This part of GB/T 31983 specifies low voltage narrowband power line communication (PLC) physical layer protocol specifications based on Orthogonal Frequency Division Multiplexing (OFDM) technology, including physical layer protocol data unit format (PPDU), channel coding, interleaving, OFDM. Modulation, physical layer signal frame generation and continuous transmission mode and power frequency synchronization zero-crossing time slot transmission mode. This section applies to data transmission and communication in the 3 kHz to 500 kHz band through indoor or outdoor low voltage AC distribution lines or DC transmission lines. Based on the physical layer protocol specification in this part, a complete PLC system composed of multiple communication nodes established on the low-voltage power distribution network also includes a data link layer (DLL, which is controlled by the medium access control sub-layer MAC and logical link). Control sub-layer LLC composition), and the application layer related to the specific application scenario. Typical low-voltage narrow-band power line communication applications include intelligent meter reading (AMR), AMI/AMM, home intelligence control, street lighting control, intelligent building, four-set copying, and other applications of Smart Grid, such as: Electric vehicle charging control, etc. This section is also applicable to medium voltage power line communications, as well as long-distance power line communications in urban and rural areas.

This part of GB/T 778 deals with terminology, technical characteristics, metrological characteristics and pressure loss. It applies to water meters of various metrological classes (see clause 5) which can withstand permanent flow-rates from 0.6 to 4 000 m3/h, maximum admissible working pressures (MAP) equal to or greater than 1 MPa and a maximum admissible temperature (MAT) of 30 ℃. The recommendations of this part of GB/T 778 only apply to volumetric water meters and velocity water meters. Legal requirements take precedence over the recommendations of this part of GB/T 778.

This National Standard specifies criteria for the selection of water meters, associated fittings, installation, special requirements for some meters and the first operation of new or repaired meters to ensure accurate constant measurement and reliable reading of the meter. The field of application is as defined in clause 1 of GB/T 778.1. This National Standard deals only with singlemeter installations. Particular requirements dealing with installations including several meters are specified in Annex A (normative) of this part. Where legal requirements exist, they will in all cases take precedence over the specifications in this National Standard.