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PQM-702, PQM-703, PQM-710, PQM-711 Operating Manual
3.10.1 Threshold method
Threshold method is chosen by selecting Threshold (in voltage settings of the measurement
point) and setting the threshold voltage in the range from 50 V to 5000 V. In this method, the analyzer detects a transient after it exceeds the pre-set amplitude in volts. Transients, whose amplitude does not exceed the set threshold will not be detected by the analyzer. In this mode, the
waveform rise time is not taken into account. Both slow and fast transients will be detected, when
the amplitude criterion is met.
NOTE: Threshold value entered is a transient amplitude, not the absolute voltage referred to
the PE earth voltage level.
3.10.2 Slew rate (dV/dt) method
Slew rate method (dV/dt) is activated by selecting Slew rate and indicating an appropriate
sampling rate, which indirectly selects the voltage slew rate from several available values (see
Tab. 5). In dV/dt method the device analyses the voltage waveforms in a specific time window and
detects transient, if the slew rate in the window exceeds the value set by the user in settings. The
absolute amplitude of the transient is not important - both transients of small and large amplitude
will be detected, provided that the minimum rise requirement is met.
3.11 Current limiting function
In situations where the measured current has very low values or measuring clamps were removed from the analyzer, resetting function may be useful for parameters related with the current
channel. This is particularly important for parameters such as THD, which in case of noise indicate
high and sometimes confusing values. When current clamps are disconnected during event detection, then the analyzer almost instantly detect exceeding the threshold, which may mislead the
user. To avoid such situations, limiting function is introduced for current parameters, when RMS
value of the measured current is below the threshold specified by the user. To enable this function
check box "Current limit", located in the main settings of the measurement point, under the list of
clamp types. When the option is enabled, the user may specify the limit threshold as the percentage of the nominal range of selected clamps, (0.00 to 0.50% of I nom).
Checking whether the current value is below the specified threshold, is carried out every
10/12-period window (approx. every 200 ms). If the RMS value of the measured current in the
channel is lower than the specified threshold, then the following parameters are zeroed:
 RMS current,
 current direct component (DC),
 current crest factor,
 current harmonics/interharmonics amplitudes,
 current THD and TID,
 all power values in a given channel,
 power factor and cos,
 the angles between voltage and current harmonics,
 harmonics active and reactive power
 tan and K-factor.
Total values of the system are zeroed only if all current channels are below the reset threshold. Then, the following values are also reset:
 current unbalance factors and current symmetrical components.
For events, some parameters are managed in a way that takes zeroing into account. The parameter value is taken into account (when detecting start and end of the event and calculating extreme and average values) only when the current value is above the threshold. Parameters managed in this way include:
 current crest factor,
 current THD and TID,
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