>From: Lawrence Lile >Reply-To: Lawrence Lile >To: PICLIST@MITVMA.MIT.EDU >Subject: [PIC]: The tintinnabulation of the noise >Date: Tue, 7 Nov 2000 09:21:00 -0600 > >(above quote is from Poe) >(yes, tintinnabulation is a word) > > >I'm sampling a DC voltage with lots O noise. I've set up a routine that >takes a sample, waits a few milliseconds, then takes another sample, etc. >When 15 samples are taken, it takes the median of the samples as the >result. Still get false alarms due to noise pulses every once in a while. > >Now, I am not real sure if I will have 60 hz noise (picked up from the air) >or 120 hz noise (from a full wave rectified power supply) as the major >noise component. It may actually be both, at various times. > >Does Old Nyquist rule in this situation, should I sample at twice 120 hz or >more to cancel out the effects of noise? I'm not interested in the >frequency of the signal at all, just in an accurate DC level. The sampling frequency should be based on 60Hz period, when the noise comes from. Sampling input signal with higher frequency, for example 5 * period, and averaging during a whole period of 60Hz works in this case like digital filter. Niquist said about the theoretical minimum sampling frequency, but in reality, it is much higher. Andrej _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. Share information about yourself, create your own public profile at http://profiles.msn.com. -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu