Flowserve 520MD Digital Positioner - Manual (Page 7)

7
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User Instructions Logix 520MD - LGENIM0520-01 09/09
CAUTiOn: Never connect a voltage source directly across
the positioner terminals. This could cause permanent
circuit board damage.
In order to determine if the loop will support the Logix
520MD, perform the following calculation:
Available Voltage = Controller Voltage (@Current
MAX
)
- Current
MAX
*(R
barrier
+ R
wire
)
The calculated available voltage must be greater than 10
VDC in order to support the Logix 520MD.
Example:
DCS Controller Voltage = 19 V
R
barrier
= 300 Ω
R
wire
= 25 Ω
CURRENT
MAX
= 20 mA
Voltage = 19 V - 0,020 A*(300 Ω + 25 Ω)
= 12,5 V
The available voltage 12,5 V is greater than the required
10.0 V; therefore, this system will support the Logix 520MD.
The Logix 520MD has an input resistance equivalent to 500 Ω
at a 20 mA input current.
8 CAbLE REQUiREMEnTS
The Logix 520MD digital positioner utilizes the HART
communication protocol. This communication signal is
superimposed on the DC 4-20 mA current signal. The two
frequencies used by the HART protocol are 1200 Hz and
2200 Hz. To prevent distortion of the HART communication,
cable capacitance and cable length restrictions must be cal-
culated. The cable length must be limited if the capacitance
is too high. Selecting a cable with lower capacitance/mm
rating will allow longer cable runs. In addition to cable
capacitance, the network resistance also affects the
allowable cable length.
65 Ω
(R
barrier
+ R
wire
+ 390 Ω)
Example:
R
barrier
= 300 Ω (if present)
R
wire
= 50 Ω
C
cable
= =
Max. Cable Length =
Max. Cable Length = = 1111 m
To control cable resistance, No. 24 AWG cable can be
used for runs less than 1500 m. For cable runs longer
than this, No. 20 AWG cable should be used.
Electromagnetic Compatibility
The Logix 520MD digital positioner has been designed
to operate correctly in electromagnetic (EM) fields
found in typical industrial environments. Care should
be taken to prevent the positioner from being used in
environments with excessively high EM field strengths
(greater than 10 V/m). Portable EM devices such as
hand-held two-way radios should not be used within
30 cm of the device.
Figure 3: Compliance Voltage
510
Controller
Voltage
Compliance
Voltage
12V
C
network
(µF) < - 0,0032
72 ρF 0.000072 µF
m m
- 0,0032 = 0,08 µF= C
network
(µF)(Max)
65
(300 + 50 + 390)
C
network
(µF)
C
cable
0,08 µF
0.000072 µF/m
520MD
10V