Motion controller sampling an analog voltage (from a load cell)

[nstroud]

Do either the NI PCI-7354 or NI PCI-7344 have the capability of sampling an analog voltage (load cell) at a rate of 100hz while simultaneously activating 3 stepper motors? If so, will it have any effect on the maximum rate at which the motors can be controlled (as in the ability to change the desired position of an actuator for a given number of times per second )?

[Nate.H · Accepted solution]

Dear nstroud,

Either of these boards should work for you. You could configure one of the axis for stepper closed loop analog feedback, and then set up the other 2 axes as slaves to the first with a 1 to 1 gearing ratio. This would cause all 3 of your axes to behave in the exact same manner. This gearing is done on the card, and you should not see any adverse effect on the axes update rate. The sampling rate you specified shouldn't be a problem either. The Control Loop Update Period is settable from the Control Loop Setting tab, and for stepper axes, it determines how ofter the step generator is updated. The default for this value is 250 microseconds. The 7340 user manual also lists the analog input multiplexor scan rate @ 25 microseconds/enabled channel.

So you would actually be sampling and updating the step generator much faster than 100hz with the analog feedback on the motion controllers.

See this KnowledgeBase for more information on the setup:

Analog Feedback with a Stepper Motor:
http://digital.ni.com/public.nsf/allkb/AB3CCA7FBFAD749A8625713B001D8581?OpenDocument

Best Regards,

~Nate