NI 73xx Velocity in Counts/s or Steps/s

Velocity values in counts/s or steps/s are also converted to the internal 16.16 fixed-point format in units of counts or steps per sample (update) period before being used by the trajectory generator. Although the motion controller can control velocity to 1/65,536 of a count or step per sample, it is impossible to load a value that small with the Load Velocity VI or function, as shown in the following formula:

Velocity in counts or step/s = Vmin ×

where:

Vmin is 1/65,536 counts/sample or steps/sample and

Ts is the sample period in seconds per sample.

Even at the fastest update rate, Ts = 62.5 × 10^–6

Load Velocity takes an integer input with a minimum value of 1 count/s or step/s. You cannot load fractional values. If you need to load a velocity slower than one count or step per second, use the Load Velocity in RPM VI or function.

You can calculate the maximum velocity with the following equation:

maximum velocity = Vmax

where

Vmax = 20 MHz for servos

8 MHz for steppers on a NI 7350 controller

4 MHz for steppers on a NI 7330, NI 7340, or NI 7390 motion controller

and is constrained by acceleration/deceleration according to the following equation:

velocity (65,536 × deceleration) – acceleration

where velocity is in counts/sample and acceleration and deceleration are in counts/sample².