How Many Volts IS ThisHow Many Volts IS This?The RMS RoleDouglas Brooks Let’s start the explanation of why with a discussion of power. Power is defined as Voltage*Current ( or P=V*I). By Ohm’s Law, V=I*R, or I=V/R. Therefore, by substitution, Power=V2/R. So if we apply a voltage sine wave (V*sin(Q)) across a resistor, the power applied to the resistor is given by the expression P=V2*sin2 (Q)/R (shown in Figure 1(b)). It can be shown that the average power delivered to the resistor is V2/2*R. Now here is the key question. What DC (direct current) voltage will deliver the SAME power to the resistor as the AC waveform we have just been considering? The answer is: Equivalent DC Volts = (V2/2).5 = .707*V. THIS is defined as the RMS voltage. It is the DC voltage that would deliver the SAME power to a resistive load……
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这篇文章由Douglas Brooks撰写，发表于2001年7月的《Printed Circuit Design》杂志中，旨在纠正对“120伏特有效值（RMS）”电压概念的普遍误解。文章首先指出，许多个人电脑杂志在解释家庭和办公室常用的120伏特RMS电源时出现了错误。RMS电压并非指电压的平均值、峰值或峰-峰值，而是交流电（AC）通过电阻时，与直流电（DC）产生相同功率的等效电压。作者通过解释功率的计算公式和欧姆定律，揭示了RMS电压实际上是峰值电压的0.707倍。例如，家庭电压的RMS值为120伏特，其峰值电压为169.7伏特，峰-峰值为339.5伏特。文章还讨论了有效值（RMS）的计算方法，即通过将波形的每个增量值平方、求和、取平均值，然后开平方根来得到。最后，作者指出，测量波形的真实RMS值并非易事，传统的AC电压表通过整流和应用校正因子来测量，但这种方法仅适用于正弦波形。而现代的“真”RMS测量设备能够分析波形形状并准确计算RMS值。
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