ABB IMASI13 - Isolated A;D Converter; Cold Junction Reference

2 - 2 WBPEEUI240766B0
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 2-1 shows a block diagram of the IMASI13 module.
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
Figure 2-1. IMASI13 Functional Block Diagram
DIGITAL
MULTI-
PLEXER
NVRAM
DUAL PORT
RAM
MEMORY
NONVOLATILE
RAM
DPRAM
MICRO-
CONTROLLER
LED
IN D IC ATO R S
8-POSITION
DIPSWITCH S1
P3 CONNECTOR
ON IMASI13
IN P U T S FR O M
TERMINATION
DEVICE
I/O
EXPANDER
BUS
IN T E R FA C E
P2
CONNECTOR
ON IMASI13
TO/FRO M
CONTROLLER
EXPANDER
BUS
PROM
SRAM
COLD JUNCTION
REFERENCE INPUT
AND A/D CONVERTER
IS O L ATED A /D
CONVERTER 1
IS O L ATED A /D
CONVERTER 2
IS O L ATED A /D
CONVERTER 3
•
•
•
•
IS O L ATED A /D
CONVERTER 16
T01062B