Technical data
Publication 1794-2.1 - January 2000
FLEX I/O and FLEX Integra Product Data
24V dc Thermocouple/RTD Input Module Cat. No. 1794-IRT8 127
Data Type
Type of Input Connect the following
HL+-
Shield
1
RTD - 2-wire 1 2
RTD - 3-wire 312
RTD - 4-wire 1a 2a 1 2
Thermocouple 1 2
Millivolt 1 2
1
Terminals 37, 38, and 39 and 46, 47, and 48 are for cold junction compensation (with
38 and 47 chassis GND).
RTD or
Thermocouple
Channel
1794-TB3G and -TB3GS Terminal Base Units
High Signal
Terminal (H)
Low Signal
Terminal (L)
RTD Source
Current (+)
Signal
Return
1
(-)
0 A-1 A-2 A-0 A-3
1 A-5 A-6 A-4 A-7
2 A-9 A-10 A-8 A-11
3 A-13 A-14 A-12 A-15
4 B-18 B-19 B-17 B-20
5 B-22 B-23 B-21 B-24
6 B-26 B-27 B-25 B-28
7 B-30 B-31 B-29 B-32
+24V dc Power 34 and 50
24V dc Common 35 and 51
1
Terminals 37, 38, and 39 and 46, 47, and 48 are for cold junction compensation (with
38 and 47 chassis GND).
2
Terminals 16, 33, and 40 thru 45 are chassis ground.
ATTENTION
!
To reduce susceptibility to noise, power analog
modules and digital modules from separate power
supplies. Do not exceed a length of 10m (33ft) for dc
power cabling.
Do not daisy chain power or ground from this
terminal base unit to any ac or dc digital module
terminal base units.
Total current draw through the terminal base unit is
limited to 10A. Separate power connections to the
terminal base unit may be necessary.
RTD Thermocouple
Millivolt
2-Wire
3-Wire
1
2
3
1
2
1
1a
2a
2
1
2
1
2
+
mV
-
41019
4-Wire
Bit 11 10 09 08 Data type for channels 0-7
0000
o
C or resistance (in Ω)
0001
o
F
0010
o
K
0011-32767 to +32767
01000 to 65535
0101 through 1111 not used
Module defaults to -4000 to 10000 in millivolt mode, and 0 to 5000 in ohms mode.
Note: For millivolts there are two implied decimals. For degrees and ohms there is one
implied decimal.
Example of 2-, 3-, and 4-wire RTD and Thermocouple Wiring to
a 1794-TB3G Terminal Base Unit
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
0-15
16-33
34-51
A
B
C
40621
Thermocouple Channel 4
2-Wire RTD Channel 1
3-Wire RTD Channel 2
4-Wire RTD Channel 3
CJC
1794-TB3G
CJC = cold junction compensation kit
1794-CJC2/A (kit supplied with module and
contains 2 compensators)
Attention: Keep exposed area of inner conductor as short as possible.
only needed when using thermocouples
Note: Module cannot be configured as shown. This is just an example of
different input connections.
This is a non-isolated module. You may need to take extra precautions like tying
the 24V dc common to the earth ground.
Example of Millivolt Wiring to a 1794-TB3G Terminal Base Unit
0-15
16-33
34-51
A
B
C
40622
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1794-TB3G
ATTENTION: Keep exposed area of inner conductor as short as possible.
Millivolt
Source
Millivolt
Source
Millivolt
Source
Millivolt
Source
+-
+-
+-
+-