Assets

An Asset is a logical representation of a field device, described by a list of Channels. The Asset uses a specific Driver instance to communicate with the underlying device and it models a generic device resource as a Channel. A register in a PLC or a GATT Characteristic in a Bluetooth device are examples of Channels. In this way, each Asset has multiple Channels for reading and writing data from/to an Industrial Device.

Assets can be used as Wire Components to access the resources referenced by the defined channels inside a Wire Graph, see the Assets as Wire Components guide for more details.

Channel Example

To further describe the concept of Channel and Asset, the following table shows a set of PLC register addresses as provided in a typical PLC documentation.

The corresponding Channels definition in the Asset is as follows:

As shown in the previous image, the Channel definition in an Asset results easily mappable to what available in a generic PLC documentation.

Once defined the Channels in an Asset, a simple Java application that leverages the Asset API can easily communicate with the Field device by simply referring the specific Channel of interest.

Channel Definition

Driver independent parameters

Driver independent parameters provide general configuration information, these parameters are available regardless of the attached Driver.

• enabled: each channel can be separately enabled using this flag.
• name: unique user-friendly name for a channel
• type: represents the type of operation supported. Possible values are: READ, WRITE, READ/WRITE
• value.type: represents the data type that will be used when creating the Wire Envelope for the connected components and the output value for READ channel.
• scale: an optional scaling factor to be applied only to the numeric values retrieved from the field. It is parsed as a double. See below for more details.
• offset: an optional offset value that will be added only to the numeric values retrieved from the field. It is parsed as a double. See below for more details.
• scaleoffset.type: Allows to customise the way scale and offset is applied. See below for more details.
• unit: an optional string value that will be added to the asset channel read to represent the unit of measure associated to that specific channel. The option applies only to read operations.
• listen: if supported by the associated driver, allows to receive notifications by the driver on events. This flag currently has effect only inside Kura Wires.

For the READ and READ/WRITE channels, the Asset typically asks the driver to provide a value based on the value.type.
If the scaleoffset.type is LONG or DOUBLE, the type requested will be one of these and the final value (after the scale and offset operation) will be transformed into the data type expected by value.type. The largest representable LONG is 2^53.

Arithmetic with scale and offset

The Asset supports applying a scale and offset to the values obtained by the attached Driver during read operations and to the values received in listen mode.

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Warning

Application of scale and offset for write operations is not supported.

The following modes are implemented for computing scale and offset:

• DOUBLE
• INTEGER
• LONG
• FLOAT

The values of the scale and offset configuration parameters and the value obtained from the Driver are all converted to the mode type using the Java casting and then the following operation is performed: channel_value * scale + offset. The operation result is casted again to value.type to produce the final channel value.

The values of the scale and offset parameters are parsed from channel configuration as doubles.

The mode can be selected in the following way:

• If the scaleoffset.type is set to DOUBLE or LONG the corrisponding mode will be used.
• If the scaleoffset.type value is DEFINED_BY_VALUE_TYPE the operation mode is determinated by value.type.

Example of DOUBLE mode:
channel configured with:

• value.type: INTEGER
• scaleoffset.type: DOUBLE
• scale: 3.25
• offset: 1.5

Since scaleoffset.type is DOUBLE, the scale and offset mode is forced to DOUBLE.

If channel_value is 5 (INTEGER) the result is: (int) ((double) channel_value * (double) 3.25d + (double) 1.5d) = 17.

Example of INTEGER mode:
channel configured with:

• value.type: INTEGER
• scaleoffset.type: DEFINED_BY_VALUE_TYPE
• scale: 3.25
• offset: 1.5

Since scaleoffset.type is DEFINED_BY_VALUE_TYPE, the mode determined by the value.type parameter (INTEGER) will be used.

If channel_value is 5 (INTEGER) the result is: (int) (channel_value * (int) 3.25d + (int) 1.5d) = 16.

Example of DOUBLE mode:
channel configured with:

• value.type: DOUBLE
• scaleoffset.type: DEFINED_BY_VALUE_TYPE
• scale: 3.25
• offset: 1.5

If channel_value is 5 (DOUBLE) the result is: (double) (channel_value * (double) 3.25d + (double) 1.5d) = 17.75.

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Warning

If the mode is LONG or INTEGER the decimal part of the scale and offset value will be discarded

As the examples show the final result can be different depending on the used mode and value.type.

Driver specific parameters

The parameters that are not included in list of driver independent parameters above are driver specific. These parameters are used to identify the resource addressed by the channel.

Examples of such parameters are unit.id, primary.table and memory.address parameters defined by the Modbus driver, that allow to address a specific register/coil on a Modbus slave.

Driver specific parameters are described in the driver documentation.

Other Asset Configurations

• asset.desc: a user friendly description of the asset
• emit.all.channels: specifies wheter the values of all READ or READ_WRITE channels should be emitted in case of a channel event. If set to true, the values for all channels will be read and emitted, if set to false, only the value for the channel related to the event will be emitted.
• timestamp.mode: if set to PER_CHANNEL, the component will emit a driver-generated timestamp per channel property. If set to SINGLE_ASSET_GENERATED, the component will emit a single timestamp per request, generated by the Asset itself before emitting the envelope. If set to SINGLE_DRIVER_GENERATED_MAX or SINGLE_DRIVER_GENERATED_MIN, the component will emit a single driver generated timestamp being respectively the max (most recent) or min (oldest) among the timestamps of the channels.
• emit.errors: Specifies whether errors should be included or not in the emitted envelope. Default is false.
• emit.on.change: If set to true, this component will include a channel value in the output emitted in Kura Wires only if it is different than the one from the previous read operation or event. Channel errors will always be emitted if emit.errors is set to true.
• emit.empty.envelopes: If set to false, this component will not emit empty envelopes. This property can be useful if combined with emit.on.change.