Measuring Conductance; Leakage Testing - Fluke 27/FM Operator's Manual

Conductance and Leakage Testing
the multimeter. Voltages greater than 2.08V or open test leads produce an
overload (OL) condition. Negative inputs produce a negative indication (they
are not suppressed). In the diode test function ( ((to
), the beeper
produces a continuous tone if the input is less than 0.1V, and the beeper
beeps once when the input descends through a 0.7V threshold.
Audible continuity testing is also performed with the function selector
switch in the (
)
position. A continuous tone sounds for resistances
below approximately 150 ohms. An intermittent connection produces erratic
beeps, and can be a valuable troubleshooting aid. Erratic beeps can also
occur, due to environmental noise, if a test value is very close to the
threshold (150 ohms). Test resistances from approximately 150 ohms to 1000
ohms produce a short tone similar to a forward biased diode. Test
resistances less than approximately 20 kilohms will produce an on-scale
reading.
Measuring Conductance
Measuring conductance is performed with the function selector switch in
the ohms (11) function. The conductance range can only be entered when the
meter is in the manual ranging mode. The conductance range can be used both
to measure conductance (1/ohms, the inverse of resistance) and to measure
very high resistances (greater than 32 megohms).
High value resistance measurements are susceptible to induced noise, and may
require careful shielding. Conductance measurements are displayed in
nanosiemens (nS). Calculate megohms by dividing 1000 by the nanosiemens
displayed (1000/nS is equivalent to megohms). Example: 2 nS converts to 500
megohms (1000/2).
Leakage Testing
The conductance range effectively extends the resistance measurement
capability of the multimeter to the point where it can provide useful leakage
measurements on passive components. For example, the operator can detect
leaky diodes, cables, connectors, printed circuit boards, etc. In all cases,
the test voltage is less than 2V dc.
Leakage testing on purely resistive components such as cables and printed
circuit boards is straightforward. Select the ohms function and manually
increment the range to conductance (nS). Connect the test leads to the test
points on the unit under test, and read the leakage in terms of conductance.
NOTE
In the conductance range, there is normally a small
residual reading with open test leads. To ensure accurate
measurements, connect clean test leads to the multimeter
and (with the leads open) read the residual leakage in
nanosiemens. Correct subsequent measurements by
subtracting the residual from the readings. This can be
done automatically using the Relative mode (REL
).