As this condition is simply a state of an “open
circuit” or “nothing connected” to the DVM
circuitry. A flashing display (on and off usually
all zeros) indicates an over-range condition when-
ever the test lead terminals are open, or the resis-
tance under test is a higher value than the range
selected on the AMPTEC 620 tester.
Connecting
V
HI
to I
HI
and V
lo
to I
lo
eliminates the wander-
ing (open circuit) display condition
.
By using a 4-wire Kelvin type lead set or by
shorting the
V
and
I
terminals together and
HI
HI
V
and
I
terminals together the instrument
low
low
is in the 2 wire resistance mode.
Resistance Offset in 2 Wire mode
All wiring including harness wires from the two
wire test connection out, are "
in series
" with the
test squib resistance and become part of the actual
two wire measurement (
another potential source
of measurement error if not compensated for
) .
Many Ordnance test procedures have the 620
series Igniter Tester user short their wiring
harnesses at the very end (by the squib) and
record the resistance value or offset. Then when
the 620 series Igniter Tester leads, including the
in-series harness wiring resistance, is connected
to the test squib, the squib test resistance can be
calculated (via subtraction of the 2 wire harness -
test lead resistance offset).
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.
Identifying a Test Connection problem
A precision 1.0 Ohm test resistor test resistor can
be used for testing mid-scale performance of the
2.0 Ohm range. Performing a similar Functional
Test with the 620LM meter across the 1.0 Ohm
test resistor should get a reading close to 1.00
Ohm (i.e. 0.9995 Ohms is OK). If the 620 Series
Igniter Tester appears OK after checking eaqch
range against a known resistance 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 +1(512) 858-4045 (International
Overseas) or FAX+1(512) 858-4340, email
[email protected]
The AMPTEC 620 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 2.0 Ohm
range of the meter, test for a zero offset problem
first. Plug the 620 with Kelvin test leads into a
0.10 test resistor (i.e. AMPTEC # FTB-620ES).
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.
D-5.
Failsafe Operation
The AMPTEC 620LM Igniter Tester uses a fail-
safe 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 with
most AMPTEC models 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 620LM Igniter
Tester is line isolated from the AC line to 3 KV
DC or AC when only used 620LM-DC AC wall
Power Adapter/conditioner (supplied with the
meter).
As this meter is fitted with the Diode Test
function the nature of this circuit uses higher
compliance voltage. As a result the failsafe
current limit is 25 mA.
