How to count rpm by using NI-DAQ and LabView?

[kang3]

I have an IR sensor which gives analogue output signal. May I know how can I measuring the rpm of a rotating wheel by using NI-DAQ and LabView?

[RavensFan]

What kind of analog output does it have?  It is a voltage signal?  Is it a voltage that is variable with speed?  Or a pulse waveform caused by teeth interrupting the IR sensor and you need to measure the frequency of that?

[kang3]

It is a voltage signal.It has a pulse waveform caused by teeth interrupting the IR sensor. The sensor will only be triggered once every revolution. How can I measure the rpm?Do I need to use a clock in LabView software?

[RavensFan]

I think if you did a basic hardware timed analog input acquisition where you are acquiring multiple pulses at a high rate, you could do an FFT on the pulse waveform, and get the frequency.  Or do an analysis of zero crossings of the pulses relative to the time interval of your samples and come up with a good RPm frequency.

[kang3]

Thank you for your help.

[PaulieQ]

Hi,

Your signal can be also interpreted as a digital signal. On "1" and off "0". If the voltage levels are 0 and +5V you can drive your signal in the counter input and use the DAQmx Pulse Measurement or Frequency Measurement features. It's easier than using analog acquisition + signal processing with fft/zero crossing. Also the measurement accuracy is superior when using counters.

Paul

[SilkySav]

Hi I am using a myDAQ and have a optical sensor and a flywheel with a hole in it.

When the hole lines up with the sensor my digital Boolean lights up so i know it working...

Then I selected acquire signal / counter / edge counting and using channel DI 0 which is PFI0.

When I run the motor at max speed 300 RMP it just counts up, QUESTION is how do I get this to show as a value of 300 RPM on my front panel.

Any help appreciated as I am new to all this and are finding it quite daunting...