Data Rate

By default the data rate is set to 20 samples per second. The maximum data rate possible depends on the processing power of the computer and graphics card and the bandwidth (sample rate). 512 data points from the Doppler shift signal is always used to calculate each sample, (256 points for a 64 point FFT) therefore a slow Doppler sample rate means the data takes longer to acquire. For example the lowest bandwidth (6.25kHz)takes about 70ms for 512 samples. The ADC sample rate is hardware controlled but the processing of each 512 sample block to produce the velocity measurement is achieved by software polling of a hardware timer. The hardware timer is polled continuously whilst waiting for user input. If the PC cannot process and display the data fast enough then missing samples will be filled in by copying the latest value into all missing data points. This can be seen in the trace as horizontal lines in the output at high x scale magnification.Because of this any user operations which delay the software polling by over one sample period will cause missing data and flats in the trace.