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Power Automation and Protection Division
Schematic - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 1612C20
Component Location diagram - - - - - - - - - - - - - - - - - - 1611C23
The block diagram of this module is shown in Figure H-1. The module interfaces with the voltage and current
transformers that are mounted on the Backplane module. These transformers provide the following ac values:
V
, V
, V
, I
, I
, I
. The values are applied to active third-order Butterworth antialiasing filters (U8 thru U13),
A
B
C
A
B
C
with a cut-off frequency determined by the Nyquist criterion and the system sampling rate. Values I
summed to produce 3I
in U5. All seven values (V
0
whose output connects to the A/D converter (U15) via autoranging circuitry.
The A/D converter is a 12 bit plus sign with an internal sample-and-hold amplifier. Additionally, on request, the
A/D converter executes a self-calibrating routine that corrects zero errors and, also, full-scale and linearity er-
rors. Device U16 provides stable, precision 5.000 V reference to the A/D converter. The autoranging circuitry
provides 16 bits of dynamic range needed to measure high current values during power system faults.
The 13 bit output is available from the A/D converter (12 bit plus sign). To achieve a 16-bit range requires a
multiplication of the A/D converter output (or gain) by eight.
If the input value satisfies the expression:
+ 0.5 V < V
then the comparators (U3.1 and U3.2) select the Y
Microprocessor software.
For the range:
- 0.5 V < I
the (Y
- Y) path of U4 is selected (by U3.1 and U3.2), connecting the output of U2 (analog input with a gain of
1
8) to the A/D converter, performing a multiplication by 8 in the analog domain.
NOTE:
REL 352 Version 1.00
ANALOG INPUT MODULE
, V
A
< - 0.5 V
IN
- Y) switch of U4, and multiplication by 8 takes place in the
0
< + 0.5 V
IN
Adjust potentiometer (R59) for 5.000V at the test point (TP2) to ground.
, V
, I
, I
, I
, 3I
) are applied to the multiplexer (U5),
B
C
A
B
C
0
I.L. 40-201.9
, I
, I
are
A
B
C
A
P
P
E
N
D
I
X
H
H-1
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