Masoneilan SVI II AP Installation and Maintenance Manual =| 111© 2017 Baker Hughes, a GE company, LLC. All rights reserved.Grounding PracticesTo ensure proper grounding make sure that case and ground connections are made incompliance with the plants normal grounding practices. There must never be more than oneground point for the shield of the signal wiring. Normally ground is connected at the controlleror at the intrinsic safety barrier.The case grounding screws are located on the outside of the case at the lower right of thedisplay cover and inside the cover. The case is isolated from all circuitry and can be groundedlocally in accordance with applicable codes.If noise or instability is present set the positioner to MANUAL mode of operation and manuallyposition the valve over its entire range. If the valve is stable in MANUAL mode then theproblem can be noise in the control system. Recheck all wiring connections and groundpoints.Compliance Voltage in Single Drop Current ModeThe SVI II AP requires 9.0 V at 20 mA and 11.0 V at 4 mA. Typical smart devices require MOREvoltage at higher current. The controller supplying the current has LESS voltage available athigher current. The SVI II AP is noteworthy in that it requires LESS Voltage at higher currentthat complements the characteristic of the source requiring only 9 V at 20 mA. See“Determining an SVI Positioner Compliance Voltage in a Control System” on page 199.NOTE Improperly or inadequately grounded installations can causenoise or instability in the control loop. The internal electronics areisolated from ground. Grounding the case is unnecessary forfunctional purposes but grounding the case may be necessary toconform to local codes.Table 15 through Table 17 on page 112 provide examples of several SVI II AP installations andcalculating the compliance voltage necessary to supply 9 V at 20 mA.Conclusion: The control system must have a compliance voltage equal to or greater than17.64 V; contact the DCS vendor to verify compliance.Table 15 Compliance Voltage for Single Channel Zener with 22 AWG CableVoltage at SVI II AP at 20 mA 9.0 VDrop in single channel Zener barrier with 342 Ohms end to end resistance 6.84 VDrop in 22 AWG cable, 3000’ long (30 Ohms per 1000’) 1.8 VDrop in passive HART ® Filter 0.0 VVoltage required at controller 17.64 V
