ABB IMASI13, Instructions Manual

Page: 64 / 128

Functional Operation
WBPEEUI240766B0 2 - 3
connections made by terminating the field wires (thermocou-
ple wires) onto the terminal blocks of the termination unit.
The block address of the cold junction reference used by ther-
mocouple inputs on the ASI module is contained in FC 215,
specification S3.
Each analog input module configured for a thermocouple
input requires a cold junction reference. Each analog input
module can only have one reference which can be used by up
to 16 thermocouple inputs. The exception to this is when one
of the inputs is used as a remote cold junction reference.
Refer to Section 4 for more information.
Digital Input Multiplexer (MUX)
Once isolated, digitized, and buffered, the input signal is sent
to the microcontroller by a digital multiplexer. All the inputs,
including the references and cold junction input, are multi-
plexed as shown in Figure
2-1 .
Microcontroller and Memory
The onboard microcontroller coordinates ASI functions. The
main functions are:
•
Channel and cold junction reference switching.
•
Programming A/D converters.
•
Reading the A/D converters and applying all necessary
correction factors.
•
Interfacing to switch and LEDs (used for diagnostic mode).
•
Background integrity checking.
•
Reading and writing expander bus data through dual port
RAM (DPRAM).
Switch Settings
The ASI module has one eight-position dipswitch to select the
I/O module address on the I/O expander bus. This switch also
selects built-in diagnostics for stand-alone testing.