Foundation Fieldbus; Wiring Procedure - Honeywell SLG 700 User Manual

Consideration is required when selecting intrinsic safety barriers to ensure that they will
supply at least minimum Transmitter voltage (V
250ohms of resistance (typically within the barriers) needed for digital communications.
Transmitter loop parameters are as follows:
R = maximum loop resistance (including barriers and wiring) that will allow
LOOP MAX
proper Transmitter operation and is calculated as
Where:
V
XMTR MIN
If the total loop resistance is too high considering the HART load resistance and intrinsic
safety barrier, consider the following options:
5. Using HART multi-drop mode will effectively allow a higher loop resistance.
See section
is required.
6. Shunt the HART load resistor with a large inductor so that the HART load
impedance remains high at HART signal frequencies, but much lower at DC.
This solution, while it does work, may be physically inconvenient. For example,
a 0.5 Henry 30 Ohm choke in parallel with a 250ohm HART resistor will serve
this purpose.
7. Use an intrinsic safety isolator instead of a shunt diode barrier. These devices
will provide more voltage to the transmitter since the HART load resistance in
the safe area is isolated from the transmitter loop. These devices are sometimes
called smart transmitter barriers or supplies, or repeater power supplies. Ensure
that the isolator will pass HART signal frequencies in both directions.

3.3.4 FOUNDATION Fieldbus

FOUNDATION Fieldbus transmitters require a terminal voltage of 9.0V to 32.0V. See
page 152 for intrinsically safe and FISCO parameters.

3.3.5 Wiring Procedure

1.
2.
3.
4.
5.
6.
7.
Page 80
R = (V
LOOP MAX SUPPLY MIN
= 14V
1.4.1 for details. This option is not possible if a 4-20mA output signal
Ensure the loop power supply is off.
See Figure 3-37 for parts locations. Loosen the end cap lock using a 1.5mm
Allen wrench.
Remove the end cap cover from the terminal block end of the Electronics
Housing.
Feed loop power leads through one end of the conduit entrances on either
side of the Electronics Housing. The Transmitter accepts up to 16AWG
wire.
Plug the unused conduit entrance with a conduit plug appropriate for the
environment.
Connect the positive loop power lead and the negative loop power. The
Transmitter is polarity insensitive.
Replace the end cap, and secure it in place.
SLG 700 SmartLine Level Transmitter User's Manual
), including the required
XMTR MIN
)  21.8 mA.
– V
XMTR MIN
Revision 7