When Measuring Resistance, True RMS Measurements

Applications 4

When Measuring Resistance

Two-Wire Configuration

The meter measures resistance in a two-wire configuration using a resistance ratio (some- times called ratio-ohms) technique. Two-wire resistance measurements are simple to set up and yield good results for most measurement conditions.

The full-scale voltage for each resistance range is shown in Table 4-5. The zinput test lead is positive with respect to the COM lead.

Correcting for Test Lead Resistance

The resistance of the test leads can introduce error when measuring low resistances. Typi- cal test leads may add as much as 0.5 Ω to readings.

To correct for this error using the relative modifier (REL):

1.Insert test leads in the Xand COM input terminals.

2.Turn the meter on and press Oto select the resistance function.

3.Select the manual range mode by pressing E, T, or U. Then press Uor Tto select the desired range. This is necessary because autoranging is turned off (and the meter is locked in the range it is in) when the relative mode is selected.

4.Touch the test leads together. The display will show the resistance of the test leads.

5.With the test leads still touching, press K. The resistance in the test leads becomes the relative base and the meter should show 0 Ω .

6.As long as the relative modifier remains selected, the resistance readings shown on the display will be the resistance measured minus the relative base, which in this case is the resistance in the test leads.

Table 4-5. Ohms Test Voltage

Medium and Fast Reading Rates

Range	Typical Full Scale Voltage

Range

Slow Reading Rate

Typical Full Scale Voltage

300Ω

3kΩ

30kΩ

300kΩ

3MΩ

30MΩ

300MΩ

0.25

0.24

0.29

0.3

2.25

2.9

100Ω

1000 Ω

10kΩ

300kΩ

1000 kΩ

10MΩ

100MΩ

0.09

0.10

0.11

0.12

0.65

2.75

Open circuit voltage is 3.2 V (maximum) on the 100 Ω , 300 Ω , 30 MΩ , 100 MΩ , and 300 MΩ ranges, and 1.5 V (maximum) on all other ranges.

True RMS Measurements

The meter measures the true rms value of ac voltages and currents. In physical terms, the rms (root-mean-square) value of a waveform is the equivalent dc value that causes the same amount of heat to be dissipated in a resistor. True rms measurement greatly simplifies the analysis of complex ac signals. Since the rms value is the dc equivalent of the original waveform, it provides a reliable basis for comparing dissimilar waveforms.

4-9

45 specifications

The Fluke 45 is a versatile and high-precision Digital Multimeter that is designed for a wide range of applications in electrical testing, troubleshooting, and maintenance. Known for its reliability and advanced features, the Fluke 45 is an essential tool for engineers, technicians, and professionals who require accurate measurement capabilities.

One of the standout features of the Fluke 45 is its ability to measure both AC and DC voltage and current. With a maximum input voltage of 1000 volts and current ranges up to 10 amps, users can conduct a variety of electrical tests with confidence. The device is equipped with an intuitive dual display, allowing for simultaneous viewing of multiple measurements. This feature enhances usability during complex diagnostics.

The Fluke 45 also boasts an impressive resolution of 0.1 mV and a basic accuracy of 0.25%, which translates to highly reliable readings. The auto-ranging capability simplifies the measurement process, automatically selecting the appropriate range based on the input signal, thus saving time and reducing user error.

In addition to voltage and current measurements, the Fluke 45 features resistance measurement capabilities, with a range of up to 40 MΩ. This makes it an effective tool for testing circuits, identifying faults, and ensuring the integrity of electrical systems. The continuity test function, complete with a built-in beeper, assists in quickly diagnosing wiring issues.

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To enhance functionality, the Fluke 45 features a data hold function that freezes the displayed measurement for easier reporting. Additionally, it can store data for later retrieval, making it convenient for users who need to compile test results over time.

In summary, the Fluke 45 Digital Multimeter is an advanced instrument that combines precision, versatility, and user-friendly design. Its wide measurement capabilities, high accuracy, and durable build make it an invaluable tool for professionals in diverse electrical and electronic applications. Whether for routine maintenance or complex troubleshooting, the Fluke 45 stands out as a reliable partner in achieving accurate and efficient results.

Fluke 45 user manual When Measuring Resistance, True RMS Measurements, Two-Wire Configuration

Models: 45

Applications 4