Rockwell Automation 1790P-T4T0 CompactBlock LDX I/O Thermocouple Modules - Manual (Page 13)

Publication 1790-UM003A-EN-P
Overview 1-5
Module Operation - DeviceNet Example
When the module recieves a differential input from an analog device, the
module’s circuitry multiplexes the input into an A/D converter. The
converter reads the signal and converts it as required for the type of input.
The module also continuously samples the CJC sensors and compensates
for temperature changes at the terminal block cold junction, between the
thermocouple wire and the input channel. See the block diagram below.
Figure 1.3 Block Diagram
Each channel can receive input signals from a thermocouple or millivolt
analog input device, depending upon how you configured the channel.
When configured for thermocouple input types, the module converts the
analog input voltages into cold-junction compensated and linearized
digital temperature readings. The module uses the National Institute of
Standards and Technology (NIST) ITS-90 standard for linearization for all
thermocouple types (J, K, T, E, R, S, B, N).
When configured for millivolt inputs, the module converts the analog
values directly into digital counts.
Input
CH0
Multiplexer
VA2
A/D
VREF Vref
Channel Select
Channels 1 through 3 same as
channel 0 above.
43309
A
B
VA1
Vcc
Optical
Isolation
AIN-
AIN+1
VA3
A-GND
Micro-
Controller Transmit
Receive
GND
Network
Power
Supply
Analog
Power
Supply
DeviceNet
24Vdc
Power
Vcc
GND
VA1
VA2
VA3
A-GND
VDC
GND
1
2
3
Auxiliary
24Vdc
Power
Transceiver
+
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