Masoneilan SVI II ESD Installation and Maintenance Manual =| 191© 2016 General Electric Company. All rights reserved.Output Channel IsolationThe designer of the signaling circuit where the SVI II ESD has to be installed must consider theeight design rules in Wiring Guidelines (see “HART® Wiring Guidelines” on page 171). Inparticular, the control system output interface has galvanically isolated analog outputchannels and share a common ground or are separated from ground by a current controltransistor 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 acontrol transistor. Dual channel barriers apply excessive loop resistance and can causecompliance voltage problems. An Intrinsically Safe galvanic isolator operates with all threetypes of output channels, isolated, grounded or separated from ground, and providessufficient compliance voltage. The galvanic isolator must be certified by the manufacturer tobe HART ® compliant if the HART® connections are supported on the safe area side of theisolator (Figure 89 on page 190). Consult barrier and isolator manufacturer for devices ratedfor use with SVI II ESD positioner I.S. entity parameters in Hazardous Area Approvals.HART® Filter RequirementsThe control system output interface must allow the HAR ® T frequencies to coexist with a 4 - 20mA DC signal. Circuits not designed for HART® may need a HART® filter. Consult controller orDCS manufacturer for interfacing to any system. HART ® communications can cause anon-HART ® compliant output circuit to malfunction, in some cases. In other cases HART ®communications tones are disabled by the control circuit.SVI II ESD can be used with non-HART ® compliant output circuits but remote communicationsfunctionality are disabled.Use pushbuttons for operation and maintenance. If remote maintenance is desired, alwaysisolate the control valve from the process. Disconnect non-compliant controller beforeconnecting a current source and HART ® master device.If a HART® filter is required, then its voltage drop must be considered when calculatingcompliance voltage.
