Vega VEGABAR 67 4 … 20 mA_HART Bedienungsanleitung PDF herunterladen (Seite 20)

5 Connecting to power supply

VEGABAR 67 • 4 ... 20 mA/HART

36742-EN-130321

housing.Thiswouldinuencethestabilityoftheconnectionandthe

tightness of the housing.

If screened cable is necessary, 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

suppressed,buttheprotectiveeectagainsthighfrequencyinterfer-

ence signals remains.

Warning:

Considerablepotentialdierencesexistinsidegalvanicplantsaswell

as vessels with cathodic corrosion protection. Very large equalisa-

tioncurrentscanowthroughthecablescreenwhenthescreen

is grounded on both ends. To avoid this, the cable screen must be

connected to ground potential only on one end (inside the switch-

ing cabinet) in such applications. The cable screen must not be

connected to the internal ground terminal in the sensor and the outer

ground terminal on the housing not to potential equalisation!

Information:

Themetallicpartsoftheinstrument(transmitter,processtting,etc.)

are conductively connected with the inner and outer ground terminal

on the housing. This connection exists either as a direct metallic

contact or via the shielding of the special connection cable on instru-

mentswithexternalelectronics.Youcanndspecicationsonthepo-

tentialconnectionswithintheinstrumentinchapter"Technical data".

Take note of the corresponding installation regulations for Ex applica-

tions. In particular, make sure that no potential equalisation currents

owoverthecablescreen.Incaseofgroundingonbothsidesthis

can be achieved by the use of a capacitor or a separate potential

equalisation.

5.2 Connection procedure

Proceed as follows:

1. Unscrewthehousingcover

2. If a display and adjustment module is installed, remove it by turn-

ing it to the left.

3. Loosen compression nut of the cable entry

4. Remove approx. 10 cm of the cable mantle, strip approx. 1 cm

insulation from the individual wires

5. Insert the cable into the sensor through the cable entry

6. Lift the opening levers of the terminals with a screwdriver (see

following illustration)

7. Insert the wire ends into the open terminals according to the wir-

ing plan

Cable screening and

grounding

Single/Double chamber

housing

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