Auto-tune self-setting function, Conditions

2. Hints

2.7 Auto-tune (self-setting function)

RWF40 user manual section 6.2.4 and 9.1

The RWF40 User manual refers to a ‘self-setting-function’

that for the purposes of this manual will be refered to as ‘Auto-tune’.

Technical Explanation

Auto-tuneis a self-setting software function, that is integrated into the RWF40 controller, and can be repeated as often as desired.

Auto-tunetests the reaction, in the modulating mode of operation, of the process-control loop, to steps in the actuator position, according to a special procedure.

The data, during the forced oscillations, is then recorded, and used to calculate new values, that are optimized for your specific controlled system.

Auto-tune items summary:

Items at the user level that will affect Auto tune

SP 1 Set Point 1

HYS1 Switch-on threshold, HYSteresis 1

HYS3 Switch-off threshold, HYSteresis 3,

Items at the Parameter level that Auto-tunewill adjust
Pb.1	Proportional band 1	(Factory setting	10)
dt	derivative time	(Factory setting	80)
rt	Integral action time	(Factory setting	350)

Item at the configuration level that Auto-tunewill adjust

dF1 Time constant for digital Filter, analog 1

Values for Pb.1, dt, rt and dF1, can always be changed.

Auto-tune uses two different methods to force oscillations, and will automatically select and use, a method, based on, at the start of Auto-tune, what the difference is,

between the setpoint (w), and the process value.

When Auto-tuneis started with a large difference, (typically before the process-control loop has stabilized) Auto-tuneperforms a forced oscillation around a switching level.

When Auto-tune is started with a small difference, (typically after the process-control loop has stabilized)

Auto-tuneperforms a forced oscillation, around the setpoint (w).

If for any reason the controller exceeds the switch off threshold (HYS3) Auto-tunewill be cancelled.