Masoneilan SVI II AP Installation and Maintenance ... - GE Energy

GE Oil and Gas
SVI II AP Instruction Manual
Grounding Practices
To ensure proper grounding make sure that case, signal, and ground connections are
made in compliance with the plants normal grounding practices. Any point in the loop can
be referenced to ground, but there must never be more than one ground point. Normally
ground is connected at the controller or at the intrinsic safety barrier.
The case grounding screws are located on the outside of the case at the lower right of the
display cover and inside the cover. The case is isolated from all circuitry and can be
grounded locally in accordance with applicable codes.
If noise or instability is present set the positioner to MANUAL mode of operation and
manually position the valve over its entire range. If the valve is stable in MANUAL mode
then the problem can be noise in the control system. Recheck all wiring connections and
ground points.
Compliance Voltage in Single Drop Current Mode
The SVI II AP requires 9.0 V at 20 mA and 11.0 V at 4 mA. Typical smart devices require
MORE Voltage at higher current. The controller supplying the current has LESS Voltage
available at higher current. The SVI II AP is noteworthy in that it requires LESS Voltage at
higher current that complements the characteristic of the source requiring only 9 V at 20
mA.
NOTE
Improperly or inadequately grounded installations can cause
noise or instability in the control loop. The internal electronics
are isolated from ground. Grounding the case is unnecessary
for functional purposes but grounding the case may be
necessary to conform to local codes.
Table 13 through Table 15 on page 111 provide examples of several SVI II AP
installations and calculating the compliance voltage necessary to supply 9 V at 20 mA.
Table 13
Compliance Voltage for Single Channel Zener with 22 AWG Cable
Voltage at SVI II AP at 20 mA
9.0 V
Drop in single channel zener barrier with 342 Ohms end to end resistance 6.84 V
Drop in 22 AWG cable, 3000 ft. long (30 Ohms per 1000’) 1.8 V
Drop in passive HART Filter* 0.0 V
Voltage required at controller
17.64 V
* Such as MTL HCU16AO
Conclusion:
The control system must have a compliance voltage equal to or greater than
17.64 V; contact the DCS vendor to verify compliance.
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