Wiring Proline Promag 53 MODBUS RS485
40 Endress+Hauser
4 Wiring
#
Warnung!
When connecting Ex-certified devices, please take note of the instructions and wiring diagrams in
the Ex-specific supplement to these Operating Instructions. Should you have any questions, please
contact your Endress+Hauser sales office for assistance.
!
Note!
The device does not have an internal circuit breaker. An external switch or circuit breaker must
therefore be installed which can be used to disconnect the device from the main power source.
4.1 Cable specification MODBUS RS485
4.1.1 Cable type
In the EIA/TIA-485 standard, two versions (cable type A and B) are specified for the bus line and
can be used for all transmission rates. However, we recommend you use cable type A. The cable
specification for cable type A are provided in the following table:
Note the following points for the bus structure:
• All the measuring devices are connected in a bus structure (line).
• Using cable type A and with a transmission rate of 115200 Baud, the maximum line length
(segment length) of the MODBUS RS485 system is 1200 m. The total length of the spurs may not
exceed a maximum of 6.6 m here.
• A maximum of 32 users are permitted per segment.
• Each segment is terminated at either end with a terminating resistor.
• The bus length or the number of users can be increased by introducing a repeater.
Cable type A
Characteristic impedance 135 to 165 Ω at a measuring frequency of 3 to 20 MHz
Cable capacitance < 30 pF/m
Core cross-section > 0.34 mm
2
, corresponds to AWG 22
Cable type Twisted pairs
Loop-resistance ≤ 110 Ω/km
Signal damping Max. 9 dB over the entire length of the cable cross-section
Shielding Copper braided shielding or braided shielding and foil shielding
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