Imasi23 Functional Block Diagram - ABB Symphony Harmony Series Instructions Manual

Functional Operation
Each channel provides underrange, overrange, and open input
detection. Onboard circuitry detects either open field wires or a
disconnected termination unit cable. Open input detection is
provided for millivolt, thermocouple, RTD, 1 to 5 VDC, and 4 to
20 milliampere input types and can detect any combination of
open input wires.
Figure
P 3 C O N N E C TO R
O N IM A S I2 3
IS O L AT E D A /D
C O N VE R T ER 1
IS O L AT E D A /D
C O N VE R T ER 2
IN P U T S F R O M
IS O L AT E D A /D
T E R M IN AT IO N
C O N VE R T ER 3
D E VIC E
•
•
•
•
IS O L AT E D A /D
C O N V E RT E R 16
R E FE R E N C E IN PU T
A N D A/D C O N V E RT E R
Figure 2-1. IMASI23 Functional Block Diagram
Isolated A/D Converter
Each input channel has an A/D converter (delta-sigma type).
Isolation is done by DC/DC converters (one per channel) and
optocouplers on the digital serial line of the A/D converter.
Each channel accepts voltage and resistance inputs. Resis-
tance measurements are made by digitizing the voltage drop
created across the input resistance source. A precision con-
stant current source supplies the current used to measure the
input.
Cold Junction Reference
The ASI module measures the cold junction RTDs on the ter-
mination unit of the analog input module. This results in an
accurate reading of the ambient temperature at the field wire
termination area. This value can be used by the ASI module to
compensate for voltages generated from the bimetal
2 - 2
2-1 shows a block diagram of the IMASI23 module.
D IG ITA L
M U LTI-
P L E X E R
P RO M
SR A M
C O LD J U N C TIO N
M E M O RY
L ED
IN D IC ATO R S
M IC R O -
C O N T RO LL E R
8 -P O S IT IO N
D IP S W IT C H S 1
N O N VO LAT IL E
R A M
N V R A M
I/O
E X PA N D E R
BU S
IN T E R FAC E
D P R A M
D UA L P O R T
R A M
P 2
C O N N E C TO R
O N IM A S I2 3
TO /F RO M
C O N T RO L L ER
E X PA N D E R
B U S
T 01 06 2C
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