Rockwell Automation 1769-IR6 Compact I/O 1769-IR6 RTD/Resistance Input Module - Manual (Page 18)

18 Rockwell Automation Publication 1769-UM005B-EN-P - March 2012
Chapter 1 Overview
Module Operation
As shown in the block diagram below, each input channel of the module
consists of an RTD/resistance connection that accepts excitation current; a
sense connection that detects lead wire resistance; and a return connection.
The signals are multiplexed to an A/D converter that reads the RTD or
resistance value and the lead wire resistance.
From the readings taken by the converter, the module returns an accurate
temperature or resistance to the controller user program through the
microprocessor. The module uses two bidirectional serial ports for
communication, each using an optocoupler for isolation. A third optocoupler
is used to reset the microprocessor if the module detects a loss of
communication.
VA2
A-GND
VA1 VA1
AIN+1
AIN+2
AIN-
VREF Vref
VA3
VA1
TXD
VA1
VA2
VA3
A-GND
VS2
VS1
S-GND
1
2
3
4
5
Input
EXC0
SENSE0
RTN0
CHN0
Multiplexer
EXC
Current
A/D MCU ASIC
BU
S
Channel Select
DC/DC
Power Supply
Channels 1…5 same as
channel 0 above.