64
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t.
CHECKING AND ADJUSTING
5.1.
GENERAL
The tolerances in this chapter correspond
to the factory data, which only apply
to a completely
re-adiusted
instrument. These tolerances
may
deviate
from
those
mentioned in
the
Technical Data
(Chapter
1).
For
a
complete re-adjustment
o{ the
instrument the sequence in
this
chapter should be adhered too. When
individual components, especially semi-conductors are replaced, the relevant section should
be completele
re'adjusted.
To calibrate
this
measuring instrument only relerence voltages and measuring equipment
with
the
required
accuracy should be applied. lf such equipment is not available, comparative
measurements can be made with
another calibrated
PM
2517 . However, theoreticallV the tolerances
mav
be doubled
in
the
extreme case.
The
measuring
arrangement should be such that the measurement cannot be aftected by external
influences.
Protect
the
circuit
against temperature
variations
(fans,
sun).
With
all the
measurements
the cables should be kept as short as
possible;at
hiqher frequencies co.axial leads
should be used.
Non-screened measuring cables aot as serials so that the measuring instrument will measure
HF voltage values
or
hum voltages.
Before checking
and adjusting
remove
bottom
cover. For
calibratinq the instrument the adiusting elements
are reacheable at
the
back of
the bottom
p.c.
board
N1.
In case of a complete adjusting of the
instrument it
may
also be
necessary
to
replace
the adjusting resistors. which are reacheable at
the
tront of the bottom
o.c.
board. ln
this
case
the toD'and bottom cover should be removed.
Fig.44.
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