
The default setting on delivery for the password protection is
ON
but can be changed to
OFF
after the first-time use if so de-
sired. Activate or deactivate the password with this key.
Internals
Certain internal delays are measured in order to correct the re-
sults of real measurements. This is done without applying ex-
ternal signals. This procedure needs only be run after firm-
ware upgrading, or if repair work has been done on the mea-
suring logic or the analog interpolators.
Press
Start Calib
to run the procedure. The new calibration
will be the active calibration.
n
Calibration via the GPIB or the USB
The calibration can also be performed by sending commands
over one of the interface buses.
Always end the commands with the Operation Complete
Query
*OPC?
Use the following command sequence:
:CAL:DEL:INIT;*OPC?
:CAL:DEL:START;*OPC?
:SYST:ERR? -- check for errors --
:CAL:DEL:STOR
Timebase
A reference frequency with adequate accuracy must be con-
nected to Channel A. Timebase calibration should be per-
formed regularly at intervals that depend on the timebase it-
self and the user application. Read more about the procedure
under
Frequency Reference below.
Voltage
A sequence of voltage levels from a dedicated calibrator must
be applied to Channel A and Channel B. Voltage calibration
should be performed regularly if the user application calls for
traceable voltage measurements. Read more about the proce-
dure under
Voltage Reference below.
Restore
You can make a stored set of calibration data, either a user set
or the factory set, the active calibration. If the previous active
calibration was a new user calibration, then it will be lost.
Frequency Reference
The frequency of the reference crystal oscillator is the main
parameter that influences the accuracy of a counter. External
conditions, such as ambient temperature and supply voltage,
affect the frequency, but aging is also an important factor.
Note that frequency adjustment only compensates for devia-
tion due to aging.
Some important points
The two optional high-stability oscillators, type OCXO, have
been built into an oven to keep the oscillator temperature as
stable as possible. Continuous operation is also important for
optimum stability. Option PM6690/_6_, for example, has an
aging/24h that is 1x10
-10
when operating continuously. After a
power interruption, the oscillator drift is higher and the speci-
The Calibration Submenu 7-3