Conductance; Leakage Testing - Fluke 27 User Manual

27
Users Manual

Conductance

Conductance measurement is performed with the
function selector switch in the ohms (e) function. The
conductance range can only be entered using manual
range selection; autorange cannot enter the conductance
range. The conductance range can be used both to
measure conductance (1/e, 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 Fluke 27 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 2 V
dc.
10
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 (nS). Connect the test leads to the test points
on the unit under test, and read the leakage in terms of
conductance.
There is normally a small residual reading with
open test leads in the conductance range. To
ensure accurate measurements, connect clean
test leads to the Fluke 27, 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).
Diode leakage tests require that the diode junction be
reverse biased when being measured. This is
accomplished by connecting the anode of the diode to
the COMMON input terminal and the cathode (ring) of the
diode to the volts/ohms/diode test terminal. Leakage at
the test voltage being applied can then be read in terms
of conductance.
Note