SMART I/O User’s Manual
©1996 PEP Modular Computers GmbHMarch 12, 1996 Page 5 - 31
5
Chapter 5 Analog Modules
5.2.5 Functional Description
Figure 5.2.5.1: SM-PT100 Schematic Diagram
The SM-PT100 has provision for 4 sets of 4-wire PT100 sensors driven by
an on-board generated 400µA constant current source. The differential
analog input consists of a channel multiplexer, operational amplifier voltage
feedback impedance converter and a high-resolution 16-bit delta-sigma
converter. 1000V DC system isolation is provided by an optoisolated DC/DC
converter while system flexibility is provided by a 256 bytes of serial
EEPROM for ID number, production and board-specific calibration data.
Two front-panel LEDs show the conversion/calibration activity.
The PT100 is a platinum resistance, which at 0ºC has a resistance of 100Ω
and conforms to the international DIN IEC 751 standard for Industrial
Platinum Resistance Thermometer Sensors. Two classes A and B exist under
this standard with class B experiencing a slightly worse initial error.
Figure 5.2.5.2 Supported Sensor Connections
Multiplexer
A/D
Converter
System
Interface
LED
Driver
Impedance
Converter
Serial
I/O
R
L
R
L
PT100 Sensor , 4-wire Input
CUR
IN+
IN-
AGND
400 µA
400 µA
SENSE LINE
SUPPLY LINE
SUPPLY LINE
SENSE LINE
User Interface System Interface
Pt 100/ /2
Red White
Pt 100/ /3
Red WhiteRed
Pt 100/ /4
Red WhiteRed Red
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