ML0038 September 27, 2017 - 60 - Copyright 2017 Bitronics, LLC
6.0 MEASUREMENTS
Basic measurement quantities are calculated and updated every 100ms. These
quantities include RMS Amperes and RMS Volts, and some average or demand
values.
Note: For all of the following measurements, it is important to keep in mind that the
specific protocol used to access the data may affect the data that is available, or the
format of that data. No attempt is made here to describe the method of accessing
measurements - always check the appropriate protocol manual for details.
6.1 Changing Transformer Ratios
The M350 has the capability to store values for Current Transformer (CT) in the A3 or
Potential Transformer (VT) turns ratios in the V3. The CT and VT values are factory
set to 1:1 CT or 1:1 VT depending upon the model. These values can be entered into
the M350 over the network or via front display buttons or web page, and will be stored
in internal non-volatile memory. All measurements are presented in primary units,
based on these ratios. Please note that the value entered via the front display should
be the result of the division of the primary value by 5. For example for a ratio of
6000:5, you would enter a value of 1200 through the front display. The web interface
allows you to choose either 1A or 5A for the denominator, and the primary value is
entered directly. The PT ratio is to 1 when entering through the front display. The
web allows other denominators (110, 115, or 120) to be used. Refer to the
appropriate protocol manual for more information on changing transformer ratios.
6.2 Current (M350 A3)
The M350 A3 has three current inputs, with an internal CT on each channel. These
inputs can read to 2x nominal (2A
RMS
for 1A input, 10A
RMS
for 5A input
(symmetrical)
under all temperature and input frequency conditions. No range switching is used,
allowing a high dynamic range.
The current signals are transformer coupled, providing a true differential current signal.
Additionally, a continuous DC removal is performed on all current inputs. Instrument
Transformer Ratios can be entered for each current input, as described above.
6.3 Voltage Channels (M350 V3)
All voltage inputs are measured relative to a common reference level (essentially
panel ground). See Appendix 1 for input connection information. Common mode
signals can be removed by signal processing algorithms, instead of the more
traditional difference amplifier approach. This greatly simplifies the external analog
circuitry, increases the accuracy, and allows measurement of the Neutral-to-Ground
voltage at the panel. The 7kV input divider resistors are accurate to within +/-
25ppm/DegC, and have a range of 400V
PEAK
, from any input to panel ground. Each
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