How Does The SRM Training System Work?

How Does The SRM Training System Work?

1. The SRM uses 8 strain gages, 16 grids in a Wheatstone measuring bridge. When force is applied to the crank arms, opposing resistance from the drive train puts stress on the measuring bridge (see pics).

2. This stress causes an increase or decrease in the length of the strain gages, thereby changing the electrical resistance of each strain gauge.

3. The change of the electrical resistance is converted into a modulated output frequency and transmitted to the PowerControl. If in “Zero Offset” mode, the PowerControl displays the output frequency (514 Hz).

4. When there is no force applied to the PowerMeter, the zero-offset is shown (as a frequency between 300-800 Hz). This number is recorded as the base level from which all power measurement begins by pressing the SET button.

514

5. Any increase of the pedaling force will increase the output frequency.

6. While pedaling the SRM PowerMeter, the forces change constantly. At any given moment, the applied torque is represented by the subtraction of the zero-offset from the output frequency.

1687 Hz - 514 Hz = 1173 Hz
1173 Hz / 20,5 Hz/Nm = 57,22 Nm

7. Each PowerMeter has a mutually exclusive “Slope” value calculated during the calibration of that specific PowerMeter. The Slope is notated as Hz/Nm or Hertz per Newton meter. For example, 20 Hz/Nm means for each Newton meter of torque applied to the PowerMeter, the output frequency will increase by 20 Hertz.

8. At the time the torque value is measured and defined, the angular velocity of the power meter is also recorded. The value is derived from the cadence of the pedal stroke.

Cadence (rpm) x 2 Pi / 60 = Angular Velocity (rad/s)

9. The SRM PowerControl calculates the power of your pedal stroke by multiplying angular velocity by the torque being applied to the
PowerMeter.

Power (W) = Torque (Nm) x Angular Velocity (rad/s)