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Picolog frequency measurement problem

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Picolog frequency measurement problem

Postby PaulF » Tue Dec 11, 2007 5:20 pm

I have posted on this problem before but have had no resolution to date.
I cannot get the ADC-11/10 USB to display Frequency when used with a software version later than 5.13.9.
It works fine with 5.13.9 or with this & later versions using the ADC-11/10 parallel port device.
I have tried with inputs ranging froma few hz up to several khz & scan times up to several seconds.
Anyone got any ideas?
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Postby ziko » Wed Dec 12, 2007 2:53 pm

Hi I have just tried to recreate this. It works fine on my computer, could you send me your settings file zipped up (so it can get passed the filters).

Also what kind of frequency are you trying to measure.

Kind regards

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Picolog frequency measurement problem

Postby PaulF » Wed Dec 12, 2007 5:07 pm

Hi Ziko,

The signal I am actually trying to measure is from an anemometer so is low frequency up to about 50Hz. We have been doing this for many years via the parallel ADC-11 & the USB ADC-11 up to rev 5.13.9.

As a simple test I set up 1 channel with the measurement type as Frequency & scan time I have varied up to several seconds. I input a square wave of 0 - 2.5v (I have tried varying this) from a function generator so can vary the frequency from 0 to 200kHz.
I can see the signal ok via the USB ADC-11 on picoscope but the frequency does not display on Picolog on software revisions later than 5.13.9. However on 5.13.9 it works fine.
If I change to the parallel ADC-11 with the same setup it works fine with all software revisions up to 5.18.0.
The PC I am currently using has XP but have tried on other PCs with W2000 with identical results.
I have attached a Zipped file containing the settings file for 5.18.0 & a screen dump of the signal from Picoscope.
I am sure I am missing something but can't see what at the moment.

Thanks for your help.
Best Regards
Paul
Attachments
Frequency.zip
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Postby ziko » Thu Dec 13, 2007 10:44 am

Your frequency measurement depends on a number of factors:

1) the frequency of the signal you are measuring,
2) your scan time.

Your scan time has to be at least 3 times longer than the wavelength of signal you are measuring.

So in your case if you choose 1000000 us for your scan time (i.e.100ms) you should then be able to measure this low frequency.

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Picolog frequency measurement problem

Postby PaulF » Thu Dec 13, 2007 12:45 pm

Hi Ziko,

Thanks for the reply.
Yes I know about the relationship between scan rate & frequency.
I have tried various scan rates & frequencies.
The setup file I sent was using an input frequency of 1kHz with a scan rate of 1s. Both of these I varied over a wide range.
I don't understand how it can work ok with all software revisions & parallel ADC-11 but not with USB ADC-11 & software later than 5.13.9.

Best Regards
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Postby ziko » Fri Dec 14, 2007 12:41 pm

Hi, I have not got 5.13.9 to try out.

What I can say is that I would choose 100ms as your scan time instead of 1 second. You should really have your scan time to be less than you sampling interval.

It could be that some default settings in PicoLog recorder changed in later release. There is parameter callled QuickSampleMS which is set to 1000ms by default, you can reduce that if you want a bigger scan time. You can achieve this by modifying your plw.ini file

This can be found under:

C:\Documents and Settings\USER\Local Settings\Application Data\Pico Technology

where USER denotes your login name.

One of the folders will have the plw.ini file.

Once you opened the file add the following lines

[Preferences]
QuickSampleMs= x


where x denotes your ms.

Warning: reducing this will significantly slow down the sampling speed of some ADC units by preventing the Quick sample mode from being active at sampling intervals up to 1000 ms

Hope this helps.
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Postby PaulF » Fri Dec 14, 2007 2:01 pm

Hi Ziko,
Sorry, none of this works.
I had already tried 100ms scan time. The 1sec sampling rate in my setup file was only what I had ended up with after trying lots of different values & input frequencies.
I tried altering the plw.ini file as you suggested but the problem is still the same - no frequency display in the monitor.

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Postby ziko » Fri Dec 14, 2007 2:20 pm

What I did notice is that you need to click on the record button to get the frequency measurement otherwise it will not give any meaningful values.

Have you tried that?
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Postby PaulF » Thu Jan 03, 2008 10:27 am

Thanks Ziko,
Sorry for the long delay in replying, been tied up with other things.
Pressing record does give me the frequency display.
The problem now is that most of the time the recorder needs to display the readings without recording. This was possible in the older software revisions but not in the latest.
Is there any way around this?
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Postby ziko » Mon Jan 14, 2008 1:34 pm

Hi PaulF,

I just realised that you do not have to press the record button for it to work!

Kind regards
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