Honeywell 5704

4-18
MAN0448_Issue 13_01-2010 5704 Control System
005704-M-5001 A03249
CHAPTER 4 - INSTALLATION INSTRUCTIONS
11.5 4 - 20mA Loop Powered Sensors:
The maximum line resistance of cabling for a 4 - 20mA loop powered
sensor varies with the voltage drive requirements of the type of sensor
installed.Itisalsosubjecttoa24Vmaximumloopdrivevoltage.
Maximum line loop resistance is calculated as follows:
24 - V
s
R
L =
0.025
Where: R
L
= Total Line Resistance (ohms)
V
s
= Minimum Sensor Operating Voltage (V)
11.6 4 - 20mA Transmitters
The maximum line resistance of cabling for a 4 - 20mA transmitter
powered from the System 57 varies with the voltage and current
requirementsofthetransmitter.Itisalsosubjecttotheminimumsupply
voltage available from the System 57.
Maximum line loop resistance is calculated as follows:
V
r
- V
s
R
L
=
I
s
Where: R
L
= Total Line Resistance (ohms)
V
r
= Minimum DC Supply to System 57 (V)
V
s
= Sensor Voltage (V)
I
s
= Sensor Current (A)
Making the above calculation using a V
r
of 18V will accommodate the
worst case low dc supply situation.
The maximum resistance per core can be calculated from the above
congurationsasfollows:
R
L
Maximum Resistance of Core = ohms
2