Eaton Crouse-Hinds MTL5500 Series Instruction Manual page 80

10 .3 .2 Hazardous-area interfacing
Displays/terminals: For details of interfacing with MTL640 and MTL650 displays/terminals (as
an alternative to the MTL696 communications interface) see the appropriate product instruction
manual.
Table 10 .2
Table 10 .3
Figure 10 .5:
Top label
for MTL5051
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
10.4. 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:
where
For example, with a 2km cable of 100pF/m capacitance and 40mΩ/m resistance, the maximum
baud rate = 0.25/(40mΩ x 100pFx 2km2) = 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:
Note: the normal RS232 limitations of bandwidth versus cable length are applicable. As a rule
of thumb, speed (baud) x length (metres) <150,000.
72
MTL5051 MTL640
Terminals mode
1 Common
2 V signal
3 I return
4 -
5 -
6 -
Switch
1a On
1b On
Terminals RS232 mode
7 -
8 -
9 -
10 Tx
11 Common
12 Rx
13 Supply -ve
14 Supply +ve
Switch
2a Off
2b On
max baud rate = K/(RxCxL2)
K = 0.25 (constant)
R = cable resistance (Ω/m)
C = cable capacitance (F/m)
L = length (m)
+12V mode
+12V mode
+5V mode5.6V ±5% (load >23mA to <50mA)
MTL650 Comms
mode mode
Common Common
12V -
Rx Rx
Tx Tx
- -
- -
Off Off
On On
TTL mode RS422 mode
-
-
Tx
-
Common Common
Rx
Supply -ve Supply -ve
Supply +ve Supply +ve
On
Off
12.0V ±5% (load <23mA)
8.0V min (load >23mA to <50mA)
Other IS
devices
Common
5V/12V
-
-
Tx
Rx
Off
Off/On
Rx-
Rx+
Tx+
Tx-
-
On
Off
INM 5500 Rev 11