count revolution per minute with NI 9237 and strain gauges

[bonushead]

Hello community,

i am a labview beginner and i need some help.

I work on a alternating bending machine which is bending a specimen. An AC motor produces the alternating bending. The AC motor in question has a revolution of 1380 per minute. My aim is to count the load cycle. For this i will use a NI 9237 Modul. I installed four strain gauges on the machine, wired them with a wheatstone full-bridge and connect this with the NI 9237. I want to count load cycle out of the determined continuous signal with the zero crossing function. I tried to do this but i always get a different and wrong value. I also tried to adjust the sample values as advised in other posts.

Thank you all in advace for your help.

Engin

[Duffy2007]

Hello Bonushead,

i tried your programm with a simulated modul and it seems that the zero line crossing is detected correct.

Can you please post an example what is measured and what you expect?

Thanks a lot.

[bonushead]

Hi Duffy2007,

thanks for your fast answer.

I want to measure the bending moment in the specimen and count the load cycles until the fraction of it.

When i turn on the machine, begin recording data for a time of 60s, sometimes it gives me a value far below of

what i expect.

Maybe i have to try adjusting again my samplerate.

Best regards

[Duffy2007]

Hello bonushead,

i change the acquisition so it delivers every 100ms new values, also the stop from the measurement and the elapsed time is changed. I think the different valus can came from the strain so in my DAQ a offset nulling is done before the measurement starts is implemented.

Hope it helps.

[bonushead]

Hello Duffy 2007,

first of all thanks for your idea and time.

I tried the vi. It helped me to think further.

When i start it, it was counting right. But after severel load cycles the counting slows down. Because of that, I

put a sequens in the loop that performs the analysing of the strain signal to shorten the looptime.

Now I got a problem with detecting the minimum and maximums of every cycle. Like you can see in attached text editor data,

I get 2 to 3 minimums and maximums for each load cycle. Is there a possibility to measure only the highest and lowest amplitude of one cycle?

best regards

[Duffy2007]

Hello Bonushead

if you only want min and max read out the array from the waveform you want to analyse and use the min max function

Hope it helsp a little bit.

[bonushead]

Hello Duffy2007,

I tried it out before with array max&min but in this case their where outputed more values per loadcycle then I did it with the amplitude function.

Nevertheless, many thanks for your suggestions. They helped me to solve the problem.

best regards.