1. True RMS/Average Response
The true RMS means that at a given frequency (such as power frequency), if the magnitude/amplitude of the current changes greatly, the true RMS is calculated based on the integral algorithm simulation, and the changed current can be measured. The average RMS is calculated based on the given average value of the peak value of the sine wave, and it is difficult to display the excess part more accurately.
Products with true RMS clamp meter: Fluke 319/381/365/369/902FC, etc.
2. Resolution and range
Resolution and precision are 2 concepts. From the user's point of view, resolution refers to the minimum amount of change in the current waiting signal that the meter can identify. And it is often necessary to combine a suitable range in order to display a more accurate value, or to exert the maximum accuracy of the instrument at hand.
For example, assuming that the current to be measured is 2.0A, the current variation is +/- 0.03A, and 2 clamp meters are assumed: the same 1% accuracy + 5 digits, the same display digits; Table 1 (resolution 0.1A, range 600A) , Table 2 (resolution 0.01A, range 3A). but:
Table 1 cannot identify the current change of 0.03A, and the reading may be unchanged at 2.5A.
Table 2 can identify the 0.03A current change, combined with the 5-digit reading accuracy, the reading change may range from 1.965-2.035 (the +/- 0.02 accuracy range has not been considered).
3. Frequency Response
The standard working current is the power frequency, so most clamp meter products are designed and calibrated based on the power frequency response. In different environments, there are different frequency requirements. For example, the widely used inverter/VFD has a working frequency range of 30~50Hz. At this time, if you need to accurately measure the VFD output current, you need to consider the frequency response of the clamp meter.
Specific product recommendations:
In the working mode of Fluke 381 annotation accuracy, it supports down to 10Hz
4. Low-pass filter
When it comes to frequency, we have to mention the low pass filter (LPF). Many loops are actually affected by high-frequency harmonics, which may cause the signal measured by the clamp meter to be higher than the actual value. Such as rectifiers, inverters, etc. Therefore, the loop measurement of such equipment requires the use of a clamp meter with a low-pass filter.
