7
tacts. Some overload conditions may cause the fuses to burn out as well as
open the relay contacts.
d. When an overload of sufficient magnitude is applied to the VOM, the reset
button will “pop-up” approximately 3/16" above the surface of the panel. To
reset the VOM for normal operation, first remove the overload and depress
the button. If the overload remains connected to the Instrument, resetting the
overload protection reset button will not connect the VOM input circuit.
In addition to the overload protection circuit, two diodes protect the indicating
instrument circuit. These diodes limit the current through the coil in case of over-
load.
Fuses:
Basic Overload protection is provided by a small inexpensive and easily
obtainable 3 AG type, 1 Amp, quick-blow fuse. This fuse is rated to interrupt circuit
voltages up to 250 volts. A supplemental high energy fuse is provided for addi-
tional protection from severe overloads. This fuse is the Bussman Type BBS 2A
600V. A Littlefuse Type BLS 2A 600V fuse may be used as a substitute replace-
ment.
NOTES:
If the 260-8P fails to indicate a reading, the 1 Amp or 2 Amp fuse may be
burned out. (Refer to paragraph 5.4 for fuse replacement.) Use only the specified
fuse type.
The 0-10A range is not fused. The shunt connects directly to the -10A and +10A
jacks.
The relay, fuse and diodes will prevent serious damage to the Instrument in most
cases of accidental overload. However, no overload protection system is com-
pletely foolproof and misapplication on high voltage circuits can damage the
Instrument. Exercise care and caution to protect both the user and the Instrument.
1.3
Internal Batteries
There are two batteries in the ohmmeter circuits, a NEDA 13F size D cell that
furnishes 1.5-volts for the R X 1 and R X 100 ranges and a NEDA 1604A alkaline
battery that furnishes 9-volts for the R X 10,000 range and overload circuit. The
1.5-volt D cell is held in place with two spring clips which also serve as battery
contacts. The polarity symbols for the D cell are marked near the battery contacts.
The 9-volt battery is held in place with a spring clip, but contact is made with a
separate connector that is polarized. Always observe correct polarity when re-
placing the 1.5-volt D cell.
The 9-volt battery must be installed and tested before the Instrument is ready for
use. Perform the overload test described in Paragraph 1.4 to ensure proper over-
load circuit operation prior to using the Instrument.
1.4
Overload Circuit Test
a.
Set the range switch to R X 10,000 POSITION and the function switch to -DC
POSITION.
b.
Plug the black test lead into the -COMMON jack terminal and touch the other
end of the test lead to the +1 volt input terminal. (The relay reset button
should rise, indicating that the overload circuit is in working condition.)
NOTE:
No damage will occur to the 260-8P as a result of this test.
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