Appendix B MTL Power Supplies for Intrinsically Safe
Fieldbus Applications
The MTL9121 IS and the MTL9122 IS Power Supplies can be used to power field
devices in hazardous areas for FISCO (Fieldbus Intrinsically Safe COncept) IS
applications. The MTL9121 IS power supply can power up to five (5) 20 mA devices
in Gas Group IIC and the MTL9122 IS power supply can power up to twelve (12), 20
mA devices in Gas Group IIB. Ensure that the fieldbus devices and all components
used in the application are rated and certified for IS applications in these Gas Groups.
With the exception of the IS power supplies, many fieldbus components (H1 card,
terminators, and wiring components) are the same for IS and non-IS installations.
The MTL9122 IS and 9121 IS power supplies have a host side terminator switch and
a host side power switch on the front of the unit. The terminator on the IS side is
permanently connected. Both power supplies are fieldbus repeater power supplies
that repeat the fieldbus signal from the field to the host and power both the fieldbus
segment and the host.
This chapter addresses FISCO IS applications with devices in Class I Division 1 or
Zone 1 EExib locations. If a field device in your application is not certified for FISCO
IS, an MTL Fieldbus Entity Spur Adapter can be used. Similarly, if a field device in
your application is located in a Zone 0 Hazardous area, an MTL Fieldbus IS EExia
Spur Adapter can be used.
Refer to the MTL documentation and/or visit the DeltaV website
(www.easydeltav.com) and follow the links to MTL for additional information on their
products.
Note The Series 2 H1 card requires a power supply for each port in IS applications. The
MTL9121 and 9122 IS Power Supplies can provide this power.
MTL Power Supplies for Intrinsically Safe Fieldbus Applications 71
DC Power Considerations for IS Power Applications
The available current to power a field device depends on the length and resistance
characteristics of the fieldbus cable. Table 8 shows the maximum distances in meters
for a given load on the 9121 IS power supply and Table 9 shows the same information
for the 9122 IS power supply. The following assumptions are made:
MTL9121 IS Power Supply voltage is 12 VDC at 110 mA at 0º C
MTL9122 IS Power Supply Voltage is 12.8 VDC at 250 mA at 0º C
Minimum Device Voltage = 9.5 VDC (.5V device margin)
Each device has an average load of 20 mA
Fieldbus Type A 18 AWG cable @ 22 ohms/km is used
Cable Resistance (Type A) = 22 Ohms/km x 2 (loop) = 44 Ohms/ km
Devices are connected on one end of the cable and the fieldbus power supply is
connected on the other end of the cable
Maximum Distance (km) = (Allowed Loop V drop / Loop current) / Loop
resistance per km
There will be different restrictions and limitations on your segment if these
assumptions do not hold for your segment layout. If your devices average more than
20 mA per device, reduce the maximum cable length indicated in the table for that
number of devices or reduce the number of devices on that segment.
Table 8 Distance per Load on 9121 IS Power Supply
Number of field
devices
120
240
360
480
5 100
5110
Power Supply Load
(mA)
Maximum
Distance
(meters)
1000
1000
940
710
560
510
72 Fieldbus Installations in a DeltaV Digital Automation System
Table 9 Distance per Load on 9122 IS Power Supply
Number of field
devices
120
240
360
480
5 100
6 120
7 140
8 160
9 180
10 200
11 220
12 240
12 250
Power Supply Load
(mA)
Maximum Distance
(meters)
1900
1870
1250
930
750
620
530
460
410
370
340
310
300
Warning In any hazardous area installation it is important to read and follow the device
manufacturer's design and installation documents. Failure to follow the
documentation could result in an unapproved and unsafe application.
Additionally, in hazardous locations follow your plant's procedures for making
the area safe during installation and maintenance operations.
Host Power
Both the MTL9121 IS and 9122 IS power supplies can provide power to the host in
the safe area. The supplies are rated at 30 mA and are capable of providing host power
for either the simplex or redundant Series 2 H1 cards. The distance between the host
and the IS power supply can exceed 1000 meters.
MTL Power Supplies for Intrinsically Safe Fieldbus Applications 73
Installing the MTL Intrinsically Safe Power Supplies
The MTL9121 and 9122 Intrinsically Safe power supplies install on a DIN Rail and
are powered by a typical bulk 24 VDC power supply. The IS power supplies connect
to the segment wiring to power the fieldbus devices that are not self-powered. On the
top of each supply is a 3 pin connector for connection to the safe area host fieldbus
and a 3 pin connector for connection to the safe area 24 V power. On the bottom of
each supply is a 3 pin connector for connection to the IS area. The following figure
shows the connectors.
Power Host
Host Pwr
On
+
6S5-4
Safe
Area
+1+
3-2
T
Host
Power Supply - IIB
Pwr
Fault
Host
IS
Figure 17 Connectors on the MTL 9122 IS Power Supply
74 Fieldbus Installations in a DeltaV Digital Automation System
9122-IS
+
IS
T
Hazardous
8S7
9
Area
-
IS
Note The hazardous area wiring must remain separated from the safe area wiring. This
includes the shield drain wires as they must be separate wires all the way to the ground
connection.
¾ To wire the safe area
The 24 VDC power input and host connectors are on the top of the power supply.
1. Connect the primary power supply positive (+) wire to pin 1.
2. Connect the primary power negative (-) 24 V return to pin 2.
3. Connect a secondary power supply positive (optional) (+) wire to pin 3.
If using a primary and secondary 24 VDC power supply, be sure to connect the power
supply returns together.
4. Connect the host segment negative (-) to pin 4.
5. Connect the host segment shield to pin 5.
6. Connect the host segment positive (+) to pin 6.
¾ To wire the hazardous area
The IS connector is on the bottom of the power supply.
1. Connect the IS area fieldbus segment positive (+) wire to pin 7.
2. Connect the IS area fieldbus segment shield (S) wire to pin 8 and to a shield
ground connection.
3. Connect the IS area fieldbus segment negative (-) wire to pin 9.
MTL Power Supplies for Intrinsically Safe Fieldbus Applications 75
Switches
The power supplies have a switchable host side terminator and host power switch.
(The field side terminator is permanently connected.)
Host terminator ON is the upper position; host terminator OFF is the lower
position
Host power ON is the upper position; host power OFF is the lower position
Host Pwr
T
On
Host
Figure 18 Terminator and Power Switches
The segment layout determines the location of the terminator and if the switchable
terminator on the power supply is used. Be sure that two terminators are on the host
side and two terminators are on the fieldbus side of each power supply. Similarly, the
use of the switchable power capability is dependent upon the needs of the particular
IS application. The Series 2 H1 card requires power; therefore, the host power switch
should be ON. If more than one IS power supply is connected to the same segment
(as in Figure 19), host power should be provided by one unit only. Be sure the
additional unit’s host power switches are in the OFF position.
76 Fieldbus Installations in a DeltaV Digital Automation System
Intrinsically Safe Application Example with an MTL9122
T=ON
HP=OFF
The following figure shows an IS application that allows up to 16 devices on the
segment. The maximum cable length on the MTL9122 portion of the segment is 1900
meters and the maximum total cable length per segment is 1900 meters.
Red
24 V
power
supply
-
+
24 V
Power Host
+1+
3-2+6S5-4
Host Pwr
T
T=ON
On
Host
Power Supply - IIB
HP=ON
Pwr
IS
Fault
T
Host
IS
9122-IS
8S7+9
-
Port 1 Port 2
Power Host
+1+
3-2
T
Host
Power Supply - IIB
Pwr
Fault
Host
IS
9122-IS
-
4
Host Pwr
On
IS
T
S
+
6
5
8S7+9
-
H1H1
T=ON
T=ON
HP=OFF
HP=OFF
Redundant
Series 2
H1 cards
Carrier
shield bar
Ground
Power Host
S
-
+1+
5
3-2
4
Host Pwr
T
On
Host
Power Supply - IIB
Pwr
IS
Fault
T
Host
IS
9122-IS
8S7+9
Shielded
pair with
drain wire
+
6
T=ON
HP=ON
-
MB8
Megablock
MB8
Megablock
0.4 Km cable
Terminator
Surge
protection
ground
Terminator
Surge
protection
ground
Figure 19 16 IS Devices on a Segment
Note Ensure that all components are rated and certified for IS applications.
MTL Power Supplies for Intrinsically Safe Fieldbus Applications 77
78 Fieldbus Installations in a DeltaV Digital Automation System
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