National Instruments NI 6711 User Manual

Also see for DAQCard-6715: User manual User manual

Contents

National Instruments NI 6711 User Manual Manual pdf 88 page image

© National Instruments Corporation B-1 Analog Output Series User ManualBTroubleshootingThis section contains some common questions about AO Series devices. Ifyour questions are not answered here, refer to the National InstrumentsKnowledgeBase at ni.com/kb. It contains thousands of documents thatanswer frequently asked questions about NI products.Calculating Frequency ResolutionHow can I calculate the frequency resolution of the analog output onthe AO Series device?The analog frequency (fa ) you can generate is determined by the updateclock frequency (fu) and the number of samples per cycle (Sc ):The onboard 20 MHz clock that generates fu can only be divided by aninteger. For example, suppose you want to generate a sine wave at 2 kHzwith 50 samples per cycle. Substitute 2 kHz and 50 samples into theprevious equation to get:So fu equals 100 kHz. The 20 MHz clock must be divided by 200 asshown by:Suppose now you want to slightly increase or decrease the frequency of thesine wave. The closest available update clock you can generate occurs usinga divisor of 199 or 201. If you choose 201, fu equals 99.5 kHz, as thefollowing equation shows:fafuSc-----=2 kHz fu50------=20 MHz200------------------- 100 kHz=20 MHz201------------------- 99.50 kHz=