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SIGNALPOINT PRO OPERATING MANUAL MAN0853 Issue 3 10/08
11
6.2 Terminal connections
6.3 Maximum cable length calculation
The limiting factors in calculating maximum cable lengths when using barriers and
isolators are the total capacitance and inductance. Barriers and isolators have a fixed
amount of capacitance and inductance that can be connected to their outputs. The
cable between the field device and barrier/isolator will have a value for capacitance
and inductance per metre or kilometre that will be available from the manufacturer or
supplier.
To calculate the maximum cable lengths, calculate the total capacitance and
inductance for the length of cable, add any capacitance or inductance due to the field
device (Signalpoint Pro capacitance and inductance = 0). The resulting totals should
not be greater than the value shown for the barrier or isolator.
Example using
dual channel zener barrier:
Capacitance permitted by the barrier = Cb
Inductance permitted by the barrier = Ib
Internal capacitance of the field device = Cf
Internal inductance of the field device = If
Capacitance of the cable per metre = Cc
Inductance of the cable per metre = Ic
Total allowable capacitance for the cable = Ca
Total allowable inductance for the cable = Ia
Connection
Sensor Wire Colour
Terminal 1
+VE Red
Terminal 2
Signal White
Terminal 3
Not used
Black
Terminal 4
Screen Braid
4
3
2
1
Diagram 5: Terminal connections
Note: The maximum cable length is determined by
the capacitance and inductance of the cable, but
must be equal to, or less than, the capacitance (Ca)
and inductance (La) values indicated on the barrier
used. If the cable capacitance and inductance are
not known, 60 pico-farads and 0.20 micro-henry per
foot should be used for calculation.
Summary of Contents for SGPTPRXXA1
Page 1: ...Technical Manual Signalpoint Pro ...
Page 30: ...SIGNALPOINT PRO OPERATING MANUAL MAN0853 Issue 3 10 08 29 16 Control Drawing ...
Page 31: ...SIGNALPOINT PRO OPERATING MANUAL MAN0853 Issue 3 10 08 30 ...
Page 32: ...SIGNALPOINT PRO OPERATING MANUAL MAN0853 Issue 3 10 08 31 17 Certification Label ...