MTL Instruments MTL646 Operating Manual

MTL646

IS Panel Mounting Serial Text Display

Instruction Manual

INM646

ii

INM646-1

Contents July 2003

1. Description

2. Operation

2.1 MTL646/7 protocol

2.2 MTL643/4 protocol

3. Intrinsic Safety Certification

3.1 Apparatus certificate (ATEX)

3.2 System certificates

3.3 Zones, groups and T rating

3.4 Power supply

3.5 External switches

3.6 Switch outputs

3.7 Certification label information

4. System Design for Hazardous Area

4.1 Cable length

4.2 Two wire system

4.3 Three wire system

4.4 Four wire system

4.5 Switch outputs

5. Installation

5.1 Location

5.2 Installation procedure

5.3 EMC

6. Configuration

6.1 Default configuration

6.2 Accessing the configuration menus

6.3 Summary of configurable functions

6.4 Quick access menu

The MTL646 is CE marked to show compliance with the

European Explosive Atmospheres Directive 94/9/EC,

the European EMC Directive 89/336/EEC

and the European Low Voltage Directive 73/23/EEC

7. Programming

7.1 Summary of MTL646/7 protocol

7.2 Command format

7.3 Response format

7.4 Operational modes

7.5 Multidrop operation

7.6 Summary of commands

7.6.1 Screen handling & text

7.6.2 Attributes

7.6.3 System commands

7.6.4 Line graphics

7.6.5 Pixel graphics

7.7 Graphics download

7.7.1 <DL> command

7.7.2 <DG> command

7.8 Cyclic Redundancy Check

7.8.1 Procedure for generating
CRC.

8. Maintenance

8.1 Fault finding during commissioning

8.2 Fault finding after commissioning

8.3 Servicing

8.4 Routine maintenance

8.5 Guarantee

8.6 Customer comments

9. Accessories

9.1 Tag number

9.2 MTL646/647 Programming Guide.

10. Index

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iv

MTL646 INM646-1
IS PANEL MOUNTING SERIAL TEXT DISPLAY July 2003

1. DESCRIPTION

The MTL646 is an intrinsically safe instrument
that can display text and simple graphics in a
hazardous area. Incorporating six operator
switches, two solid state outputs and a backlit
graphical display, it forms a simple operator
interface for machine or process control
applications.

The MTL646 text display has been certified
intrinsically safe by European Notified Body
Intertek Testing Services (ITS) to the ATEX
Directive 94/9/EC.

Safety approvals from authorities outside
Europe are being obtained, please contact
MTL for the latest information.

Housed in a robust 144 x 72 panel mounting
DIN enclosure, the text display has an IP65
front panel and is supplied with a gasket to
seal the joint between the instrument and the
panel.

2. OPERATION
Fig 1 shows a simplified block diagram of a
MTL646 serial text display. The instrument is
connected to a serial data galvanic isolator in
the safe area via two, three or four wires that
carry both power and bi-directional
communication. The switch outputs may be
controlled and the operator switches
interrogated from the safe area via the serial
communication link.

The MTL646 serial text display has been
designed to operate with a certified galvanic
isolator that has an RS232 or RS422 safe area
port. This enables the MTL646 to be controlled
and interrogated by a process computer or a
dedicated instrument such as a PLC.

Installation and commissioning are simple. An
MTL646 serial text display may be operated on
a simple two-wire system that provides both
power and bi-directional communications. Two
MTL646 displays with separate addresses may
be multi-dropped from a two-wire system and
up to four displays from a three-wire system.
Up to 14 serial text displays may be address
from one RS232 or 422 port.

Section 7 of this manual includes a summary of
the MTL programming protocol and instruction
set. Detailed information is contained in the
Programming Guide, which may be
downloaded from the MTL web site

www.mtl-inst.com

Fig 1 Simplified block diagram of MTL646

2.1 MTL646/7 protocol

MTL646/7 protocol enables text to be written
anywhere on the screen in five different font
sizes, together with lines, boxes and
bargraphs. Simple bit map graphics may also
be downloaded to the display and all
characters can be reversed or flashed.
Information may also be written to a hidden
screen that may be displayed when required.

The protocol enables each of the six front
panel push-buttons to be interrogated so they
may be used for operator controls. By
displaying the switch function on the screen
adjacent to the button, ‘soft switches’ can be
created. If larger industrial size push-buttons
are required, these may be connected to the
MTL646 terminals. When external switches
are used the instrument front panel switches
are disabled.

Two single pole solid state outputs may be
used to switch certified hazardous area loads
such as sounders, beacons and valves.

2.2 Legacy protocol

The legacy protocol contained in the MTL646
allows the instrument to replace an MTL644 IS
text display. All the functions of an MTL644
are replicated, but with the advantage of a
backlit display and certification to the ATEX
Directive.

Legacy protocol only allows three external
switches S1, S2 & S3, not the front panel push­buttons, to be used for operator inputs.
Similarly, the MTL644 only has one output
control, so the two switch outputs operate in
parallel.

When using the legacy protocol, the
configuration menus are only operational
between power being applied to the MTL646
and the first message being received.

1

3. INTRINSIC SAFETY CERTIFICATION

3.1 Apparatus certificate (ATEX)

The MTL646 has been issued with EC-Type
Examination Certificate ITS03ATEX21172 by
Intertek Testing Services (ITS) confirming
compliance with the European ATEX Directive
94/9/EC for Group II, Category 1, gas
atmospheres, EEx ia IIC T5. The instrument
bears the Community Mark and, subject to
local codes of practice, may be installed in any
of the European Economic Area (EEA)
member countries, which currently comprise:
Austria, Belgium, Denmark, Finland, France,
Germany, Greece, Iceland, Ireland, Italy,
Liechtenstein, Luxembourg, The Netherlands,
Norway, Portugal, Spain, Sweden and the
United Kingdom. Certificates to the ATEX
Directive are also accepted in Switzerland and
the Czech Republic. This instruction manual
describes installations that conform with
PD60079-14:2000 Electrical Installation in
Hazardous Areas. When designing systems
for installation outside the UK, the local Code
of Practice should be consulted.

3.2 System certificates

In addition to the EC-Examination Certificate,
ITS have issued three system certificates of
conformity.

Ex03E21194 2 wire system SCI-976
Ex03E21195 3 wire system SCI-977
Ex03E21196 4 wire system SCI-978

3.3 Zones, groups and T rating
The MTL646 has been issued with EC-Type
Examination certificate ITS03ATEX21172
confirming that it complies with the
requirements for Group II Category 1 G EEx ia
IIC T5 (T

–40oC to +60oC) specified in the

amb

ATEX Directive. When connected to a suitable
system the MTL646 may be installed in:

Zone 0 explosive gas air mixture
continuously present

Zone 1 explosive gas air mixture
likely to occur in normal operation

Zone 2 explosive gas air mixture not likely to

occur, and if it does will only exist for
a short time,

for use with gases in groups:
Group A propane
Group B ethylene
Group C hydrogen

and having a temperature classification of:
T1 450

T2 300
T3 200
T4 135
T5 100

at an ambient temperature between –40

o

+60

C.

o

C

o

C

o

C

o

C

o

C

o

C and

Note: the guaranteed operating temperature
range of the text display is –20

o

C to +60oC

This allows the MTL646 to be installed in all
Zones and to be used with most common
industrial gases.

3.4 Power supply

When installed in a hazardous area the
MTL646 must be powered from an MTL5051
serial data galvanic isolator, or from an
MTL5051 plus an MTL5025 solenoid driver.

Although there are other certified barriers, or
galvanic isolators, with IS parameters
compatible with the MTL646, the MTL5051
must be used because it is the only one,
currently, providing the required data
conversion.

The maximum permitted cable parameters are
shown on the system certificates.

3.5 External switches

For applications requiring operator inputs to be
made by large industrial push-buttons,
terminals S1 to S7 allow external switches to
be connected to the text display. When the
external push-buttons are enabled in the
configuration menu, the front panel push­buttons are automatically disabled.

Terminals S1 to S7 have the following
combined output safety parameters:

Uo = 14.7V dc
Io = 99mA dc
Po = 0.6W

The switches and associated wiring connected
to the terminals must comply with the
requirements for simple apparatus, i.e. they
must have IP20. Most industrial push-buttons
satisfy these requirements

2

The total maximum permitted cable parameters
for all the cables connected to terminals S1 to
S7 in Group IIC must be less than:

Co = 0.22µF
Lo = 0.26mH

Although these are the lowest figures specified
by any of the three system certificates, they are
not restrictive and allow a significant distance
between the switches and the instrument. See
system certificates for maximum limits for each
of the three configurations

3.6 Switch outputs

Each of the two switch outputs is a separate,
galvanically isolated, solid-state switch. The
EC-Type Examination Certificate specifies that
under fault conditions the voltage, current and
power at each switch output will not exceed
those specified for simple apparatus in Clause

5.4 of EN50020:2002. This allows each of the
MTL646 switch outputs to be connected to any
intrinsically safe circuit protected by a certified
Zener barrier or galvanic isolator providing that
the output parameters of each circuit are less
than:
Uo 28V dc
Io 200mA
Po 0.85W

The two switch outputs are not shown on the
MTL646 system certificates because they will
be covered by the certificate for the system to
which the contacts are connected.

The maximum equivalent capacitance and
inductance of each MTL646 switch output is:

Ci = 40nF
Li = 20µH

To determine the maximum permissible cable
parameters, Ci and Li must be subtracted from
the maximum cable capacitance and
inductance specified by the system certificate
of the circuit connected to the switch.

3.7 Certification Label Information
The certification label is fitted in a recess on
the top outer surface of the enclosure. It shows
the certification information plus the MTL
name, location, instrument serial number and
year of manufacture. Other non-European
certification information may also appear on
this label.

S/No ??????/ ??/ ???

Measurement Technology Ltd
Luton England

1180 Ex II 1 G

ITS03ATEX21172

EEx ia IIC T5,

-40oC ≤ Ta ≤+60oC

Manufactured: ????

MTL646 SERIAL TEXT DISPLAY

3

4. SYSTEM DESIGN FOR HAZARDOUS

AREAS

There are three configurations that may be
used for hazardous area installations. The
choice depends upon how many text displays
are required, the backlight brilliance and the
communication speed required. The following
table summarises the performance.

When two MTL646 text displays are multi­dropped from a common galvanic isolator the
brilliance of both display backlights will be
significantly reduced.

.

4.1 Cable length

The dc loop resistance of the cable between
the MTL646 and the associated galvanic
isolator in the safe area must not exceed 20Ω.
This applies for 2, 3 and 4 wire systems
irrespective of the number of text displays
connected to the loop. Most instrument cables
have a loop resistance of between 50 and
200mΩ per metre, thus limiting the maximum
cable length to between 100 and 400 metres.

The maximum permitted intrinsic safety cable
parameters specified on the system certificates
must also not be exceeded. However, in
practice only the capacitive limit in IIC gases is
likely to be restrictive.

Communication speed will also limit the
transmission distance. At 9.2k baud a
screened twisted pair should provide reliable
communication up to 100 metres. If data
corruption occurs the communication speed
should be reduced.

4.2 Two wire system
This is the simplest and probably the most
frequently used system. One or two MTL646
serial text displays are connected to a
MTL5051 in the safe area via two wires that
provide both power and bi-directional
communication.

Fig 2 shows the wiring diagram that is defined
by ITS System Certificate Ex03E21194.
With this configuration data may be transmitted
and received at 1.2, 2.4, 4.8 or 9.6kbaud.

Fig 2 Two wire system

4.3 Three wire system

The three-wire system illustrated in Fig 3 can
be used for multidrop applications. Up to four
MTL646 serial text displays may be powered
and addressed but, if more than two are used,
the backlight brilliance of all the displays will be
significantly reduced.

With this configuration data may be transmitted
and received at 1.2, 2.4, 4.8 or 9.6kbaud.

ITS System Certificate Ex03E21195 defines
this system.

Up to three

MTL646

Fig 3 Three wire system

4

4.4 Four-wire system

The four-wire system, which is defined by ITS
System Certificate Ex03E21196, allows
communication at higher and lower rates than
the other two configurations. It should be used
for applications requiring fast display updates,
or with slow data rates when long cable runs
are required. The four-wire system does not
support multidrop operation.

Data may be transmitted and received at 0.3,

0.6, 1.2, 2.4, 4.8, 9.6 and 19.2kbaud.

MTL646

Fig 4 Four wire system

4.5 Switch outputs

Each switch output is a galvanically isolated
single pole solid state switch output as shown
in Fig 5.

5. INSTALLATION

5.1 Location

The MTL646 is housed in a robust aluminium
enclosure with a toughened glass window
mounted in a Noryl bezel. The front of the
instrument provides IP65 protection and a
gasket seals the joint between the instrument
enclosure and the panel. The instrument may
be installed in any panel providing the
environmental limits shown in the specification
are not exceeded.

Fig 6 shows the overall dimensions of the
MTL646 and the panel cut-out. To achieve an
IP65 seal between the instrument enclosure
and the panel, the smaller cut-out must be
used and the instrument secured with four
panel mounting clips.

The MTL646 liquid crystal display has
maximum contrast when viewed from directly
ahead and slightly below the centre line of the
instrument.

Fig 5 Equivalent circuit of each switch output

The outputs are polarised and current will only
flow in one direction. Terminals A1 and A3
should be connected to the positive side of the
supply.
R
R

= 5Ω + 0.6V

on

= greater than 1MΩ

off

Note: Because of the series protection diode,
some test meters may not detect a closed
alarm output

WARNING

These switch outputs should not be
used for critical safety applications
such as an emergency shut down

system.

When the MTL646 power supply is turned off
or disconnected, both MTL646 switch outputs
will open irrespective of how they have been
programmed.

Fig 6 MTL646 dimensions

5

5.2 Installation Procedure

a. Insert the MTL646 into the instrument

panel cut-out from the front of the
panel.

b. Fix panel mounting clips to opposite

sides of the instrument and tighten until
the instrument is secure as shown in Fig

7. Four clips are required to achieve an
IP65 seal between the instrument
enclosure and the panel.

c. Connect the panel wiring to the rear

terminal block(s) as shown in Fig 7. To
simplify installation, the terminals are
removable so that panel wiring can be
completed before the instrument is
installed.

5.3 EMC

The MTL646 complies with the requirements of
the European EMC Directive 89/336/EEC. For
specified immunity all wiring should be in
screened twisted pairs.

To prevent circulating currents, cable screens
should only be earthed at one point in the safe
area.

Fig 7 Installation and terminal connections

6