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Entry type: FAQ, Entry ID: 35509140, Entry date: 04/07/2009

SINUMERIK 802D sl, SMC30: Encoder fault incorrect zero mark distance or failed zero mark

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How to proceed if, when operating TTL / HTL encoders on the SMC30, the messages 3n100 and/or3n101 (n stands for encoder 1 or 2) are displayed resp. the higher-level controller is deactivated with encoder fault?

These messages may be caused by the following:
1) The encoder evaluation input frequency was exceeded or
2) The zero pulse signal is too short in time.

SMC30 comprises a zero mark monitor counting the number of encoder pulses between two zero marks. If the encoder frequency exceeds 300 kHz, encoder pulses may get lost or the zero mark can no longer be identified. In this case, the drive sets the fault bit 15 in the encoder status word Gn_ZSW, which is displayed in SINAMICS parameter r0481[n-1]. The SINAMICS messages 3n100 and/or 3n101 are also output.
The SINUMERIK responses to the fault bit with fault 25000.

This problem can be solved by switching over to encoderless mode. For this, set the drive machine data ENCODERLESS MODE CHANGEOVER SPEED Servo-p1404 to a speed supplying reliable signals. Further, the drive machine data CURRENT CONTROL AND MOTOR MODEL CONFIGURATION must be set to Servo-p1402.2=1.

Set the axis machine data ENCODER LIMIT FREQUENCY MD36300 in the axis machine data.

A SIMODRIVE position encoder with 5000 pulses/rev has been attached as direct measuring system to an axis (6FX2001-2CF00). That means, the critical encoder pulse frequency of 300kHz is reached at 3600 rpm. With a certain safety margin, the SINAMICS shall be operated without encoder as from 3000 rpm:
p1404 = 3000 rpm
Park the encoder as soon as the drive is operated without encoder:
p1402.2 = 1
On the SINUMERIK, the encoder limit frequency value may not exceed
MD36300 <= 0.95 * (p1404 * p0408) / 60 = 237500 Hz

The number of encoder pulses is stored in SINAMICS parameter p0408.
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