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Fluke 27 [14/30] Resistance and diode test continuity

Users Manual

Resistance and Diode Test/Continuity

Caution

To avoid possible damage to the meter or to

the equipment under test, disconnect circuit

power and discharge all high voltage

capacitors before measuring resistance,

testing for continuity, or diode test.

Resistance Measurement

Test lead resistance may influence measurement

accuracy on the 320-ohm range. To determine the error,

short the test leads together and read the lead

resistance. Correct the measurement by subtracting the

lead resistance from the measurement, or use the

Relative (REL) mode to zero the display. The error is

usually 0.1 to 0.2 ohms for a standard pair of test leads.

Some in-circuit resistance measurements can be made

without removing diodes and transistors from the circuit.

The full-scale measurement voltage produced on ranges

below 32 megohms does not strongly forward bias silicon

diodes or transistor junctions. Use the highest range you

can (except 32 megohm) to minimize the possibility of

turning on diodes or transistor junctions. Full scale

measurement voltage in the 32-megohm range does

strongly forward bias a diode or transistor.

Diode Test and Continuity

In diode test, there is only one range: 0 to +2.08 volts.

Voltage is developed across the component(s) under test

by a test current output from the Fluke 27. Voltages

greater than 2.08 V or open test leads produce an

overload (OL) condition. Negative inputs produce a

negative indication (they are not suppressed). In the

diode test function S the beeper produces a

continuous tone if the input is less than 0.1 V, and the

beeper beeps once when the input descends through a

0.7 V threshold.

Audible continuity testing is also performed with the

function selector switch in the diode test/continuity

position. A continuous tone sounds for test resistances

below approximately 270 ohms. An intermittent

connection produces erratic beeps, and can be valuable

troubleshooting aid. Erratic beeps can also occur, due to

environmental noise, if a test value is very close to the

threshold (270 ohms). Test resistances from

approximately 270 ohms to 2600 ohms produce a short

tone similar to a forward biased diode. Test resistances

less than approximately 36 kilohms will produce an on-

scale reading.

Fluke 27 [14/30] Resistance and diode test continuity

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