User manual

3 Design and measurement methods
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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.
3.10.2 Slew rate (dV/dt) method
Slew rate method (dV/dt) is activated by selecting Slew rate and indicating an appropriate sam-
pling rate, which indirectly selects the voltage slew rate from several available values (see Tab. 4).
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
Current limiting function is available only in PQM-703.
In situations where the measured current has very low values or measuring clamps were re-
moved 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 detec-
tion, 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 pa-
rameter value is taken into account (when detecting start and end of the event and calculating ex-
treme and average values) only when the current value is above the threshold. Parameters man-
aged in this way include:
 current crest factor,
 current THD and TID,
 power factor and cos,
 tan and K-factor,
 current unbalance.