Electro-Voice 250, 1252 Instantaneous Flicker Evaluation, Short Term Flicker Evaluation, Summary

•Instantaneous Flicker Evaluation

An output of 1.00 from Block 4 corresponds to the Reference Human Flicker Perceptibility Threshold for 50% of the population. This value is measured in Perceptibility Units (PU) and is labeled Pinst. This ia a real time value and it is continuously updated.

•Short Term Flicker Evaluation

An output of 1.00 from Block 5 (corresponding to the Pst value) corresponds to the conventional threshold of irritability per IEC 1000-3-3. In order to evaluate flicker severity, two parameters have been defined: one for the short term called Pst (defined in this section) and one for the long term called Plt (defined in the next section).

The standard measurement time for Pst is 10 minutes. Pst is derived from the time at level statistics obtained from the level classifier in Block 5 of the flicker meter. The following formula is used:

Pst = 0.0314P0.1 + 0.0525P1s + 0.0657P3s + 0.28P10s + 0.08P50s

Where the percentiles P(0.1), P(1), P(3), P(10), P(50) are the flicker levels exceeded for 0.1, 1, 2, 20 and 50% of the time during the observation period. The suffix S in the formula indicates that the smoothed value should be used. The smoothed values are obtained using the following formulas:

P(1s) = (P(.7) + P(1) + P(1.5))/3

P(3s) = (P(2.2) + P(3) + P(4))/3

P(10s) = (P(6) + P(8) + P(10) + P(13) + P(17))/5 P(50s) = (P(30) + P(50) + P(80))/3

The .3-second memory time constant in the flicker meter ensures that P(0.1) cannot change abruptly and no smoothing is needed for this percentile.

•Long Term Flicker Evaluation

The 10-minute period on which the short-term flicker severity is based is suitable for short duty cycle disturbances. For flicker sources with long and variable duty cycles (e.g. arc furnaces) it is necessary to provide criteria for long-term assessment. For this purpose, the long-term Plt is derived from the short-term values over an appropriate period. By definition, this is 12 short-term values of 10 minutes each over a period of 2 hours. The following formula is used:

∑Psti3

Plt = 3 i=1NN

Where Psti (i = 1, 2, 3, ...) are consecutive readings of the short-term severity Pst.

Summary

Flicker = Changes in the illumination of light sources due to cyclical voltage variations. Pinst = Instantaneous flicker values in Perceptibility Units (PU).

Pst = Value based on 10-minute analysis. Plt = Value based on 12 Pst values.

Electro Industries/GaugeTech Doc # E107706 V1.25 12-2