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IEC62056 is a set of standards for Electricity metering – Data exchange for meter reading, tariff and load control by International Electrotechnical Commission. The IEC62056 standards are the International Standard versions of the DLMS/COSEM specification. DLMS or Device Language Message Specification (originally Distribution Line Message Specification), is the suite of standards developed and maintained by the DLMS User Association and has been co-opted by the IEC TC13 WG14 into the IEC 62056 series of standards. The DLMS User Association has established a D Type liaison with IEC TC13 WG14 responsible for international standards for meter data exchange and establishing the IEC 62056 series. In this role, the DLMS UA provides maintenance, registration and conformance testing services for IEC 62056 DLMS/COSEM. COSEM or Companion Specification for Energy Metering, includes a set of specifications that defines the Transport and Application Layers of the DLMS protocol. The DLMS User Association defines the protocols into a set of four specification documents namely Green Book, Yellow Book, Blue Book and White Book. The Blue book describes the COSEM meter object model and the object identification system, the Green book describes the Architecture and Protocols, the Yellow book treats all the questions concerning conformance testing, the White book contains the glossary of terms. If a product conforms to DLMS Yellow Book then it automatically implies conformance to IEC62056 set of standards.
The IEC TC13 WG 14 groups the DLMS specifications under the common heading: "Electricity metering - Data exchange for meter reading, tariff and load control". DLMS protocol suite is not specific to electricity metering.
In DLMS/COSEM, all the data in electronic meters and devices are represented by means of attribute values. Any real world thing can be described by attributes; methods allow operations to be performed on the attributes. Attributes and methods constitute an object. The first attribute in any object is the logical_name. It is one part of the identification of the object. Objects that share common characteristics are generalized as an interface class with a class_id. Instantiations of an interface class are called COSEM objects. IEC 62056-62 defines 19 interface classes for COSEM object model.
IEC 61107 or currently IEC 62056-21, was an international standard for a computer protocol to read utility meters. It is designed to operate over any media, including the Internet. A meter sends ASCII (in modes A..D) or HDLC (mode E) data to a nearby hand-held unit (HHU) using a serial port. The physical media are usually either modulated light, sent with an LED and received with a photodiode, or a pair of wires, usually modulated by a 20mA current loop. The protocol is usually half-duplex.
The following exchange usually takes a second or two, and occurs when a person from the utility company presses a meter-reading gun against a transparent faceplate on the meter, or plugs into the metering bus at the mailbox of an apartment building.
The general protocol consists of a "sign on" sequence, in which a handheld unit identifies itself to the metering unit. During sign-on, the handheld unit addresses a particular meter by number. The meter and hand-held unit negotiate various parameters such as the maximum frame length during transmission and reception, whether multiple frames can be sent without acknowledging individual frames (Windowing), the fastest communication rate that they can both manage (only in case of mode E switching to HDLC) etc. Next the meter informs the hand held unit about the various parameters that are available with it in various security settings viz. the 'no security logical group', ' the low security logical groups' and ' the high security logical groups'.
If the parameter required is in no security group, just a get.request will provide the HHU with the desired response. If the parameter required is in low security group, a password authentication of the HHU is required before information can be read.
In case of high security parameters,the meter challenges the hand held unit with a cryptographic password. The hand held unit must return an encrypted password. If the password exchange is ok, the meter accepts the hand held unit- it is "signed on."
After signing on, the hand held unit generally reads a meter description. This describes some registers that describe the current count of metered units (i.e. kilowatt hours, megajoules, liters of gas or water) and the metering unit's reliability (is it still operating ok?). Occasionally a manufacturer will invent a new quantity to measure, and in this case, a new or different data type will appear in the meter definition. Most metering units have special modes for calibration and resetting meter registers. These modes are usually protected by anti-tampering features such as switches that sense if the meter enclosure has been opened.
The HHU may also be given limited rights to set or reset certain parameters in the meter.
The hand held unit then sends a sign-off message, and the meter automatically signs off after a previously negotiated time interval after the last message, if no sign-off message is sent.
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