Precise measurement of frequency and Q

garyg · Post by **garyg** » Thu Apr 29, 2004 11:56 pm

I need to measure two signals - basic sine waves at nominally 30 Hz and 60 Hz. I need to know the actual frequency with a resolution of 0.05 Hz or better. I would also like to measure the Q of the signal(s), which are generated by mechanically resonat systems. The Q is pretty high in these systems, somewhere around 100.

This is a single channel requirement. I have looked at the ADC-42, which looks like it has the spec's to do the job. I downloaded the demo software and the interface looks promising. What I couldn't tell from the demo is:

1) Can I use the spectrum analyzer to measure 30 and 60 Hz with the required resolution?

2) Is there any "automated" way of determining the resonant frequency (short of picking it off the screen)?

3) Is there any "automated" way of determining the Q of a signal?

4) Is there an easy way to export a captured signal in terms that excel or another math package can get the raw data (ascci text?) to determine the Q?

Thanks for a good looking product that I'm hoping to try!

- garyg

markspencer · Post by **markspencer** » Tue May 04, 2004 8:44 am

Hi,

Thank you for your post.

Unfortunately, the software cannot measure the Q of a signal, but it is possable to get raw readings from the software or by writing your own software.

It is also possible to get the resolution of 0.05 Hz per bin, as the unit can max bandwidth set to 100 Hz from DC. The down side is the that the convertion time takes a very long time. The unit does not take measurements onboard and thus gives the appearance that you PC has locked up. The time spaces between each reading is not the same so you would need to apply interpolation, to perform any calculations.

I would recommend one of the ADC-2xx series units, for this kind of application.

Best regards,