8.1 Speed Calculation

Speed can be calculated by measuring the number of edges of encoder pulses encountered (position difference) in a fixed time interval, or by measuring the time elapsed between the fixed number of edges of encoder pulses encountered.

• Calculating speed by measuring the position difference in a fixed time interval.

  ${\displaystyle {\omega }_m=\frac{{\mathrm{\Theta }}_{m(n+1)}-{\mathrm{\Theta }}_{m\left(n\right)}}{\mathrm{\Delta }t}}$

• Calculating speed by measuring the time elapsed between a fixed number of encoder pulses

  ${\displaystyle {\omega }_m=\frac{\mathrm{\Delta }{\mathrm{\Theta }}_m}{t_{(n+1)}-t_{\left(n\right)}}}$

Equation 8-1 provides good accuracy at higher speeds, and Equation 8-2 provides good accuracy at lower speeds though timer overflows must be addressed. In this document, the first method is used for the entire speed range. In this case, it must be considered that the minimum speed can be measured as follows:

${\displaystyle {\omega }_{\mathrm{m(min)}}=\frac{120}{\frac{\mathrm{no.\; of\; encoderpulses}}{\mathrm{mech.rev}}*(Speed\; sampling\; rate\; in\; sec)}}$