5 connecting to power supply, 1 preparing the connection – VEGA VEGAFLEX 81 4 … 20 mA_HART two-wire Coax probe With SIL qualification User Manual

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5 Connecting to power supply

VEGAFLEX 81 • 4 … 20 mA/HART two-wire

44216-EN-130823

5 Connecting to power supply

5.1 Preparing the connection

Always keep in mind the following safety instructions:

Connect only in the complete absence of line voltage

If overvoltage surges are expected, overvoltage arresters should

be installed

Power supply and current signal are carried on the same two-wire

cable. The operating voltage can differ depending on the instrument

version.
The data for power supply are specified in chapter "Technical data".
Provide a reliable separation between the supply circuit and the

mains circuits according to DIN EN 61140 VDE 0140-1.
Keep in mind the following additional factors that influence the operat-

ing voltage:

Lower output voltage of the power supply unit under nominal load

(e.g. with a sensor current of 20.5 mA or 22 mA in case of fault

message)

Influence of additional instruments in the circuit (see load values in

chapter "Technical data")

The signal conditioning instruments VEGAMET and VEGASCAN

have digital sensor recognition. When connecting VEGAFLEX 81, an

up-to-date version of the signal conditioning instrument software is

required. For a software update go to "www.vega.com/downloads"

and "Software".

The instrument is connected with standard two-wire cable without

screen. If electromagnetic interference is expected which is above the

test values of EN 61326-1 for industrial areas, screened cable should

be used.
For instruments with housing and cable gland, use cable with round

cross-section. A cable outer diameter of 5 … 9 mm (0.2 … 0.35 in)

ensures the seal effect of the cable gland. If you are using cable with

a different diameter, exchange the seal or use a suitable cable gland.

With plastic housing, the NPT cable gland or the Conduit steel tube

must be screwed without grease into the threaded insert.
Max. torque for all housings see chapter "Technical data".

If screened cable is required, connect the cable screen on both ends

to ground potential. In the sensor, the screen must be connected

directly to the internal ground terminal. The ground terminal on the

outside of the housing must be connected to the potential equalisa-

tion (low impedance).
If potential equalisation currents are expected, the connection on the

processing side must be made via a ceramic capacitor (e. g. 1 nF,

1500 V). The low-frequency potential equalisation currents are thus

Safety instructions

Voltage supply

Connection to signal con-

ditioning instruments

Connection cable

Cable gland ½ NPT

Cable screening and

grounding

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