Clamp-on ammeters to measure both AC and DC True RMS current for the industrial electrician. Models available for use on conductors up to 2" and up to 2000A along with measurment of voltage and resistance (model features vary).
Why Select True RMS Current vs. Averaging Current?
The nature of AC (alternating current) measurement is complicated by the fact that the current travels back and forth along a conductor and is exhibited graphically by a sine wave which comprises a 'cycle'. Because at any point in the cycle the amplitude of the wave varies, the current measurement at any given point would not be the same. There are two common ways to address the measurement of AC Current with an ammeter, and these include Averaging Current and True RMS Current methods.
AC Average Responding Current Mesurement: As a practical measure of a waveform's total value, “average” is most commonly defined as a summation of all the points' absolute values over a cycle. This is accomplished by adding all points on the wave, positive or negative, as contributing to the positive addition to the total current of one cycle. But the measurement is not quite this easy when the demands of operating equipment are introduced...
True RMS Current Measurement: Another method of mesuring waveform amplitude is based on the waveform's ability to do useful work when applied to a resistive load. In a practical sense, an AC measurement based on work performed by a waveform is different from the waveform's “average” value, because the power dissipated by a given load (including energy disspated as heat or mechanical motion) is not directly proportional to the magnitude of the voltage or current. Instead, the measurement is proportional to the square of the voltage or current applied to a resistance (P = E2/R, and P = I2R). Thus, for AC currents represented by a sine wave, the RMS current would always be 0.707 multiplied by the peak current value. But the presence of a perfect sine wave in industrial current measurement is not reality. Sine waves are typically not linear due to the demands of machinery and variable current demands. Thus, the heat dissipated by the constant resistive load is factored into the equation above, with the result being a 'True RMS' measurement value. So, why is this important?
To determine the proper size of wire (ampacity) that conducts electric power from a source to a load, RMS current measurement is the best choice because the primary concern with current is overheating of the wire from power dissipation caused by current flow through the resistance of the wire. Due to the increased accuracy of True RMS measurement, it is the best method to avoid overheating that could cause a fire hazard or the nuisance of blown circuits. The accuracy of RMS measurement is independent of waveshape, providing a comprehensive industrial solution.
