Siemens SINAMICS S120 Function Manual page 146

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Servo control

4.12 Encoderless operation

Commissioning/optimization

1. Estimate the motor current p1612 on the basis of the mechanical conditions (I = M/kt).

2. For synchronous motors with high overload setting (p0640 significantly higher than

p0305), it may be necessary to reduce the current limiting in encoderless operation

3. For a third-party motor, carry out the stationary measurement - and if possible - also the

rotating measurement and accept the determined data (see Chapter "Motor data

identification (Page 149)"). Check the current controller setting.

4. If the total moment of inertia has not already been determined using the rotating

measurement, you have the possibility of determining the total moment of inertia as

– If an encoder is being used, and the motor has a restricted traversing path (e.g.

– If the motor can endlessly rotate (with and without encoder)

– You can also determine the moment of inertia using the "Moment of inertia estimator"

encoderless operation is only used when an encoder develops a fault or only for the

upper speed range):

Determine the moment of inertia using the rotating measurement of the motor data

identification (p1959 = 420 hex (i.e. only commutation angle and Lq characteristic),

p1960 = 1). If you carry out the motor data identification using the STARTER screen,

set p1959, start the measurement and accept the result.

Determine the moment of inertia using the rotating measurement of the motor data

identification (p1959 = 404 hex (i.e. only commutation angle and moment of inertia),

p1960 = 1). If you carry out the motor data identification using the STARTER screen,

set p1959, start the measurement and accept the result.

function module (see Chapter "Moment of inertia estimator (Page 583)"). As the

moment of inertia is also determined in operation using this function module, we

recommend that the "Moment of inertia estimator" function module is used if the total

moment of inertia changes during operation.

Function Manual, 11/2017, 6SL3097-4AB00-0BP5

Drive functions

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