Using RMS Measurements

What are the RMS? RMS values obtained by the mathematical procedure used to calculate a single value from a sequence of samples. This allows you to compare one series with another, or one phase to another. RMS-voltage is the effective value of changing or alternating voltage. This value must match the same power as in the case of a constant voltage applied to pure resistance. In today's world of discrete wave signals produced by the crystals of digital signal processing (DSP), such measurements are among the most easily implemented. Each value data within a predetermined period (usually one cycle) is multiplied by itself (squaring), and then all these values are averaged over the period (summed then divided by the total number) and value obtained from the square root.

For a stable DC signal each sample has the same value, so any of them can serve as the equivalent RMS-value. In the case of sinusoidal values of the wave is increasing within the first quarter cycle, then decrease to zero and go to negative values until a minimum value within the second quarter of the cycle (see Fig. 1). Figure 1. Waveform the load-phase power supply with a full-wave meter. RMS-value of pure sine wave is approximately 70.7% of the peak value.

When the distorted waveform is not true, that is a response to Asked why instruments that measure not in terms of true-rms, can produce quite different results for different degrees of distortion and, hence, can not be used if harmonics. Those devices which are only calculated for 71% of the peak will give a wrong result for the shape of the current shown in Fig. 1. The figure shows the classical form of the current signal-phase power supply with full-wave rectification, which is present in many electronic devices. This form of the wave with harmonic distortion (THD) at 108% had a peak value of 3.6 A and the true RMS value of 1.4 A, that does not coincide with calculated value of 0.707 * 3.6 = 2.55 A. poor quality of electricity analyzers that are configured on the RMS-value, may miss some data. A number of devices calculate RMS-values in the course of several cycles. Vesmaveroyatno, These monitors do not lock the multi-phase failure during one cycle in Fig. 2. Figure 2. Failure during one cycle in two phases. Such a distortion of the signal is typically the case when the problem is eliminated with a security guard. Fig. 3 failure during one cycle, arising from the breakdown at the peak voltage (possibly due to faulty insulation, or a lightning strike) will give different RMS-values on each of three cycles. Figure 3. Single-phase failure in breakdown peak voltage. Depending on the mechanism and enable the trigger thresholds, perhaps not detected until the failure of the third cycle, because RMS-value defective loops can exceed the threshold of the trigger. Fault, which is expressed in phase shifts, can have identical values from one cycle to the next, despite variations in the amplitude of the wave. This occurs when used with many elektroanalizatory enable the trigger mechanisms, such as transient or distortion of the waveform. It should be remembered that although the device does not notice these faults, this does not mean they do not exist. Many writers such as John Grayken offer more in-depth analysis. To work on a recording of distortion power quality company 'Energometrika' recommends model PM175 – Analyzer electricity meter electrical energy quality indicators.

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