Item Properties
An item, also known as a tag or signal, represents a data value of some sort. Either originating from an external system (PLC, DCS, etc.), or calculated/derived from such values within the Apis environment.
Item types
There are three main item types; scalar values, vector values and matrix values.
A scalar value may typically be a flow signal, temperature, etc. from an external system. A vector value typically is a spectrum from a NIR instrument or a control vector in a model based predictive control (MPC) system, and basically is a one-dimensional array. A matrix value typically is a system matrix in an MPC system, and basically is a two-dimensional array.
Supported data values
Apis Honeystore supports all common data types, ie. 32/64 bits floating point values, 8/16/32/64 bits signed/unsigned integer values, boolean values, date values, string values, as well as arrays (vectors/matrices) of all these types.
Apis Honeystore items have several properties (also called attributes) associated with them. Some of these properties are mandatory for all items. Other properties may apply or exist only for some items, this apply to properties like description, engineering units, normal minimum/maximum values etc. The properties are added to items and maintained by the application writing to the database, typically an ApisLoggerBee module within the Apis Hive framework.
Mandatory properties
| Name | Description |
|---|---|
| Handle | An internal handle (placeholder) of the item. |
| ItemID | The name of the item. This name is unique within one database. |
| Datatype | The data type of the item, eg. floating point, boolean, string, etc. |
| Recordtype | The record type of the item. This tells what and how the item is sampled. Three types are defined:
|
| Resolution | For the two Sampled record types; the sampling interval of the item. For the Eventbased with quality recordtype: the minimum period between two subsequent samples. |
| HistoryLength | The minimum time horizon of the trend of an item, meaning that trend data will not be deleted/overwritten until at least the time period specified by this attribute has elapsed. |
| SampleSize | The uncompressed size of one data sample in bytes. |
Optional properties that may occur
| Name | Description |
|---|---|
| Description | A description of the item |
| Engineering unit | Specifies the label to use in displays to define the units for the item (e.g., kg/sec) |
| Normal maximum | The upper limit for the normal value range for the item. Used for trend display default scaling etc. |
| Normal minimum | The lower limit for the normal value range for the item. Used for trend display default scaling etc. |
| PDS Engineering Unit | The PDS Engineering unit (engineering unit) associated with this item. This attribute only have meaning inside an Apis Click & Trace™ configuration |
| Display | Operator display associated with the item |
| HiLimit | The Hi alarm limit of this item |
| HiHiLimit | The HiHi alarm limit of this item |
| LoLimit | The Lo alarm limit of this item |
| LoLoLimit | The LoLo alarm limit of this item |
| UpperBound | The upper bound of vector item |
| LowerBound | The lower bound of vector item |
| ArgumentItem | The argument item of this item, meaning is client specific |
| MaxCacheDuration | This attribute determines the maximum duration (in seconds) of item cache before it is flushed to disk. |