Problem with DAQmx Timing VI (Sample Clock)

[Czechmarty]

Hello to you all,

I'm new to this board, so please bare with me. I have some experience with LV, but I'm fairly new to data acquisition projects. I'm using LV2009.

I want to make sure I'm using the hardware timing (instead of software timing) in my project so I followed up some of the threads here that sugested to use the DAQmx Timing VI. The problem is that no matter how I set the system I get the same error -200300 Invalid timing type.

The project is simple. I have encoder with 1000 pulses per rev and it is mounted on a shaft of a turbine that has water going thru. I'm trying to monitor the frequency and thus the rotation of the shaft which tells me how much water is flowing thru the turbine. At the end there will be 2 channels per each encoder and ~3 encoders (turbines) total and calibrated master meter that will give me steady pulses and all the encoders will be compared to this master frequency.

I'll be using PCI6602 DAQ, but right now for the development I'm using USB6221. Let's say the frequency is between 500Hz and 10kHz. What am I doing wrong?? Or maybe better to ask - what would be the correct approach to this project?

Thanks

Marty

[John_P1 · Accepted solution]

Hi Marty,

It looks like your question was already answered here, but Jason is correct that neither the 6602 nor the 6221 support a Sample Clock for frequency measurements.

Also like Jason mentioned, your best bet is likely to set the timing mode to "Implicit". This means that the frequency value is sampled at the end of every period of your input signal. Also, a software-timed (On-Demand) solution might be acceptable.

The X Series DAQ devices do allow an external sample clock to be used for frequency measurements (described in the X Series Manual). Sample-clocked frequency measurements are useful in very specific circumstances but it doesn't sound like you need this functionality based off what you've described so far.

Bus-Powered M series (621x) can also be configured to use an external sample clock like the X Series but do not have all of the same functionality described in the X Series manual.

I hope this helps!

-John

Message Edited by John P on 11-04-2009 12:54 AM

[Czechmarty]

Thank you both guys! I decided to go with the implicit solution. Consider I have to average the frequency samples to get decent stable number it should be good enough. The new X line looks interestin, but unfortunatelly I bought my 6602 before it came out.

Marty