Novatech Bitronics M87X Series, Руководство пользователя

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ML0021 August 15, 2018
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Copyright 2018 Bitronics, LLC
3.1.3 System Clock
The M87x has an internal System Clock with a capacitor backed RAM (typical data
retention of 7 days at room temperature) when no power is applied to the unit. The clock
is located on the Host board. The time settings may be changed via the Serial Port (P1) or
various communication protocols. Refer to Section 3.1.1a and the appropriate protocol
manuals for details.
3.2 A10 Analog-Digital Signal Processor Board
The Analog/DSP board is part of the modular M87x system. This board contains
amplifiers, track and hold circuits, multiplexers, an analog to digital converter, a digital
signal processor (DSP), and a PCI bridge. Analog signals from the CT/VT board are
routed through the backplane to the Analog/DSP board. Once on the board each signal is
connected to the track and hold circuitry. The track and hold circuitry is designed to hold
the channel’s present value during the time required for the analog to digital converter to
sample all of the channels. This effectively allows the M87x to simultaneously sample all
of its input channels, eliminating any channel-to-channel skew. A single 16-bit analog to
digital converter is used for all measurements. The DSP uses the samples to calculate all
of the measured parameters. Each sample is corrected for offset and gain using factory
calibration values stored in non-volatile memory on the board. Additionally, a continuous
DC removal is performed on all inputs, except the AUX Voltages. An adaptive sampling
system is used to maintain 128 samples per cycle over the input frequency range of 15 to
70 Hz. See Section 3.2.2.
3.2.1 Calibration
Routine re-calibration is not recommended or required. A field calibration check every few
years is a good assurance of proper operation.
3.2.2 Instantaneous Measurement Principles
The M87x measures all signals at 128 samples/cycle, accommodating fundamental signal
frequencies from 15 to 70 Hz. Samples of all bus signals are taken at the same instant in
time, using a 16-Bit A/D converter, effectively creating 128 "snapshots" of the system
voltage and current per cycle.
3.2.2a Sampling Rate and System Frequency
The sampling rate is synchronized to the frequency of any of the bus voltage or current
inputs, prioritized as follows: V1
A-N
, V1
B-N
, V1
C-N
, V2
A-N
, V2
B-N
, V2
C-N
, IA, IB, IC. This is the
frequency reported as the "System Frequency". The AUX voltage inputs and Neutrals are
not used to synchronize the sampling. The sampling rate is the same for all channels.
The default system frequency may be set in the Configurator to either 50 or 60 Hz. This
will have no effect on the frequency that is reported, or the sample rate when signals are
present. It is used to set the default sample rate when the unit cannot detect any applied
signal.