IM-P736-02 EMM Issue 3
47
VLM30 In-Line Vortex Flowmeter
3.20 Cable specification
The maximum permissible length depends on the baud rate, the cable (diameter, capacity and surge
impedance), the number of loads in the device chain, and the network configuration (2-core or 4-core).
-
At a baud rate of 9600 and with a conductor cross-section of at least 0.14 mm
2
(AWG 26), the maximum
length is 1000 m (3280 ft).
-
If a four-core cable is used in a two-wire system, the maximum length must be divided in half.
-
The spur lines must be short (maximum of 20 m (66 ft)).
-
When using a distributor with ‘n’ connections, the maximum length of each branch is calculated as
follows: 40 m (131 ft) divided by ‘n’.
The maximum cable length depends on the type of cable used. The following standard values apply:
-
Up to 6 m (20 ft): cable with standard shielding or twisted-pair cable.
-
Up to 300 m (984 ft): double twisted-pair cable with overall foil shielding and integrated earth cable.
-
Up to 1200 m (3937 ft): double twisted-pair cable with individual foil shielding and integrated earth cables.
Example: Belden 9729 or equivalent cable.
A category 5 cable can be used for Modbus
®
RS485 up to a maximum length of 600 m (1968 ft). For the
symmetrical pairs in RS485 systems, a surge impedance of more than 100 Ω is preferred, especially at a
baud rate of 19200 and above.
3.21 Connection to remote mount design
NOTE
Impairment of the device function
Impairment of the device function due to incorrect allocation of sensor and transmitter.
Correct allocation can be identified via the serial number on the name plate.
- Make sure that the sensor and transmitter are correctly allocated.
The signal cable connects the measuring sensor to the transmitter. The cable is fixed to the transmitter,
however, it can be separated as needed. When laying the signal cable, observe the following points:
-
Install the signal cable in the shortest path between the measuring sensor and the transmitter. Shorten
the signal cable accordingly as needed.
-
The maximum permissible signal cable length is 30 m (99 ft).
-
Avoid installing the signal cable in the vicinity of electric equipment or switching elements that can create
strayfields, switching pulses and magnetic induction. If this is not possible, run the signal cable through
a metal pipe and connect this to operational ground.
-
Carry out all terminal connections carefully.
-
Lay the wires in the terminal box in such a way that they are not affected by vibrations.
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