Dynamometers and rope brake power

(a) Classification of dynamometers

A dynamometer measures torque, and with speed the shaft power of an engine, motor or turbine.

Absorption types are used for engine testing, and transmission types are used for in-line measurement on shafts.

(b) Rope brake

Brake torque is the net tangential force times the effective radius. The rope has finite thickness, so the effective radius is measured to the rope's centre line:

$$r_e = \frac{D + d}{2} = \frac{1.0 + 0.025}{2} = 0.5125\ \text{m}$$

Net load on the brake: $W - S = 600 - 50 = 550$ N.

$$T = (W - S)\,r_e = 550 \times 0.5125 = 281.9\ \text{N m}$$

Brake power:

$$P = \frac{2\pi N T}{60} = \frac{2\pi \times 300 \times 281.9}{60} = 8855\ \text{W} = 8.86\ \text{kW}$$

        drum (rotating)
         .---.
        ( r_e )----- rope ends: W (dead load) below
         '---'                  S (spring balance) above

Answer: brake torque $= 281.9$ N m, brake power $= 8.86$ kW.