RPM Measurement using Quadrature Encoder and PXI 6602 counter

[glstill]

Hi,

I am on a project at work where I need to verify the speed (in RPM) of an unloaded motor which can operate up to 1400 rpm.  After doing some research, i determined that a quadrature encoder could be used to make the measurement.  I am looking at this encoder  http://sine.ni.com/nips/cds/view/p/lang/en/nid/205321.

I have a PXI 6602 counter/timer module in which I would like to interface to the quadrature encoder.  I would like to create a VI that allows me to calculate the speed using the encoder.  Can someone provide me with details of what needs to be in the VI or an example which can do this?  At the most basic level, i want to calculate the speed on demand.  After doing this, i would like to figure out how to quickly calculate the speed so that i can determine response time of the speed changing within sub-millisecond resolution (1 ms resolution max).

Further, i created a VI that allows me to change the pulse width of a 100 Hz pulse train at run-time which tells the motor controller the desired speed.  I would like to be able to use this VI to change the speed of the motor and the first VI (that I am seeking help about) to calculate the response time (time between the initial speed and settling at the new setpoint).

I am familiar with the NI example finder, but have not been able to find an example that I can use.

Thanks,

Gary

[Luke_W]

Hey Gary,

I think for you setup, you should try using the Meas Dig Frequency - Low Freq 1 ctr. You can find it by searching example finder with 'low freq'. This vi tells you the frequency of a digital signal by sampling between two pulses and inverting the time between pulses. If you hook up your encoder to a counter and have that counter specified in the vi, it will be able to give you on demand readings of frequency (you can do some multiplication to get the rpm value, freq*60/pulses per revolution of encoder). A simple way to take continuous readings is to put a while loop around the daqmx read and the data output of the read. You can also replace the numeric indicator to a waveform chart to graphically display the change of frequency or rpm readings over time.

You should be able to integrate this as two separate tasks with the pulse train vi you created earlier.

Hope this helps

Luke W