Signal Wire Carrying Voltage - Siemens SIMATIC 505 PPX:505–6108A User Manual

Signal Wire To help ensure accuracy within module specifications, consider the following
Carrying Voltage in choosing wire that carries voltage:
The load imposed by a field device must be at least 5000 Ω. The maximum
capacitance that can be driven by the output is 0.01 µ F. The maximum
cable length is a function of cable capacitance. To determine the maximum
distance for a given cable, obtain the nominal value of cable capacitance per
unit length as given by the manufacturer. Use this value in the following
equation.
NOTE: Nominal capacitance is capacitance between conductors. However, if
one conductor is connected to the shield via a grounded power supply, the
nominal value roughly doubles.
You can use the length and conductor resistance of the cable to find the
fixed error appearing at the field device. To determine the fixed error, use
the following equation.
where
R1
CL
RFT =
Series 505 Analog I/O Modules User Manual
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Load imposed by the field device
Type and length of wire
Wiring practices
Maximum cable length
Fixed error (%) + 1 *
= field load resistance
= cable length
conductor resistance (Ω/unit length)
0.01 µ F
=
Nominal cable capacitance (per unit length)
R1
R1 ) (2 CL RFT)
100
Installation 2-5