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PosErr spikes with serial encoder


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We have a motor using Renishaw Resolute 26 bit BissC absolute serial encoder that is being controlled from a PowerBrick AC with the BissC option (ACC84B card). When moving the motor and monitoring the PosErr using the IDE scope, we occasionally see spikes on the order of 200,000 motor units. This error is seen only on a single phase cycle, and then goes away. This does not seem to impact the motion performance, but we are curious why this is occurring.


I thought maybe the encoder clock frequency was too fast for our cable lengths, but our cables are ~9m, and Renishaw recommends 1MHz clock frequency for cable lengths up to 20m without any line delay compensation.


We are using the encoder for phase commutation and servo loop. Phase clock is 9.035KHz and encoder clock is 1MHz BissC (SerialEncCtrl=$63000B).


Do you have any ideas why these spikes may be occurring?



Config file and plot screen show attached.

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Try setting Sys.BusCtrl[10] = $747.

If that does not work, please send us your settings, including clocks.


Has this error been seen on the ACC24E3 with the ACI? We have configured it with default timing, and using the serial interface. We throw a random position jump that is far in excess of any error expected. (250mm on a 6mm stage).

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