Installation
UMSITRPDS3-1
November
2010
4-18
4.3.6.2 Maximum Cable Length Calculation
The maximum permissible single-pair cable length is 10,000 feet (3000 meters) or less as determined by
the following formula:
L = (65,000,000 / R x C) – (C
f
+ 10,000 / C)
Formula Definitions:
L: The maximum total length of cable permitted to construct the network. L = feet when C is in pF/ft;
L = meters when C is in pF/meter.
R: The Network Resistance which is the ohmic sum of the current sense resistance and barrier
resistance (both return and supply), if any, in the network and the resistance of the wire.
C: Cable capacitance per unit length between one conductor and the other conductor connected to the
shield. C may be in pF/ft or pF/meter.
C
f
: Total input terminal capacitance of field instruments; the Primary Master is excluded. C
f
is given
by the following formula:
C
f
= (sum of all C
n
values) x (5000)
Where C
n
is an integer (e.g., 1, 2, 3) corresponding to the input terminal capacitance of a Field
Instrument. C
n
values are determined as follows:
FIELD INSTRUMENT CAPACITANCE C
n
VALUE
Less than 5000 pF
1
5000 pF to less than 10000 pF
2
10000 pF to less than 15000 pF
3
15000 pF to less than 20000 pF
4
20000 pF to less than 25000 pF
5
For field instruments without C
n
values, use C
n
= 1
WARNING
For an intrinsically safe installation, refer to the Control Drawing(s) in Appendix
B for entity parameters, which include C
i
transmitter input capacitance, and other
installation data.
Summary of Contents for 7MF4033 series
Page 48: ...Model 275 Universal Hart Communicator UMSITRPDS3 1 November 2010 2 26 ...
Page 86: ...Installation UMSITRPDS3 1 November 2010 4 34 ...
Page 152: ...Calibration and Maintenance UMSITRPSD3 1 November 2010 7 20 ...
Page 158: ...Circuit Description UMSITRPDS3 1 November 2010 8 6 ...
Page 197: ......
Page 198: ......
Page 200: ...Model Designations and Specifications UMSITRPDS3 1 November 2010 9 42 ...
Page 204: ...Glossary UMSITRPDS3 1 November 2010 10 4 ...
Page 208: ...Appendix A Online Configuration Map UMSITRPDS3 1 11 4 November 2010 ...
Page 216: ...Appendix C Elevation and Suppression Correction UMSITRPDS3 1 13 4 November 2010 ...