Baker Hughes Masoneilan SVI II AP Series, Quick Start Manual

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Masoneilan SVI II AP Digital Positioner Quick Start Guide = | 49
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.
In the frequency range of the HART
®
tones, the
controller must have a circuit impedance of more than
220 Ohms, typically 250 Ohms.
HART
®
tones may be imposed by the positioner and a
communication device located anywhere on the
signaling circuit.
Cabling must be shielded to prevent electrical noise that
would interfere with the HART
®
tones, with the shield
grounded.
Shield must be properly grounded in only one place.
For details and calculation methods for wiring
resistance, and capacitance and for calculation of cable
characteristics, refer to the HART
®
FSK Physical Layer
Specification.
For split range installations the output voltage must be
sufficient to operate two positioners (11 V @ 4 mA, 9 V
@ 20 mA) and the expected voltage drop in the cable.
Use of a low impedance voltage source damages the
SVI II AP The current source must be a true high
impedance current limiting device. A proper current
source explicitly enables adjustment of the current, not
the voltage.
When wiring a position retransmit:
Use the same gauge wires as the 4-20 mA control
loop.
Ensure that the position retransmit signal is
connected to the control system’s analog input card.
Ensure the control loop is powered while making
make measurements with a meter.