Category: Eaton

The analog-input multiplexer system

The MTL838C is an analog multiplexer receiver that is used with the MTL831C

hazardous area millivolt input multiplexer transmitter. The status of up to 32 analog

inputs may be communicated from the hazardous area to the safe area via a data

highway, comprised of a simple twisted pair – over distances up to 2km.

Each data highway must be protected by an MTL5553/5053 digital isolator when

the inputs are located in a Zone 0 or 1 hazardous area.  The MTL831C is typically

used with thermocouple and RTD inputs and is intrinsically safe.  It can be mounted

in a Zone 0 or 1 hazardous area and will accept 16 inputs.  For systems that do not

require Zone 0 or Zone 1 installation, the MTL5553/5053 can be eliminated.

Up to two MTL831C transmitters can be combined on a single MTL838C receiver

input – up to a total of 32 analog inputs – as shown in Figure 1.

The MTL838C acts as a Modbus slave . It may be connected into any standard

Modbus network, with up to 31 MTL838C slaves on each network.  If each unit has

its full complement of 32 analog inputs, the status of a total of 992 analog inputs

may be passed to a Modbus master using a single RS485 network.

Mounting on T-section DIN-rail (Figure 1)

Hook the side opposite the central mounting clip onto standard 35mm

DIN46277 T-section rail and push downwards until the unit clicks into

place.

To remove, ease the central clip below the base of the unit outwards

(with a screwdriver) and unhook the clips on the other side.

Mounting on a flat surface (figures 2 and 3)

Turn the unit upside down.

With a screwdriver, apply an anti-clockwise force against the

retaining arm of one of the base clips to release it from its recess.

Hold the arm in this position and slide the clip outwards.

Release the retaining arm to engage the tooth in the base moulding.

Adjust the position of the other two clips with a similar procedure.

Mount on any flat surface using three M4 bolts or screws (or other

suitable fasteners with a shank diameter of 4mm or less) through the

three clips according to the mounting centres shown in figure 3.

Mounting in an ENC8. ENC8-SS, ENC83 or

ENC83-SS enclosure (figure 4)

Remove the upper and/or lower undrilled gland plates and drill

suitable holes for the entry glands required. Possible hole

configurations are listed in the table.

Mount the unit on the internal T-section rail of the enclosure as

described in (1).

Mount the enclosure on any flat surface using four M8 bolts (or other

suitable fasteners with a shank diameter of 8mm or less) through the

four fixed lugs according to the mounting centres shown in figure 4.

GETTING STARTED

Installation of the MTL831B multiplexer transmitter is divided into

three main topics.

♦ Mechanical Installation – how to mount the MTL831B and

how it may be fitted into our enclosure.

♦ Electrical Connections – the sensor and highway

connections. If units are installed in our enclosures, it details any

special wiring arrangements.

♦ Configuration-  the address and input mode selection by the

setting of internal switches.

Note:  A new user might find it helpful to set up the system, or a

simple version of it, in an indoor test area to gain familiarisation

before undertaking installation on site.

MECHANICAL INSTALLATION

Location

The MTL831B can be installed in either safe or hazardous areas

(including Zone 0 or Division 1) depending upon the requirements of

the application.

Mounting options

The unit can be mounted on T-section DIN-rail or onto a flat surface.

Eaton has a range of enclosures – ENC8. ENC8-SS, ENC83 or

ENC83-SS – to provide suitable IP67 protection if the transmitter is

located in an exposed area.

Product description

The MTL831B analogue transmitter can transfer a number of

hazardous area input signals to the safe area down a data highway

consisting of a single twisted pair cable. It is intrinsically safe and can

therefore be mounted in Zone 0 hazardous areas or Class I, Division

1 hazardous locations.

The MTL831B can monitor up to 16 inputs from THC or millivolt

sources or up to 15 inputs from 2. 3 or 4-wire RTDs.

Two (i.e. dual redundant) data highway outputs are provided that can

carry both signal and power over distances up to 3km, depending on

the application, the cable and the (noise) environment – see Section

4.4. The highway cables can be simple twisted-wire pairs or pairs of

wire within an IS multi-core cable.

At the other end of the data highway, MTL838B-MBF receivers are

used to translate the information transmitted from the MTL831B. The

MTL838B-MBF provides a Modbus®serial data output representation

of the inputs together with status information.

When the MTL831B transmitter is mounted in the hazardous area,

each data highway mustbe protected by an MTL3052 digital isolator

mounted in the safe area.

Outdoor mounting

In addition to the General Requirements above, if the Megablock is mounted in an 

outdoor location, use a suitable enclosure with a minimum of IP54 ingress protection.  

A higher level of ingress protection rating will be necessary if the working atmosphere 

is, or can be, corrosive, or if the enclosure is subject to wet or dusty environments.

DIN-rail mounting

The Megablocks are designed for mounting on 35mm x 7.5mm T-section “top hat” DIN 

rail to EN50022 and use built-in DIN rail clips to attach to the rail.  

Mounting procedure

Megablocks are attached to the DIN rail using a “push-and-tilt” method – as illustrated 

on the body label and in Figure 4.1 below.

Tilt the Megablock towards the trunk-connector side of the Megablock and then 

engage the DIN-rail clips under the ledge of the DIN rail. Push the Megablock against 

the edge of the rail then rotate the Megablock until it sits flat onto the DIN rail, then 

release the pressure to allow the clips on the other side to engage.

Enclosure requirements

General requirements

Megablocks may be mounted in hazardous (classified) areas – see section 8.  The 

following conditions must also be satisfied to ensure safe and reliable operation.

a) Prevent any form of pollution that could compromise the operation of the unit. 

For example, choose an unpolluted location or a suitable enclosure to protect the 

assembly.

b) Provide an adequate level of mechanical protection. This can be achieved by 

selecting a protected location, a suitable enclosure, or a combination of both.

c) Ensure that all cable entries and connections are secure by making provision for 

the careful routing and securing of all cables.

d) Provide adequate security against unauthorized interference.

e) Conform to the permitted ambient temperature range of –45°C to +70°C.

Outdoor mounting

In addition to the General Requirements above, if the Megablock is mounted in an 

outdoor location, use a suitable enclosure with a minimum of IP54 ingress protection.  

A higher level of ingress protection rating will be necessary if the working atmosphere 

is, or can be, corrosive, or if the enclosure is subject to wet or dusty environments.

DESCRIPTION

Simple and reliable interconnection

Each Megablock has dedicated connections for the fieldbus “home run” or trunk 

cable. Trunk connections are identified by their black connectors. Numbered 

(grey) connectors are provided for each spur.

Wiring connections to the Megablock are made using pluggable connectors 

(screw terminal type are standard, but other connection styles are available). 

These allow wire terminations to be made to the individual connectors, which are 

then plugged into the Megablock.  Devices can be connected and disconnected 

easily during commissioning. On completion, the connector retaining screws are 

tightened to secure each connector to the Megablock

MECHANICAL

Mounting orientation

Megablocks mount vertically or horizontally on 35mm DIN rail within a field junction 

box  The use of DIN rail end stops are recommended to prevent sliding (especially for 

vertical installations).

Eight, and twelve port Megablocks have areas on their body for labelling so that 

segments can be easily identified according to plant standards.

F300 Megablocks are DIN-rail mounted, device couplers for Foundation™ fieldbus 

or Profibus PA networks. They allow connection of field devices to the segment 

trunk cable and provide short-circuit protection to the segment.

Megablocks minimize hand wiring and allow individual devices to be added to 

and removed from the segment without disrupting network communication.

Megablocks are available in four, eight, and twelve port versions. Multiple 

Megablocks are easily wired together to allow larger segments to be constructed.

Each F300 Megablock includes an F97 Terminator for installation in the trunk 

terminals, which is clearly marked with a large ‘T’ for easy identification by field 

personnel.

Individual surge-protector modules (FS32) can also be fitted to any of the 

Megablock fieldbus terminals to provide protection against induced surges and 

transients that can potentially destroy or degrade certain components inside the 

F300 Megablocks.

DIN-rail mounting

The Megablocks are designed for mounting on 35mm x 7.5mm T-section “top hat”

DIN rail to EN50022 and use built-in DIN rail clips to attach to the rail.

Mounting procedure

Megablocks are attached to the DIN rail using a “push-and-tilt” method – as illustrated

on the body label and in Figure 4.1 below.

Tilt the Megablock towards the trunk-connector side of the Megablock and then

engage the DIN-rail clips under the ledge of the DIN rail. Push the Megablock against

the edge of the rail then rotate the Megablock until it sits flat onto the DIN rail, then

release the pressure to allow the clips on the other side to engage.

Removal from DIN-rail

Refering to Figure 4.1. push the Megablock against the edge of the DIN rail, tilt the

other side of the Megablock up and away from the DIN rail, then release the side

pressure to disengage the DIN rail clips from the DIN rail ledge.

Enclosure requirements

General requirements

Megablocks may be mounted in hazardous (classified) areas – see sections 8 & 9.

The following conditions must also be satisfied to ensure safe and reliable operation.

a) Prevent any form of pollution that could compromise the operation of the unit.

For example, choose an unpolluted location or a suitable enclosure to protect the

assembly.

b) Provide an adequate level of mechanical protection. This can be achieved by

selecting a protected location, a suitable enclosure, or a combination of both.

c) Ensure that all cable entries and connections are secure by making provision for

the careful routing and securing of all cables.

d) Provide adequate security against unauthorized interference.

e) Conform to the permitted ambient temperature range of –50°C to +70°C.

Outdoor mounting

In addition to the General Requirements above, if the Megablock is mounted in an

outdoor location, use a suitable enclosure with a minimum of IP54 ingress protection.

A higher level of ingress protection rating will be necessary if the working atmosphere

is, or can be, corrosive, or if the enclosure is subject to wet or dusty environments.