Gossen Metrawatt M817S Mains-analysis device, Mains analyser M817S Scheda Tecnica

6-3

CH 6/ Advanced Setup Options

RMS stands for root mean square, a mathematical formula used to compute the 

equivalent value of the voltage and current. Voltage and current changes are measured 

and checked against the programmed limits. Thresholds are preset as high limits 

(threshold above the programmed limit) and low limits (threshold below the 

programmed limit). RMS variations result whenever voltage or current rms value rise 

above or fall below the threshold limits. 

The Energy Platform limits are fixed at IEEE 1159 standard default values of 90% of 

normal for sag (dip), 110% for swell, and 10% for interrupts. However the user has the 

option to enable/disable rms variations.

In order for the instrument to trigger on rms variation, any one of the measured 

quantities for which a trigger is enabled must go above the High Limit or below the 

Low Limit for a period of at least one rms sample point (which are taken twice per 

cycle with a one cycle sliding integration window).

The disturbance end point is defined as the cycle when all channels for which triggers 

are enabled have come back within limits (plus hysteresis). Until this criteria is met, 

any subsequent excursions beyond the thresholds are considered part of the original 

disturbance. To minimize the number of triggers recorded for a sequence of closely 

spaced disturbances, hysteresis is employed in both voltage and time for the begin-

event and end-event thresholds.

NOTE: Hysteresis values assigned to limits are set by the system and not 

programmable by the user.