Encoder receiver transmitter
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Encoder Receiver Transmitter (ERT) is a wireless meter protocol developed by Itron. The technology is used to transmit consumption 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. More technical detail is explained in later US patent 4,799,059.
Technical Details
ERT is implemented as an AM radio signal which is transmitted in the unlicensed 900-920 MHz band. The simplest message - UMSCM (standard consumption message) is a 96-bit packet which contains the meter's serial number, commodity type, consumption register, and a checksum. The packet is not encrypted but uses a frequency-hopping algorithm to avoid interference with other nearby meters.
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.