Next connect the 4 wire Kelvin (Option "300")
Clip Test Leads into the AMPTEC 620 Igniter
Tester . The AMPTEC 620 front panel input jacks
are spaced to only allow horizontal access (i.e.
V
high and
I
high) if using dual banana jacks. All
AMPTEC 620ES Kelvin leads have the 4 wire
current high, current low as well as the voltage
sense high and voltage sense low routed to the
end of the leads. The 4 wire Kelvin wires then
terminate in a pair of gold plated clip jaws (upper
and lower jaws). One Kelvin Clip for current and
voltage high, and another Kelvin Clip for current
and voltage low.
For 620 series test leads other than those termi-
nated with banana plugs, RG-58 Shielded Coax
Cabling is recommended. Customer built test
wiring should maintaining the four wire Kelvin
measurement if possible. Make the current con-
ductor the largest conductor and keep the voltage
sense input shielded or inside the current shield.
The AMPTEC 620 series Igniter Tester's five way
input jacks allow for customized wire connec-
tions, extended kelvin wiring (beyond 100 feet
depending upon conductor gauge), cables termi-
nated with spade lugs, and special banana jacks
can all be used with the AMPTEC 620 Tester.
All AMPTEC ohmmeters use a high impedance
voltmeter as part of the resistance measurement
process. This voltmeter is a highly accurate and
stable 4½ digit analog-to-digital converter (A to
D). The high impedance DVM must receive a
voltage drop in order to display the proper value.
When the DVM is not receiving a definite input
signal, the output reading from the Analog to
Digital Convertor can appear random and wan-
dering. The display may indicate a randomly
wandering number or it may indicate an
overrange (flashing) condition. This unpredict-
able display (No input to the DVM) condition is
not a malfunction, in fact, just a characteristic of
the high impedance voltmeter circuit and
should
not be mistaken for a fault in the instrument
- As
this condition is simply a state of an “open cir-
cuit” or “nothing connected” to the DVM cir-
cuitry. 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
low
low
instrument 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 is also located
in the optional Functional Test Box (FTB-
620ES) available from AMPTEC. The 1.0 Ohm
test resistor can be used for testing mid-scale
performance of the 2.0 Ohm range. Performing
a similar Functional Test with the 620ES 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 the test resistors in the
Functional Test Section 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 in the
Functional Test Box, 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]
