Rockwell Automation 1770-HT8 SMART TRANSMITTER - Manual (Page 121)

Cable Length and Power Supply
Requirements
Appendix C
C-4
One way of overcoming the maximum power length restrictions required
to carry power to the Terminal Blocks is to use a local power supply at the
site of the Terminal Blocks, rather than providing 24 VDC via the cable
between the Communications Controller and the Terminal Blocks. This
power supply must be connected to pins 2 (+) and 3 (–) of the 17 position
connector.
Important: No matter how the Terminal Blocks are powered, the total
length of the digital communications cable between the Communications
Controller and all the Terminal Blocks must not exceed 1000 feet (300
meters) and a signal ground must still connect the Communications
Controller and the Terminal Blocks at pin 3 via the cable in order to
provide a common ground reference.
Figure C.5
Using a Separate Power Supply
HART FIELD
DEVICE
90054
+24 VDC for
HT1 only
+24 Ć 32 VDC
for loops
24 VDC
HT1
HT8
HT16
HART FIELD
DEVICE
+
ground signal 3
-
2
3
2
3
CONTROL LINES
Connecting Power to the Terminal Blocks
To connect an external 24 VDC power supply to a Terminal Block do the
following:
1. Make sure the power supply is turned off.
2. Connect the wire from the positive terminal in the power supply to
pin 2 in the 17 pin connector on the cable.
Using a Separate Power
Supply for a Terminal Block