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Wiring Guidelines
Guidelines for a successful implementation of DC current signal, DC power, and HART®
communication to the SVi1000:
o
Compliance voltage at the SVi1000 is approximately 9 V at the current of 20 mA.
Determining an SVI Positioner Compliance Voltage in a Control System
on
page 58.
o
Signal to the SVi1000 must be a regulated current in the range 3.2 to 22 mA.
o
Controller output circuit must be unaffected by the HART
®
tones which are in the
frequency range between 1200 and 2200 Hz.
o
In the frequency range of the HART
®
tones, the controller must have a circuit
impedance of more than 220 Ohms, typically 250 Ohms.
o
HART
®
tones may be imposed by the positioner and a communication device located
anywhere on the signaling circuit.
o
Cabling must be shielded to prevent electrical noise that would interfere with the
HART
®
tones, with the shield grounded.
o
Shield must be properly grounded in only one place.
o
For details and calculation methods for wiring resistance, and capacitance and for
calculation of cable characteristics, refer to the HART
®
FSK Physical Layer
Specification.
o
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.
o
Use of a low impedance voltage source damages the SVi1000. 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.
o
Position Retransmit: when wiring this feature:
o
Use the same gauge wires as the 4-20 mA control loop.
o
Ensure that the position retransmit signal is connected to the control system’s
analog input card.
o
Ensure the control loop is powered while making measurements with a meter.
WARNING
This process can cause the valve to move.
Before proceeding be sure the valve is isolated
from the process. Keep hands clear from moving
parts.
