Siemens MD-12HD, User Manual, Page: 53 / 74

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Pre-Processing Aids
The MD-xxHD has several registers that can aid in pre-processing or post-processing data that otherwise
may need seconday operations.
Snap Thresholds
The signal to noise ratio of the MD-xxHD is above 80 db at full scale (1 part in 10,000). When the signal
amplitude becomes so small that it is indistinguishable from noise it is often better to record 0 than a
small random value. Snap Threshold registers (
Advanced tab in ViewPoint HD) tell the meter when to
record 0 instead of the measurement result. The factory defaults for CTs are expressed in percent and
have a default value of 0.04% Full Scale. The voltage thresholds are in absolute value, the recommended
minimum voltage is 1.0 volt
Multipliers
The MD-xxHD has registers that allow potential transformers and series current transformers to be used
with the MD-xxHD meter. These registers allow for transformer winding ratios or other scaling
adjustments to be included in the meter processing to eliminate post process scaling. Adjustments for
voltage are global to the meter while CTs can be adjusted on a channel by channel basis. The multiplier
is a floating-point number and can also be used for post installation calibration if desired. Default values
are
1.0 .
CT Phase Shifts
Current transformers like all other transformers experience a small magnetizing current that is out of
phase with the measurement current. Phase shift registers are available on a per channel basis and
allow corrections of +/- 3 degrees. Viewpoint HD loads the default phase shift for the CT types available in
the picker list. If no phase shift information is available, enter the accuracy class in degrees (for example,
1% = 1.0 degree).
Demand
MD-xxHD meters keep track of electrical demand using a 15-minute sliding window. The Peak Demand
and Present Demand registers contain the highest average power consumption in any 15-minute interval
and the average power consumption in the last 15-minute interval respectively. The Clear Peak Demand
register is used to reset the peak demand detector.