Fluke FLK-1555FC/IR [30/50] Guard terminal use

1550C/1555

Users Manual

To charge the battery with the ac power supply:

1. Turn the Tester off.

2. Disconnect the test leads from the Tester.

3. Move the safety shutter to access the power supply connection.

4. Connect the ac power cord to the IEC ac power socket on the Tester.

5. Connect the other end of the power cord to an ac power supply. See

“General Specifications” for ac charger input specifications.

The LCD displays CHARGING. Downloading is possible when the

Tester is in Charging mode.

Guard Terminal Use

Note

Insulation resistance is measured between the (

) and (

−

) output

connections. The Guard terminal (G) is at the same potential as the

negative (−) terminal but is not in the measurement path.

For most tests, only two test leads are used. Connect the positive (+) and

negative (−) test leads to the corresponding inputs on the Tester. Connect the

test lead probes to the circuit under test. The Guard (G) terminal is left

unconnected.

For the best accuracy when you measure very high resistances, use three-wire

measurements and the Guard terminal. The Guard terminal is at the same

potential as the negative (−) terminal, and can be used to prevent surface

leakage or other unwanted leakage currents from degrading the accuracy of the

insulation resistance measurement.

Figure 6 shows how to measure the resistance from one of the conductors to

the outer shield. In this case, there is a leakage current along the surface of the

inner insulation near the cables end. This leakage adds to the current that the

negative terminal senses, and causes the Tester to read a lower resistance than

it should.