Figure D-1. Error Sources in Resistance
Measurements eliminated with Four Wire
Kelvin Connections
D-5.
Connections
Connections are made to the front panel
terminals using a 4-wire configuration as
described in section D-4. Only use
AMPTEC test leads supplied with the
630ES Failsafe Ohmmeter. When using
AMPTEC test leads, the notched connector
end plugs directly into the single access
notched main connector (see J1 manual
section E-6) of the 630ES.
Next turn the
connector clockwise until you feel the
notch or click of the mating connector of
the 630ES
. All AMPTEC 630ES 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
single banana plugs. One banana plug (
red
)
for current and voltage high, and another
banana plug (
black
) for current and voltage
low.
The 630ES’s keyed single access connector
also make it extremely difficult if not
virtually impossible during normal operation
to mis-connect measurement leads to the
630ES .
For 630ES leads other than those terminated
with banana plugs, RG-58 Coax Cabling is
used. This insures that using the four wire
Kelvin measurement system - the current is
carried in the largest conductor and that the
voltage input is shielded.
In addition, the 630ES keyed test lead
connector is optionally available for
customized wiring connections , kelvin
clips, cables terminated with spade lugs, and
special banana jacks.
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).
Unless it is receiving a definite input signal,
the output reading of this A to D is
ambiguous. The display may indicate a
randomly wandering number or it may
indicate an overrange condition. This
unpredictable display may make it seem to
appear that the instrument is experiencing
some sort of malfunction. It is, in fact, just a
characteristic of the voltmeter circuit and
should not be mistaken for a fault in the
instrument.
A flashing display (on and off usally all
zeros) indicates an over-range condition
whenever the terminals are open, or the
resistance under test is a higher value than
the selected 630ES resistance range. By
using a 4-wire Kelvin type lead set or by
shorting the V
HI
and I
HI
terminals together
and Vlow and Ilow terminals together the
instrument is in the 2 wire resistance 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 630ES
user short their wiring harnesses at the very
end (by the squib) and record the resistance
