Rockwell Automation 1770-HT8 SMART TRANSMITTER - Manual (Page 120)

Cable Length and Power Supply
Requirements
Appendix C
C-3
Figure C.3
Determining Maximum Cable Lengths for Linear Connection
90055
1170-HT1
a
b
d
1770-HT8 1770-HT8 1770-HT8 1770-HT8
c
Control Signals
Total cable lengths <= 1000 ft
or <= 305 m
+24 VDC Power Ċ Pin 2
a + b + c + d <= 1000 / (0.065 * R)
where R = cable resistance per 1000 ft
or a + b + c + d <= 1/(0.065 * R)
where R = cable resistance per meter
Figure C.4 illustrates the formula as it applies to a star connection
configuration in which each Terminal Block is wired directly to the
Communication Controller with its own cable.
Figure C.4
Determining Maximum Cable Lengths for Star Connection
90059
1170-HT1
d
1770-HT8
1770-HT8
1770-HT8
1770-HT8
Channel Select and Data Signals
a + b + c + d <= 1000 ft
or a + b + c + d <= 305 m
+24 VDC Power Ċ Pin 2
a, b, c, and d <= 1000 / (0.065 * R)
where R = cable resistance per 1000 ft
or a, b, c, and d <= 1/(0.065 * R)
where R = cable resistance per meter
c
b
a