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 US Patent 4,614,945 which was issued in 1986.[2] More technical detail is explained in later US 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 US Patent 7830874 as follows:[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.
| Field | Length (bits) | Default Value | Notes |
|---|---|---|---|
| Sync bit | 1 | 1 | |
| Preamble | 20 | 0xF2A60 | |
| ERT ID MS bits | 2 | This is the highest two bits of the meter serial number | |
| Reserved | 1 | ||
| Physical Tamper | 2 | ||
| ERT Type | 4 | This is the commodity type (e.g. water, gas or electric) | |
| Encoder Tamper | 2 | ||
| Consumption Data | 24 | This is the actual meter reading value | |
| ERT ID LS bits | 24 | This is the remaining bits of the meter serial number | |
| Checksum | 16 |
IDM packet
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 | |
| Version | 1 | 0x01 | |
| ERT Type | 1 | 0x17 | |
| 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 | ||
| Transmit Time Offset | 2 | ||
| Serial no. CRC | 2 | ||
| Packet CRC | 2 |
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, 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.
References
- ↑ 1.0 1.1 "Itron ERT technology". gridinsight.com. Retrieved 20 September 2012.
- ↑ "Patent US4614945 - Automatic/remote RF instrument reading method and apparatus". google.com. Retrieved 20 September 2012.
- ↑ "Patent US4799059 - Automatic/remote RF instrument monitoring system". google.com. Retrieved 20 September 2012.
- ↑ "Patent US7830874 - Versatile radio packeting for automatic meter reading systems". google.com. Retrieved 20 September 2012.
Further reading
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