Alternative ways to measure frequency

Question

Are there better and more accurate ways of measuring frequency beside an Oscilloscope or a counter? I need to monitor frequency changes in a signal that ranges from 15-30kHz at least 3 times a second. Of course, I need to save that data and access it digitally. Thoughts? Zero

jvdberg@ieee.org · Answer

Zero, There are several ways to measure a frequency. In a frequency counter the frequency is compared with a reference oscillator. The accuracy depends on the accuracy of the reference oscillator and the duration of the measurement, because the result is always + or – one digit. So, with a measurement time of one second, the last digit error is + or – one Herz. With a measurement time of 10 seconds, the last digit error is + or – 0.1 Herz. A way to reduce the last digit error without using a very long measurement time is using a phase locked loop and divider. You can make an oscillator, operating at 100 times the frequency you want to measure. Behind this oscillator is a digital divider by 100. The output of this divider is compared with the signal you want to measure in a phase detector. The output of the phase detector is used to keep the oscillator at exactly 100 times the frequency you want to measure. A CD4046 IC could be used as oscillator and phase detector. By measuring the frequency of the oscillator, the last digit error is reduced 100 times. Another way to measure a frequency is a delay line and phase detector. The phase between the direct and delayed signal depends on the frequency. This method is mainly used to measure the frequency of pulsed signals, using an analogue phase detector with X and Y outputs. Another way to measure a frequency is using a frequency to voltage converter and measure the voltage. A sample and hold circuit can be used to measure at specified moments. Another way to measure a frequency is using FFT analysis. The easiest way to solve your problem is connecting the signal to the sound card of a computer. Then, using FFT software, you are able to measure the frequency and store it on the same computer. There are several FFT analysis programs to download on the internet.