DAQmx and Labview needs an Express VI and/or Shipping Example for doing a rotational speed measurement using a quadrature encoder.

[Frank-L]

Multiple people have requested that there be a natural way for Labview and SignalExpress to do a rotational speed measurement using a quadrature encoder. An express VI under "Acquire Signals>>Counter Input>>Rotational Speed" that asks you basic quadrature encoder type questions and computes the rotational speed would be very useful. The information it asks would be things such as Ticks per Revolution, Decoding type (x1, x2, x4) would be useful in computing rotational speed. In addition, this can be then converted into a shipping example for DAQmx relatively easily. I have had multiple people ask this question and believe that especially within SignalExpress, this would be very useful.

[Brad_K]

Hi Frank,

What scaled units would you expect this measurement type to support? Hz and RPM?

Would you expect this measurement type to be directional? Should rotation in the reverse direction return negative speed values? This seems like a good reason for this measurement type to know the decoding type. Without directionality, you can probably approximate a rotational speed measurement by doing a frequency measurement on one of the encoder outputs and scaling the result into the correct units. I suspect that ignoring the other encoder output reduces the precision of the rotational speed measurement, at least at low speeds.

By the way, when we add a new measurement type to the DAQ Assistant, we also add the corresponding DAQmx Create Channel VI, ANSI C function, .NET method, etc. This idea wouldn't be limited to the DAQ Assistant.

Brad

[Frank-L]

Brad,

I think that rpm would be the best unit to use, but we could also use Hz, or Angular speed as additional units.

I also agree that the directional speed value (positive vs. negative values) would be useful in order to signify clockwise vs. counter clockwise rotations. The addition of the DAQ assistant, Signal Express VI, DAQmx Create Channel VI, ANSI C function, and .NET method would prove useful to a multitude of users.

Frank,

[Izzzzz]

There are two new tasks introduced in DAQmx 15.1 that when used with the NI 9361 allows for a velocity measurement.

Izzy