IEC 62056-21 protocol driver

Description

The IEC 62056-21 is a standard for communication with energy metering devices. It is used mainly for readouts of electrical energy meter data. In Mervis IDE version 2.2.0.X and later there is supported the substandard which communicates using modes A, B or C with OBIS (OBject Identification System) addressing code (groups A-B:C.D.E*F) over a serial line.

Platforms supported

Process stations with Mervis RT containing a serial interface. (markMX, mark100, mark150/485, mark125, mark220, mark320, IMIO105 and ICIO205)
IPLC5xx and WIN RT + converter with SoftPLC RT, client supported over a serial line

PLC interface

Serial RS485 / RS232

Restrictions and notes

In the IEC 62056-21 implementation supported in Mervis IDE 2.2.0.X and later there is no service writing into the meters This means that only establishing of the communication, baud rate setting, and value readouts are supported.
Communication modes E and F are not supported.

Communication parameters

To communicate over the IEC 62056-21 protocol, the meter address must be known (defined by the meter manufacturer, usually same as the meter serial number), parameters of the serial line (mostly default settings  9600/7/E/1) and OBIS value codes, supported by the meter.


Client communication channel

When defining the IEC 62056-21 communication channel, the following parameters shall be set:

Link protocol - for version 2.2.0.X and older only Serial is supported
Read timeout -  how long the communication driver waits for the response from the meter to come
Byte timeout-  how long the communication driver waits between the individual bytes of the response

Serial line parameters:

Port number - COM port number of the PLC, a RS232 or RS485 port.
Baud Rate- initial communication speed in bit/s, this is how the driver strats communication with the meter. If the meter does not support baud rate change, this baud rate is also used for further communication.
Data Bits - number of data bits in a byte.
Parity - select communication parity here - None, Odd, or Even.
Stop bits - number of stop bits to indicate end of the transmitted byte.

Device

Address - meter address, usually its serial number: consult the meter supplier please
Baud rate - if the meter supports baud rate change, this is the baud rate the driver tries to negotiate

Communication group

The meter is edited in the device editor. The communication group defines variables which are communicated together in a single telegram. Mervis IDE versions 2.2.0.X and older only support readout of a single group. There is no direct limitation of number of datapoints in a group.

Data point
The data points are edited in the device editor. The definition of variables is similar to this at other generic device types, see Creating of HW variables and communication channels.  

The data point must have defined following information:

Value address- OBIS code formatted A-B:C.D.E*F; most of the values is coded just C.D.E
Value order - default is 0, the first value is read; enables e.g. reading of time stamp at historical values (e.g. from a response
1.6.1(00.000*kW)(0002040400)
enter value order of 0 to read 00.000; or enter value order of 1 to read 002040400).