encoder counts setting in MAX

[Ya-hoo]

When I configured my motion controller PCI 7342, there is a encoder counts in Axis configuration, I am not sure how I could set this number. The encoder has 1000counts/revolution. So here what should I put, 1000 or 4000?

And in encoder setting branch, there is "filter frequency", what does this mean and where can I found this number?

Thanks.

[Jochen]

If the unit of the encoder resolution is in counts/revolution then this value equals with the encoder counts/revolution setting. A quadrature encoder produces 4 counts per line. So if the unit of the encoder resolution was lines/revolution then you would have to multiply this value by 4. For the case that you are not 100% sure about the unit of the resolution of your quadrature encoder then simply turn the motor by one revolution while the amplifier is turned off or disabled and check the position display in the 1D interactive in MAX.

The 7342 has low-pass filters for the encoder inputs. Decreasing the filter frequency limits the risk of wrong countings caused by electrical noise. This is from the online help for the frequency setting in MAX:

Default: 1.6 MHz.
Maximum count frequency for the specified encoder. Set the maximum allowable count frequency for an encoder to reduce the effect of noise on the encoder lines, since noise on the encoder lines can be interpreted as extra encoder counts.

Setting the frequency to the lowest possible setting required for your motion application ensures the highest degree of accuracy in positioning. When choosing the appropriate value, consider the counts per revolution of your encoder and the maximum velocity for the axis in question.

Best regards,

Jochen Klier
Applications Engineering Group Leader
National Instruments Germany GmbH

[Ya-hoo]

Thanks Jochen.

I am still confused. If the motor's spec shows that encoder resolution is 2500ppr, do I have to give 2500*4 in MAX. What number I have to give here, encoder counts from motor or encoder counts what the controller sees?

Thanks.

[Buechsenschuetz]

I mostly agree with Jochen Klier, suggesting the 'empirical way' to check correct settings. Another (probably more accurate) method would be to run the motor just one revolution. You can do that in the interactive mode of MAX and setting the motor control to 'steps per revolution' rather than 'rpm'. In the axis set up area set your axis to 'open loop'. Reset the encoder values in the interactive mode, enter the number of steps required for one revolution (this should be specified by your motor/driver supplier). After the movement has finished, check the number of encoder counts in the 'advanced data' section - fortunately MAX counts the encoder signals even in open loop mode. We have succesfully 'explored' several partially unknown drives this
way.