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915U-2 Wireless Mesh I/O and Gateway
Cooper Bussmann
User Manual
Version 1.2.2
Cooper Bussmann 915U-2 Wireless Mesh I/O and Gateway User Manual
ATTENTION!
Incorrect termination of supply wires may cause internal damage and will void the warranty. To ensure that your
915U-2 Wireless Mesh I/O and Gateway enjoys a long life, check this user manual to verify that all connections are
terminated correctly before turning on power for the first time.
CAUTION
To comply with FCC RF exposure requirements in section 1.1310 of the FCC rules, antennas used with this
device must be installed to provide a separation distance of at least 20 cm from all persons to satisfy RF exposure
compliance.
AVOID
• Operating the transmitter when anyone is within 20 cm of the antenna
• Operating the transmitter before ensuring that all RF connectors are secure and all open connectors are
properly terminated
• Operating the equipment near electrical blasting caps or within an explosive atmosphere
NOTE All equipment must be properly grounded for safe operations. All equipment should be serviced
only by a qualified technician.
Safety Notice
Exposure to RF energy is an important safety consideration. The FCC has adopted a safety standard for human
exposure to radio frequency electromagnetic energy emitted by FCC regulated equipment as a result of its actions
in Docket 93-62 and OET Bulletin 65 Edition 97-01.
GNU Free Documentation License
Copyright (C) 2009 Cooper Bussmann.
Cooper Bussmann is using a part of Free Software code under the GNU General Public License in operating the
915U-2 product. This General Public License applies to most of the Free Software Foundation’s code and to any
other program whose authors commit by using it. The Free Software is copyrighted by Free Software Foundation,
Inc., and the program is licensed “as is” without warranty of any kind. Users are free to contact Cooper Bussmann
at the following Email Address: elpro-sales@cooperindustries.com for instructions on how to obtain the source code
used for the 915U-2.
A copy of the license is included in GNU Free Document License at the end of the manual.
Industry Canada
This Class [A] digital apparatus complies with Canadian ICES-003.
This device complies with Industry Canada license-exempt RSS standard(s). Operation is subject to the following
two conditions:
• This device may not cause interference, and
• This device must accept any interference, including interference that may cause undesired operation.
This radio transmitter has been approved by Industry Canada to operate with the antenna types listed below with
the maximum permissible gain and required antenna impedance for each antenna type indicated. Antenna types
not included in this list that have a gain greater than the maximum gain indicated for that type are strictly prohibited
for use with this device.
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Manufacturer Model Number Coax Kit Net
ELPRO SG-900-6 CC10/900 5 dB Gain
ELPRO SG-900-6 CC20/900 2 dB Gain
ELPRO SG-900EL CC10/900 2 dB Gain
ELPRO SG-900EL CC20/900 -1 dB Loss
ELPRO YU6/900 CC20/900 4 dB Gain
ELPRO CFD890EL Includes 5m Cellfoil Unity Gain
ELPRO DG900-1 Includes 1m Cellfoil -2 dB Loss
ELPRO DG900-5 Includes 5m Cellfoil -3 dB Loss
FCC Notice
The 915U-2 module complies with Part 15.247 of the FCC rules.
Operation is subject to the following two conditions:
• This device may not cause harmful interference, and
• This device must accept any interference received, including interference that may cause undesired operation.
The 915U-2 module must be installed in a suitable enclosure that provides mechanical, shock, and fire hazard
protection. This device must be operated as supplied by ELPRO. Any changes or modifications made to the device
without the written consent of ELPRO may void the user’s authority to operate the device.
This device must be installed by professional installers, in compliance with 47 CFR Part 15 Subpart C Section
15.203 and 15.205, who will be responsible for maintaining EIRP no greater than 36 dBm, in accordance with
47CFR Part 15 Subpart C Section 15.247 (b)(2)(4).
In accordance with 47 CFR Part 15 Subpart C Section 15.203, only the following antenna/coax cable kits
combinations can be used.
Manufacturer Model Number Coax Kit Net
ELPRO SG-900-6 CC10/900 5 dB Gain
ELPRO SG-900-6 CC20/900 2 dB Gain
ELPRO SG-900EL CC10/900 2 dB Gain
ELPRO SG-900EL CC20/900 -1 dB Loss
ELPRO YU6/900 CC20/900 4 dB Gain
ELPRO CFD890EL Includes 5m Cellfoil Unity Gain
ELPRO DG900-1 Includes 1m Cellfoil -2 dB Loss
ELPRO DG900-5 Includes 5m Cellfoil -3 dB Loss
Part 15—This device has been tested and found to comply with the limits for a Class B digital device, pursuant to
Part15 of the FCC rules (Code of Federal Regulations 47CFR Part 15). Operation is subject to the condition that this
device does not cause harmful interference.
NOTE Any changes or modifications not expressly approved by ELPRO may void the users authority to
operate this device. This device should only be connected to PCs that are covered by either FCC DoC or
are FCC certified.
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Hazardous Location Notices
This device complies with 94/9/EC – ATEX Directive Ex nA IIC T4A, II 3 G, –40 °C ≤ Ta ≤ +60 °C.
WARNING: EXPLOSION HAZARD
Do not disconnect equipment unless power has been switched off or the area is known to be
non-hazardous.
This equipment is suitable for use in Class I, Division 2, Groups A, B, C and D; Tamb –40˚C to
+60˚C or non-hazardous locations only.
This equipment shall be installed in accordance with the requirements specified in Article 820 of
the National Electrical Code (NEC), ANSI/NFPA 70-2011. Section 820-40 of the NEC provides
guidelines for proper grounding, and in particular specifies that the antenna ground (shield) shall
be connected to the grounding system of the building, as close to the point of cable entry as
practical.
This equipment shall be installed in a Restricted Access Location (such as a dedicated equipment
room or service closet).
The earthing/grounding terminal of the equipment shall be connected to earth ground in the
equipment installation.
The external power supply installed with this equipment shall be a Listed, Class 2 power supply,
with a rated output between 15 Vdc and 30 Vdc, and min. 2500 mA.
Important Notice
ELPRO products are designed to be used in industrial environments by experienced industrial engineering
personnel with adequate knowledge of safety design considerations.
ELPRO radio products are used on unprotected license-free radio bands with radio noise and interference. The
products are designed to operate in the presence of noise and interference, but in an extreme case radio noise
and interference can cause product operation delays or operation failure. Like all industrial electronic products,
ELPRO products can fail in a variety of modes due to misuse, age, or malfunction. We recommend that users and
designers design systems using design techniques intended to prevent personal injury or damage during product
operation, and provide failure tolerant systems to prevent personal injury or damage in the event of product failure.
Designers must warn users of the equipment or systems if adequate protection against failure has not been
included in the system design. Designers must include this Important Notice in operating procedures and system
manuals.
These products should not be used in non-industrial applications, or life-support systems, without consulting
ELPRO first.
A radio license is not required in some countries, provided the module is installed using the aerial and equipment
configuration described in the 915U-2 Installation Guide. Check with your local distributor for additional information
on regulations.
Operation is authorized by the radio frequency regulatory authority in your country on a non-protection basis.
Although all care is taken in the design of these units, there is no responsibility taken for sources of external
interference. Systems should be designed to be tolerant of these operational delays.
To avoid the risk of electrocution, the aerial, aerial cable, serial cables and all terminals of the 915U-2 module
should be electrically protected. To provide maximum surge and lightning protection, the module should be
connected to a suitable ground and the aerial, aerial cable, serial cables and the module should be installed as
recommended in the 915U-2 Installation Guide
To avoid accidents during maintenance or adjustment of remotely controlled equipment, all equipment should be
first disconnected from the 915U-2 module during these adjustments. Equipment should carry clear markings to
indicate remote or automatic operation. For example: “This equipment is remotely controlled and may start without
warning. Isolate at the switchboard before attempting adjustments.”
The 915U-2 module is not suitable for use in explosive environments without additional protection.
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The 915U-2 operates unlicensed radio frequencies and proprietary protocols to communicate over the radio.
Nevertheless, if your system is not adequately secured, third parties may be able to gain access to your data or
gain control of your equipment via the radio link. Before deploying a system, make sure that you have carefully
considered the security aspects of your installation.
Release Notice
This is the December 2013 release of the 915U-2 Wireless Mesh I/O and Gateway User Manual version 1.2.2, which
applies to version 1.2.2 firmware.
Follow Instructions
Read this entire manual and all other publications pertaining to the work to be performed before installing,
operating, or servicing this equipment. Practice all plant and safety instructions and precautions. Failure to follow
the instructions can cause personal injury and/or property damage.
Proper Use
Any unauthorized modifications to or use of this equipment outside its specified mechanical, electrical, or other
operating limits may cause personal injury and/or property damage, including damage to the equipment. Any such
unauthorized modifications: (1) constitute “misuse” and/or “negligence” within the meaning of the product warranty,
thereby excluding warranty coverage for any resulting damage; and (2) invalidate product certifications or listings.
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CONTENTS
Chapter 1 - INTRODUCTION ...................8
1.1 Overview ...............................8
1.2 Module Structure .........................9
1.3 Getting Started .........................10
Chapter 2 - INSTALLATION ...................11
2.1 General ................................11
2.2 Power/Supply ..........................11
Requirements ............................11
Expansion I/O Supply .....................12
Internal I/O .............................13
Grounding ..............................13
2.3 Radio .................................14
900 MHz Spread Spectrum Radio ............14
869 MHz Fixed Frequency Radio ............14
Meshing Capability. . . . . . . . . . . . . . . . . . . . . . . . 15
2.4 Antenna ...............................15
Dipole and Collinear Antennas. . . . . . . . . . . . . . . 16
Yagi Antennas ...........................17
2.5 Connections ............................18
Bottom Panel Connections .................18
Ethernet Port .......................18
USB Device Port for Configuration ......18
RS-232 Port ........................19
RS-485 port with Modbus Support ......19
Side Access Configuration Panel ............20
Factory Boot Switch .................20
USB Host Port ......................20
DIP Switches .......................20
Front Panel Connections ...................21
Digital or Pulsed Inputs ....................21
Digital Outputs (Pulsed Outputs) .............22
Digital Output Fail-safe Status .........23
Analog Inputs ............................23
Differential Current Inputs .............24
Voltage Inputs ......................26
Analog Outputs ..........................26
Chapter 3 - OPERATION .....................27
3.1 Overview ..............................27
3.2 LED Indicators ..........................27
Front Panel Indicators .....................27
LED Boot Sequence .......................27
Input and Output Indicators .................28
Digital Inputs .......................28
Digital Outputs ......................28
Analog Inputs .......................28
Analog Outputs .....................28
Ethernet LED Indicators ....................28
3.3 System Design ..........................29
Radio Channel Capacity ...................29
Dual Band Operation ......................29
Radio Path Reliability ......................29
Design for Failures ........................30
Indicating a Communications Problem ........30
WIBNet Communication Registers ...........31
Testing and Commissioning ................31
3.4 WIBMesh ..............................31
Chapter 4 - CONFIGURATION .................32
4.1 Connecting to the Module .................32
4.2 MConfig Utility ..........................34
Downloading and Installing MConfig ..........34
Starting MConfig .........................35
Project Screen ......................36
Adding Units to a Project ...................37
Displaying the IP Address List ...............40
Editing Module IP Addresses ................41
Mappings ...............................42
Adding or Editing Mapping Parameters ..43
Startup or Force Configuration .........45
Address Map .......................46
Common I/O Registers for the 915U-2 ...47
I/O Configuration .........................47
Digital Inputs .......................47
Digital Outputs ......................48
Pulsed Outputs .....................49
Analog Inputs .......................49
Analog Outputs .....................51
Adding Expansion I/O Modules ..............52
115S Expansion I/O Memory Map ......52
Adding an Expansion I/O to MConfig ....53
Fail-safe Blocks ..........................53
Invalid Register State .................55
Sensitivity Blocks .........................55
Serial Configuration .......................56
Modbus RTU Master ................57
Serial Expansion I/O .................58
Serial Modbus RTU Slave .............59
Modbus Configuration .....................59
Modbus TCP Server and RTU Slave Tab . 60
Modbus TCP Client and RTU Master Tab 61
Adding Mapping Parameters ...........61
Modbus TCP Mapping Examples .......62
Modbus RTU Master ................63
RS-232/RS-485 Modbus Parameters ....64
4.3 Web-Based Configuration Utility ............65
Connecting and Logging On ................65
Mesh Parameters .........................66
Neighbor RSSI Configuration ................67
IP Routing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
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Radio Settings ...........................69
Mesh Fixed Routes .......................70
Module Information Webpage ...............74
System Tools ............................74
Patch File Firmware Upgrade ..........75
Full Firmware Upgrade ...............75
Product Reconfiguration ..............78
Feature License Keys ......................78
Chapter 5 - DIAGNOSTICS ...................80
5.1 IO Diagnostics ..........................80
Watchdog Error Log .......................81
Module Information Registers ...............81
Expansion I/O Error Registers ...............81
5.2 Mesh Connectivity .......................82
Link Quality Indicator .................83
5.3 Mesh Neighbor List .....................83
5.4 Mesh Neighbor RSSI
.....................84
5.5 Mesh Network Diagnostics ................85
Ping ...................................85
Trace Route .............................85
5.6 Mesh Network Statistics ..................86
5.7 Monitor Communications .................88
Monitor WIBMesh Radio Communications .....88
Monitor WIBMesh IP Comms ...............89
Monitor WIBNet Radio Comms ..............90
5.8 Statistics for WIBMesh and WIBNet .........91
Chapter 6 - SPECIFICATIONS .................92
Appendix A - DBM TO MW CONVERSION
.......94
Appendix B - I/O STORE REGISTERS ..........95
Output Coils ...............................95
Input Bits .................................95
Input Registers
.............................95
Holding Registers ...........................96
Appendix C - EXPANSION I/O REGISTERS ......97
I/O Store for 115S-11 Expansion I/O Modules ....97
I/O Store for 115S-12 Expansion I/O Modules ....97
I/O Store for 115S-13 Expansion I/O Modules ....98
Appendix D - MODBUS ERROR CODES ........99
Appendix E - PHYSICAL I/O REGISTERS
.......100
115S Serial Expansion Modules I/O Registers ...101
Appendix F - GNU FREE DOCUMENT LICENSE . 103
Appendix G - OVER-THE-AIR CONFIGURATION . 107
Appendix H - GLOSSARY
...................110
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ChapTEr 1 - INTrODUCTION
1.1 Overview
The 915U-2 Wireless Mesh I/O and Gateway is designed to provide standard off-the-shelf telemetry functions for an
economic price. Telemetry is the transmission of data or signals over long distances via radio or twisted-pair wire
cable.
Although the 915U-2 module is intended to be simple in its application, it also provides many sophisticated
features, which are described in this manual. This manual should be read carefully to ensure that the modules are
configured and installed to provide reliable performance.
The 915U-2 module extends the functionality provided by the earlier 105U and 905U-E Series modules. It provides
on-board I/O via a front mounting 20-way connector, and has provision for extra expansion modules (ELPRO 115S
or Modbus devices), that can be connected using a standard RS-485 serial connection.
The module can monitor the following types of signals:
• Digital (on/off) signals, such as a contact closure or switch
• Analog (continuously variable) signals, such as tank level, motor speed, or temperature
• Pulsed signal, frequency signals, such as metering, accumulated total, or rainfall
• Internal signals, such as supply voltage, supply failure, or battery status
The modules monitor the input signals and transmit the values by radio or Ethernet cabling to another module
(or modules) that have been configured to receive this information. The 915U-2 radio is designed to meet the
requirements of unlicensed operation for remote monitoring and control of equipment. A radio license is not
required for the 915U-2 in many countries.
Input signals that are connected to the module are transmitted and appear as output signals on other modules. A
transmission occurs whenever a change of state (COS) occurs on an input signal. A COS of a digital or an internal
digital input is a change from “off” to “on,” or a change from “on” to “off.” For an analog input, internal analog
input, or pulse input rate, a COS is a configurable value referred to as sensitivity. The default sensitivity is 1000
counts (3%), but this value can be changed using the Sensitivity Block configuration page in the MConfig Utility, as
described in “Sensitivity Blocks” on page 55.
In addition to COS messages, update messages are automatically transmitted on a configurable time basis. These
updates ensure system integrity. Pulse inputs counts are accumulated and the total count is transmitted regularly
according to the configured update time.
The 915U-2 modules transmit the input/output data using radio or Ethernet. The data frame includes the address
of the transmitting module and the receiving module, so that each transmitted message is acted upon only by the
correct receiving unit. Each message includes error checking to ensure that no corruption of the data frame has
occurred due to noise or interference. The module with the correct receiving address will acknowledge the message
with a return transmission (acknowledgment). If the original module does not receive a correct acknowledgment, it
will retry up to five times before setting the communications status of that message to “fail.” For critical messages,
this status can be reflected on an output on the module for alert purposes. The module will continue to try to
establish communications and retry each time an update or COS occurs.
The 915U-2 comes from the factory with ELPRO WIBMesh protocol as standard. This protocol provides enhanced
features, including IP addressing, and it allows thousands of modules to exist in a system and automatic routing of
messages through repeater stations. The module can also be configured with the legacy WIBNet protocol, which
provides operation with existing ELPRO wireless I/O devices (905 series and 105 series 869 MHz modules). The
module can easily be switched between the two protocol versions by selecting the appropriate protocol from a
built-in webpage (see “Product Reconfiguration” on page 78).
A system can be a complex network or a simple pair of modules. An easy-to-use configuration procedure allows
you to specify any output destination for each input. Each 915U-2 radio can have up to 24 expansion I/O modules
(ELPRO 115S) connected by RS-485 twisted pair cable. Any input signal at any module may be configured to
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appear at any output on any module in the entire system.
Modules can be used as repeaters to re-transmit messages on to the destination module. Repeaters can repeat
messages on the radio channel or from the radio channel to the serial channel (or serial to radio). The meshing
protocol automatically selects other stations to act as repeaters if required (up to ten hops). If you configure the
module to use the legacy WIBNet protocol, up to five repeater addresses may be configured for each input-tooutput link. For more information about using WIBNet, see “Product Reconfiguration” on page 78.
The units can be configured using the MConfig Utility via Ethernet or USB, or by accessing the internal webpages
using a Web browser. The MConfig Utility is described in “4.2 MConfig Utility” on page 34. For Web-based
configuration, see “4.3 Web-Based Configuration Utility” on page 65.
1.2 Module Structure
The 915U-2 module is made up of different areas that all interface with a central input and output storage area (I/O
store). The I/O store is an area of memory made available for the status of the physical on-board I/O and internal
I/O registers. It also provides services for other processes within the module.
The I/O store is split into eight different blocks types:
• Two blocks made available for bit data (discrete)
• Two blocks made available for word data (analog)
• Two blocks made available for 32-bit words data (32-bit analogs)
• Two blocks made available for floating point data (floats)
Each of these block types in turn support input and output locations that can interface with the physical I/O on the
local machine and also be used for data storage when used as a gateway to external devices. These block type
locations are illustrated in Figure 1 and are described in Appendix B. There are other registers within the database
that can be used for system management.
The Radio Interface (see Figure 1) allows the 915U-2 to communicate with other modules within the system using
a proprietary radio protocol called WIBMesh. I/O Messages from other 915U-2 modules are received on the radio
port and then passed to the I/O store which will in turn update the register locations accordingly. The WIBMesh
protocol is designed to provide reliable radio communications on an open license-free radio channel. It is an
extremely efficient protocol for radio communications because the messages are sent using exception reporting
(only transmitting when there is a change of an input signal) rather than transmitting all of the time. Update
messages can also be configured at a predetermined time for integrity checks.
Figure 1 Module Structure
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Each message can be comprised of multiple I/O values, referred to as a “block of I/O.” The messages use error
checking and return acknowledgment for greater reliability. Up to four attempts are made when transmitting the
message over each hop of the radio path, and if no acknowledgment is received a Comms indication can be
flagged.
The on-board I/O includes eight discrete I/O, two single-ended analog inputs, two differential analog inputs, and
two current sourcing analog outputs. Each discrete I/O can function as either a discrete input (voltage-free contact
input) or discrete output (transistor output). Each I/O point is linked to separate I/O registers within the I/O data
store.
The following internal I/O can be accessed from the I/O store. The inputs can be used to interpret the status of a
single module or an entire system:
• Battery voltage—The battery terminal voltage, displayed as an analog value.
• Loop supply—The +24 Vdc analog loop supply (ALS) used to power analog current loops, displayed as an
analog value.
• Expansion module volts—The supply voltage of the connected expansion modules, displayed as an analog
value.
• RSSI – The radio signal level for the selectable address, reported as a dB level.
• Comms Fail—A selectable register can indicate a Communications Fail error for a particular message
transmission.
The expansion port, allows 115S expansion I/O modules to be added to the module. Expansion I/O is dynamically
added to the internal I/O of the 915U-2 module by adding an offset to the address.
1.3 Getting Started
Most applications for the 915U-2 module require little configuration. The 915U-2 has many sophisticated features,
but if you do not require these features you can use this section to configure the units quickly.
To get started quickly:
1. Read Chapter 2, which describes the power supply, antenna/coax connections, and I/O connections.
2. Power on the 915U-2 module and set up an Ethernet connection to your PC.
For detailed steps, see “4.1 Connecting to the Module” on page 32.
3. Log on to the module’s Web-based configuration utility and click Network on the menu to display the Network
configuration webpage.
For logon instructions, see “4.3 Web-Based Configuration Utility” on page 65.
4. On the Network webpage, configure the Ethernet interface with an IP address that is compatible with your
network or PC.
5. Save the configuration.
The 915U-2 module is now ready to use. For further configuration instructions, see Chapter 4.
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ChapTEr 2 - INSTaLLaTION
2.1 General
The 915U-2 Series modules are housed in a plastic enclosure with DIN rail mounting, providing options for up to
14 I/O points, and separate power and communications connectors. The enclosure measures 170 x 150 x 33 mm,
including the connectors. The antenna protrudes from the top.
2.2 Power/Supply
Figure 2 Power Connectors
Requirements
There are two recommended power options available for the 915U-2 module:
• 15–30 Vdc power source rated at 37W, connected to the SUP+ and SUP- terminals
• 12–15 Vdc power source rated at 24W, connected to the BAT+ and GND terminals
A primary power supply connected to the SUP+ and SUP- terminals automatically charges a 13.8V sealed leadacid battery, if connected to the BAT+ and GND terminals at up to 1A at ambient room temperature (25°C). Battery
charge current is reduced to 0.5A at 60°C. If using a battery, it is recommended that a 10A inline fuse be fitted as
prevention against battery short circuit.
If you are using the first option and the primary supply fails, the battery supply will continue to power the module
without interruption to the operation. The supply and battery charging terminals are hosted on the 4-way connector
on the bottom edge of the module labeled “Supply.” Both the supply and battery connections have reverse polarity
and over-voltage protection.
Figure 3 Supply Connections
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The power supply should be CSA Certified Class 2, approved for normal operation. If the device is being used in a
Class I Div 2 explosive area, the supply must have Class I Div 2 approval.
When powering the module, the power source must be able to provide sufficient current to power all module
operations, including quiescent current, peak transmit current, and digital and analog I/O, including loop supply and
battery charging (if applicable). To calculate the power supply current limit, use the following criteria.
Current @ 13.8V @ 24V
Quiescent current of the module 200 mA 115 mA
Module maximum I/O (4xAI, 2xAO, 8xDO) 500 mA 290 mA
Peak transmit current 500 mA 290 mA
External expansion I/O 1000 mA 575 mA
Battery charging N/A 575 mA
The following table shows typical +24V supply current limits with different module options enabled. Transmit current
is not added because it is not a constant.
Expansion I/O No Expansion I/O
No battery fitted (no charging) 1270 mA 695 mA
Battery fitted 1555 mA 980 mA
The following table shows typical +13.8V supply current limits with different module options enabled. Transmit
current is not added because it is not a constant.
Expansion I/O No Expansion I/O
Current limit 2200 mA 1200 mA
For example, if a module is powered by a 24 Vdc supply and there is no backup battery connected and it has
expansion I/O fitted, the minimum current needed is 1.3A @ 24V (32W). This is allowing for 290 mA peak transmit
current and up to 1A for the expansion I/O.
Expansion I/O Supply
To allow increased I/O capacity, a second four-way terminal labeled “Expansion I/O” provides a +12V supply
(upto1A) and RS-485 communications for any 115S serial expansion I/O modules.
Figure 4 Expansion I/O Power and RS-485
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As a guide, when using the I/O power connection from the 915U-2, the number of I/O modules is limited to
three 115S-11 (using inputs), or one x 115S-12, or one x 115S-13. If more I/O modules are required, you need
to calculate the overall current consumption using the following criteria, and power the modules from an external
supply.
• 115S module static current drain = 120 mA
• 115S digital inputs require 13 mA per active input
• 115S digital outputs require 25 mA per active output
• 115S analog inputs and outputs require 50 mA per I/O when operating at 20 mA
For example, a single 115S-11 using inputs only has a current consumption of approximately 320 mA, which
means that you can connect up to three 115S-11 modules to the expansion port without overloading the on-board
I/O power supply. Asingle 115S-12 using all analog inputs and digital outputs has a current consumption of
approximately 720 mA, so you can only connect one.
Keep in mind that when calculating the current consumption for the expansion I/O, the maximum available current
from the on-board power supply is 1A. If the overall expansion I/O current consumption is over the 1A maximum an
external power source is required.
Internal I/O
The internal supply voltage register locations shown in the following table can be monitored using the Diagnostics
webpage within the module’s Web-based configuration utility (see “5.1 IO Diagnostics” on page 80 for details).
The values can also be mapped to a register or an analog output on another module within the radio network.
Register Description
30005 Local supply voltage (0–40V scaling).
30006 Local 24V loop voltage (0–40V scaling). Internally generated +24V supply used for analog loop supply.
Maximum current limit is 100 mA.
30007 Local battery voltage (0–40V scaling).
30008 115S supply voltage (0–40V scaling).
38005–38008 Floating point registers that display the actual supply voltage, battery voltage, +24V supply, and 115S
supply. Note that these are actual voltage values, whereas registers 30005–30008 display a number
between 16384 and 49152 that represents the voltage scale 0–40V.
To calculate the supply voltages from the register value use the following calculation:
Volts = (Register Value) – 8192
1024
There are no dedicated discrete low voltage alarm indicators. However, each supply voltage does have a high and
a low set point status that can be used for this type of alarm. See “Analog Inputs” on page 23 for details on how
to configure these alarms.
Grounding
To provide maximum surge and lightning protection each module should be effectively earthed/grounded via a
GND terminal on the module. This is to ensure that the surge protection circuits inside the module are effective. The
module should be connected to the same common ground point as the enclosure ground and the antenna mast
ground.
The 915U-2 has a dedicated earth/ground connection screw on the bottom end plate next to the supply terminals.
All earth/ground wiring should be minimum 2 mm2 – 14 AWG. If using the 915U-2 with serial expansion I/O
modules, all expansion modules must have a separate earth/ground connection from the front terminal back to the
common earth or ground point. See Figure 5.
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Figure 5 Grounding
2.3 Radio
The following radio variants are available in the 915U-2, depending on the country of operation.
900 MHz Spread Spectrum Radio
The radio uses frequency hopping spread spectrum modulation, which is a method of transmitting radio signals by
switching the carrier among many frequency channels using a pseudo-random sequence, called a hopset. There
are two hopsets that cycle through the sequence and switch to a different channel after each radio transmission.
Each hopset uses a different pseudo-random sequence of 50 channels.
The radio operates in the 902–928 MHz ISM band, which is split into two frequency bands, 902–914 MHz (low) and
915–928 MHz (high). In the United States and Canada, the 915U-2 can use both high and low bands. However, in
other countries, such as Australia, only the 915–928 MHz band is available.
Some countries use fewer channels. For example, New Zealand uses 18 channels in the frequency band 922.75–
927.00 MHz. In countries that allow the two bands to be used, the frequency band can be changed by using the
MConfig Utility and selecting the hopset on the Radio Settings screen for the module. The hopset only displays the
frequency bands available for the model and country. For details, see “Radio Settings” on page 69.
The receiver is continually scanning all channels within the hopset, and when a valid data packet is received it locks
on to the channel and receives the data.
A spread-spectrum transmission offers the following advantages over a fixed-frequency transmission:
• Spread-spectrum signals are more resistant to narrow-band interference
• Spread-spectrum signals are difficult to intercept or eavesdrop because of the pseudo-random transmission
sequences
• Transmissions can share a frequency band with other types of conventional transmissions with minimal
interference
869 MHz Fixed Frequency Radio
The 869 MHz fixed frequency radio operates in the unlicensed fixed frequency band of 869 MHz and is used in
Europe. There are two frequencies. The first operates at 869.525 MHz with a maximum transmit power level of
500 mW, and is regulated with a 10% duty cycle on the channel. This duty cycle limit requires that the module not
transmit for more than 10% of the total operating time, which means other users of the unlicensed frequency are
able to transmit without interference. The second frequency operates at 869.875 MHz with a transmit power level
of 5 mW and no duty cycle regulation on the channel, which means the module can freely transmit as often as is
needed.
NOTE Care must be taken to ensure that the duty cycle limit is not exceeded when using the 869.525 MHz
frequency.
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Meshing Capability
The ELPRO WIBMesh protocol is based on the Ad hoc On Demand Distance Vector (AODV) routing algorithm,
which is a routing protocol designed for ad hoc networks. AODV is capable of unicast routing and is an on-demand
algorithm, meaning that it builds and maintains these routes only as long as they are needed by the source devices.
The AODV protocol creates a table that shows the connection routes to other device in the system. The protocol
uses sequence numbers to ensure that the routes are kept as current as possible. It is loop-free and self-starting,
and can scale to a large numbers of nodes. See “3.4 WIBMesh” for configuration details.
2.4 Antenna
The 915U-2 module operates reliably over large distances. The distance that can be reliably achieved varies
with each application and depends on the type and location of antennas, the degree of radio interference, and
obstructions to the radio path (such as hills or trees). Typical reliable distances are detailed below. However, longer
distances can be achieved if antennas are mounted in elevated locations, such as on a hill or on a radio mast.
Using the 900-MHz spread spectrum radio, the distances achievable are as follows:
• USA/Canada: 15 miles, 6-dB net gain antenna configuration permitted (4W EIRP)
• Australia/NZ: 12 km, unity gain antenna configuration (1W EIRP)
To achieve the maximum transmission distance, the antennas should be raised above intermediate obstructions
so that the radio path is a true line-of-sight path. Because of the curvature of the earth, the antennas need to be
elevated at least 15 feet (5m) above ground for paths greater than 3 miles (5 km). The modules will operate reliably
with some obstruction of the radio path, although the reliable distance is reduced. Obstructions that are close to
either antenna have a greater blocking effect than obstructions in the middle of the radio path. For example, a
group of trees around the antenna is a larger obstruction than a group of trees further away from the antenna.
Maximum Gain per Region
Country Max Gain (dB)
USA / Canada 6
Australia / New Zealand 0
Europe 0
Typical Antenna Gains
Part No Antenna Gain (dB)
DG900 Whip with 15’ (5m) cable –2
CFD890EL Dipole with 15’ (5m) cable 0
SG900-EL 5 dBi Collinear (3 dBd) 5
SG900-6 8 dBi Collinear (6 dBd) 8
YU6-900 6 element Yagi 10
YU16-900 16 element Yagi 15
Typical Coax Losses (900 MHz)
CC3-SMA 10’ (3m) Cellfoil Coax –1 dB
CC10-SMA 33’ (10m) Cellfoil Coax –3 dB
CC20-SMA 66’ (20m) Cellfoil Coax –6 dB
The 915U-2 module provides a range of test features, including displaying the radio signal strength. Line-of-sight
paths are only necessary to obtain the maximum range. Obstructions reduce the range but may not prevent a
reliable path. A larger amount of obstruction can be tolerated for shorter distances. For very short distances, it is
possible to mount the antennas inside buildings. All radio paths require testing to determine if they are reliable (see
“5.6 Mesh Network Statistics” on page 86 ). Where it is not possible to achieve reliable communications between
two modules, a third module may be used to receive the message and re-transmit it. This module is referred to as a
repeater, and it may also have input and output (I/O) signals connected to it, and may form part of the I/O network.
See “1.1 Overview” on page 8.
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An antenna should be connected to the module via 50-ohm coaxial cable (such as RG58, RG213, or Cellfoil), and
terminated with a male SMA coaxial connector. The higher the antenna is mounted, the greater the transmission
range. However, as the length of the coaxial cable increases, so do cable losses. For use on unlicensed frequency
channels, there are several types of suitable antennas. It is important to choose antennas carefully in order to avoid
contravening the maximum power limit on the unlicensed channel. If in doubt, contact your distributor.
The net gain of an antenna and cable configuration is the gain of the antenna (in dBi) less the loss in the coaxial
cable (in dB). The net gain of the antenna and cable configuration is determined by adding the antenna gain and the
cable loss. For example, a six-element Yagi with 70 feet (20m) of Cellfoil cable has a net gain of 4 dB (10–6 dB).
Connections between the antenna and coaxial cable should be carefully taped to prevent ingress of moisture.
Moisture ingress in the coaxial cable is a common cause for problems with radio systems because it greatly
increases radio losses. We recommend that the connection be taped—first with a layer of PVC tape, next with a
vulcanizing tape (such as 3M™ 23 tape”), and finally with another layer of PVC UV-stabilized insulating tape. The
first layer of tape allows the joint to be easily inspected when troubleshooting because the vulcanizing seal can be
easily removed.
Figure 6 Wrapping Coaxial Connections
Where antennas are mounted on elevated masts, the masts should be effectively earthed/grounded to avoid
lightning surges. For high lightning risk areas, surge suppression devices between the module and the antenna
are recommended. If the antenna is not already shielded from lightning strike via an adjacent earthed/grounded
structure, a lightning rod may be installed above the antenna to provide shielding.
Dipole and Collinear Antennas
Collinear antennas transmit the same amount of radio power in all directions, and are easy to install and use
because they do not need to be aligned to the destination. The dipole antenna with integral 15 ft cable does not
require an additional coaxial cable. However, a cable must be used with collinear antennas. In order to obtain the
maximum range, collinear and dipole antennas should be mounted vertically, preferably one wavelength away from
a wall or mast.
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Figure 7 Collinear Antenna Mounting
Yagi Antennas
Yagi antennas provide high gain in the forward direction, but lower gain in other directions. They may be used to
compensate for coaxial cable loss for installations with marginal radio path. The Yagi gain also acts on the receiver,
so that adding Yagi antennas at both ends of a link provides a double improvement.
Yagi antennas are directional. That is, they have positive gain to the front of the antenna, but negative gain in other
directions. Therefore, Yagi antennas should be installed with the central beam horizontal and must be pointed
precisely in the direction of transmission to benefit from the gain of the antenna. The Yagi antennas may be
installed with the elements in a vertical plane (vertically polarized) or in a horizontal plane (horizontally polarized).
However, both antennae must be in the same plane for maximum signal strength. If the antennae are mounted in
different planes the receive signal level is reduced by approximately 30 dB.
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Figure 8 Yagi Antenna Mounting
For a two-station installation with both modules using Yagi antennas, horizontal polarization is recommended.
If there are more than two stations transmitting to a common station, the Yagi antennas should have vertical
polarization, and the common or central station should have a collinear (non-directional) antenna.
NOTE Yagi antennas normally have a drain hole on the folded element. The drain hole should be located
on the bottom of the installed antenna.
2.5 Connections
Bottom Panel Connections
Figure 9 Bottom Panel Connections
Ethernet Port
The 915U-2 modules provides a standard RJ-45 Ethernet port compliant to IEEE 802.3 10/100BaseT. This port
provides full access to the module, including configuration, diagnostics, log file download, and firmware upload
of both the local and remote units. Additionally, the Ethernet port can provide network connectivity for locally
connected third-party devices with Ethernet functionality.
USB Device Port for Configuration
The 915U-2 module also provides a USB device (USB-B) connector. This connector provides configuration of the
device and remote configuration access to other devices in the radio network.
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RS-232 Port
The 915U-2 module provides an RS-232 serial port that supports operation at data rates up to 230,400 baud. This
port supports Modbus protocol. The RS-232 port is provided by an RJ-45 connector wired as a DCE according to
the EIA-562 Electrical Standard.
RJ-45 Signal Required Signal name Connector
1 RI Ring Indicator
2 DCD Data Carrier Detect
3 DTR Y Data Terminal Ready
4 GND Y Signal Common
5 RXD Y Receive Data (from 915U-2)
6 TXD Y Transmit Data (to 915U-2)
7 CTS Clear to Send
8 RTS Request to Send
RS-485 port with Modbus Support
The 915U-2 module provides an RS-485 serial port that supports operations at data rates up to 230,400 baud.
The default baud rate is 9600 baud, no parity, 8 data bits and 1 stop bit, which matches the 115S serial expansion
module defaults. This port supports the Modbus protocol.
The RS-485 port terminal is hosted on the four-way expansion connector on the bottom edge of the module. An
on-board RS-485 termination resistor provides line attenuation for long runs. As a general rule, termination resistors
should be placed at each end of the RS-485 cable. When using 115S expansion I/O modules, remember to enable
the RS-485 termination resistor switch that is located on the end module.
Figure 10 RS-485 Connections
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Side Access Configuration Panel
A small access panel on the side of the module hides a factory boot switch, USB host port, and a small bank of
DIPswitches that are used for analog input voltage and current selection, external boot, and default configuration
settings.
Figure 11 Access Panel
Factory Boot Switch
The factory boot switch is used for factory setup and diagnostics. This switch should only be used if advised by
ELPRO technical support.
USB Host Port
This port is a USB host (master port) that can interface with USB storage devices for upgrading the module
firmware. For details, see “System Tools” on page 74.
DIP Switches
The DIP switches are used to select a number of functions within the module, as shown in the following table.
• DIP switches 1 to 2—Used for measuring current or voltage on analog input 3. Set DIP switches to “on” to
measure current (0–20 mA) and “off” for voltage (0–5 Vdc).
• DIP switches 3 to 4—Used for measuring current or voltage on analog input 4. Set DIP switches to “on” to
measure current (0–20 mA) and “off” for voltage (0–5 Vdc).
• DIP switch 5—Not used.
• DIP switch 6—When set to “on” (enabled) and the module is restarted, the module boots up with a known
factory default configuration, including a default IP address for the Ethernet connection. See “4.1 Connecting
to the Module” on page 32.
NOTE When DIP switch 6 is “on,” radio and I/O functionality is disabled.
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Switch Function Current Voltage
DIP 1 and 2 Analog Input 3
DIP 3 and 4 Analog Input 4
Switch Function Disabled Enabled
DIP 5 Not used
DIP 6 Setup Mode
Front Panel Connections
The front panel on the 915U-2 module provides connections for the following:
• Eight digital input/output (DIO 1–8)
• Two 12-bit, 0.1% accuracy differential analog inputs
• Two single-ended 12-bit, 0.1% accuracy analog inputs
• Two 13-bit, 0.1% accuracy current sourcing analog outputs
• Connection terminals for common and +24V analog loop supply (ALS); maximum ALS current limit is 100 mA
Figure 12 Front Panel Connections
Digital or Pulsed Inputs
Each digital I/O channel on the 915U-2 module can act as either an input or an output. The input/output direction
is automatically determined by the connections and configuration of the I/O. If you have an I/O channel wired as
an input but operate the channel as an output, no electrical damage will occur but the I/O system will not operate
correctly. For example, if you are operating the channel as an output and performing a read inputs on this location,
it will indicate the status of the output.
Marked D1–8, the digital inputs share the same terminals as the digital outputs on the 915U-2 module. A digital
input is activated by connecting the input terminal to GND or common, either by voltage-free contact, TTL level,
or transistor switch. Each digital input has an orange indication LED that will turn on when the input has been
connected to a GND.
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Figure 13 Digital/Pulsed Input Wiring
Digital inputs 1–4 can be used as pulsed inputs. The maximum pulse frequency is 50 kHz for input 1 and 2, and
1kHz for input 3 and 4. Digital/pulsed inputs are suitable for TTL signal level, NPN-transistor switch devices, or
voltage-free contacts (a relay or switch with debounce capacitor).
Frequencies greater than 1 kHz need to use a TTL logic drive or an external pull-up resistor (1KΩ to V+). Pulsed
inputs are converted to two different values internally. The first value is the pulse count, which is an indication of
how many times the input has changed state over a configured time period. The second value is a pulse rate, which
is an analog input derived from the pulse frequency. For example, 0 Hz = 4 mA and 1 kHz = 20 mA.
All pulsed input counts are stored in non-volatile RAM, so that the values are saved in the event of a power failure
or a module reset.
Digital Outputs (Pulsed Outputs)
Digital outputs are open-collector transistors, and are able to switch loads up to 30 Vdc, 200 mA. The eight digital
outputs share the same terminals as the digital input. These terminals are marked D1–8.
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Figure 14 Digital Output Wiring
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When active, the digital outputs provide a transistor switch to EARTH (Common). To connect a digital output, see
Figure 14. A bypass diode (IN4004) is recommended to protect against switching surges for inductive loads such as
relay coils. The digital channels D1–4 on the 915U-2 module can be used as pulse outputs with a maximum output
frequency of 10 kHz.
Digital Output Fail-safe Status
In addition to indicating the digital output status (on or off), the LEDs can also indicate a communications failure
by flashing the output LED. This feature can be used by configuring a fail-safe time and status via the I/O Digital
Output screen in the MConfig Utility (see “I/O Configuration” on page 47.)
Figure 15 Digital Output Fail-safe Times
The fail-safe time is the time the output counts down before activating a fail-safe state. Normally this would be
configured for a little more than twice the update time of the mapping that is sending data to it. This is because the
fail-safe timer is restarted whenever it receives an update. If you send two successive updates and fail to receive
both of these messages, the timer counts down to zero and activates the fail-safe state.
If the fail-safe state is enabled (on), the LED flashes briefly off and the digital output turns on. If the fail-safe state is
disabled (off), the LED flashes briefly on and the digital output turns off.
Figure 16 Fail-Safe State
Analog Inputs
The 915U-2 module provides two floating differential analog inputs and two grounded single-ended analog inputs.
Analog inputs 1 and 2 will automatically measure current (0–20 mA) or voltage (0–25V), depending on what is
connected to the input. Analog inputs 3 and 4 must be configured to measure current (0–20 mA) or voltage (0–5V)
via the DIP switches on the configuration panel (see “Side Access Configuration Panel” on page 20).
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An internal 24V analog loop supply (ALS) provides power for any current loops with a maximum current limit of
100mA. The LEDs have an analog diagnostic function and will indicate the status of the input. If the current is less
than 3.5 mA, the LED is off. If the current is greater than 20.5 mA, the LED is on. The LED will flicker with the duty
cycle relative to the analog reading in this range.
NOTE By default, there is a five-second delay on the input because of the filter. Filter times can be
changed using the Analog Input screen within the MConfig Utility. For more information, see “Analog
Inputs” on page 23.
The LEDs next to AI1+, AI2+ flash according to the current on these inputs. The LEDs next to AI1- and AI2 flash
according to the voltage on the analog inputs.
Differential Current Inputs
Only analog input 1 and 2 can be wired as differential Inputs. Differential mode current inputs should be used when
measuring a current loop, which cannot be connected to ground. This allows the input to be connected anywhere
in the current loop. Common mode voltage can be up to 27 Vdc.
Figure 17 indicates how to connect loop-powered or externally powered devices to the 915U-2 differential analog
inputs. It should also be noted that the differential inputs can also be used to connect single-ended current sinking
or current sourcing devices. Figure 19 shows how to connect to these types of devices.
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Figure 17 Differential Current Inputs
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Figure 18 AI 1 & 2 Single-ended Current Inputs
Single-ended current input mode is useful if the sensor loop is grounded to the 915U-2 module. Devices can be
powered from the 24V analog loop supply (ALS) generated internally from the module.
The DIP switches (located in the side access panel) are used to determine if the inputs will be current or voltage.
DIP switches 1 and 2 are used for analog 3, and DIP switches 3 and 4 are used for analog 4. For current, set both
DIP switches to the “on” position. For voltage, set both to “off.”
Figure 19 AI 3 & 4 Single-ended Current Inputs
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Voltage Inputs
All analog inputs can be set up to read voltage. If using analog input 1 and 2, connect the voltage source across
the positive terminal of the input and ground. If using analog input 3 and 4, connect across the input terminal and
GND.
NOTE Default scaling gives 0–20V for 4–20 mA output on analog 1 and 2. Default scaling for analog
3and4 gives 0–5V for 4–20 mA output. For voltage input on analog 3 and 4, set both DIP switches to the
“off” position.
Figure 20 Voltage Inputs
Analog Outputs
The 915U-2 module provides two 0–24 mA DC analog outputs for connecting to analog inputs on equipment (such
as PLCs, DCS, and loggers) or connecting to instrument indicators for displaying remote analog measurements.
The 915U-2 analog outputs are a sourcing output and should be connected from the analog output terminal
through the device or indicator to ground (GND). See Figure 21 for connections. The LEDs provide level indication
depending on current. The LEDs appear dimmed for 4 mA and bright for 20 mA.
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Figure 21 Analog Outputs
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ChapTEr 3 - OpEraTION
3.1 Overview
The 915U-2 Series I/O modules are designed to provide standard off-the-shelf telemetry functions at an economic
price. Telemetry is the transmission of data or signals over a long distance via radio or twisted-pair wire cable.
3.2 LED Indicators
When the module is initially connected to power, it performs internal setup and diagnostics checks to determine
if it is operating correctly. These checks take approximately 80 seconds. The following table shows how the LED
indicators appear when the module is operating correctly.
Front Panel Indicators
LED Indicator Condition Meaning
PWR Green System OK
PWR Red System boot (initial or system failure)
PWR Orange Start of system boot
PWR Fast Flash System boot, stage 1
PWR Slow Flash System boot, stage 2
RF Orange Transmitting radio data
RF Red Receiving radio data
232 Green
232 Red
232 Orange
485 Green
485 Red
Transmitting RS
Receiving RS
Transmitting and receiving RS
Transmitting RS
Receiving RS
-232 data
-232 data
-232 data
-485 data
-485 data
The RF LED does not directly represent the actual radio transmission status. It only indicates the first transmission
from a mapping, an update, or an underlying AODV message. Any subsequent retry messages will not be indicated.
LED Boot Sequence
Upon reset, the PWR LED appears solid red for about 2 seconds (system boot), followed by 12 seconds of Orange
(start of system boot process). The PWR LED then fast flashes between red and green for 30 seconds (stage 1
of system boot process) followed by a slow flashes for 50 seconds (stage 2 of system boot process). At the end
of the boot sequence the PWR should appear solid green. The time periods are approximate, and depend on the
hardware and firmware revisions.
Figure 22 Boot Sequence
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Input and Output Indicators
LED Indicator Condition Meaning
D 1–8 Orange Digital input is on
D 1–8 Flashing Orange - (Long On) Update failure (fail-safe state is on)
D 1–8 Flashing Orange - (Long Off) Update failure (fail-safe state is off)
AI 1 & 2 + Orange Analog input current indication
AI 1 & 2 – Orange Analog input voltage indication
AI 3 & 4 Orange Analog input current or voltage indication
AO1 & 2 Orange Analog output current indication
Digital Inputs
LEDs display the status of each of the eight DIOs when used as inputs. If the LED is on, it indicates that the input
ison.
Digital Outputs
When the DIOs are used as outputs, the LEDs display the status of each of the digital outputs. If an LED is on, it
indicates that the output is on. The LEDs also indicate if the output is in a fail-safe state by flashing at different
rates. If an LED is mostly on (long on) it indicates that the fail-safe state shown on the Digital Output Configuration
page (in MConfig Utility) is on. If an LED is mostly off (long off) it indicates that the fail-safe state shown on the
Digital Output Configuration page (in MConfig Utility) is off. See “Fail-safe Blocks” on page 53 for details.
Analog Inputs
There are two LEDs for each differential analog input. The first LED (+) is used to indicate that the analog input is
reading a current (mA). The second LED (–) indicates that the input is reading voltage. Each of the analog input
LEDs flash with increasing speed and intensity depending on the level of the input. For example, at 4 mA, the LED
appears dimmed and flashes slowly, and at 20 mA the LED appears bright and flashes quickly.
For each of the single-ended analog channels, the LED indicates when the input is reading current or voltage by
flashing the LED according to the level of the input. For example, at 4 mA the LED appears dimmed and flashes
slowly, and at 20 mA, the LED appears bright and flashes quickly.
Analog Outputs
Each analog output has an LED in series that indicates the output current by increasing or decreasing the intensity
of the LED. For example, at 4 mA the LED appears dimmed, and at 20 mA, the LED appears bright.
Ethernet LED Indicators
On the end plate, the Ethernet socket incorporates two LEDs that indicate the Ethernet status.
• 100M—Green LED indicates presence of a 100-Mbps Ethernet connection. With a 10-Mbps connection, the
LED is off.
• LINK—Orange indicates an Ethernet connection. The LED briefly flashes with activity.
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Figure 23 Ethernet Socket
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3.3 System Design
Radio Channel Capacity
Messages sent on a cable link are much faster than on a radio channel, and the capacity of the radio channel must
be considered when designing a system. This becomes more important as the I/O size of a system increases.
The modules are designed to provide “real-time” operation or change of state (COS). When an input signal
changes, the change message is sent to the output. The system does not require continuous messages as in a
polling system. Update messages are intended to check the integrity of the system, not to provide fast operation.
Update times should be selected based on this principle. The default update time in the mappings is 10 minutes.
Itis recommended that you leave these times as-is unless particular inputs are very important and deserve a
smaller update time.
It is important that the radio paths are reliable. For large systems, we recommend a maximum radio channel
density of 300 messages per minute, including change messages and update messages. We suggest that you do
not design the system with more than 300 messages per minute because this does not take into account network
communication overheads. Note that this rate assumes that all radio paths are reliable and that the network
topology (mesh) is stable. Poor radio paths will require retransmissions and will reduce the channel density. If
there are other users on the radio channel, this peak figure will also decrease. Having remotes radios dropping
in and out of communications can also increase overall network traffic because the network needs to relearn the
communication paths each time the module comes back on line.
Dual Band Operation
The 915U-2 radio band is split into two sub-bands, 902–914 MHz (low) and 915–928 MHz (high). The radio
sub-band can be changed by selecting the hopset band on the Radio webpage of the Web-based configuration
utility (see “Radio Settings” on page 69).
In countries that utilize the full 902–928 MHz bandwidth (such as the United States and Canada) the 915U-2 uses
both sub-bands, which makes it possible to force the frequency hopping to the other band (high or low) to avoid
radio interference and to separate systems. In other countries, such as Australia and New Zealand, this option is
unavailable because of the single band.
Radio Path Reliability
Radio paths over short distances can operate reliably with a large amount of path obstruction. As the path distance
increases, the amount of obstruction that can be tolerated decreases. At the maximum reliable distance, line-ofsight is required for reliable operation. The curvature of the earth becomes more of an obstacle if the path is greater
than several kilometers (or miles), and allowance needs to be made for this. For example, the earth’s curvature over
five miles (8 km) is approx 10 feet (3m), requiring antennas to be elevated at least 13 feet (4m) to achieve line-ofsight even if the path is flat.
A radio path may act reliably in good weather, but poorly in bad weather. This is called a marginal radio path. If the
radio path is more than 20% of the maximum reliable distance, we recommend that you test the radio path before
installation (see Chapter 6 for maximum distances). Each 915U-2 module has a radio path testing feature.
See “5.2 Mesh Connectivity” for more information.
There are several ways to improve a marginal path:
• Relocate the antenna to a better position. If there is an obvious obstruction causing the problem, locating the
antenna to the side or higher will improve the path. If the radio path spans a long distance, increasing the
height of the antenna will improve the path.
• Use an antenna with a higher gain. Before doing this, make sure that the radiated power from the new antenna
remains within the regulations of your country. If you have a long coaxial cable, you can use a higher gain
antenna to cancel the losses in the coaxial cable.
• If it is not practical to improve a marginal path, you can use another module as a repeater. A repeater does
not need to be located between the two modules, although often it is. If possible, use an existing module in
the system that has a good radio path to both modules. The repeater module can be to the side of the two
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modules, or even behind one of the modules if the repeater module is installed at a high location (for example,
a tower, or mast). Repeater modules can have their own I/O and act as a normal 915U-2 module within the
system.
Design for Failures
All well designed systems consider system failure. I/O systems operating on a wire link will fail eventually, and the
same is true for a radio system. Failures can be short-term, such as interference on the radio channel or power
supply failure, or long-term, such as equipment failure.
The modules provide the following features for system failure:
• Outputs can reset if they do not receive a message within a configured time. If an output should receive an
update or change message every 10 minutes and it has not received a message within this time, some form
of failure is likely. If the output is controlling machinery, it is good design to switch off the equipment until
communications are re-established.
• The modules provide a fail-safe feature for outputs. This is a configurable time value for each output. If a
message has not been received for this output within the configured time, the output will assume a configured
value. We suggest that this reset time be a little more than twice the update time of the input. It is possible
to miss one update message because of short-term radio interference. However, if two successive update
messages are missed, long term failure is likely and the output should be reset. For example, if the input
update time is three minutes, set the output reset time to seven minutes.
• A module can provide an output that activates on communication failure to another module. This can be used
to provide an external alarm indicating that there is a system fault.
Indicating a Communications Problem
Communications problems can be indicated using fail-to-transmit alarms or fail-to-receive alarms. These alarms
can be configured using the Mapping screen within the MConfig Utility (see “Mappings” on page 42).
• Fail-to-transmit Alarm—The first method is to setup a communications indication on a register of your
choice when configuring a mapping. This can be done using an existing mapping (no need to setup a special
communications mapping). When entering a block write or gather/scatter mapping, enter a register location
for a communications failure in the Fail Register field. This register can be a local DIO (Reg 1–8) or an internal
register. Whenever the module tries to send this mapping and fails to get a response (ACK) it will turn on the
physical output if using a DIO (reg1-8) to display the alarm, or if using an internal register the value will switch
from “0” to “1.”
The communications failure indication will clear on the next successful transmission of the mapping. This
method will work with any number of repeaters in the link. However, it will only indicate a failure to transmit if
the Acknowledge checkbox is selected in the mapping. It will not provide a fail indication if the mappings are
configured as transmit only (Acknowledge checkbox is not selected).
• Fail-to-receive Alarm—The second method is to set up a communications link indication on the receiving
end using normal write mappings on the transmitting end and the fail-safe time function on the receiving end.
Setup a communications mapping from an unused digital input (can be an internal signal, such as supply
fail) and map it to the output that will indicate the communication status. The input will be updated on a time
interval (default is 10 minutes). Reconfigure a time that will provide a good indication of failure (such as 30
seconds), but not update so often that it generates too many communication check messages.
On the receiving end, configure a fail-safe block on the output configured in the above mapping. Configure
a “Fail Time Out” for a little over twice the mapping update time (for example, one minute, and 10 seconds).
Next, configure a Fail Value of “1” to turn on the output when it fails to be updated. Alternatively, you could
invert the mapping so the output is always on, and configure a Fail Value of “0” to turn off the output when not
updated.
This method will work with any number of repeaters in the link. You should use separate outputs to indicate
“Comms OK” of different remote modules.
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