Fluke 45 Measuring Voltage, Resistance, or Frequency, Measuring Current, Diode/Continuity Testing

45

Users Manual

Measuring Voltage, Resistance, or Frequency

To measure voltage, resistance, or frequency, press the desired function button and connect the test leads as shown in Figure 2-5. The meter will select the appropriate range in the autorange mode, and an annunciator on the display will indicate measurement units.

Note

After measuring high voltage to 1000 V dc, errors may occur when making measurements with 1 to 10 µV resolution. Allow up to two minutes prior to making low-level measurements.

Measuring Current

To measure current, insert the test leads in the 100 mA input terminal for currents up to 100 mA or in the 10 A input terminal for higher current. Press Cor Dand connect the test leads as shown in Figure 2-6 and described in the following procedure:

1.Turn off power in the circuit to be measured.

2.Break the circuit (on the ground side to minimize the common mode voltage), and place the meter in series at that point. (To measure current without breaking the circuit, use a current clamp.)

3.Turn on power to the circuit, and read the display. The meter will select the appropriate range automatically, and an annunciator on the display will indicate the units of the measurement value shown.

4.Turn off power to the circuit and disconnect the meter from the tested circuit.

Note

After measuring high current using the 10 A input, thermal voltages are generated that may create errors when making low-level (high sensitivity) dc measurements of volts, current, or ohms. To make the most accurate measurements, allow up to ten minutes for the thermals to settle out.

Diode/Continuity Testing

Diode and continuity tests are performed by a diode test function with a continuity beeper that can be turned on and off.

The continuity test determines whether a circuit is intact (i.e., has a resistance less than about 30 Ω ). The meter detects continuity for intervals as brief as 50 µs. The continuity test function cannot be selected for the secondary display.

To perform a continuity test, press G, and connect the test leads as shown in Figure 2-7. The beeper emits a single beep when the input drops below +0.8 V (approximately 1 kΩ ), and emits a continuous tone when the input goes below +25 mV (approximately 30 Ω ).

The diode test measures the forward voltage of a semiconductor junction (or junctions) at approximately 0.7 mA. Readings are displayed in the 3 V range at the medium and fast measurement rates. "OL" is displayed for voltages above +2.5 V. If the diode test is performed at the slow reading rate, readings are displayed in millivolts on the 1000 mV (1 V) range.

2-6