Calibration - Hameg Instruments HM 8021-4 Manuel

after the gate signal changes from high to low.
The external gate overrides the set measurement
time. The external gate signal must be in the
range 100ns ... 10sec. but the effective gate time
will never be smaller than 150 µs.
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 fre-
quencies 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
(rear side of mainframe).

Calibration

Caution! The time-base of the HM 8021-4 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
DISPLAY 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.
4) The display shows "A...O" during the push
buttons are depressed.
26
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. After
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... 1 6 if the counter has recognized a
1 MHz standard
A... 5 6 if the counter has recognized a
5 MHz standard
A... 10 6 if the counter has recognized a
10 MHz standard
During the following 45 seconds the signal is
measured and the HM 8021-4 is recalibrated.
Finally the new calibrated unit automatically
switches back to normal mode.
Subject to chance without notice