Electro Industries Nexus 1262, Installation & Operation Manual

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• 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:
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:
Where Psti (i = 1, 2, 3, ...) are consecutive readings of the short-term severity Pst.
Q
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 # E151701 14-2
s s s s st
P P P P P P
50 10 3 1 1 . 0
08 . 0 28 . 0 0657 . 0 0525 . 0 0314 . 0 + + + + =
3
1
3
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lt
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