What is the working principle of a rotational viscometer?

The working principle of a rotational viscometer can be summarized in one sentence: when the rotor rotates at a constant speed in a liquid, the liquid generates viscous resistance to the rotor, which is proportional to the viscosity. The viscosity value is calculated by measuring the resistance.
1, Core Principles (Popular Version)
Immerse the rotor into the measured liquid
The motor drives the rotor to rotate at a constant speed
The more viscous the liquid, the greater the resistance to the rotor
Instrument detects this resistance torque
Internal circuit converts torque into viscosity value (mPa · s or cP)
2, Professional principles (based on Newton's law of internal friction)
According to Newton's law of internal friction:
τ=μ⋅γ
τ
Shear stress (resistance of liquid to rotor)
μ
Dynamic viscosity (the viscosity we want to measure)
γ
Shear rate (determined by rotational speed and rotor size)
When the rotor size and speed are fixed, the shear stress ∝ viscosity instrument directly displays the detected torque as viscosity.
3, Simple workflow
Select rotor+set speed
Immerse the rotor into the sample to achieve temperature stability
The motor drives the rotor to rotate
Sensor measures torque/resistance
Display: viscosity, rotational speed, temperature, shear rate, etc
4, Key features
Belonging to dynamic measurement, suitable for on-site, production, and quality control
Measurable Newtonian and non Newtonian fluids
Different rotors/speeds can cover a wide viscosity range