DRAFT - 11 December 2014
DRAFT - 11 December 2014
INM MTL4850_54 Rev4
3
DRAFT - 11 December 2014
2.1 General purpose or IS?
The MTL HART Management System can be used to control and maintain field devices that
are located in a safe area or a hazardous areas.
For safe areas
, HART Connection Units provide the necessary terminals to connect up to
32 field devices. These may be basic connection units, linked to a HART interface board, or
they may be integrated units with an MTL4850 or MTL4854 multiplexer onboard. Section 2.3
explains this in more detail.
Hazardous-area field devices
can be handled using IS isolating interfaces conveniently
mounted on a backplane with facilities for onward connection to the host. Here also there is a
choice of a backplane with an onboard HART multiplexer (CPH models), or legacy backplanes
that can be linked to a HART interface board that carries the multipexer(s).
Having the isolators mounted on a backplane dramatically reduces the amount of hand wiring
required and therefore reduces the number of potential wiring errors. The hazardous-area
wiring terminates on the isolating modules,
not the backplane
, consequently the backplanes
do not need IS certification.
2.2 Generic or custom?
A range of generic connection units is available for both input and output field-device wiring.
These are not designed for any particular DCS type and may be used universally.
The alternative is to choose a connection unit or backplane that integrates with the type of
DCS being used on the plant. The key advantage of this method is the use of a DCS’s specific
connector type, which simplifies the wiring of the connection units into the system. Various
solutions are available to suit individual DCS types and a listing of the currently available
connection units and backplanes is given in Appendix A.
2.3 Connection methods
There are currently three methods for linking the HART signals to the MTL4850 or MTL4854:
a) using an integrated connection unit – HTP-SC32 - see Figure 2.2
b) via a connection unit to a HART interface (HMP-HM64) - see Figure 2.3
c) using an IS isolator backplane with a HART interface - see Figure 2.4
NOTE
the MTL4850/54 may also be used to update existing HART installations, but these
methods are not discussed here. Consult MTL for information if this is of interest.
The self-contained (non-IS) connection unit - see Figure 2.2 - is a 32 channel connection
unit with screw terminals for the field devices and the main system, and an integrated
multiplexers. Up to 63 of these connection units can be daisy-chained on an RS485 link to a
PC runnning HART maintenance software. Apart from an RS485 to USB (or Ethernet) protocol
converter, no other external hardware is required.
See Section 4.1 for details.
MTL4850/54
Figure 2.2
self-contained
HTP–SC32