Spirax Sarco BT1050 User manual

BT1050
OK
BT1050
Boiler Blowdown Timer
Installation and Maintenance Instructions
1. Safety information
2. User instructions and
delivery information
3. System overview
4. Mechanical
installation
5. Electrical
installation
6. Commissioning
- Quick set-up
- Full
7. Communications
8. Maintenance
9. Fault nding
10. Technical
information
- Default settings
11. Appendix
- Summary of the
Modbus protocol
12. Menu map
IM-P405-39
AB Issue 4
4058152/4
© Copyright 2013
Printed in GB
IM-P405-39 AB Issue 4
Commissioning password
Current legislation states that in order to prevent tampering and potentially
hazardous programming errors, access to the pass codes required to enter
commissioning mode should only be available to qualified and trained
personnel.
Enter commissioning
This is done from the run mode by pressing and holding down the OK button
for 5 seconds.
The run mode display will disappear and the display
will show 'PASS CODE' with '8888' at the bottom
right corner of the screen. The flashing leading digit
indicates the position of the cursor. The default,
or factory set pass code is 7452 but this can be
changed from within the commissioning mode. The
pass code can be entered by using the and
buttons to increase or decrease the flashing value
and the and buttons to move the cursor.
Pressing the OK button will enter the pass code. If an
incorrect pass code is used, the display automatically
returns to the run mode.
This page MUST be removed
after commissioning
and kept in a safe,
access controlled location.
PASS CODE
8888

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1. Safety information
Safe operation of this product can only be guaranteed if it is properly installed,
commissioned, used and maintained by qualified personnel (see Section 1.11) in
compliance with the operating instructions. General installation and safety instructions
for pipeline and plant construction, as well as the proper use of tools and safety
equipment must also be complied with.
Your attention is drawn to IEE Regulations (BS 7671, EN 12953, EN 12952 and EN 50156).
Elsewhere, other regulations will normally apply.
All wiring materials and methods shall comply with relevant EN and IEC standards
where applicable.
Warning
This product is designed and constructed to withstand the forces encountered
during normal use. Use of the product other than as a boiler controller, or failure
to install the product in accordance with these Instructions, product modifications
or repair could:
- Cause injury or fatality to personnel.
- Cause damage to the product / property.
- Invalidate the marking.
These instructions must be stored in a safe place near the product installation at all
times.
Warning
This product complies with Electromagnetic Compatibility Directive 2004 / 108 / EC
and all its requirements.
This product is suitable for Class A Environments (e.g. industrial). A fully detailed EMC
assessment has been made and has the reference number UK Supply BH BT1050 2008.
The product may be exposed to interference above the limits of Heavy Industrial
Immunity if:
- The product or its wiring is located near a radio transmitter.
- Excessive electrical noise occurs on the mains supply. Power line protectors (ac)
should be installed if mains supply noise is likely. Protectors can combine
filtering, suppression, surge and spike arrestors.
- Cellular telephones and mobile radios may cause interference if used within
approximately 1 metre (39") of the product or its wiring. The actual separation
distance necessary will vary according to the surroundings of the installation
and the power of the transmitter.
This product complies with Low Voltage Directive 2006 / 95 / EC by meeting the
standards of:
- EN 61010-1:2010 Safety requirements for electrical equipment for measurement,
control, and laboratory use.
Static precautions (ESD)
Static precautions must be observed at all times to avoid damage to the product.
IM-P405-39 AB Issue 4

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3
Symbols
Equipment protected throughout by double insulation or reinforced
insulation.
Functional earth (ground) terminal, to enable the product to function
correctly.
Not used to provide electrical safety.
Clean earth / ground.
Safety earth.
Caution, risk of electric shock.
Caution, risk of danger, refer to accompanying documentation.
Optically isolated current source or sink.
Caution, Electrostatic Discharge (ESD) sensitive circuit. Do not touch
or handle without proper electrostatic discharge precautions.
ac, alternating current.

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1.1 Intended use
i) Check that the product is suitable for use with the intended fluid.
ii) Check material suitability, pressure and temperature and their maximum and
minimum values. If the maximum operating limits of the product are lower than
those of the system in which it is being fitted, or if malfunction of the product could
result in a dangerous overpressure or overtemperature occurrence, ensure a
safety device is included in the system to prevent such over-limit situations.
iii) Determine the correct installation situation and direction of fluid flow.
iv) Spirax Sarco products are not intended to withstand external stresses that may be
induced by any system to which they are fitted. It is the responsibility of the installer
to consider these stresses and take adequate precautions to minimise them.
v) Remove protection covers from all connections and protective film from all
name-plates, where appropriate, before installation on steam or other high
temperature applications.
1.2 Access
Ensure safe access and if necessary a safe working platform (suitably guarded)
before attempting to work on the product. Arrange suitable lifting gear if required.
1.3 Lighting
Ensure adequate lighting, particularly where detailed or intricate work is required.
1.4 Hazardous liquids or gases in the pipeline
Consider what is in the pipeline or what may have been in the pipeline at some
previous time. Consider: flammable materials, substances hazardous to health,
extremes of temperature.
1.5 Hazardous environment around the product
Consider: explosion risk areas, lack of oxygen (e.g. tanks, pits), dangerous gases,
extremes of temperature, hot surfaces, fire hazard (e.g. during welding), excessive
noise, moving machinery.
1.6 The system
Consider the effect on the complete system of the work proposed. Will any proposed
action (e.g. closing isolation valves, electrical isolation) put any other part of the
system or any personnel at risk?
Dangers might include isolation of vents or protective devices or the rendering
ineffective of controls or alarms. Ensure isolation valves are turned on and off in a
gradual way to avoid system shocks.
1.7 Pressure systems
Ensure that any pressure is isolated and safely vented to atmospheric pressure.
Consider double isolation (double block and bleed) and the locking or labelling of
closed valves. Do not assume that the system has depressurised even when the
pressure gauge indicates zero.
1.8 Temperature
Allow time for temperature to normalise after isolation to avoid danger of burns.

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1.9 Tools and consumables
Before starting work ensure that you have suitable tools and / or consumables
available. Use only genuine Spirax Sarco replacement parts.
1.10 Protective clothing
Consider whether you and / or others in the vicinity require any protective clothing
to protect against the hazards of, for example, chemicals, high / low temperature,
radiation, noise, falling objects, and dangers to eyes and face.
1.11 Permits to work
All work must be carried out or be supervised by a suitably competent person.
Installation and operating personnel should be trained in the correct use of the
product according to the Installation and Maintenance Instructions.
Where a formal 'permit to work' system is in force it must be complied with. Where
there is no such system, it is recommended that a responsible person should know
what work is going on and, where necessary, arrange to have an assistant whose
primary responsibility is safety.
Post 'warning notices' if necessary.
1.12 Handling
Manual handling of large and / or heavy products may present a risk of injury. Lifting,
pushing, pulling, carrying or supporting a load by bodily force can cause injury
particularly to the back. You are advised to assess the risks taking into account the
task, the individual, the load and the working environment and use the appropriate
handling method depending on the circumstances of the work being done.
1.13 Residual hazards
In normal use the external surface of the product may be very hot.
Many products are not self-draining. Take due care when dismantling or removing
the product from an installation.
1.14 Freezing
Provision must be made to protect products which are not self-draining against
frost damage in environments where they may be exposed to temperatures below
freezing point.
1.15 Disposal
On disposal of the unit or component, appropriate precautions should be taken in
accordance with Local / National regulations.
Unless otherwise stated in the Installation and Maintenance Instructions this product
is recyclable and no ecological hazard is anticipated with its disposal providing due
care is taken.
1.16 Returning products
Customers and stockists are reminded that under EC Health, Safety and Environment
Law, when returning products to Spirax Sarco they must provide information on any
hazards and the precautions to be taken due to contamination residues or mechanical
damage which may present a health, safety or environmental risk. This information
must be provided in writing including Health and Safety data sheets relating to any
substances identified as hazardous or potentially hazardous.

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2. User instructions and
delivery information
Certain computer programs contained in this product were developed by Spirax-Sarco
Limited ("the Work(s)").
Copyright © Spirax-Sarco Limited 2013
All rights reserved
Spirax-Sarco Limited grants the legal user of this product (or device) the right to use the
Work(s) solely within the scope of the legitimate operation of the product (or device).
No other right is granted under this licence. In particular and without prejudice to the
generality of the foregoing, the Work(s) may not be used, sold, licensed, transferred,
copied or reproduced in whole or in part or in any manner or form other than as expressly
granted here without the prior written consent of Spirax-Sarco Limited.
2.1 General description
The BT1050 is a timer for the control of a bottom blowdown valve.
It allows a valve at the bottom of the boiler to open, removing precipitated solids that could
otherwise build up, eventually causing damage.
2.2 Front panel
The front panel has an LCD graphics display and five-button keypad:
Scroll down menus
Scroll up menus
Hold down for 5 seconds
to clear the error screen
Graphic display
BT1050
OK
Not used in run mode
Fig. 1 Front panel keypad and definitions

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The display is divided into four main sections:
- Current time.
- Information line / Date.
- Timer information.
- Recovery time.
Operating parameters are selected using a software menu.
2.4 Information line details (in priority order)
Alarm:
- 'TEST ALM' - the operator is testing the alarm relay. The relay is either energised (OFF) or
de-energised (ON) for 5 minutes. See the commissioning mode TEST-OUTPUT-ALARM
menu.
- 'ALARM' - an error or fault has occurred. See details in the error screen in run mode and
Section 9, 'Fault finding'.
Bottom blowdown valve (BB):
- 'TEST BB' - the operator is testing the blowdown relay. The relay is either energised (ON)
or de-energised (OFF) for 5 minutes. See the commissioning mode TEST-OUTPUT-VALVE
menu.
- 'MAN OFF' - the timer is switched off. e.g. manual override. The timer will ignore all
pre-recorded times. See the commissioning MODE-OFF menu.
- 'MAN OPEN' - the valve has been opened continuously. e.g. manual override. See the
commissioning MODE-ON menu.
- 'DELAYED' - a blowdown is overdue but cannot occur until the RECOVERY TIMER elapses.
- 'BLOWDOWN' - a timed blowdown is occurring. i.e. the valve is open.
Fig. 2 Graphic display
5
Another timer is blowing down
or
Recovery timer:
Indicates the time before
another blowdown can safely
occur, because the blowdown
vessel is still cooling down.
Features only available on
linked BT1000 or BT1050
timers.
Timer information
Which timer is to time-out next:
Timer number
Day
Time
Indicates an error or alarm
2.3 LCD display
Time
Information line / Date

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2.5 Timers information menu
This menu details the duration, start, repeat and stop time that has been selected. It
also displays which days have been selected. A ' - ' means that day has not been selected.
2.6 Alarm / error display messages
If an error occurs, an exclamation mark (!) will flash in the bottom left corner of the run
display (see Figure 2). The details of the error or alarm will appear on a new message
screen (see Figure 4), which can be accessed by scrolling through the run menu. Pressing
and holding the OK button for 3 seconds can clear a message and re-energize the alarm
relay(s). If the cause has not been corrected, the same message will reappear. If the
error or alarm is of a latching type, only the message will disappear. The alarm relay will
remain de-energised until the correct pass code is entered in the commissioning menu.
If more than one error or alarm has occurred, the next message will appear (in priority
order) after the previous one has been cleared. See Section 9, 'Fault Finding'.
If there are any problems with the product, error or alarm will appear. The example shows
a power failure.
Timer 1
duration
5 s
start
08:00
repeat
01:00
stop
16:00
sm-w-fs
Saturday
Friday
Thursday
(not selected)
Sunday
Monday
Tuesday
(not selected)
Wednesday
Fig. 3
Fig. 4 Error display
PRESS OK
TO CLEAR

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2.7 Other features
A test function provides the operator with a diagnostic tool.
The BT1050 can communicate via an Infrared link between adjacent units. It can be designated
as either a slave or a master unit -see Section 7, 'Communications'.
2.8 Equipment delivery, handling and storage
Factory shipment
The product is tested, calibrated and inspected prior to shipment, to ensure reliable
operation.
Receipt of shipment
Each carton should be inspected at the time of delivery for possible external damage. Any
visible damage should be recorded immediately on the carrier's copy of the delivery slip.
Each carton should be unpacked carefully and its contents checked for damage. If it is found
that some items have been damaged or are missing, notify Spirax Sarco immediately and
provide full details. In addition, damage must be reported to the carrier with a request for
their on-site inspection of the damaged item and its shipping carton.
Storage
If the product is to be stored for a period prior to installation, the environmental storage
conditions should be at a temperature between 0°C and 65°C (32°F and 149°F), and between
10% and 90% relative humidity (non-condensing).
Ensure there is no condensation within the unit before installing and connecting the power.
Operator instructions
An alternative operator instruction manual, in place of this manual, for operating the equipment
is required. This will avoid the commissioning menu passcode being disclosed to the operator.
The alarm reset passcode may optionally be disclosed if this is deemed necessary.

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Installation A
3. System overview
The BT1050 controls the opening and closing of a valve at the bottom of the boiler to
remove precipitated solids that could otherwise build up, eventually causing damage.
Each BT1050 has three timers. Three timer sequences are available. Only one timer
sequence can be allocated to any one day.
The timers are also used to prioritise boiler blowdown cycles. This:
-allows recovery time (for water in a blowdown vessel to cool),
-minimises waste of heat and water,
- selects the most suitable blowdown time (i.e. avoiding peak steam demand times).
Up to nine BT1050 units can be installed and linked for multi-boiler installations, preventing
more than one boiler blowing down at a time. This feature avoids the possibility of overloading
a blowdown vessel, which could lead to water being discharged to drain at too high a
temperature.
Inputs
The timer is connected directly to the mains supply.
Function / output
When a blowdown is due, a relay energises to open the bottom blowdown valve for the
duration selected. After this, the valve closes until the next blowdown cycle.
If the blowdown valve is fitted with a switch box, an alarm relay can be released if the valve fails
to open or to close within a set time (see Commissioning -Section 6.3.9, 'Alarm sub-menu').
SUN MON TUE WED THU FRI SAT
TIMER 1
sequence
SUN MON TUE WED THU FRI SAT
TIMER 2
sequence
CLOCK - 24 hrs
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00
Start time = 8:00
Start time = 00:00
Repeat = 01:00
Start time = 8:00
SUN MON TUE WED THU FRI SAT
TIMER 3
sequence

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BT1050 functional timing diagram
(Multi-blowdowns per day)
Setting up the timers - explanation:
1. Three TIMER sequences / patterns available
2. For each day, only one timer sequence can be allocated.
3. Timers 2 and 3 are not available if timer 1 is not being used or all of timer 1 days are
used.
4. Timers 3 is not available if timers 1 and timer 2 use all the days.
Four user variables are available:
DURATION: The time duration of the blowdown
START: The time (HRS, MINS), the timer sequence is to start.
STOP: The time (HRS, MINS), the timer sequence is to stops.
REPEAT time: The time (HRS, MINS) for the next repeated blowdown. If REPEAT = 00:00,
only one blowdown will occur at start.
CLOCK - 24 hrs
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00
Repeat = 00:00
Duration = 20 seconds
Stop time = 17:00
Stop time = 17:00
Stop time = 17:00
Repeat = 08:00

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Installation B
Installation C
Not available
Not available
Not available
SUN MON TUE WED THU FRI SAT
TIMER 1
sequence
CLOCK - 24 hrs
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00
SUN MON TUE WED THU FRI SAT
TIMER 2
sequence
SUN MON TUE WED THU FRI SAT
TIMER 3
sequence
SUN MON TUE WED THU FRI SAT
TIMER 1
sequence
CLOCK - 24 hrs
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00
SUN MON TUE WED THU FRI SAT
TIMER 2
sequence
SUN MON TUE WED THU FRI SAT
TIMER 3
sequence

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CLOCK - 24 hrs
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00
CLOCK - 24 hrs
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00

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4. Mechanical installation
Note: Read the 'Safety information'in Section 1 before installing the product.
The product must be installed in a suitable industrial control panel or fireproof enclosure
to provide impact and environmental protection. A minimum of IP54 (EN 60529) is
required. If installed in a harsh environment (conductive dust and / or wet conditions),
extra protection is required.
During installation or maintenance, the rear of the product must be protected from
environmental pollutants entering the product. Alternatively, the tasks can be performed
in a dry clean environment.
Caution 1: The product must only be installed in the vertical orientation.
Caution 2: Do not cover or obstruct the infrared beam between products.
Ensure that the display can be easily read by the operator.
Warning: The boiler control panel or enclosure doors must be kept closed at all
times unless installation or maintenance work is being carried out.
4.1 Environmental conditions
Install the product in an environment that minimises the effects of heat, vibration, shock and
electrical interference (see Section 1 -'Safety information').
Do not install the product outdoors without additional weather protection.
Do not attempt to open the product -it is sealed and has no replaceable parts or
internal switches.
4.2 Installation on a DIN rail
The product is provided with a clip and a set of self-tapping screws to secure it to a 35 mm DIN
rail. On the rear of the enclosure, two sets of holes are provided to give two height positions.
The clip can be adjusted to give further positions. Locate the clip onto one set of holes and
secure it using the two screws provided. Ensure the spring clip is fully engaged with the rail.
Warning: Only use the screws provided with the product.
4.3 Installation on a chassis plate:
- Drill holes in chassis plate as shown in Figure 5.
- Fit unit to chassis plate and secure with 2 screws, nuts and washers, using the slots
provided at the top and bottom of the case.
Warning: Do not drill the product case or use self-tapping screws.
4.4 Installation in a panel cutout:
(Minimum panel thickness 1 mm if the bezel is used).
- The product has integral threaded inserts (M4 x 0.7) at the top and bottom of the front
panel.
- Two M4 x 25 mm screws are provided, together with fibre washers and a bezel.
Warning:
Do not use screws over 25 mm in length -danger of electric shock.

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Fig. 5 Chassis plate / panel -cutout diagram
Fixing template cutout notes:
- Solid line indicates cutout required for panel mounting.
- Broken line indicates product outline.
- A minimum gap of 15 mm between units must be provided for product cooling.
- Mounting hole dimensions are the same for both panel and wall mounting.
112 mm
67 mm
10 mm
45 mm
92 mm
22 mm
22.5 mm
Ø 4.2 mm
Ø 4.2 mm
15 mm
Ø 4.2 mm
Ø 4.2 mm
10 mm
- Cut the panel to the dimensions given in Figure 5. Drill the screw holes in the panel in the
positions indicated.
- Remove the backing from the gasket supplied and apply to front face of the product.
- The bezel can be used to enhance the appearance of the panel cutout. If required, fit this
to the outside of the panel.
- Fit the unit from the rear of the panel, and secure using the screws, washers (and bezel)
provided.
- Tighten the M4 screws to 1.0 - 1.2 Nm.
WARNING: Do not drill the product case or use self-tapping screws.

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Note: Before installing read the 'Safety Information'in Section 1.
Warning:
Isolate the mains supply before touching any of the wiring terminals as
these may be wired to hazardous voltages.
Use only the connectors supplied with the product, or spares obtained from
Spirax Sarco Limited. Use of different connectors may compromise product
safety and approvals. Ensure there is no condensation within the unit before
installing and connecting the power.
Connecting the mains supply incorrectly can cause damage and may
compromise safety.
5.1 General wiring notes
Every effort has been made during the design of the product to ensure the safety of the
user but the following precautions must be observed:
1. Maintenance personnel must be suitably qualified to work with equipment having
hazardous live voltages.
2. Ensure correct installation. Safety may be compromised if the installation of the product
is not carried out as specified in this IMI.
3. The design of the product relies on the building installation for overcurrent protection
and primary isolation.
4. Overcurrent protection devices rated at 3 amps must be included in all phase conductors
of the installation wiring. If overcurrent protection is included in both supply wires then the
operation of one must also cause the operation of the other. Refer to IEC 60364 (Electrical
Installations of Buildings) or National or Local standards for full details of requirements
for overcurrent protection.
5. A 3 A quick-blow overcurrent protection device must be fitted to the relay circuit(s).
6. Relay contacts must be supplied on the same phase as the mains supply.
7. The product is designed as an installation category III product.
8. Install wiring in accordance with:
- IEC 60364 - Low-voltage electrical installations.
- EN 50156 Electrical Equipment for furnaces and ancillary equipment.
- BS 6739 - Instrumentation in Process Control Systems: Installation design and practice
or local equivalent.
9. It is important that the cable screens are connected as shown in order to comply with
the electromagnetic compatibility requirements.
10. All external circuits must meet and maintain the requirements of double / reinforced
installation as stated in IEC 60364 or equivalent.
5. Electrical installation

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11. Additional protection must be provided to prevent accessible parts (e.g. signal circuits)
from becoming Hazardous Live if a wire or screw is accidentally loosened or freed. Ensure
all wires are secured to at least one other wire from the same circuit. The attachment
must be as close to the terminal block as possible but must not apply undue stress on
the connection. Example: Use a cable tie to secure the live and neutral wire together. If
one wire becomes loose the other wire will prevent it from touching accessible parts.
12. A disconnecting device (switch or circuit breaker) must be included in the building
installation. It must:
-Have a rating with sufficient breaking capacity.
-Be in close proximity to the equipment, within easy reach of the operator, but not fitted
in a position that makes it difficult to operate.
-Disconnect all phase conductors.
-Be marked as the disconnecting device for the product.
-Not interrupt a protective earth conductor.
-Not be incorporated into a mains supply cord.
-Comply with the requirements for a disconnecting device specified in IEC 60947-1
(Specification for low-voltage switchgear and control gear -General rules) and
IEC 60947-3 (Switches, disconnectors, switch-disconnectors and fuse-combination
units).
13. See Section 10 -'Technical information' for terminal and cable specification.

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5.2 Mains wiring notes:
1. Read Section 5.1, General Wiring notes, before attempting to wire the supply to the product.
2. Fuses must be fitted in all live conductors.
Disconnect device conforming to
IEC 60947-1 and IEC 60947-3 Disconnect device conforming to
IEC 60947-1 and IEC 60947-3
2
12
1
L
NL1
L2
3 A fuse
Product
Product
3 A fuses
Mains circuit
(View from the underside)
Relays are shown in the power off position
Caution live
terminals
ac supply
Control relay
Alarm 1 relay
Front
Back
3 A
fuse
Input
Alarm L N
See Section 5.2
Mains wiring notes
3 A
fuse
Input
Norm
8 7 6 5 4 2 13
Open 3 A
fuse
3. Double or reinforced insulation must be maintained between:
-Hazardous live conductors (mains and relay circuits) and
-Safety extra low voltages (All other components/ connectors/ conductors).
4. The wiring diagrams show relays and switches in the Power off position.
N L
N
Blowdown solenoid valve
Fig. 6 Mains circuit

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5.3 Signal wiring notes
An earth current loop is created if a wire or screen is connected between two earth points
that are at different potential (voltage). If the wiring diagram is followed correctly, the screen
will only be connected to the earth at one end.
The earth terminal is a functional earth rather than a protective earth.
A protective earth provides protection from electric shock under a single fault condition. This
product has double insulation and therefore does not require a protective earth. A functional
earth is used in order for the product to operate. In this application, the earth is used as a
sink or drain for any electrical interference. The earth terminal must be connected to a local
earth in order to conform to the EMC directive.
Front
Back
Notes:
E= Functional earth -Connect these pins to a clean earth local to the panel.
Switch battery back-up switches ON to activate battery.
Fig. 7 Signal circuit
Connect to
clean earth
local to the
panel
Signal circuit
(view from the top)
E97 96 95 94 93 92 91 90 75 74 73 72 71 70
LockoutBB switch
On
Off
Battery
back-up
switch
Link to
other bottom
blowdown
timers
Bottom blowdown
switch (shown with valve
closed)
COM SCN Tx- Tx+ Rx- Rx+ H / D H / D

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5.4 EIA / TIA-485 communication wiring diagram
The product can be connected as a slave to a two or four-wire EIA / TIA-485 multi-drop network.
A
B
A'
B'
Fig. 8 RS485 / Modbus full duplex circuit (view from the top)
EIA / TIA-485 wiring notes:
EIA / TIA-485 symbols are used (A = Tx-, B = Tx+ and A' = Rx-, B' = Rx+).
The signal direction is relative to the product being the Modbus slave, i.e. Tx+ from the product
(slave) is to be connected to the Rx+ of the master.
- Twisted pair cable should not be required for short lengths of cable < 1.5 m (< 5 ft). Standard
screened cable should suffice.
- The H/D (Half duplex) pins are used to select two or four-wire Modbus:
i) For two-wire mode, connect terminal 91 and 90 together.
ii) For four-wire mode, do not connect terminals 91 and 90 together.
Continued on page 17
Rx Tx
Master
Common
Earth*
R*R** See
wiring
notes
Front
Slave(s)
(Boiler controller)
9091929394959697E
H / DH / DRx+Rx-Tx+Tx-SCNCOM
R*R*