Flowserve 420 IOM - Manual (Page 12)

User Instructions - Logix® 420 Series Digital Positioners FCD LGENIM0106-06 12/13
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7
ELECTRICAL CONNECTIONS
7.1 Electrical Terminals
Figure 6: Terminal Diagram
7.2 Command Input (4-20 mA) Connection
The Logix 420 is reverse polarity protected, however, verify
polarity when making field termination connection. Wire 4-20
mA current source to the input termin
al labeled “HART 4-
20mA INPUT”. See Figure 6: Terminal Diagram.
Depending on the current source, a HART filter may be
required. See 14.1 Troubleshooting Guide.
7.2.1 Compliance Voltage
Output compliance voltage refers to the voltage limit the
current source can provide. A current loop system consists of
the current source, wiring resistance, barrier resistance (if
present), and the Logix 420 impedance.
The Logix 420 requires that the current loop system allow for
a 10 VDC drop across the positioner at maximum loop
current. The operating current range is from 3.8 to 24 mA.
In order to determine if the loop will support the Logix 420,
perform the calculation in Equation 1. The Available Voltage
must be greater than 10VDC in order to support the Logix
420. Also, see Table 1: Input Signal.
Equation 1
( )
( )
Example:
( )
The available voltage (12.5 V) is greater than the required
voltage (10.0 V) therefore; this system will support the Logix
420. The Logix 420 has an input resistance equivalent to 500
Ω at a 20 mA input current.
CAUTION: The current must always be limited for 4-20
mA operation. Never connect a voltage source directly
across the Logix 420 terminals. This could cause permanent
circuit board damage.
HART 4-20
mA
Inp
ut
-
Housing EARTH
Terminal
Internal
External