MTL Instruments SD Specifications

• RangeofATEXCertifiedintrinsically

safesurgeprotectors

• Ultra-slimspace-savingdesign;easy

installation

• Multistagehybridprotectioncircuitry

–20kAmaximumsurgecurrent

• Rangeofvoltageratings–tosuitall

processI/Oapplications

• Highbandwidth,lowresistance,RTD,

PSTNand3-wiretransmitterversions
available

• 10yearproductwarranty

technical datasheet

SD Series

Ultra-slim user-friendly devices for protecting electronic equipment
and systems against surges on signal and I/O cabling.

The SD Series is a range of surge protection
devices combining unparalleled packing
densities, application versatility, proven
reliable hybrid circuitry, simple installation and
optional ‘loop disconnect’ facilities – features
which make the series the ultimate surge
protection solution for process equipment, I/O
systems and communications networks.

The exceptionally high packing densities
are the consequence of an ultra slim ‘footprint’
for individual modules which can thus ‘double­up’ as feedback terminals. Each module
provides full hybrid surge protection for 2 and
3 wire loop protection.

Modules with a comprehensive range
of voltage ratings cover all process related

signals such as RTDs, THCs, 4 to 20mA loops,
telemetry outstations, shut-down systems and
fire and gas detectors.

Optional ‘loop disconnect’, is a feature
which allows commissioning and maintenance
to be carried out without removal of the surge
protection device. This facility is provided by
the SD07, SD16, SD32 and SD55 units. In
addition, a third connection on the field and
safe side of the protector is provided in order
to terminate screens safely.

For three wire applications the specially
designed SDRTD (Resistance Temperature
Detector) and the SD32T3, (for separately
powered 4-20mA loops) provide full 3-wire
protection in a single compact unit. The
recommended choice for the protection of
3-wire pressure transducers on low power
circuits is the SD07R3.

For higher bandwidth applications, the
SDR series has been developed to meet
the demands of today’s highest speed
communication systems.

120V and 240V AC versions are available
for I/O and power supplies up to three Amps
of load current and telephone networks can
be protected by the SDPSTN.

One simple manual operation clamps
modules securely onto DIN rail, which
automatically provides the essential high­integrity earth connection.

‘Top-hat’ (T-section) DIN rail is generally
suitable for mounting SD modules although
for adverse environments, a specially-plated
version is available. A comprehensive range of
mounting and earthing accessories can also
be supplied, see page 7 for further details.

901-107RevS220513

www.mtl-inst.com [e-mail]

Guide to applications and selection

The SD Series of SPDs includes models for almost all possible applications operating at voltages up to 250V AC. The optional ‘fuse/disconnect’
package provides both fused protection against fault currents and a convenient method of isolating field circuitry from protected circuitry without
needing additional disconnect terminals. The standard fuse (which is replaceable) is rated 250mA with 50mA fuses also being available by special
request. Where only the disconnect feature is required, solid links can be used.

As an example, this feature is of particular value in applications in which an SPD is used with a bulk power supply feeding multiple loops. The
individual module fuse prevents a fault or follow on current on one loop disrupting the power supply to the others. Also, loops can be removed from
the circuit for maintenance reasons or added without needing additional disconnect terminals.

The following guide to selection suggests the most suitable SDs for a number of specific applications. For technical information, see the detailed
specifications on the back page of this publication (some field circuit protection is shown for completeness).

FIELD CIRCUIT PROTECTED CIRCUIT

Analogue inputs (high-level)

2-wire transmitters, 4-20mA, conventional and
smart

The SPDs recommended for use with
‘conventional’ and ‘smar t’ 4-20mA transmitters
(fed by a well-regulated supply) are the SD32 and
SD55, the choice depending upon the maximum
working voltage of the system (32V and 55V
respectively). The diagram illustrates a prime
example of an application for which the fuse/
disconnect facility is particularly useful, however,
both models are available in ‘X’ versions without
the optional fuse/disconnect feature.

2-wire transmitters

Analogue inputs (low-level)

RTDs

These applications are best served using the
SDRTD. For optimum accuracy, the energising
current should be chosen to ensure the voltage
across the RTD does not exceed 1V over the full
measurement range. When using a PT100 device,
we recommend an energising current of 1mA.

Photocells, THCs, mV sources and turbine
flowmeters

The SD07 or SD16 (depending upon the
operational voltage) are the favoured choices
for this application. SD07X and SD16X are also
suitable.

3-wire RTDs

Photocells, THCs,
mV sources and
turbine flowmeters

The give n data is only inten ded as a product de scription an d should not be reg arded as a lega l warranty of pro perties
or guara ntee. In the i nterest of fu rther te chnica l develop ments, we re serve the r ight to make d esign cha nges.

EUROPE (EM EA): [phone] THE AMER ICAS: [phone] ASIA-PACIF IC: [phone]

[e-mail] [e-mail] [e-mail] 901-107 Rev S 220513

Analogue outputs

Controller outputs (I/P converters)

For this application, the recommendations are
the SD16, SD32 and SD55 (and the equivalent
‘X’ versions), the final choice depending upon the
operating voltage.

Digital (on/off) inputs

Switches

Suitable SPDs for switches include the SD07,
SD16, SD32 and SD55 modules – the choice de­pending upon the operating voltage of the system.
The ‘X’ versions of these are also suitable.

FIELD CIRCUIT

Controller outputs
(I/P converters)

Switches

PROTECTED CIRCUIT

Digital (on/off) outputs

Alarms, LEDs, solenoid valves, etc

The recommended choice for this application is
the SD32 or SD32X.

Telemetry (PSTN)

Telemetry outstations

The SDPSTN has been designed specifically for
the protection of signals transmitted on public
switched telephone networks.

AC supplied equipment

PLC, I/O systems

For systems on 110-120V ac, the SD150X is
the recommended choice and for 220-240V ac
systems, the SD275X is recommended.

Alarms, LEDs,
solenoid values,
etc.

Telecom line

PLC, I/O systems

The give n data is only inten ded as a product de scription an d should not be reg arded as a lega l warranty of pro perties
or guara ntee. In the i nterest of fu rther te chnica l develop ments, we re serve the r ight to make d esign cha nges.

EUROPE (EM EA): [phone] THE AMER ICAS: [phone] ASIA-PACIF IC: [phone]

[e-mail] [e-mail] [e-mail] 901-107 Rev S 220513