IET Labs, Inc. 1864-1644, Руководство пользователя и обслуживания

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SERVICE AND MAINTENANCE
1864-1644 Positive Polarity Megohmmeter
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If the instrument is completely inoperative, be sure to
check the power-line connection and the fuse (located
in the IEC power input assembly on the rear panel).
6.4.2 Test Voltages
Tables 6.3 and 6.4 list a number of typical test voltages
to assist in trouble analysis. Figures 6.2 through 6.5
and the diagrams of Section 7 will assist in locating
components for testing purposes.
6.5 Calibration Procedure
6.5.1 General
The accuracy of the 1863 and 1864 depends on the
accuracy of the range resistors, the accuracy of the
applied voltages and the meter tracking accuracy.
The over-all accuracy can be checked most easily by
checking each one of these contributing quantities
separately, for to check all points on all ranges at
all voltages would require a tremendous number of
measurements.
6.5.2 Meter Tracking
The scale tracking can be easily checked using a de-
cade resistance decade box with 100-k
Ω
and 1-M
Ω
steps. Steps a through m of paragraph 6.2 should be
performed to check the tracking. If all readings are
corrected by the amount of the error found at a read-
ing of 0.5 they should be better than the speci
fi cation.
6.5.3 Voltage Accuracy
While the voltage can be checked to be within its
speci
fi cation, a more important check is to see that
the voltage and meter sensitivity track to give a cor-
rect resistance reading. Such a check is generally
adequate for it would be an unusual coincidence if
both the voltage-control and meter-sensitivity resis-
tors were in error, such that a good reading is obtained.
To check this tracking, perform steps n through s of
paragraph 6.2. If a reading is incorrect, the voltages
should be checked with a DMM connected between
the
+UNKNOWN and -UNKNOWN terminals. The
function switch can be set to either the CHARGE or
MEASURE positions.