How does a dynamometer measure torque?

Short Answer:

A dynamometer measures torque by applying a controlled resistance to a rotating shaft and observing the resulting force. It typically uses a brake or load device to absorb the energy from the rotating object, and a force arm to measure the twisting force produced.

The torque is calculated by multiplying the measured force by the length of the arm from the center of rotation. Dynamometers are used in testing engines, motors, and machines to measure both torque and power output accurately under different load conditions.

Detailed Explanation:

Working of a dynamometer in torque measurement

A dynamometer is an instrument used to measure the torque and power produced by rotating machines such as motors, engines, turbines, and pumps. It operates by creating a mechanical load on the machine and then measuring the force and speed to calculate torque.

Torque is the turning force applied around a shaft. By measuring how much force is needed to resist the rotation of the machine and how far that force is applied from the center of rotation, torque can be calculated.

Main Components:

  1. Load Device or Brake:
    Absorbs or resists the rotational energy from the machine. Types include hydraulic, eddy current, or mechanical brakes.
  2. Torque Arm:
    A lever connected to the brake housing. As torque is applied, this arm pushes against a load cell or scale.
  3. Force Sensor or Scale:
    Measures the force applied by the torque arm due to rotation.
  4. RPM Sensor:
    Measures the rotational speed of the shaft (used to calculate power as well).

Working Process:

  1. Connection:
    The rotating shaft of the engine or motor is connected to the dynamometer shaft.
  2. Applying Load:
    The dynamometer applies a controlled resistance (braking force) to the rotation.
  3. Reaction Force on Torque Arm:
    As the machine tries to rotate, the reaction force is applied on the torque arm connected to the brake housing. This force tries to rotate the brake in the opposite direction.
  4. Force Measurement:
    The torque arm pushes against a load cell or force gauge, which measures the force (F).
  5. Torque Calculation:
    Torque (T) is calculated using the formula:

T=F×rT = F \times rT=F×r

Where:

    • T = Torque (Nm)
    • F = Force (N)
    • r = Radius or length of torque arm (m)
  2. Optional Power Calculation:
    Power can be calculated using:

P=2πNT60P = \frac{2\pi N T}{60}P=602πNT​

Where:

    • P = Power (watts)
    • N = RPM
    • T = Torque

Types of Dynamometers:

  • Absorption Type: Absorbs energy (e.g., hydraulic, eddy current)
  • Transmission Type: Measures torque transferred through shafts
  • Driving Type: Applies torque to the machine to test its response

Applications:

  • Testing vehicle engines and motors
  • Measuring torque and power in industrial machines
  • Calibrating torque sensors
  • Research and development of automotive systems
  • Performance evaluation of electrical drives
Conclusion:

A dynamometer measures torque by resisting the rotation of a machine and detecting the force acting on a torque arm. The combination of force and distance from the shaft gives the torque value. This method is accurate and widely used in engine and machine testing, where knowing the torque helps evaluate the performance, safety, and efficiency of the system.