Fluke DDS Function Generator 271, User Manual

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271
Users Manual
14-2
Introduction
All parameters can be calibrated without opening the case, i.e. the generator offers
‘closed-box’ calibration. All adjustments are made digitally with calibration constants
stored in EEPROM. The calibration routine requires only a DVM and a frequency
counter and takes no more than a few minutes.
The crystal in the timebase is pre-aged but a further ageing of up to ±5 ppm can occur in
the first year. Since the ageing rate decreases exponentially with time it is an advantage to
recalibrate after the first six month’s use. Apart from this it is unlikely that any other
parameters will need adjustment.
Calibration should be carried out only after the generator has been operating for at least
one hour in normal ambient conditions.
Equipment Required
•
3½ digit DVM with 0.25 % dc accuracy and 0.5 % ac accuracy at 1 kHz.
•
Frequency counter capable of measuring 10.00000 MHz and 50 µs ±0.1 µs pulse
widths.
The DVM is connected to the
MAIN OUT
socket and the counter to the
AUX OUT
socket.
The accuracy of the frequency meter will determine the accuracy of the generator’s clock
setting and should ideally be ±1 ppm.
It may be quicker to use an oscilloscope for steps 05 and 15 (see Calibration routine
below).
Calibration Procedure
The firmware provides for a four-digit password in the range 0000 to 9999 to be used to
access the calibration procedure. If the password is left at the factory default of 0000 no
messages are shown and calibration is accessed directly, as described under
Calibration
routine below; only if a non-zero password has been set will the user be prompted to
enter the password.
Setting the Password
Press the
EDIT
key followed by
CAL
(the numeric
6
key) to show the opening screen of
the calibration routine. With this screen displayed press
EDIT
again to show the
password screen:
ENTER NEW PASSWORD
----
Enter a 4-digit password from the keyboard; the display will show the message
NEW PASSWORD STORED!
for two seconds and then revert to the main menu. If any
keys other than
0
-
9
are pressed while entering the password the message
ILLEGAL PASSWORD!
will be shown.
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