That is the 2 wire lead length shorted offset
resistance (without the squib resistance) can be
subtracted for the total resistance (including the
squib resistance) to determine the actual squib
(test) resistance.
The display should indicate a stable reading
when the test leads are securely attached to the
device under test. If the display appears to be
erroneous when connected to the resistance
under test, recheck the test leads for integrity
and cleanliness. If all external items appear to
be functioning properly, the next step in
problem isolation and diagnosis envolves
general trouble-shooting principles. If a
measurement problem appears on the 20 Ohm
range of the meter, test for a zero offset problem
first. Plug the 620A-4R with test leads into a
0.10 test resistor. If the meter doesn’t display a
value close to 0.1 Ohms adjust the zero (see
calibration procedure chapter). The zero
adjustment trimpot only has enough span to zero
out the 620 series test leads. The meter’s zero
adjustment pot wasn’t designed to zero out a
100 feet of 2 wire harness.
A 10.0 Ohm test resistor can be used for testing
mid-scale performance of the 20 Ohm range.
Performing a similar Functional Test with the
620A-4R across the 10.0 Ohm test resistor you
should get a reading close to 10.0 Ohms (i.e
9.995 Ohms is OK). If the 620 Series Igniter
Tester appears OK after checking a test resistor
then the connection problem must be outside of
the 620 series meter (i.e your wiring harness or
the actual device under test connection.) If the
620 series meter doesn’t agree with the test
resistors, then the meter or it’s test leads are
most likely broken. If this case, please contact
your local AMPTEC RESEARCH Service
Office, or call 1-800-350-5105 or (512) 447-
7456 (International Overseas) or FAX (512)
447-7455, email [email protected]
D-7.
Failsafe Operation
The AMPTEC 620 Series of Igniter Testers or
failsafe ohmmeters incorporate a constant
current source design that renders them
incapable of delivering excessive voltage or
current to the device under test. The typical
fail-safe current for each range is indicated
under the corresponding range switch on the
620 series meter front panel. Please refer to
section E-6 for a technical description of the
failsafe circuitry specifics.
As a further precaution the 620 Series Igniter
Tester is isolated from the AC line whenever the
POWER switch is in the ON position.
The 620 series igniter tester receives its power
from an internal rechargeable battery pack (4
“D” Cell Ni-Cad batteries). The 620 series
igniter tester “main power” switch (see item 12
of the Front Panel Diagram) must be in the
OFF/CHARGING position in order to charge
the batteries. Of course, the battery charger must
also be plugged into the unit’s keyed single
access connector. As mentioned earlier, the 620
tester’s AC line powered slim-line battery
charger must be connected to the front panel
charging jack. This “main power switch” must
be switched to “OFF” to charge safety feature
electrically (mechanically also) prevents any
possibility of the operator measuring with the
620 series igniter tester test leads while also
connected to an AC line powered battery
charger.
D-8.
Battery Monitoring Circuitry
The 620 series igniter tester display has a ±
polarity display indicator preceding the unit’s
regular 4 ½ digit numeric display. The negative
polarity display LED (see item 6 of the 620
series igniter tester Front Panel Diagram) is
used as a Low Battery indicator.
If the low battery LED is illuminated, 620
Series Igniter Tester readings should not be
trusted. An overnight recharge should be
performed before using the 620 series igniter
tester for critical testing.
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