User's Manual

Page 30 SITRANS LC 500 – INSTRUCTION MANUAL 7ML19985GE01
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Interconnection
Safety Grounding
The safety grounding requirements are determined by the application and the connected
instruments. The SITRANS LC 500 transmitter does not have any special requirements
due to the galvanic separation between the measurement section and the loop section.
Depending on the DCS characteristics, there are three possible grounding options:
• If the DCS measures the current through the loop compared to a common zero Volt
point, do not ground the negative side of the current loop because measurement
inputs can be short-circuited.
• If the DCS measures the current in the positive wire or connector, the negative side
of the current loop can be grounded.
• If the DCS has galvanically separated inputs for each measurement channel the
grounding method can be chosen as required.
In hazardous applications a Stahl-type barrier is required, and it is typically mounted on a
DIN rail inside a customer-supplied enclosure located in the non-hazardous area.
Example 1
If no specific Ex conditions apply, the SITRANS LC 500 can be directly connected to the
DCS. The supply voltage, however, should remain within the limits set by the
SITRANS LC 500. Connecting a SITRANS LC 500 to a DCS does not influence that
equipment. One of the connection cables can be grounded if desired.
Example 2
In the case of Intrinsically Safe applications, where the DCS equipment measures the
current in the positive connection and the negative connection can be grounded, a
barrier type as shown below is sufficient.
DCS APPARATUS
13 < Vsupp < 32 Vdc.
3,6 - 22 mA
Type:
Ser.:
Date:
Rev.:
Tamperingvoids warranty
COAX
GND
3
1
2
PA
PA
277
110 mA
Rmeas
DCS APPARATUS
0V
28V
4
Type:
Ser.:
Date:
Rev.:
Tamperingvoids warranty
Stahl barrier: 9002/01-280-
110-00 (or equal)
COAX
GND
non-hazardous area
hazardous area