MTL Instruments MTL7000 Specifications

ultra-slim safety
barriers that can be
used like terminals

MTL7000 SERIES

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.

◆

Direct connection of cable screens
and 0V lines – third terminal on
both hazardous and safe sides

◆ Patent US 5838547

◆ Exceptionally high packing

densities – only 7mm barrier width

◆ 24V dc supply connections

simplified – optional power comb
feeds many barriers

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June 2004

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June 2004

MTL7000 SERIES – SPECIFICATIONS

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Key barriers shown in blue

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Vibration probes

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Transmitters,

controller outputs,

switches

Transmitters,

controller outputs,

switches

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Model Safety Application Basic circuit Max. end- Vwkg at Vmax Internal safety
No. description to-end 10µA fuse/fuse­MTL resistance disconnect(FD)†

(V) (ΩΩ) (mA) (ΩΩ) (V) (V) (mA)

SINGLE CHANNEL +VE

7122+ 22 150 147 18V dc systems 189 19.0 21.7 50 (FD)

7028+ 28 300 93 332 26.0 27.0 50

7128+ 28 300 93 Controller outputs, 342 26.0 27.2 50 (FD)

solenoids

7128P+ 28 234 120 275 26.0 27.1 50 (FD)

7129P+ 28 164 171 Controller outputs, 211 25.0 26.5 50 (FD)

solenoids (IIB)

SINGLE CHANNEL –VE

7028– 28 300 93 For negative/ 332 26.0 27.0 50

floating power

7128– 28 300 93 supplies 342 26.0 27.2 50 (FD)

DOUBLE CHANNEL +VE

7162+ 10 50 200 6V dc systems 87 8.0 9.1 50 (FD)

10 50 200 87 8.0 9.1 50 (FD)

7164+ 12 1k 12 Low-level/logic 1058 9.0 10.0 50 (FD)

12 1k 12 return signals 1058 9.0 10.0 50 (FD)

7167+ 15 100 150 12V dc systems 140 13.0 14.2 50 (FD)

15 100 150 140 13.0 14.2 50 (FD)

DOUBLE CHANNEL (NON-SYMMETRICAL) –VE

7096– 26 300 87 332 23.5 24.4 50

20 390 52 424 18.5 19.2 50

7196– 26 300 87 342 23.5 24.6 50 (FD)

20 390 52 434 18.5 19.3 50 (FD)

RETURN-DIODE TYPE

7087+ 28 300 93 332 26.0 26.8 50

28 diode – 33 + 0.9V 26.0 26.8 50

7187+ 28 300 93 342 26.0 26.9 50 (FD)

28 diode – 43 + 0.9V 26.0 26.9 50 (FD)

7087P+ 28 234 120 261 26.0 26.8 80

28 diode – 30 + 0.9V 26.0 26.8 80

7187P+ 28 234 120 274 26.0 26.9 50 (FD)

28 diode – 43 + 0.9V 26.0 26.9 50 (FD)

SIMPLE AC, LOW LEVEL

7055ac 3 10 300 2- or 3-wire (floating) 241 0.6 at 1µA 3.0 1 0 0

3 10 300 RTDs 241 0.6 at 1µA 3.0 1 0 0

7056ac 3 10 300 3-wire (grounded) 24 0.3 at 1µA 2.3 100

3 10 300 RTDs 24

1

0.3 at 1µA 2.3 100

3 10 300 24

1

0.3 at 1µA 2.3 100

SIMPLE AC, HIGHER VOLTAGE

7261ac 9 90 100 Strain-gauge bridges 115 7.2 8.3 80

9 90 100 4-wire RTD's 115 7.2 8.3 80

7061Pac 9 350 26 384 7.2 8.5 50

9 350 26 Strain-gauge 384 7.2 8.5 50

7161Pac 9 350 26 bridge, sense, output 393 7.2 8.8 50 (FD)

9 350 26 393 7.2 8.8 50 (FD)

7264ac 12 1k 12 Strain-gauge 1048 10.0 11.1 50

12 1k 12 bridge sense 1048 10.0 11.1 50

7066Pac 12 75 160 97.2 9.8 10.9 80

12 75 160 Strain-gauge 97.2 9.8 10.9 80

7166Pac 12 75 160 bridge supply 110.1 9.8 11.2 50 (FD)

12 75 160 110.1 9.8 11.2 50 (FD)

EUROPE (EMEA) Tel: [phone] Fax: [phone]
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June 2004

CERTIFICATION

MTL7000 Series barriers protect devices located in all normally
occurring explosive atmospheres, including air/flammable gas­mixtures, 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:

KEY BARRIERS SUMMARISED

TYPE APPLICATION KEY BARRIER

Analogue Resistance temperature detectors 7055ac 7060ac
input (low level) Thermocouples, ac sensors 7160ac
Analogue Controller outputs, one line earthed 7028+ 7128+
output Controller outputs, neither line earthed 7087+ 7187+

dc power supply

26.0V 20-35V
Analogue Transmitters, 2-wire, 4/20mA 7087+ 7206
input (high level) 7187+
Digital (on/off) Switches 7087+ 7207+
input 7187+
Digital (on/off) Solenoids, alarms, LEDs 7028+ 7208+
output 7128+

Note: the circuit shown is as an example only.
Standard, fuse- or link-disconnect options are shown shaded in the
'basic circuits' in the specifications tables.

MTL7000 standard

MTL7100 fuse-disconnect

MTL7200 link-disconnect

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†All barriers have internal, inaccessible, safety fuses. MTL7100 barriers have additional
replaceable fuses, lower in value than the internal fuses. It is the value of the replaceable fuse
that is quoted for MTL7100 barriers.
Note 1: 24

Ω

±0.15Ωat 20°C, channels track within 0.15Ωfrom –20 to +60°C.
Note 2: In star-connected barriers (eg, MTL7060/7160), the two channels are interlocked
such that the voltage between them cannot exceed the working voltage, V

wkg

.
Note 3: MTL7278ac: the working voltage between the two interlocked channels is 24.0V;
V

max

is 25.3V.

Note 4: Limited availability. Use MTL7706+ as an alternative.

‘P’ suffix – Barriers with a ‘P’ suffix are higher-power versions of the standard devices

with lower end-to-end resistance, except the MTL7061Pac/7161Pac. They are suitable for
type IIC gas groups, except MTL7129P+ which is designed for IIB.

WARNING – Check compatibility of the electrical safety
parameters of the field equipment with those of the barriers to
make sure that the combination is safe.

Model Safety Application Basic circuit Max. end- Vwkg at Vmax Internal safety
No. description to-end 10µA fuse†/fuse­MTL resistance disconnect (FD)

(V) (ΩΩ) (mA) (ΩΩ) (V) (V) (mA)

STAR-CONNECTED AC

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7060ac 9 75 120 Active dc and 101 7.2 8.5 50

9 75 120 ac sensors, 101 7.2 8.5 50

7160ac 9 75 120 thermocouples 110.1 7.2 8.8 50 (FD)

9 75 120 110.1 7.2 8.8 50 (FD)

7265ac 15 100 150 131 12.0 13.0 50

15 100 150 2-wire dc/ac 131 12.0 13.0 50

7278ac

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28 600 47 systems 640 +24.0 +25.9 50

–22.3 –23.8

28 600 47 640 +24.0 +25.9 50

–22.3 –23.8

ACTIVE BARRIERS

7106

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28 300 93 Transmitters – – 35 50

7206

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28 300 93 Transmitters – – 35 50

7207+ 28 300 93 Switches 348 + 1.2V – 35 50

28 diode 31 + 0.9V – – 50

7208+ 28 300 93 Solenoids, alarms, 348 + 1.2V – 35 50

LEDs

DUMMY BARRIERS

7099 – – – Securing and earthing – – – –

unused cables and screens.

7299 – – – Feed-through connections – – – –

for power comb.

SPECIFICATIONS (continued)

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June 2004

The MTL7106/MTL7206 is a single-channel barrier designed
primarily for energising a conventional or 'smart' 2-wire 4/20mA
hazardous-area transmitter. They can be thought of as an MTL7128–
or an MTL7028– barrier with a built-in floating power supply and
electronic over-volt protection. It provides a high voltage output (which
is negative with respect to earth) to power the transmitter and delivers
a 4/20mA signal into an earthed load in the safe-area. The novel
design is noted for its extreme accuracy.

Supply voltage

20 to 35V dc

Supply current

40mA typical at 20mA with 28V dc supply
45mA typical at 20mA with 24V dc supply
60mA maximum at 20mA with 20V dc supply

Voltage for transmitter and lines

16.0V minimum at 20mA with 250Ω load

11.25V minimum at 20mA with 500Ω load

Note that the output voltage is negative with respect to earth.

Safe-area load resistance

0 to 500Ω

Output current

0 to 23.6mA

Accuracy

±2µA (4 to 20mA)

Out of range capability

Over-range; >20mA to 23.6mA
Under-range; <4mA to 0mA

ACTIVE BARRIERS

MTL7106/7206

for 2-wire 4/20mA and ‘smart’
transmitters

HART®is a registered trademark of HART Communication Foundation

SPECIFICATION

MTL7106/MTL7206, MTL7207+ and 7208+ active barriers

The MTL7106/MTL7206, MTL7207+ and 7208+ barriers have
built-in overvolt protection, allowing their use with unregulated power
supplies. In many applications, eg, sensor inputs or controller outputs,
there is insufficient power available to blow the barrier fuse and this
additional protection is not necessary. But, where the barrier is
connected to a power supply, eg, for energising transmitters, switches,
solenoids or local alarms, overvolt protection allows the barriers to be
used with unregulated supplies up to 35V dc and also gives protection
against faulty wiring during commissioning. The MTL7206, 7207+,
7208+ are equipped with a loop disconnect at power supply terminal
1 while the MTL7106 has a fuse-disconnect.

Nearest equivalent passive barriers

MTL7106 nearest equivalent MTL7128–/7187+
MTL7206 nearest equivalent MTL7028–/7087+
MTL7207+ nearest equivalent MTL7087+/7187+
MTL7208+ nearest equivalent MTL7028+/7128+

‘Smart’ compatibility

HART Communication Foundation HART

®

Honeywell DE
Yokogawa BRAIN
Foxboro ‘smart’
Fuji ‘smart’
Chessel 3500 Series

Patent Nos

UK: 2205699
European (Germany, France, Italy): EP 0 294 139 BI
USA: 4967302

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4/20mA

0V

+20 to 35V

4/20mA

+

–

Load
resistor

250mA

MTL7206

Loop disconnect link

MTL7106

Fuse

disconnect

100mA

Hazardous
area

Safe area