6 INSTALLATION – ELECTRICAL
CONNECTIONS
CAUTION: Connect only wires with compatible electrical
signals to the terminals. Voltages or currents outside the
specified range can damage the circuit boards.
6.1 Electrical Terminals
Figure 14 shows the terminals on the positioner unit labeled
for HART protocol.
Figure 14: Terminal Diagram (HART ONLY)
6.2 Command Input (4-20 mA)
Connection
Wire 4-20 mA current source to the input terminal labeled
“HART 4-20”. The Logix 3800zb has spring loaded terminal
blocks that do not require tools. Depending on the current
source, a HART filter may be required. See section 12,
Maintenance – Troubleshooting.
NOTE: The polarity of the terminals is labeled on the
cover; however, the command input connection is polarity
insensitive.
6.2.1 Compliance Voltage
Output compliance voltage refers to the maximum voltage the
current source can provide. A current loop system consists of
the current source, wiring resistance, barrier resistance (if
present), and the Logix 3800zb impedance.
The Logix 3800zb requires that the current loop system allows
for a 10 VDC drop across the positioner at maximum loop
current. The current loop system should have a minimum
compliance voltage greater than 10 VDC and a maximum less
than 32 VDC. The current operating range is from 4 to 20 mA.
See Figure 15: Compliance Voltage.
To determine if the loop will support the Logix 3800zb, perform
the calculation in the following equation. The Available Voltage
must be greater than 10VDC to support the Logix 3800zb.
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
3800zb. The Logix 3820 has an input resistance equivalent
to 500 Ω at a 20 mA input current.
CAUTION: Always limit the current for 4-20 mA
operation. Never connect a voltage source directly across the
Logix 3800zb terminals. Permanent circuit board damage
may occur.
Figure 15: Compliance Voltage
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