Operating Instructions

59 Siemens Industry, Inc.

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

Changing the current Snap Threshold may affect the ANSI C12.20 compliance.

Multipliers

The PSHD has registers that allow potential transformers and series current transformers to be used with

the PSHD 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 CT’s 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 value is 1.0. Values below 0.9 are

not allowed.

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