Battery Comparison for GPS Tracking Device

Overview

Many different types of batteries may be used with Raveon’s M7 series of GPS transponders.  This Technical Brief describes how well some common battery types will work with the M7 radios. 

Actual battery life will vary based upon how often the M7 GPS transponder transmits, but the data in this Technical Brief may be used to predict the battery life of most configurations.

Test Setup

For the tests in this brief, a UHF GPS transponder, model RV-M7-UC-GX was configured in GPS mode 2 to transmit its position every 10 seconds.  In GPS mode 2, the radio’s receiver is on 100% of the time, and the current draw of the M7 was an average of 90mA.  The peak current draw was 2.1 amps for 68mS each time the M7 transmitted its GPS position.

Summary Data

Brand Type Recharge-able mAh Life
(RX on)		 Life
(RX off)
Duracell Alkaline NO 1600 18 hours 36
Energizer Lithium NO 2500 28 hours 56
Lenmar NiMH Yes 1500 17 hours 34

Duracell Alkaline

These batteries are the common Duracel batteries found at most department stores.

Test Result Summary

Initial Voltage:                                   12.57 volts

Voltage at ½ discharge:                   10.2 volts

Usable life (hours)                           18 hours

Voltage drop when transmitting       2.4V  (1.1 ohm resistance)

Approximate mAh capacity             1600mAh

Discharge Curve

Transmit Transient

The plot below shows the dip in voltage as the transmitter turns on and off.


Summary

The Duracell is an OK battery to power the M7 transponder.  But its high internal resistance will reduce the RF power output after the first few hours of operation.  The DC to the radio should stay above 9V while transmitting for full power, above 8V for 3-4 watts.


Energizer Lithium

These batteries are the common Energizer Lithium batteries for cameras and digital electronics found at many department stores.

Test Result Summary

Initial Voltage:                                      12.1 volts  (14V for a few moments)

Voltage at ½ discharge:                      12.0 volts

Usable life (hours)                              28 hours

Voltage drop when transmitting          3.5V  (1.6 ohm resistance)

Approximate mAh capacity                2520mAh

Discharge Curve

Transmit Transient

The plot below shows the dip in voltage as the transmitter turns on and off.

Summary

Even though the internal resistance of the cell is higher than the alkaline, the Energizer Lithium is a good battery to power the M7 transponder.  Its high internal resistance will not reduce the RF power output because its voltage is fundamentally fairly high.  The DC to the radio should stay above 9V while transmitting for full power, above 8V for 3-4 watts, so the 3.5V dip means the radio will have full power at 12.5V, and 3-4 watts out at 11V DC at the battery pack.


Lenmar R2G NiMH pack, 2150mAh cells

These batteries are Nickel Metal Hydride rechargeable batteries.  They were fully charged before the test.

Test Result Summary

Initial Voltage:                                      11.0 volts

Voltage at ½ discharge:                      10.3volts

Usable life (hours)                              17 hours

Voltage drop when transmitting          2.0V  (.95 ohm resistance)

Approximate mAh capacity                1500mAh

Discharge Curve

Summary

These batteries should be a good power source for the M7 GX transponder.

The internal cell resistance is low, but the voltage is also low. The RF power output stayed at full power for most of the life of the battery, dropping to about 4 watts at the end of the battery life.  The double dip at end of live was due to the fact the radio keep working down to 6 volts (albeit with almost no RF output because the RF PA is off), and the batteries keep putting our very low voltage for another couple hours.

This article describes batteries that may be used for an AVL system, but Raveon’s UHF Radio Modems may also be battery powered, so this article can be applied to these radios also.

Raveon Technologies Corporation

990 Park Center Drive, C

Vista, CA 92081

sales@raveontech.com

760-727-8004

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TDMA Transmission Overview

TDMA, or Time-Division-Multiple-Access is a very effective way of allowing a lot of radios to share one radio channel.  Used extensively in GSM cellular and APCO public-safety systems, TDMA excels at allowing quick and reliable access to radio channels.  Raveon’s M7 series of GPS tracking radios use TDMA to send GPS position information, status, and data. It allows 2-10 times more radios to share a radio channel than conventional carrier-sense methods.  This allows 2-10 times more tracking radios on one channel, as compared to radios that do not have TDMA capability.

The following diagram illustrates how it works.

When a RV-M7 GX wants to report its position and status, it waits until its assigned time-slot, and then transmits its data.  By default, TDMA time slot positions are assigned by unit-ID, so RV-M7 GX with ID 1 uses the first slot, and ID 2 uses the second slot, and so on.

A TDMA “Frame” time is the time it takes all units to transmit once.  This is configured with the TDMATIME xx command.  The factory default is 10 seconds, so every 10 seconds, each RV-M7 GX may transmit.  The TDMA frame must be set long enough for all units to transmit.  For example, if you have 50 RV-M7s, and use 200mS TDMA slots, then the TDMATIME should be set to 10 seconds.  The simplest way to set it the TDMATIME is to make it equal to the TXRATE, the rate you wish to report position

The duration of a TDMA time slot is programmed into the RV-M7 GX with the SLOTTIME command. If SLOTTIME is set to 200 milliseconds (factory default), then every 10 seconds, the RV-M7 will have a 200mS window to report its position in.

All TDMA frames are synchronized automatically in all RV-M7 GX Transponders to the top of the minute.  Slot 0, frame 0 is at the top of each minute. They use the internal GPS receiver to determine the current time, and calculate when their are supposed to transmit their position and status information.

A unit may be allocated additional time slots.  The SLOTQTY command sets the number of slots each unit receives.  It is normally set to 1.

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Criterion International

After searching for and testing several UHF radios to upgrade a municipal water department’s wireless SCADA system, RAVEON’s Fireline modem was chosen as the best performance/value solution. The simple and versatile ability of the Fireline to be quickly configured easily beat out the other radios on the market. Thirty + radios have been installed and in service continuously operating with no problems for over two years.

Regards.

Chris Carda

President

Criterion Industrial

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Identifying Digital Input States in a $PRAVE message

The $PRAVE message has the status of each input as represented by a single digit hexadecimal number in field 12. For example, the the $PRAVE message below, the last 3 represents the digital inputs from transponder 0001.

$PRAVE,0001,0001,3308.9051,-11713.1164,195348,1,10,168,31,13.3,3,-83,0,0,,*66

In this example field 12 has value 3.  The field 12 value is the hexadecimal binary representation of the bits.  Refer to the following table:

IN 2
(TXD)

IN 1
(RTS)

IN 0
(DTR)

Hexadecimal Representation

0

0

0

0

0

0

1

1

0

1

0

2

0

1

1

3

1

0

0

4

1

0

1

5

1

1

0

6

1

1

1

7

The stock RV-M7 GX has up to 3 digital inputs, using the input pins of the RS-232 serial port.  An open circuit or ground is a 0, and if they are connected to a positive voltage greater than 3V, they are a digital 1. If all 3 pins are allowed to float (nothing connected – same as ground) the value should be 0.  If positive voltage is applied to a pin the pin value will be 1.  The field 12 value will be 1 or 2 or 4, depending on which pin had the voltage applied.

RS-232 Pin

Function

4 – DTR

Input 0

7 – RTS

Input 1

3 – TXD

Input 2

5 – Ground

GND

Connect to vehicle chassis or other ground point.

Note that the weatherproofed (-WX) model has less RS-232 pins and only 2 digital inputs.  Inputs 1 and 2 are valid, but input 0 is indeterminate (state can float).

In the RavTrack PC software it is easy to not monitor this missing pin, so any change of state or change of value of this pin would not matter to the software.  Simply configure this input as unused.

1aa

RS-232 Pin

Function

4 – RTS

Input 1

3 – TXD

Input 2

5 – Ground

GND

Connect to vehicle chassis or other ground point.

On the M7 series of transponders, if an input is left floating/unconnected, the transponder will read it as a digital 0 (low), and report it this way.

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Dual Bandwidth Capable. Wide and narrow-band explained.

Raveon Technologies data radio modems can have either wide band IF filters, which are used on 25kHz or 30kHz spaced channels, or narrow-band IF filters, which are used on 12.5kHz spaced channels. 

As the picture above illustrates, it is possible to have twice the number of radio channels, when everyone uses 12.5kHz narrow band radios. 

So, why is this important?  There are two big reasons:

1. Your radio system must have receivers with the proper IF bandwidths to perform properly and meet regulatory specifications.

2. In the USA, the government has mandated that all all Part 90 Business, Educational, Industrial, Public Safety, and State and Local Government VHF (150-174 MHz) and UHF (421-512 MHz) private PLMR (Private Land Mobile Radio) system licensees convert to narrow-band operation by 2013. 

Raveon Technologies is here to help you migrate your system to narrow-band technology.  Our M7 series of radios supports both wide and narrow-band operation, and our new VHF M7 supports both in the same radio. 

  Wide Band Narrow Band
Channel Spacing 25kHz or 30kHz 12.5kHz
Actual receiver IF filter bandwidth 15kHz 7.5kHz
Maximum data rate with  standard modulation 9600 baud 4800 baud
Maximum data rate with  4-level modulation 19200 baud 9600 baud

Because the IF bandwidth in a narrow-band radio must be 1/2 the bandwidth of a wide-band radio, the over-the-air data rate will be 1/2 also.   And unlike other brand radio modems that loose sensitivity when operating on narrow channels, the M7 series of radios has the same high receiver sensitivity on both wide and narrow-band channels.

Raveon’s UHF data radio modem, the RV-M7-U, may be ordered as either a wide-band or a narrow-band radio.  It is configured at the factory for one or the other.

Raveon’s new VHF data radio modem, the RV-M7-V, is dual-bandwidth capable and user-configurable for either  wide-band or narrow-band .  It has 6-channel memories in it, and each channel may be set to either wide or narrow band. 

A narrow-band radio can usually communicate with a wide-band radio, if they are set to the same over-the-air data rate as the narrow-band radio.  But because the wide-band radio has overly-wide IF filters for the signal, the communication range will not be as good as two narrow-band or two wide-band radios communicating.

A wide-band radio will not communicate with a narrow-band radio.  In the voice world it might work, but in the data world, the narrow IF filter in a narrow-band radio will filter off the wide-band signal, and no reliable communications will be possible.  

So, if you are migrating your wire data system, SCADA system, or telemetry system from wide to narrow-band, you must make sure all radios in the system have the same IF bandwidths and over-the-air data rates.  Please contact Raveon Technologies for either wide-band or narrow-band data radio modems.

Links to FCC Documents regarding the narrow-band migration:

< http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-04-292A1.doc>

< http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-04-292A1.pdf>

< http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-04-292A1.txt>

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GPS Position Accuracy

The accuracy of a position determined by using a GPS receiver is limited by the accuracy of the GPS signal itself.  The US government controls the precision of the GPS signals sent from the GPS satellite constellation.   It varies from day to day, and the following graph shows historically, how precise the GPS position information is.

gpsaccuracyRaveon’s GPS transponders utilize the WAAS signal, so accuracies of 2-3 meters are possible.  Laboratory tests with the M7 series of GPS transponders confirm that this is possible, but typically, the accuracy is in the 3-5 meter range.

If the GPS transponder is located indoors, or if there are very tall buildings near the transponder, the accuracy will be degraded due to multipath of the GPS signal.

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Repeating For Extended Range/Serial Port

For longer communication ranges, high RF noise environments or obstructed line of sight applications it may be necessary to use a repeater to establish a reliable communications link. 

Incorporated in the M7 radio is a built in store-and-forward repeater function.  The repeater function works only in the Packet Mode, and will not repeat streaming messages.   A repeater can extend the range of a system by 2-20 times, depending upon how high-up above the average terrain the repeater is mounted. 

The following table shows a typical repeater system configuration in packetized mode. 

AT
Command		 Radio Modem
#1		 Repeater
Modem		 Remote
Modem #2		 Description

ATMY

 1234 1235 1236 Individual unit address for this particular modem.
ATDT 1236 1234 (not important) 1234 Destination address to send data to.
ATMK FFFF FFFF FFFF Address mask. FFFF means all bits are used.
ATXR 0 1 0 Enable/Disable repeater function. Only enable it on the particular radio that will be the repeater.
ATX1 N/A 1234 FFF0 1234 FFF0 N/A In the repeater, set the addresses this unit will store-and-repeat to/from.  By setting the repeater address mask to FFF0, this repeater will repeat any data packet with an address having 123 in the first 3 digits.  (1230 through 123F). 

 

 

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Configuring the M7 Data Radio for SCADA

For SCADA applications, configure the M7 radio as per the user manual.  In most cases, the factory defaults are the best place to start.  Set the frequency using the ATFX xxx.xxxx command to your system frequency.  Then, based upon your system, configure the following parameters: 

ATBC Enable/disable Busy Channel Lockout.  Normally, the radio modem does not check for a busy channel. If you are running a large system, with asynchronous data on the radio channel, you should enable BCL so the modem does not transmit while another device is on the air.  For polled systems, do not enable this feature.
ATCH Enable/Disable hardware flow control.  By default this is off and will work fine in most applications.   Enabling hardware flow control will ensure that the modem buffers data and only outputs it to the user’s device or RTU when the device is ready to receive it. 
ATFX Used to set the radio frequency of the modem.
   
ATR2 The over-the-air data rate.  For long-range, set it at 4800bps.  For lowest latency, set it at 8000bps or 9600bps.  ATR2 3 for 4800baud.  ATR2 4 for 8000 baud.
ATR3 Serial port time out.  This is the amount of idle-time (in mS) before the FireLine will begin to transmit a packet of data.  When no data comes into the modem for this amount of time, the FireLine will transmit the contents of its data buffer over the air.  The factory default setting is 20mS.  For SCADA systems using MODBU, 2mS is suggested  (ATR3 5).
ATMY The M7 series modems have 16 bit IDs.  Most SCADA systems work in a broadcast configuration, where all modems hear all other modems.  Be sure to set the unit ID in each modem to a unique ID number, so that the duplicate packet filtering works properly. 
ATMK To turn off address filtering, and allow all units to receive data from all other units, set the net mask to all zeros  (ATMK 0000). 

 For example, with a modem configured for 8000 baud over the air,  9600baud serial ports, 2mS time-out, the total time for a MODBUS “Read Module Name” command ($01M) command to receive the response back is 150mS in Packet Mode.

A DF1 polling system with M5 Fireline or M7 modems configured for 8000 baud over the air,  9600baud serial ports, 2mS time-out, and Streaming Mode will allow RTU’s to be polled and responses returned in about 80mS round-trip.

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Going Wireless

Wired Connection

The telemetry industry has standardized on a number of different protocols to use in these types of applications. Most protocols were based upon the assumption that the cabling between the monitoring station and the RTU/PLC is an RS-232 or RS-422 serial link.  The protocols commonly used on these serial links are MODBUS-RTU, MODBUS-ASCII, DF1, DNP-3, and IEC870. All of these protocols can operate using hard-wired connections.  Because the Raveon Radios  mimic a hard-wire (data-in equals data-out), in most cases, the protocols will also work using a wireless modem. 

M5 and M7 Modems with Modbus

Raveon  radio modems support Modbus-ASCII networks with no special configuration.  Modbus-ASCII was designed specifically to work well over wired and wireless modems, and uses 7-bit data.  All Raveon  modems support 7-bit data. 

Modbus-RTU uses 8-bit data. Some modems and older systems do not work with 8-bit data, but Raveon’s  wireless modems support both 7 bit and 8 bit data.  There are some considerations when using radio modems with Modbus-RTU:

Latency    The difference between M5 and M7 series wireless modems and a multi-drop wired network is that the wireless modems introduce some additional latency (delay) into the system.  Most Modbus-RTU applications can tolerate this latency, but some cannot.  If your Modbus application does not tolerate latency, then use Modbus –ASCII.  Modbus-ASCII is compatible with Raveon  radio modems. The following table shows Latency vs. Over-the-air bit rate for Raveon narrow band radio modems in the packetized mode. 

Bit Rate ATR2 Setting Latency (Seconds)
800 (2L) 0 0.8-0.9
1200 (2L) 1 0.5-0.6
2400 (2L) 2 0.3-0.4
4800 (2L) 3 0.2-0.3
5142 (2L) 7 0.2-0.3
8000 (4L) 4 0.2-0.3

Time-Outs    Some versions of the Modbus protocol have short response timeout requirements that may not be compatible with radio modem latencies.   Modbus-RTU is compatible with the normal FireLine latencies but does have inter-character delay requirements that must be met. Raveon modems have programmable time-outs to facilitate the control of latency.

Modem IDs       The M5 and M7 series modems have 16 bit IDs.  Most SCADA systems work in a broadcast configuration, where all modems hear all other modems.  To do this, set the net mask to all zeors  (ATMK 0000).  Be sure to set each unit ID in each modem to a unique ID number, so that the duplicate packet filtering works properly.  All Raveon modems filter out duplicate packets, so that operation with repeaters does not cause duplicate packets being received.

For lowest latency, Raveon’s unique “Streaming” mode of operation provides data transfer with latency only slightly higher than wired configurations.  No other radio modem on the market offers both error-free packetized operation AND Streaming data operation.

M5 and M7 Modems with DF1

The DF1 protocol works well with the Raveon radio modems as long as the over-the-air data rate is set to 4800 bps or higher.  The stock-configuration of the radio modem works with the Rockwell  “DF1 Polling Driver”. 

To reduce latency in the polling, it is suggested that certain stock-parameters in the FireLine be a adjusted to values more optimized for use in a polled environment.  The following is a list of parameters in the radio that may be adjusted to reduce latency when using the DF1 protocol. 

1)   Reduce the serial-port time-out value down to 2mS (ATR3 2)

2)   Set the serial port to 19200bps  (ATBD 4)

3)   Configure the Over the air data rate to 8000bps (ATR2 4)  This will reduce the communication range, so only do this if the link-margin on the system is adequate.

Use the “Streaming Mode” of communications.  (ATMT 2)   The factory default is the “Packet Mode”, where all data is error checked and sent in packets.  The Streaming mode initiates transmissions faster, and sends characters over-the-air as they stream in, but does not check for errors.  DF1 is tolerant of noise and over-the-air bit errors, and in most cases works well in streaming mode.  In mission-critical or safety situations, packet mode would be more appropriate as it’s data transmission is more deterministic.

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Raveon’s Features for SCADA Applications

Following is a list of Raveon’s data radio modems features that make them an ideal choice for SCADA and wireless telemetry.

High-speed over the air data rates. 19200bps in 25kHz channel, 9600bps in 12.5kHz.

Remote status monitoring including DC voltage, packet error statistics, modem “up time”, and receiver signal strength. 

Easy to use. Plug-in, Turn-on, and GO.  Transmit data in = Receive data out.

Lowest current draw in industry.  The M5 wireless modems draw less than 110mA when fully operational, and the M7s less than 90mA. 

Wide input voltage with high-efficiency switching voltage regulator.

Packetized AND Streaming Data.  Integrated Packetized data protocol with error correction and built-in Streaming Real-Time operation. User selectable.

ARQ error correction and retransmission capability.  Totally transparent to the application.

Capable of store-and-forward repeating operation.

Small size.   Extruded aluminum enclosure is small, and very rugged.

16 bit addressing for up to 65,525 different unique device addresses per channel.  Radio channels may be shared with no interference between users.

Supports group and broadcast transmissions.  Network mask allows groups of any size.

Easily to configure.  Raveon  modems are configured using “AT” commands through the modem’s serial port.  Raveon also provides free of charge, Radio Manager, a easy-to-use PC program with a graphical user interface to configure and program all Raveon Radios.

RS-232, RS422, or RS485 serial port.  Programmable serial baud rates up to 57600 make the FireLine M5 and the M7 radio modem compatible with most every PLC, PC, and HMI device made.  

Programmable over-the-air data rates.   With the M5 and M7 radios, you  can choose how your system will work.  Set the OTA data slower for extended communication range, or set it fast for lowest latency.  Your choice.

SkyLine compatibility mode for use in older Sonik radio systems.

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