USB-1808x High Speed DAQ - Counter Function

[K-Y]

Hi,

I am trying to use the USB-1808x High Speed DAQ with LabVIEW to measure RPM up to 112,000. I am using the counter function and have been able to measure up to 40,000 before LabVIEW stops displaying the data. The rpm sensor I am using has 7 pulses per revolution. At max rpm there should be a total of 13,000 pulses per second.

The device is advertised to be able to measure up to 50khz and the frequency at 112,000 is 48khz. Is there a setting I must change in either instacal or the labview script to max out the sampling rate? 

Thank you,

KY 

 

[JRys]

With seven pulses per sensor revolution, 13,000 pulses per second is approximately 1800 RPM. On the other hand, RPMs up to 112,000 would be 784,000 pulses per second. Could you confirm the sensor's RPM range and the number of pulses per revolution?

 

[K-Y]

The rpm sensor has 7 pulses per revolution. 

My measurement range for rpm is 0-112,000 rpm 

Right now I have been able to measure 40,000 rpm before the labview script stops printing the data. At this rate, the DAQ is sampling about 4,666 pulses per second. At max rpm of 112,000, the sampling rate should be 13,000 pulses per second. 

 

I attached a copy of the script I am running. 

I am having the DAQ pick up the falling edge of the sensor. I am not sure if there somehting I have to unlock to obtain the faster sampling rate? 

 

[K-Y]

The RPM sensor is the second group in the code with the ULx library. There is another flow meter being used on a seperate DAQ. I have changed the RPM 1080x to a seperate program and have recieved similar results. 

[JRys]

The counter input uses a 50 MHz clock (20nS per tick) and counts repeatedly from the leading edge of your sensor's signal to the next lead edge. At 112,000 RPM (784k Hz), the ideal count is 63.75, 784,000 Hz. However, in the real world, the count may be only 60 or 833,333.3 Hz. There will be more errors in the upper frequencies because the counter input has less time to count. With that said, could you review the attached VI? It will demonstrate a better (more straightforward) way to measure frequency. You can ignore the counter output (TMR0) I used for a test signal. 

ULx Meas Dig Freq-Buffered-Cont-test.vi