View source for Encoder receiver transmitter


'''Encoder receiver transmitter (ERT)''' is a [[packet radio]] protocol developed by [[Itron]] for [[automatic meter reading]].<ref name="gridinsight">{{cite web|url=http://www.gridinsight.com/community/documentation/itron-ert-technology/|title=Itron ERT technology|publisher=gridinsight.com|accessdate=20 September 2012}}</ref>  The technology is used to transmit data from [[Electricity meter|utility meters]] over a short range so a [[Public utility|utility]] vehicle can collect meter data without a worker physically inspecting each meter.

The ERT protocol was first described in {{US Patent|4614945}}.<ref> {{cite patent | country = US | number = 4614945 | status = patent | title = Automatic/remote RF instrument reading method and apparatus. | gdate = 1986-09-30 | fdate = 1985-02-20 | inventor = Robert E. Brunius, Jon R. Nelson | assign1 = Diversified Energies, Inc.}} </ref>  More technical detail is explained in later {{US patent|4799059}}.<ref>{{ cite patent | country = US | number = 4799059 | status = patent | title = Automatic/remote rf instrument monitoring system. | gdate = 1989-01-17 | fdate = 1986-03-14 | inventor = Mervin L. Grindahl, Quentin S. Denzene | assign1 = Enscan, Inc. }}</ref>

== Technical details ==

ERT is an [[On-off keying|OOK]] modulated radio signal which is transmitted in the unlicensed [[33-centimeter_band|900-920 MHz band]].<ref name="gridinsight" /> The message is transmitted in the clear and uses [[Manchester encoding]]. The protocol uses [[frequency-hopping]], a [[multiple access method]] to avoid interference with other nearby meters. SCM and IDM packet formats are described in {{US Patent|7830874}}<ref>{{cite patent | country = US | number = 7830874 | status = patent | title = Versatile radio packeting for automatic meter reading systems. | gdate = 2010-11-09 | fdate = 2007-02-05 | inventor = Mark Cornwall, Matt Johnson, John Buffington | assign1 = Itron, Inc.}} </ref>

=== SCM packet ===

SCM messages are 12 bytes.  Each message contains single, cumulative meter reading value along with the meter serial number, commodity type and checksum and tamper flags.  

{| class="wikitable"
|-
! Field !! Length (bits) !! Default Value !! Notes
|-
| Sync bit         || 1  || 1       ||
|-
| Preamble         || 20 || 0xF2A60 ||
|-
| ERT ID MS bits   || 2  ||         || highest two bits of meter serial number
|-
| Reserved         || 1  ||         ||
|-
| Physical Tamper<ref name="CENTRON® Meter Technical Reference Guide - CS1R Tamper Detection (Page 32)">{{cite web|title=CENTRON® Meter Technical Reference Guide - CS1R Tamper Detection (Page 32)|url=http://www.smartmetereducationnetwork.com/uploads/how-to-tell-if-I-have-a-ami-dte-smart-advanced-meter/Itron%20Centron%20Meter%20Technical%20Guide1482163-201106090057150.pdf|accessdate=6 July 2017}}</ref>  || 2  ||         ||
|-
| ERT Type         || 4  ||         || commodity type:  water, gas or electric
|-
| Encoder Tamper   || 2  ||         ||
|-
| Consumption Data || 24 ||         || meter reading value
|-
| ERT ID LS bits   || 24 ||         || lower bits of meter serial number
|-
| Checksum         || 16 ||         || A [[BCH code]] with generator polynomial: <math>p(x) = x^{16} + x^{14} + x^{13} + x^{11} + x^{10} + x^9 + x^8 + x^6 + x^5 + x + 1</math> 
|}

=== IDM packet ===

IDM messages are 92 bytes and contain [[Net_metering#Time_of_use_metering|time of use]] consumption data.

{| class="wikitable"
|-
! Field !! Length (bytes) !! Value !! Notes
|-
| Training Sync                     || 2  || 0x5555 || 
|-
| Frame Sync                        || 2  || 0x16A3 || 
|-
| Packet Type                       || 1  || 0x1C   || 
|-
| Packet Length                     || 2  || 0x5CC6 || Number of remaining bytes (MSB) and Hamming code of first byte (LSB)
|-
| Version                           || 1  || 0x01   || 
|-
| ERT Type                          || 1  || 0x17   || LSB nibble is equivalent to SCM's ERT Type.
|-
| ERT Serial Number                 || 4  ||        ||
|-
| Consumption Interval Count        || 1  ||        || 
|-
| Module Programming State          || 1  ||        || 
|-
| Tamper Count                      || 6  ||        ||
|-
| Async Count                       || 2  ||        ||
|-
| Power Outage Flags                || 6  ||        || 
|-
| Last Consumption Count            || 4  ||        ||
|-
| Differential Consumption Intervals || 53 ||        || 47 intervals of 9-bit integers
|-
| Transmit Time Offset              || 2  ||        ||
|-
| Serial no. CRC                    || 2  ||        || CRC-16-CCITT of ERT Serial Number
|-
| Packet CRC                        || 2  ||        || CRC-16-CCITT of packet starting at Packet Type
|}

Later patents describe further variations of packets with variable length.

== Implementations ==

Several vendors (besides Itron) have implemented ERT receivers (usually in order to read consumption data from Itron meters.)  Notably, [[Digi International|Digi]] sells an ERT gateway,<ref>{{Cite web |url=http://www.digi.com/products/wireless-routers-gateways/gateways/ert-ethernet |title=digi.com, ERT Ethernet |access-date=2012-09-13 |archive-date=2012-11-05 |archive-url=https://web.archive.org/web/20121105121411/http://www.digi.com/products/wireless-routers-gateways/gateways/ert-ethernet |url-status=dead }}</ref> and Grid Insight sells a PC-based product called the [http://www.gridinsight.com/products/amrusb-1/ AMRUSB-1].

It should be possible to decode ERT signals using general purpose UHF packet radios such as the [http://www.ti.com/product/cc1101 Texas Instruments CC1101] or [http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MC33696&webpageId=M10PHKGTk Freescale MC33696]. A [[software-defined radio]] receiver has been implemented using inexpensive hardware: [https://github.com/bemasher/rtlamr RTLAMR], and the [https://github.com/merbanan/rtl_433/issues/1378 rtl_433] software will decode SCM messages. [[Kismet (software)]] has an [https://www.kismetwireless.net/docs/readme/datasources_sdr_rtlamr/ rtlamr data source] {{Webarchive|url=https://web.archive.org/web/20200919052207/https://kismetwireless.net/docs/readme/datasources_sdr_rtlamr/ |date=2020-09-19 }}.

==References==
{{reflist}}

== Further reading ==
{{refbegin}}
* [http://www.gridinsight.com/community/documentation/itron-ert-technology/ Grid Insight - Itron ERT technology]
* [http://davestech.blogspot.com/2008/02/itron-remote-read-electric-meter.html Dave's Tech Blog - Itron Remote Read Electric Meter] 
* [https://github.com/bemasher/rtlamr RTLAMR - An rtl-sdr receiver for the ERT protocol]
{{refend}}

{{Packet radio}}

[[Category:Packet radio]]
[[Category:Smart grid]]