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August 2025
Achieving 10 GWMeasurements at 100 VDC By Christopher E. Strangio, Founder and President, CAMI Research, Inc. M
easurement of insulation resistance (IR) occurs by applying a voltage between two conductors and observ-
ing how much current flows through the insulation. Dividing the applied voltage by the flowing current using Ohm’s law pro- duces a value of insulation resistance.
involve fitting complex circuitry into ever- smaller spaces, particularly in airborne or spaceborne applications. Consequently, the interconnects between increasingly compact electronic modules must shrink as well. Nano-D connectors have typical contact spac- ing of 0.025 in. (0.635 mm), half the spacing of micro-D connectors which them- selves reflect a similar reduction in contact spacing from the generation before micro-Ds appeared on the mar- ket.
As connector design forces pins
into smaller spaces, pin spacing shrinks, and high voltage testing for proper electrical isolation between pins pushes the applied test voltage down to avoid air breakdown. Requirements presented by CAMI’s customers over the last few years now require an IR of 10 gigohms at 100 VDC, and this, in turn, demands a cur- rent measurement sensitivity of 10 nA or better.
Figure 1: Low-voltage continuity and resistance test.
Typical PVC or Teflon electrical insula-
tion work extremely well, and as a result, only a miniscule current can be detected, so little, in fact, that we refer to the current as “leakage current” and need to raise the volt-
The Method CAMI Research’s Cable -
Eye® HVX-21 multi-channel high voltage cable test system
offers a leakage current sensitivity limit of 200 nA which can be reduced to 100 nA for special applications using a sample-averaging method. However, the company still remains unable to reach the 10 nA sen- sitivity required for new appli- cations.
to a standard Microsoft Windows PC running CAMI’s test software which issues control commands to the tester and reads responses from it as the measurements are completed. Test results appear on a video monitor
for immediate review and diagnostics, and these results may be printed, if desired, to fully document the test. Referring to Figure 1, the tester receives commands through a USB channel to first perform a low-voltage continuity and resistance test on the attached wiring, also referred to as unit under test (UUT). If the wiring matches the model cable
and the connection resistances comply with the set limit, we disengage the low voltage
Figure 3: Replacing the internal high-voltage generator with the Keithley SourceMeter.
Rather than re-engineer the pro-
Figure 2: High-voltage distribution bus and five typical relays.
age to hundreds or thousands of volts to achieve detectable current flow. This, in fact, motivated the development of high voltage testers many years ago. Recently, testing cables and connectors
at high voltages poses some new challenges. Advances in electronic packaging often
grammable high voltage power supply in the tester to meet the new require- ment, CAMI uses an existing single- channel high-voltage test instrument, the Keithley 2400 series SourceMeter™, which has the needed sensitivity, and provides a remote- control capability allowing it to be integrated with CAMI’s existing con-
trol software. The successful result met the objective quickly and efficiently and offers increased-sensitivity IR measurements at a much lower test voltage than had previously been possible. Under normal operation, CAMI’s HVX tester serves as a data-acquisition peripheral
module seen in the diagram through the relay matrix and drive a high voltage signal onto a distribution bus. Relays switch the high voltage stimulus
signal onto the test points to which the UUT is attached. The system then sequentially applies high voltage to individual wires in the cable through the relay matrix while col- lecting leakage results from each wire tested. Figure 2 illustrates a high-voltage distri-
bution bus and five typical relays. When a relay is energized, it connects the bus to a test point which drives a signal into the UUT. For a two-ended connection, two relays energize, one at each end of the wire.
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