Siemens RWF40 manual Auto-tune self-setting function, Technical Explanation, Conditions, Procedure

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.

Conditions

The controller must be :

-in the modulating output mode (D1 is open and the step icon is off)

-burner is released (green LED above is on, relay 1, is activated, contact between terminals Q14 and Q13 is closed)

-controller is not in manual mode (red LED above is off)

Procedure

Start Auto-tuneby pressing and release.

The current temperature value, (175) is shown in the actual value display.

The current function item (tunE) is flashing in the setpoint display.

You can cancel Auto-tunewhile it is flashing

pressing and releasing.

When tunE stops flashing on it’s own

Auto-tuneis complete.

You can save the new values for Pb.1, dt, rt and dF1, by pressing , and holding for at least 2 seconds.

Possible results,and their correction. A favorable value for dt is rt/4.

Block diagram of Auto-tune.

8/16 CC1B-Hints-en Preliminary 04.02.2003 HVAC Products