Encoder

An encoder (bliss.common.encoder.Encoder object) can be defined on its own, or can be associated to an axis to add some extra checks before and after a movement.

Note

There are 2 tolerance parameters in configuration: one for Axis and the other for Encoder.

If an encoder is associated to the axis:

  • after a movement, the encoder position is read and compared to the target position of the movement. In case of difference outside the limit fixed by Encoder tolerance, an exception is raised with message: "didn't reach final position"

  • the method measured_position() uses encoder.read() to calculate the value returned in user units.

Note

This measured_position() method is used in particular by TangoDS and can be easily compared to the target position with atk-moni for tuning purposes.

  • dial_measured_position() returns the dial encoder position in user units.

An encoder can be used to define events to trig on special positions. See: Writing a motor controller - position-triggers

Encoder as a counter

A SoftCounter object can be defined to use an encoder as a BLISS counter in a scan by putting in the setup of a BLISS session:

<counter> = SoftCounter(<encoder>, <function used to read>, name=<counter_name>)`

example: 

hpz_enc = SoftCounter(hpzrotid16_enc, 'read', name='hpz_enc')

Note

hpz_enc can be used in a measurement group, but do not add "hpz_enc" in the config-objects list of the BLISS session.

development

For details on how to implement an encoder in a new motor controller, see Writing a motor controller / Encoder methods