Encoder receiver transmitter

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Encoder receiver transmitter (ERT) is a packet radio protocol developed by Itron for automatic meter reading. [1] The technology is used to transmit data from utility meters over a short range so a utility vehicle can collect meter data without a worker physically inspecting each meter.

Contents

The ERT protocol was first described in U.S. patent 4,614,945 . [2] More technical detail is explained in later U.S. patent 4,799,059 . [3]

Technical details

ERT is an OOK modulated radio signal which is transmitted in the unlicensed 900-920 MHz band. [1] 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 U.S. patent 7,830,874 [4]

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.

FieldLength (bits)Default ValueNotes
Sync bit11
Preamble200xF2A60
ERT ID MS bits2highest two bits of meter serial number
Reserved1
Physical Tamper [5] 2
ERT Type4commodity type: water, gas or electric
Encoder Tamper2
Consumption Data24meter reading value
ERT ID LS bits24lower bits of meter serial number
Checksum16A BCH code with generator polynomial:

IDM packet

IDM messages are 92 bytes and contain time of use consumption data.

FieldLength (bytes)ValueNotes
Training Sync20x5555
Frame Sync20x16A3
Packet Type10x1C
Packet Length20x5CC6Number of remaining bytes (MSB) and Hamming code of first byte (LSB)
Version10x01
ERT Type10x17LSB nibble is equivalent to SCM's ERT Type.
ERT Serial Number4
Consumption Interval Count1
Module Programming State1
Tamper Count6
Async Count2
Power Outage Flags6
Last Consumption Count4
Differential Consumption Intervals5347 intervals of 9-bit integers
Transmit Time Offset2
Serial no. CRC2CRC-16-CCITT of ERT Serial Number
Packet CRC2CRC-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 sells an ERT gateway, [6] and Grid Insight sells a PC-based product called the AMRUSB-1.

It should be possible to decode ERT signals using general purpose UHF packet radios such as the Texas Instruments CC1101 or Freescale MC33696. A software-defined radio receiver has been implemented using inexpensive hardware: RTLAMR, and the rtl_433 software will decode SCM messages. Kismet (software) has an rtlamr data source Archived 2020-09-19 at the Wayback Machine .

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References

  1. 1 2 "Itron ERT technology". gridinsight.com. Retrieved 20 September 2012.
  2. USpatent 4614945,Robert E. Brunius, Jon R. Nelson,"Automatic/remote RF instrument reading method and apparatus.",issued 1986-09-30, assigned to Diversified Energies, Inc.
  3. USpatent 4799059,Mervin L. Grindahl, Quentin S. Denzene,"Automatic/remote rf instrument monitoring system.",issued 1989-01-17, assigned to Enscan, Inc.
  4. USpatent 7830874,Mark Cornwall, Matt Johnson, John Buffington,"Versatile radio packeting for automatic meter reading systems.",issued 2010-11-09, assigned to Itron, Inc.
  5. "CENTRON® Meter Technical Reference Guide - CS1R Tamper Detection (Page 32)" (PDF). Retrieved 6 July 2017.
  6. "digi.com, ERT Ethernet". Archived from the original on 2012-11-05. Retrieved 2012-09-13.

Further reading