GE Grid Solutions
D20/D200 Technical Overview
GE Information
PRPI-019-3.00-10
51
Y
X
5
25
45
+16383
0000
-16383
Frequency (kHz)
Digitized
Raw
Analog
Line A: Y = m
1
X + b
1
Line C: Y = m
2
X + b
2
Line B
Figure 33 Three-point Linearity Correction
2.4.7.2 D20A Analog Input Processing
The following analog input processing is carried out by the D20A:
•
Line Noise Filtering
: Filters 50 or 60 Hz line noise, configurable on a per-system basis.
•
Deadbanding
: Technique used to virtually reduce the resolution of analog input points.
Deadbanding maps the set of all possible
measured
values to a smaller set of
reported
values.
The number of bits removed from the analog input values is configurable, on a per-point
basis, from 0 to 13.
2.4.7.3 D20A Base Application
The base application of the D20A controls four main functions:
•
Analog Multiplexing and Inputting
: Field inputs and reference points are multiplexed.
Inputs are scaled by a programmable gain amplifier then fed into a voltage-to-frequency
converter that is part of the analog-to-digital conversion circuitry. From the output of this
converter, a digitized analog input is derived.
•
Analog Processing
of the raw analog input data, using two different methods, depending on
whether the data comes from a field point or a reference point. There are full-scale voltage
range reference points for every group of 32 analog inputs.
If the data comes from a reference point, it is compared to a reference value stored in
EEPROM of the microprocessor. If it is too far out of range, it is stored in a reference table
and marked as an error. If the data is within range, it is stored as the new reference table.
If the data comes from a field point, it is compared against its corresponding full-scale
reference value. If it is over range, it is noted as such and is set to a value of 16383. If it is
under range, it is noted as such and is set to a value of -16383.
