Output Channel Isolation; Hart® Filter Requirements - GE Masoneilan SVI II ESD Installation And Maintenance Manual

Output Channel Isolation

The designer of the signaling circuit where the SVI II ESD has to be installed must consider the
eight design rules in Wiring Guidelines (see "HART® Wiring Guidelines" on page 171). In
particular, the control system output interface has galvanically isolated analog output
channels and share a common ground or are separated from ground by a current control
transistor or sense resistor.
If outputs are isolated a single channel Zener diode barrier can be used.
If outputs share a common ground a single channel Zener diode barrier can be used.
If outputs are separated from ground a dual channel Zener barrier is required.
Controller outputs are internally separated from ground by a current sense resistor or a
control transistor. Dual channel barriers apply excessive loop resistance and can cause
compliance voltage problems. An Intrinsically Safe galvanic isolator operates with all three
types of output channels, isolated, grounded or separated from ground, and provides
sufficient compliance voltage. The galvanic isolator must be certified by the manufacturer to
®
be HART
isolator (Figure 89 on page 190). Consult barrier and isolator manufacturer for devices rated
for use with SVI II ESD positioner I.S. entity parameters in Hazardous Area Approvals.
®
HART Filter Requirements
The control system output interface must allow the HAR
mA DC signal. Circuits not designed for HART
DCS manufacturer for interfacing to any system. HART
®
non-HART
communications tones are disabled by the control circuit.
SVI II ESD can be used with non-HART
functionality are disabled.
Use pushbuttons for operation and maintenance. If remote maintenance is desired, always
isolate the control valve from the process. Disconnect non-compliant controller before
connecting a current source and HART
®
If a HART
compliance voltage.
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®
compliant if the HART
compliant output circuit to malfunction, in some cases. In other cases HART
filter is required, then its voltage drop must be considered when calculating
connections are supported on the safe area side of the
®
®
may need a HART
®
communications can cause a
®
compliant output circuits but remote communications
®
master device.
Masoneilan SVI II ESD Installation and Maintenance Manual
T frequencies to coexist with a 4 - 20
®
filter. Consult controller or
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