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SMART I/O User’s Manual
©1996 PEP Modular Computers GmbHMarch 12, 1996 Page 5 - 61
5
Chapter 5 Analog Modules
Multiplexer
A/D
Converter
System
Interface
Serial
I/O
Impedance
Converter
Thermo Sensor
LED
Driver
IN+
IN-
AGND
SENSE LINE
SHIELD LINE
SENSE LINE
External PT100 Sensor, 2-wire Cold Junction Input
TMP+
TMP-
SUPPLY/SENSE LINE
SUPPLY/SENSE LINE
The SM-THERM allows four sets of three-wire thermocouples to be con-
nected together with one additional PT100 element used as a cold junction
point reference. The differential analog input consists of a channel multi-
plexer, operational amplifier voltage feedback impedance converter and a
high-resolution 16-bit delta-sigma converter. 1000V system isolation is
provided by an optoisolated DC/DC converter while system flexibility is
provided by 256-bytes of serial EEPROM for ID number, production and
board specific calibration data. Two front-panel LEDs show the conversion/
calibration activity.
In principle any thermocouple conforming to the DIN43710 or IEC584
specifications can be connected. Sensor breakdown recognition is performed
by the software which also caters for and corrects absolute temperature
readings with a connected cold junction point (PT100).
5.3.5 Functional Description
Figure 5.3.5.1: SM-THERM Schematic Diagram