MTL MTL5021 - MTL5053 Isolator;Power Supply for 31.25 Kbit;S Fieldbuses

6.24.3 Testing
Remove all safe- and hazardous-area connections and apply 24V dc to
terminals 13 and 14 as shown in figure 6.55. Check that the green
power LED (on top of the unit) is on. Put all switches in the On position.
With no load, check for nominal current of 60mA ±5mA at terminal 14.
Correct operation of the communication modes is indicated by signals
received and/or transmitted.
6.25 MTL5053 isolator/power supply for
31.25kbit/s fieldbuses
The MTL5053 has been specifically developed to extend 31.25kbit/s
(H1) fieldbus networks into hazardous areas. It provides power,
communication and IS isolation to devices powered through the signal
conductors. The MTL5053 complies with the requirements of Fieldbus
Foundation™ specified power supply Type 133 (IS power supply).
To comply with fieldbus standards, each bus must be terminated at both
ends. MTL's FBT1-IS or FCS-MBT fieldbus terminators (see section 6.33)
can be supplied for this purpose or, for installations in which the safe-
area bus length is small, the MTL5053 includes an internal safe-area
terminator which is enabled by a switch located on the top of the unit.
For network and termination criteria, check applicable fieldbus
standards and specification
IEC 61158-2, ISA-S50.02 for 31.25kbit/s
fieldbus systems, Foundation™ Fieldbus 31.25kbit/s Physical Layer
Profile Specification FF-816 and MTL's Application Brief AB002.)
6.25.1 Wiring connections
See figure 6.56 for wiring connections and refer to MTL's Application
Brief AB002.
Note: To assist the process of terminating cable screens,
screw terminals have been provided in terminal positions 3 and 6 and
7 and 10. Please note, however, that there is no internal connection for
these terminals so they are not earthed.
25
INM5000-6 Jul 2010
Across hazardous areas: For communication across hazardous
areas MTL5051 devices are used in pairs to transfer bi-directional full-
duplex data across hazardous areas, as shown in figure 6.53. Current
switching is used to minimise the bandwidth-limiting effects of long cables.
The maximum baud rate in this mode is the lesser of 19.2k baud or the
cable-related rate produced by the following formula.
Remote signalling baud rate formula, for back-to-back mode across a
hazardous area:
max baud rate = K/(RxCxL
2
)
where K = 0.25 (constant)
R = cable resistance (Ω/m)
C = cable capacitance (F/m)
L = length (m)
For example, with a 2km cable of 100pF/m capacitance and 40mΩ/m
resistance, the maximum baud rate = 0.25/(40mΩ x 100pFx 2km
2
) =
15k baud. This assumes that the cable is 2 cores plus screen, with the
screen used for the 'common' connection.
RS232-level devices: Communication with RS232-level interfaces, such
as a suitably certified IS keyboard, mouse, etc, is achieved by using one
or more MTL5051 units as required by the IS device.(TTL level interfaces
are accommodated by the TTL compatibility of RS232 receivers.)
The supply to IS equipment at terminal 2 can be set to either 5V or
12V, by a switch located on top of the unit, as follows:
+12V mode 12.0V ±5% (load <23mA)
+12V mode 8.0V min (load >23mA to <50mA)
+5V mode5.6V ±5% (load >23mA to <50mA)
Note: the normal RS232 limitations of bandwidth versus cable length are
applicable. As a rule of thumb, speed (baud) x length (metres) <150,000.
6
5
4
3
2
1
7
8
9
10
11
12
13
14
dc supply

+
Figure 6.55: Test circuit for MTL5051
Terminal Function
1 Hazardous-area fieldbus device(s) connection –ve
2 Hazardous-area fieldbus device(s) connection +ve
4 Optional HHC connection –ve
5 Optional HHC connection +ve
8 & 11 Safe-area fieldbus device(s) connection –ve
9 & 12 Safe-area fieldbus device(s) connection +ve
13 Supply –ve
14 Supply +ve
FBT1
fieldbus
terminator
**
6
5
4
3
2
1
7
8
9
10
11
12
13
14
T
*Hand-held communicator
** See section 6.33 for details of FBT1
T
Vs+
Vs
20 to 35V dc
HHC*
Fieldbus
devices
T
FBT1
fieldbus
terminator
**
+

+

devices
Fieldbus
devices
Figure 6.56: MTL5053 wiring diagram and connections
Hazardous area Safe area
2a
2b
ON
MTL5051
PWR
1a
1b
Figure 6.54: Top label, MTL5051
Table 6.11 (see also figure 6.54)
Table 6.12 (see also figure 6.52)
MTL5051 MTL640 MTL650 Comms Other IS
Terminals mode mode mode devices
1 Common Common Common Common
2 V signal 12V - 5V/12V
3 I return Rx Rx -
4 - Tx Tx -
5---Tx
6---Rx
Switch
1a On Off Off Off
1b On On On Off/On
Terminals RS232 mode TTL mode RS422 mode
7 - - Rx -
8 - - Rx+
9 - Tx Tx+
10 Tx - Tx-
11 Common Common Common
12 Rx Rx -
13 Supply -ve Supply -ve Supply -ve
14 Supply +ve Supply +ve Supply +v
Switch
2a Off On On
2b On Off Off
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