In a viscometer, torque refers to the twisting force that is applied to the spindle as it rotates in the liquid being tested. The torque measurement helps determine the resistance of the liquid to flow, which is related to its viscosity.

The torque is typically measured using a motor and a sensor. As the spindle rotates, the motor applies a force, and the sensor measures the amount of torque required to maintain the rotation at a constant speed. This torque reading is then used to calculate the viscosity of the liquid.

Now, let’s talk about why torque is often expressed as a percentage. The torque measurement in a viscometer is not an absolute value but rather a relative one. It represents the resistance to flow of the liquid being tested compared to a reference liquid with a known viscosity.

The viscometer is calibrated using a reference liquid of known viscosity. The torque required to rotate the spindle in the reference liquid is determined and assigned a value of 100%. When testing other liquids, the torque reading obtained is expressed as a percentage of the torque observed in the reference liquid.

By using a percentage scale, it allows for easier comparison and understanding of viscosity differences between different liquids. For example, if a liquid requires 50% of the torque compared to the reference liquid, it means it has half the viscosity of the reference liquid. If it requires 200% of the torque, it means it has twice the viscosity.

Using a percentage scale also makes it possible to compare measurements obtained using different spindles or rotational speeds. It provides a standardized way of expressing viscosity regardless of the specific viscometer configuration used.

So, torque in a viscometer is expressed as a percentage to represent the relative resistance to flow of a liquid compared to a reference liquid with a known viscosity.