Hameg Instruments HM 8021-3 Manuel page 19

100ns ... 10sec. but the effective gate time will
never be smaller than 150µs.
External gate is selected by means of the
pushbutton (3) and indicated by means of LED.
External gate can be used in all functions.
Example applications are multiple burst
frequencies and masked time intervals. Note that
if RF bursts are to be measured using frequency
C, the burst should contain at least 128 cycles of
the f requency to be measured. External gating
is active according to the level applied to the input
(16) (rear side of mainframe).
Calibration
Caution! The time-base of the HM8021-3
unit should only be re-aligned, if a high-
precision frequency standard is available.
Crystal oscillators are subject to natural aging
during operation, which leads to deviations from
their basic accuracy. Therefore they should be
re-aligned at least twice peryear to ensure the
accuracy indicated in the specification.
If recallibration is necessary it is carried out
as follows:
1) Select function FA (Frequ.A), OFFSET and DIS-
PLAY HOLD should be in OFF position.
2) Apply a frequency standard of 1,5 or 10MHz
to input A and adjust channel A trigger setting
for a stable reading.
3) Depress RESET (7) and then GATE TIME (3)
for approx. 5secs.
Sous réserve de modifications / Reservado el derecho de modificación
4) The display shows "A...O" during the push
buttons are depressed.
5) When the switches are released the display
shows the date of the last recalibration (DD-
MM-YY or 00-00-00).
6) You may leave calibration mode by
depressing RESET T. In this case no changes
are made and the unit is working in normal
mode.
7) If you want to change the date of the last
calibration youshouidproceedfromste 5:
Using the key ← or → (left or right function
shift keys) you can choose the digit that has
to be changed (not flashing). The different
digits are changed by pushing down the GATE
TIME (3) key several times. When the last
digit is corrected (now the last digit should
light brightly e.g. 20-02-89) you can leave the
calibration procedure (continue with step 7a)
or frequency calibration can be performed
(continue with step 7b).
7a) If you only want to store the date of the last
calibration without changing the timebase
calibration, there should not be any signal
at the input A during the following steps. Af-
ter depressing the right function key "A..."
will be indicated in the display after a few
seconds. If you now depress the reset button
you are again in the normal mode.
7b) If there is a standard frequencyof 1, 5 or
10MHz at the input A, depress the right
function shift key. A few seconds later the
display shows following informations:
A... if the standard frequency applied is not
accepted
A... 1x10 6 if the counter has recognized a 1 MHz
standard
A... 5x10 if the counter has recognized a 5MHz
6
standard
A... 10x10 if the counter has recognized a
6
10MHz standard
During the following 45 seconds the signal is
measured and the HM8021-3 is recalibrated.
Finally the new calibrated unit automatically
switches back to normal mode.
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