PowerQualityRecorders.com

Waveform capture in a power monitor

Many power monitors will typically record voltage, current, deviations from one cycle to another via waveform capture. So any changes that occur in RMS values will cause a capture to occur. Is that what the RMS graphs are for? Normal power monitor graphs can have a minimum and maximum rms graph as far off as 59 seconds and 59 cycles (if the interval is set to 1 minute). Folks we are discussing 21st century AC here, even the old chart recorders of yesteryear gave a dot once every two seconds.

While these units are good for load profiling, transformer ratings, and general circuit sizing information- when it comes to detail they don't serve the purpose. Waveform capture is meant to record waveform events such as notches, rings, and transients as well as surges and sags. The trouble starts when these power monitors claim to be power quality recorders. Based on the amount of memory that each unit has, the recording interval period may be as long as 1 minute. I will say it again, one minute. Most power quality recorders record continuously at least 320 samples per cycle. Provided the math:

320 samples per cycle x 60 cycles x 60 seconds per minute = 115200 samples over one minute. That's a lot of information! Even 15 second resolution is not enough. Compare these two graphs done on the same service at the same time.