Control Changes

Control Change Messages

Control Changes are a different kind of output Message, therefore, they require and extra flag to be set under its output definition (control_change: True):

app:
  type: kelvin
  kelvin:

    outputs:
    - data_type: number
      name: motor_speed_set_point
      control_change: true

The ControlChange Object supports the following attributes:

Attribute	Required	Description
resource	required	The KRNAssetDatastream that this Control Change is meant for.
expiration_date	required	Absolute datetime or a timedelta (from now) when the Control Change will expire.
payload	required	The desired target value for the control change (Boolean, Integer, Float or String).
retries	optional	Number of retries.
timeout	optional	Timeout for each retry.
control_change_id	optional	Sets a specific ID for the control change (UUID).
from_value	optional	Initial (trigger) value of the control change.

And this is how to create and publish them:

from datetime import timedelta

from kelvin.application import KelvinApp
from kelvin.message import ControlChange
from kelvin.krn import KRNAssetDataStream

(...)

# Create and Publish a Control Change
await app.publish(
    ControlChange(
        resource=KRNAssetDataStream("my-motor-asset", "motor_speed_set_point"),
        payload=1000,
        expiration_date=timedelta(minutes=5)
    )
)