Dwyer MTL7787 - Manual (Page 5)

1 INM7700-6 Jan 2010
MTL7700 Series
Shunt-diode safety barriers
INM7700-6
Jan 2010
Figure 1: MTL7700 Series shunt-diode safety barriers
1 OVERVIEW
This instruction manual contains all information needed to install,
maintain, fault-find and test MTL7700 Series shunt-diode safety
barriers.
Section 3 includes a checklist of essential safety factors that must
be considered when using MTL7700 Series barriers as intrinsically
safe (IS) interfaces between safe and hazardous areas.
Read section
3 before beginning installation. Users within the European
Community should also refer to the supplied MTL publication:
INA7700 MTL7700 Series
Instructions for Safe Use
It is assumed that all necessary system design, specification and
engineering factors have been taken into account BEFORE installation
work begins. To assist pre-planning, the following MTL publications
covering the theory, design, application, specifications and
certification of shunt-diode safety barriers are available:
AN9003 Application Note: A user’s guide to
intrinsic safety
AN9007 Application Note: A user’s guide to
MTL700 Series shunt-diode safety
barriers
MTL IS catalogue The MTL IS catalogue includes detailed
specifications of all MTL7700 Series
barriers and accessories
IS certificates Copies of Baseefa, FM and CSA IS
apparatus and system certificates for
MTL7700 Series barriers
If not supplied with the product, these publications are available
either from the company website (
www.mtl-inst.com) or on request
from your local MTL office.
2 DESCRIPTION
2.1 Introduction
MTL7700 Series ‘fourth-generation’ intrinsically safe shunt-diode
safety barriers are innovative successors to the MTL700 Series.
MTL7700 Series barriers are 1-, 2- or 3-channel devices that use
intrinsically safe explosion-protection techniques to pass electrical
signals between safe and hazardous areas, whilst limiting transferred
energy to a level that cannot ignite flammable atmospheres.
Connected in series with wiring entering any hazardous area on
process plant, MTL7700 Series barriers prevent explosions in all
normally occurring explosive atmospheres – including mixtures of air
with flammable gases, vapours, dusts and fibres – if a fault or faults
develop in the safe area.
2.2 MTL7700 Series – barrier ranges
The range is based on a choice of models which, between them,
cover virtually all applications – including the protection of
installations incorporating uncertified devices known as ‘simple
apparatus’ (eg, switches, thermocouples, resistive sensors, photocells
and LEDs) or separately certified ‘energy-storing’ or ‘voltage-
producing apparatus’ (eg, ac sensors, proximity detectors,
transmitters and current-to pneumatic (I/P) converters. Being
intrinsically safe, shunt-diode barriers enable maintenance work or
calibration to be carried out ‘live’ without additional precautions. To
simplify selection, several ‘key’ barriers (see table 1) are highlighted
as meeting the majority of process control requirements.