Eaton MTL MTL7000 SERIES

◆ Exceptionally high packing densities – only 7mm barrier width

◆ 24V dc supply connections simplified – optional power comb

feeds many barriers

◆ Direct connection of cable screens and 0V lines – third terminal

on both hazardous and safe sides

◆ Patent US 5838547

MTL7000 Series award-winning, intrinsic safety shunt-diode

safety barriers are innovative devices designed to provide

exceptionally high packing densities, straightforward

‘single-operation’ installation and simplified

connection, commissioning and maintenance

facilities. Many of the MTL7000 Series features

duplicate the functions of conventional field terminals

and the barriers can, therefore, ‘double up’ as

terminals for many applications, saving even more space.

A barrier width of only 7mm enables

maximum packing densities due to the use of surface

mount and thick-film hybrid circuit technologies

(subjects of patent applications).

Barrier identification is provided by one or both

of two methods. The first consists of tagging strips

mounted on posts located at each end of a row of

barriers while the other consists of separate

identifiers attached to the tops of individual barriers.

Of these, the first can be used to tag locations as well

as barriers and is recommended for large

installations while the second is better suited to

installations of a few barriers only.

An optional power comb simplifies

installations where multiple barriers are powered

from a common 24V dc source (via a power feed

module or a dummy barrier). The comb replaces

individual power supply connections to each barrier,

yet allows single barriers to be removed without

affecting the others. The power feed module powers

up to 40 barriers and incorporates a trip which

switches off the supply to the barriers if a fault (such

as an overvoltage) occurs in the power source

circuit.

Secondary replaceable fuse versions of

many barriers are available and form the

MTL7100 sub-series. These are useful where there is

a possibility of faults occurring during commissioning

which would otherwise blow the barriers' internal

safety fuses. One secondary replaceable fuse for

each barrier channel is provided and is lower in

value than the related safety fuse. Fuses are

packaged in small mouldings which can be latched

in a 'disconnect' position to break the safe and

hazardous areas during commissioning,

maintenance or fault finding, thus avoiding the need

for additional disconnect terminals.

Where a fuse is less likely to be

necessary, the MTL7200 sub-series uses a latching

out link only, to provide the basic loop disconnection

of the MTL7100 sub-series.

CERTIFICATION

MTL7000 Series barriers protect devices located in all normally

occurring explosive atmospheres, including air/flammable gas

mixtures, dusts and fibres.  MTL7000 Series barriers are certified [EEx

ia] IIC (except MTL7129P+, certified IIB) BY BASEEFA to CENELEC

standards, by FM in the USA, CSA in Canada and also by other

authorities, providing worldwide certification. MTL7000 Series

barriers are designed to the same safety descriptions as MTL700

Series equivalents (in some cases slightly stricter) and can therefore be

used for the same applications.

HOW THEY WORK

All MTL7000 Series barriers are based on the same simple principle.

Each channel contains three stages of Zener or forward-connected

diodes and an ‘infallible’ terminating resistor. In the event of an

electrical fault in the safe area, the diodes limit the voltage that can

reach the hazardous area and the resistor limits the current: active

output-current limiting circuits are not used. An internal fuse protects

the diodes, and the three stages of voltage limitation ensure continued

safety if the first or second stage should fail. MTL7100 barriers have

an additional replaceable fuse which protects the internal fuse.

The MTL7000 Series includes seven key barrier types which cover the

majority of applications, simplifying barrier selection and the

maintenance of spares stocks.

SUB-SERIES

MTL7000 Series barrier circuits are based on the well-proven designs

originally developed for the MTL700 Series. To simplify identification

for those familiar with the latter, part numbers are the same for

equivalent barriers, but with a ‘0’, ‘1’ or ‘2’ inserted after the initial

‘7’ to identify the relevant sub-series:

MTL7000 standard

MTL7100 fuse-disconnect

MTL7200 link-disconnect