Tyco 1540 - Manual (Page 57)

Time Integration Periods can be set to 8, 15, 20 or 30 minutes.
Note: During the initial period when the "sliding window" does not yet contain a full set of
readings (i.e. the elapsed time since the demands were last reset or the elapsed time since
Integra was switched on is less than the selected demand period) then maximum demands may
not be true due to the absence of immediate historical data.
The Time Integration Period can be user set either from the Integra 1540 Display or by using the
communications option.
Total Harmonic Distortion (1540 only)
The calculation used for the Total Harmonic Distortion is:
THD = ((RMS of total waveform - RMS of fundamental) / RMS of total waveform) x 100
This is often referred to as THD - R
The figure is limited to the range 0 to 100% and is subject to the 'range of use' limits. The
instrument may give erratic or incorrect readings where the THD is very high and the
fundamental is essentially suppressed.
For low signal levels the noise contributions from the signal may represent a significant portion
of the "RMS of total waveform" and may thus generate unexpectedly high values of THD. To
avoid indicating large figures of THD for low signal levels the product will produce a display of 0
(zero).
Typically, display of THD will only produce the 0 (zero) value when the THD calculation has been
suppressed due to a low signal level being detected. It should also be noted that spurious
signals (for example, switching spikes) if coincident with the waveform sampling period will be
included in the "RMS of the total waveform" and will be used in the calculation of THD.
The display of THD may be seen to fluctuate under these conditions.
55
Integra 1540, 1000, 0640, 0440, 0340, 0240 Issue 1 04/03