Instructions for use of AC and DC clamp meters
1. Measuring single-phase current
1. When using the clamp meter, special attention should be paid to safety issues, and the hand holding the watch should wear gloves. Although the instrument has high insulation performance (safety level is Class II), in order to ensure safety, it is still necessary not to measure the current of non-insulated wires; in addition, attention should be paid to prevent the live components from being connected to the ground or between phases during the measurement operation. short circuit.
2. When measuring, the wire should be in the center of the jaws as much as possible, as shown in the figure below, such measurement results are relatively the most accurate.
3. When the value to be measured is very small, in order to improve the measurement accuracy, the current-carrying wire to be measured can be wound several times on the jaw core, and the value displayed by the instrument will be expanded to a multiple of the number of windings. Divide the value displayed by the meter by the number of turns to get the actual current value. As shown in the example below, when the power cord only passes through the iron core of the clamp meter once, the meter displays a value of 0.5A; the number of times the wire passes through the iron core hole is N=5 times , the displayed value is 2.5A, that is, the actual line current I1=2.5A/5=0.5A.
4. Ordinary clamp meters cannot measure the output voltage and current of the AC drive, especially the voltage, which can hardly display stable values. This is because the output voltage of the AC drive is in the form of a modulated square wave (PWM wave) of thousands or even tens of thousands of hertz, while ordinary clamp meters can only measure the effective value of sine waves around the power frequency.
In addition, clamp meters are not suitable for measuring currents with very low frequency (such as rotor current of wound rotor asynchronous motor, etc.), because when the frequency is very low, the reading will be much smaller than the actual value.
