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

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OPERATION
1864-1644 Positive Polarity Megohmmeter
10
3.2 Measurement Procedure
3.2.1 General
Either of two measurement procedures may be used,
depending on whether or not the correct resistance-
multiplier range is known. If the range is not known,
the search procedure (paragraph 3.2.2) should be
followed. If repetitive measurements are to be made
on a given range (i.e., if similar components are to be
sorted) the sort procedure (paragraph 3.2.3) should
be used.
3.2.2 Search Procedure
When the approximate resistance of the sample to be
measured is not known, proceed as follows:
1. Set the multiplier switch to the lowest range.
2. Set the function switch to
DISCHARGE .
3. Connect the unknown between the UN-
KNOWN + and - terminals.
4. Set the function switch to MEASURE .
5. Rotate the multiplier switch cw until the
meter gives a reading of less than 5.
6. The resistance of the unknown is the meter
reading multiplied by the multiplier-switch
indication.
7. Make measurements towards the low end of
the meter scale whenever possible, for best
accuracy and resolution.
3.2.3 Sort Procedure
When the approximate resistance of the unknown is
known, proceed as follows:
1. Set the function switch to DISCHARGE .
2. Set the multiplier switch to the desired
range.
3. Connect the unknown between the UN-
KNOWN + and - terminals.
4. Set the function switch to MEASURE .
5. The resistance of the unknown is the meter
reading multiplied by the multiplier-switch
indication. For go-no-go checks, it can be
useful to make high-and-low limit lines on
the outside of the meter case with strips of
masking tape.
6. Make measurements towards the low end of
the meter scale whenever possible, for best
accuracy and resolution.
3.2.4 Shock Hazard
Every precaution has been taken in the design of
1864 Megohmmeters to reduce the possibility of
shock. However, high voltage must be present at
the terminals to make measurements at the required
voltage levels, and the operator should be aware of
the dangers involved.
The current delivered by the megohmmeters under
short-circuit conditions is approximately 5 mA. This
5-mA current is not lethal to most persons but might
be lethal to those with poor hearts, and it is painful to
all. The actual current that will
fl ow through a person
depends on the resistance of the part of the body that
makes contact with the terminals. This resistance can
be as low as 300
Ω
. Note that any of the three insulated
binding posts can be at high voltage, depending on
the position of the shorting link.
When capacitors are tested there is an especially dan-
gerous condition because a charged capacitor easily
can have enough energy to cause heart
fi brillation
and death. The capacitor should always be shunted
before connection to the megohmmeter, and the func-
tion switch should be set to
DISCHARGE for a few
seconds before the capacitor is disconnected.
We strongly recommend that additional precautions,
such as rubber gloves and insulated benchtops, chairs
and shoes should be used for anyone making repeti-
tive measurements with the megohmmeter, particu-
larly measurements on capacitors. These precautions
should not take the place of careful discharge of the
capacitors before and after measurement, but should
be used as an additional safety measure.