User manual

PQM-702, PQM-703 Operating Manual

5.11 Averaging the measurement results

Mains monitoring over a longer period means that a significant amount of data needs to be

collected. To ensure that such data analysis is possible at all, it is necessary to introduce the mech-

anisms for reducing data size to the values acceptable by both, people and machines.

Let us take the example of EN 50160 compliant power quality measurements The basic mains

test period is one week. If all 200-millisecond RMS values were to be remembered, we would get

3.024 million measurements. Processing this amount of data may be time-consuming and difficult.

Therefore, the averaging concept has been introduced which involves recording one value per

a specified time interval for the analysis purposes. For the EN 50160 standard, such time interval

is 10 minutes. In such case, the analyzer calculates an average 10-minute value basing on about

3000 of 200-millisecond values (approximately, as in reality the conventional 200-millisecond value

is 10/12-period value synchronized with the mains frequency). Each average voltage value is rec-

orded every 10 minutes which gives "only" 1008 measurement results.

Fig. 40 presents the method according to which the analyzer determines the average values at

averaging intervals equal to or greater than 10 seconds with the 10-minute averaging time. This

method meets the requirements for a Class A of IEC 61000-4-30:2009 standard.

Average values are synchronized with a real time clock as follows. When the clock counts an-

other integer multiple of the averaging period, two processes occur:

 current 10/12-cycle interval (k-th measurement in Fig. 40) is assigned as the last in the

aggregation interval (x),

 simultaneously the first 10/12-cycle interval is started for the next averaging period (x +1).

Such a resynchronization method generates Overlap 1 (see Fig. 40). The data from this area

are processed twice, as each of the 10/12-cycle interval is analyzed independently. The aim of this

kind of resynchronization is to ensure that the two analyzers of Class A, connected to the same

system, and synchronized with UTC, will give the same results. In the analyzers PQM-702 and

PQM-703, the resynchronization of intervals according to the method described above is performed

for averaging times: 10 s, 15 s, 30 s, 1 min, 3 min, 5 min, 10 min, 15 min, 30 min, 60 min, 120 min.

Fig. 40. Determining the averaging intervals longer than 10 seconds (with the 10-minute

averaging).