45

Users Manual

By contrast, many meters use average-responding ac converters rather than true rms converters. The scale factor in these meters is adjusted so that they display the rms value for a harmonic-free sine wave. However, if a signal is not sinusoidal, average-responding meters do not display correct rms readings.

Effects of Internal Noise in AC Measurements

With the input shorted in an ac function (volts ac, current ac, or frequency) the display will read approximately 50 due to internal amplifier noise. Because the meter is a true rms responding meter, this noise has only minimal contribution to the reading at the specified floor (1500 counts in the medium rate) of each range. When the rms value of the two signals (internal noise and range floor) is calculated, the effect of the noise is shown:

Total rms digits = (502 + 1500 2 ) = 1500.8

The display will read 1501. At the down-range point (2800 display counts in the medium rate), the display will read 2800 with no observable error.

Note

Do not use the relative modifier (REL) to "zero" the meter because the relative reading is simply subtracted from the present reading.

Calculated (AC + DC) RMS Measurements

When Yand Z, or Cand Dare pressed simultaneously, the meter will alternately take a dc and an ac measurement then calculate and display the rms value:

RMS value = dc 2 + ac 2

In the dual display mode, when the volts ac and volts dc functions are selected, the 10 MΩ dc input divider is in parallel with the ac-coupled 1 MΩ ac divider.

Note

When measuring AC + DC, (or any dual display combination of AC and DC) In the fast reading rate, the Fluke 45 may show significant reading errors. This results from a lack of filtering on the DC portion of the measurement for the fast reading rate. To avoid this problem, use only the "slow" and "medium" reading rates for AC + DC or AC and DC combinations.

Waveform Comparison (True RMS vs. Average-Responding Meters)

Figure 4-3 illustrates the relationship between ac and dc components for common wave- forms, and compares readings for true rms meters and average-responding meters. For example, consider the first waveform, a 1.41421 V (zero-to-peak) sine wave. Both the Fluke 45 and rms-calibrated average-responding meters display the correct rms reading of 1.0000 V (the dc component equals 0). However, consider the 2 V (peak-to-peak) square wave. Both types of meter correctly measure the dc component (0 V), but your Fluke 45 also correctly measures the ac component (1.0000 V). The average-responding meter measures 1.111 V, which amounts to an 11 % error.

Since average-responding meters have been in use for so long, you may have accumulated test or reference data based on them. The conversion factors in Figure 4-3 should help you convert between the two measurement methods.

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Fluke 45 user manual Effects of Internal Noise in AC Measurements, Calculated AC + DC RMS Measurements
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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.

Another remarkable characteristic of the Fluke 45 is its frequency measurement capabilities, which can measure frequencies up to 1 MHz. This is particularly useful in applications involving signal analysis and troubleshooting oscillators.

Moreover, the Fluke 45 is designed with user convenience in mind. It is lightweight and portable, making it easy to carry around, whether on a job site or in a workshop. The rugged construction, reinforced with high-quality materials, ensures it can withstand harsh conditions often encountered in the field.

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.
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