SECTION D - OPERATION AND USE
D-1.
General Operation
This section contains operating instructions for the
AMPTEC 620A-4 Explosive Safety Igniter Tester. A
description of the front panel controls, connection
instructions and theory behind 4-wire Kelvin
resistance measurement is discussed in this section.
D-2. Front Panel Features and Operation
When the front panel power switch is in the “
OFF
”
or charging position, all power is removed from the
(output terminals) ohmmeter measurement circuitry
and the unit's internal battery pack is connected to
the rear panel charging jack
(see diagram on next
page).
When the AMPTEC 620A-4 main power switch
(single throw double pole) is placed in the "
ON
" or
up position, the battery pack is disconnected from the
rear panel charging jack. The possibility of a voltage
between the device under test and a AC/DC Voltage
from the rear panel AC/DC Charging jack is
therefore eliminated. The operator need not be
concerned if the battery charger is plugged in while
making resistance measurements.
The AMPTEC 620A-4 ohms ranges are
manually selected by pressing the desired range
switch on the front panel. The range select
pushbutton for the
lowest resistance range 20 Ohms (left-most
resistance range button) indicated above the
range select buttons. When a given range is
selected (pushed in) the other range switches
"pop-out" and inform the user. It is obvious to
the 620A-4 user which resistance range has
been selected, as it is pushed in. Also note that
a resistance range should be selected after
powering up the 620A-4 to place it in an
operational mode. After turn "ON", a range
should be selected. If the resistance being
measured (including "Open Circuit/
Disconnected states") is a higher value than the
selected range, the instrument's display will
flash (blink), which indicates "overrange". If
the front terminals are disconnected, the
display may even wander around; this is normal
for the disconnected 4 Wire Kelvin "Open
Circuit" mode.
D-3 Rear Panel
Range Switch
Option "620-DC"
Fuse Holder
AMPTEC 620A-4 Range Switches shown
The fuse holder is mounted on the rear panel
of the unit. The fuse for the AMPTEC 620A-4
is a 2-ampere fast blow 3 AG type (1 ¼"
long).
This fuse is designed to protect the battery pack
from excessive currents. On some AMPTEC
620A-4 versions a fuse holder is mounted on
