Measurements & Commands
Measurements and commands are summarily called Communication Objects (COs).
Attributes
Overview:
| Attribute | Datatype | Measurement | Command | Category |
|---|---|---|---|---|
| name | string | yes | yes | mandatory |
| description | string | yes | yes | optional |
| datatype | enum | yes | yes | mandatory |
| raw datatype | string | yes | yes | optional |
| connector name | string | yes | yes | optional |
| address | string | yes | yes | optional |
| value | bool, string, number | yes | yes | runtime |
| quality | number | yes | no | runtime |
| timestamp | timestamp | yes | yes | runtime |
| engineering unit | string | yes | yes | optional |
| engineering range | tuple | yes | yes | optional |
| raw range | tuple | yes | yes | optional |
| deadband | string | yes | no | optional |
| initial value | bool, string, number | no | yes | optional |
| archivation mode | enum | yes | yes | optional |
| archivation period | number | yes | yes | optional |
| archivation value deadband | number,string | yes | yes | optional |
| archivation time deadband | number | yes | yes | optional |
| provider addresses | map | yes | yes | optional |
Name
[mandatory]
Uniquely identifies measurement/command. Must conform to C-language symbol name requirements (can contain only letters, digits and the underscore, can't start with digit) and must be unique among all COs.
Description
[optional]
Free text description of CO purpose.
Datatype
[mandatory]
Datatype used to store measured value expressed in engineering units. Supported datatypes:
| Datatype | Code | Storage size [B] | Range |
|---|---|---|---|
| binary | b | 1 | {0, 1} |
| quaternary | q | 1 | {0, 1, 2, 3} |
| integer | i | 4 | < -2^31, 2^31-1 > |
| long | l | 8 | < -2^63, 2^63-1 > |
| single-precision float | f | 4 | see IEEE-754 standard |
| double-precision float | d | 8 | see IEEE-754 standard |
| string | s |
Raw datatype
[optional]
Datatype used to obtain raw measured value from the connector.
Connector
[optional]
Name of connector to be used as a measurement datasource.
Address
[optional]
Address that represents this measurement in the context of connector assigned. I.e. Modbus reference, IEC-608750 Information Object Address, Persistor address etc. Not to be confused with provider addresses!
Current value
[runtime]
For measurement: Current measured value as assigned by its connector or other source. Always conforms to the configured datatype.
For command: Last value written to this command by some provider, REST API, or other source.
Current quality
[runtime]
Current measured value quality as assigned by its connector or other source, represented as a 16-bit unsigned integer value. Quality flags correspond to OPC-DA 2.05 specification.
Current timestamp
[runtime]
For measurement: Current measured value timestamp as assigned by its connector. Resolution is 1ms. For command: Timestamp of last command write. Resolution is 1us.
Engineering unit
[optional]
User-configurable engineering unit.
Engineering range
[optional]
Range of CO expressed in engineering units. Acquired raw samples would be scaled from raw range to this engineering range.
Raw range
[optional]
Range of CO in expressed in physical units.
Deadband
[optional]
Measured value deadband expressed either as a value in engineering units (i.e. 13.56), or a percent from the engineering range (i.e. 1.5%).
Initial value
[optional]
Value assigned to the command after startup. Defaults to empty.
Archivation mode
| mode | description |
|---|---|
| none | CO is not archived |
| change | CO is archived on every value change |
| periodic | CO is archived with fixed archivation period |
Archivation period
Used in conjunction with periodic archivation mode. Resolution 1ms.
Archivation value deadband
Measured value archive deadband. Expressed either as a value in engineering units (i.e. 13.56), or a percent from the engineering range (i.e. 1.5%). Applies in both change and periodic archivation modes.
Archivation time deadband
Measured value timestamp archive deadband. Applies in both change and periodic archivation modes.
Provider addresses
Provider address is an assignment of provider-specific address to the communication object. Most provider implementations provides only those measurements having provider address for that provider assigned.