Proline Promass 83E/F/O Modbus RS485 Operating Instructions

WiringProline Promass 83 Modbus RS485#Warning!!Note!4 WiringWhen connecting Ex-certified devices, see the notes and diagrams in the Ex-specific supplement tothese Operating Instructions. Please do not hesitate to contact your sales office ifyou have any questions.The device does not have an internal power switch. For this reason, assign the device a switch orpower-circuit breaker which can be used to disconnect the power supply line from the power grid.4.1 Modbus RS485 cable specificationsIn the EIA/TIA-485 standard, two versions (cable type A and B) are specified for the bus line andcan be used for all transmission rates. However, we recommend you use cable type A. The cablespecification for cable type A is provided in the following table:Cable type ACharacteristic impedanceCable capacitance135 to 165 at a measuring frequency of 3 to 20 MHz< 30 pF/mCore cross-section > 0.34 mm , corresponds to AWG 22Cable typeLoop-resistanceSignal dampingShieldingTwisted pairs 110 /kmMax. 9 dB over the entire length of the cable cross-sectionCopper braided shielding or braided shielding and foil shieldingNote 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 115 200 Baud, the maximum line length(segment length) of the Modbus RS485 system is 1200 m (4 000 ft). The total length of the spursmay not exceed a maximum of 6.6 m (21.7 ft) 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.Page 26 • MN0M030Issue/Rev. 0.2 (12/12)