Working Principle of Kinematic Viscosity Tester

The core principle of the automatic kinematic viscosity tester is based on the national standard GB/T 265 “Test Method for Kinematic Viscosity of Petroleum Products”. It adopts the gravity capillary method to measure the time required for a liquid to flow through a standard capillary at a constant temperature, and then calculates the kinematic viscosity.

1. Basic Physical Principle

The liquid flows through a calibrated glass capillary with uniform inner diameter under gravity.

According to Poiseuille’s law, the kinematic viscosity is:

ν = C × t

ν: kinematic viscosity (mm²/s)

C: capillary constant (calibrated, fixed value)

t: flow time between two marked lines (seconds)

The temperature must be strictly constant, as any variation directly affects viscosity.

2. Constant Temperature Control Principle

The instrument is equipped with a constant temperature bath (liquid bath or metal block), typically set at 40°C, 100°C, or other test temperatures, with a control accuracy of ±0.01°C.

Only under stable temperature conditions can the measured flow time be valid.

3. Automatic Sampling and Liquid Level Detection

After placing the sample into the tube, the instrument uses a vacuum pump to automatically draw the sample into the capillary to the required level.

Photoelectric sensors (infrared) are installed at both marks of the capillary.

As the liquid flows down naturally, passing the upper and lower marks, the sensor signals change, and the instrument records the time automatically with millisecond precision.

4. Automatic Calculation Principle

The controller calculates kinematic viscosity based on:

ν = C × t

It can also calculate:

Dynamic viscosity

Viscosity index (VI)

Flow index

Results are automatically displayed, stored, and printed.

5. Automatic Cleaning and Drying Principle

After testing:

The instrument automatically cleans the capillary with solvent

Then dries it with gas

This prevents residue from affecting the next test and enables continuous, unattended operation.

6. Overall Workflow

Sample loading → Temperature stabilization → Automatic suction

Gravity flow → Photoelectric timing → Viscosity calculation

Automatic cleaning → Result output

Operating Method of Kinematic Viscosity Tester

Before operation, check the instrument appearance, power supply, and bath liquid level. Ensure the capillary is clean and dry, and the environment is free from vibration and dust. After powering on, enter system settings and set the test temperature (e.g., 40°C or 100°C). Wait until the bath temperature stabilizes.

Inject the sample into the viscometer tube to the specified level, place it into the constant temperature bath, and allow it to reach thermal equilibrium.

Start the automatic test program. The instrument draws the sample into the capillary using a vacuum system. Under gravity, the liquid flows naturally. The photoelectric sensors detect when the liquid passes the upper and lower marks and record the time precisely.

After the test, the instrument automatically calculates and displays the kinematic viscosity value. It then performs automatic cleaning and drying of the capillary to avoid contamination.

During operation, do not touch the capillary. Maintain proper liquid level. After testing, record the data in time, shut down the instrument, and perform routine cleaning and maintenance.

2026-04-22 16:03