Encoder receiver transmitter
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.
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
[edit]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
[edit]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.
| 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[5] | 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: |
IDM packet
[edit]IDM messages are 92 bytes and contain time of use consumption data.
| 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
[edit]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.
References
[edit]- ^ a b "Itron ERT technology". gridinsight.com. Retrieved 20 September 2012.
- ^ US patent 4614945, Robert E. Brunius, Jon R. Nelson, "Automatic/remote RF instrument reading method and apparatus.", issued 1986-09-30, assigned to Diversified Energies, Inc.
- ^ US patent 4799059, Mervin L. Grindahl, Quentin S. Denzene, "Automatic/remote rf instrument monitoring system.", issued 1989-01-17, assigned to Enscan, Inc.
- ^ US patent 7830874, Mark Cornwall, Matt Johnson, John Buffington, "Versatile radio packeting for automatic meter reading systems.", issued 2010-11-09, assigned to Itron, Inc.
- ^ "CENTRON® Meter Technical Reference Guide - CS1R Tamper Detection (Page 32)" (PDF). Retrieved 6 July 2017.
- ^ "digi.com, ERT Ethernet". Archived from the original on 2012-11-05. Retrieved 2012-09-13.