Endress+Hauser NXA820 - 6 Connections to Gauges and Host; Systems; Field Instruments and Slave Devices

Connections to gauges and host systems Tankvision
16 Endress+Hauser
6 Connections to gauges and host systems
6.1 Field instruments and slave devices
Please take care that the signal and power cables always are separated to prevent noise
and electrical interference between them.
6.1.1 Communication variants
Field instruments or other slave devices are connected to the Tankvision Tank Scanner
NXA820. The unit is available in 3 communication versions.
• Modbus RTU RS485
According to "Modbus over serial line specification and implementation guide V1.02"
published by the Modbus-IDA organization (www.modbus.org) and based upon the EIA/
TIA-485-A physical layer specification.
• Sakura V1
V1 fieldbus is a voltage mode digital communication using up to ±30 VDC.
• Whessoe WM550
The WM550 communication protocol works using a current loop principle.
Connection
Please take into consideration that the principle of current loop connection works as
follows:
The Tankvision (master) (-) signal point connects to slave 1 (+) signal point. Slave 1 (-)
signal point connects to slave 2 (+) signal point until (the last) slave N (-) signal piont
connects back to the Tankvision (master) (+) signal point closing the current loop.
Cable specification
Please ensure to follow the following recommendations for field installation of the
Tankvision with the WM550 protocol variant.
– Cable with twisted and non-shielded pairs
– Cable with at least 0.5 mm² (AWG 20) section
– Maximum total cable resistance: 250 Ω
– Cable with low capacitance
Characteristic impedance 135 to 165 Ω at measuring frequency of 3 to 20 MHz
Cable capacitance ≤ 30 pF/m
Core cross-section ≥ 0.34 mm² (AWG 22) multi-strand cable is preferred
Cable type Single twisted pair + third conductor (for common) or
Dual twisted pair (common uses second pair with wire joined together)
Cable resistance ≤ 110 Ω /km
Signal damping Max. 9 dB over the entire length of the cable cross-section
Shielding Copper braided shielding or combined foil and braided shielding
Cable capacitance ≤ 50 nF/m
Core cross-section ≥ 0.9 mm² (AWG 17) multi-strand cable is preferred
Cable type Twisted pair
Cable resistance ≤ 30 Ω /km
Shielding Copper braided shielding or combined foil and braided shielding
Insulation ≥ 60 V
DC