Viscometer Calibration

A viscometer is an instrument used to measure fluid viscosity and the flow properties of liquids. Viscosity arises from the internal friction of a fluid and is defined as a liquid’s resistance to flow or shear stress.

Viscosity has often been referred to as the most important characteristic of base oil. Viscosity is very important in the lubrication of a machine. Too low viscosity would increase surface contact between internal components in motion to generate wear and secondly it will reduce the cooling effect by the fluid.

If the viscosity of a fluid is too high then it would force the machine to work harder to overcome the lubricant’s internal resistance and may also heat the system. Therefore it is essential to know not only the viscosity of the lubricating oil but also its characteristics with changing temperature and other environmental conditions.

 

Applications of viscometers

Viscometers have wide and varied applications in the materials science and chemical industries for materials such as paints, asphalt, oil, and plastics. They are also used for food and beverages and personal-care products.

Measuring viscosity is important when considering process conditions where fluids need to be piped or pumped. The viscosity of the material also affects its coating and dipping characteristics which are particularly important to paints, inks, adhesives, and other coatings.

Viscosity is a very useful indirect measure of material properties including molecular weight and density, both of which affect flow behavior. Viscometers are therefore be used to monitor this fluid property for quality control.

 

Use of Viscometers

Ensuring the flow of engine oil under different temperature conditions is very important for any engine and therefore viscosity of the lubricating oil should be accurately known. Analyzing the flow properties of various liquids in the food industry is an important application. Since changes in viscosity reflect changes to molecular weight, viscometers are used to characterize plastics. They are particularly useful in polymer synthesis since the flow rate can be used to determine the change of polymer length through different processes.

 

Types of viscometers

There are many ways to measure viscosity, but they may be classified into two basic types. In an assembly either an object, such as a sphere or a rotor blade, moves through a stationary fluid or the fluid flows through or past a stationary object. In both cases, the resistance to flow is measured is used to calculate the viscosity of the fluid.

 

Capillary viscometers

Capillary viscometers are also known as u-tube or glass viscometers. They are often used in the laboratory environment.  They measure viscosity by determining the time it takes for a fluid to flow between two points in a capillary tube. This method works for transparent fluids.

For opaque fluids, this method may not work so it is necessary to use reverse-flow viscometers. These viscometers only wet the timing section of the viscometer capillary during the actual measurement.

Capillary viscometers are available in manual or automatic models. Automatic devices use infrared optical sensors for transparent samples or thermal sensors for opaque samples and give quite accurate results.

 

Rotational viscometers

Simple rotational viscometers use a torsion spring to measure the torque required to rotate a spindle in the material. This leads to assessing the viscosity of the fluid. Changing rotor speed and size allows for the measurement of different ranges of viscosity.

The device is made up of a lightweight magnetic rotor that floats in a liquid-filled tube, rotating at a constant speed. The sample fluid’s viscous forces drive the rotor, which reaches an equilibrium rotor speed, which is recorded as a measure of the fluid’s viscosity.

 

Rolling ball, falling ball, sphere, and piston viscometers

In this instrument, a ball rolls through a closed, sample-filled capillary that is inclined at a defined angle. Inductive sensors determine the ball’s rolling time between two points which leads to determining the viscosity of the fluid.

In another design, a falling ball measures the time it takes for a ball to fall under gravity through a fluid-filled tube inclined at an angle that leads to the viscosity of the fluid. Another design is based on a falling piston which operates on the same principle, but it measures the resistance to the piston falling through the fluid.

Viscosity standards are used to check the accuracy of a viscometer and can be important for verifying compliance with industry quality systems.

 

Calibration of Viscometers

Viscometers measure the viscosity or thickness of fluids and are used in industrial, scientific, manufacturing, or other industries. Un-calibrated viscometers can give wrong results which can degrade the quality of products and cost you money. You may use a third-party calibration lab, such as e2b calibration to ensure their viscometer equipment is calibrated correctly and can provide accurate results. Our experts calibrate viscometers with a NIST traceable standard solution.

 

Annual calibration of your instrument should include:
  1. General inspection of the instrument.
  2. Check the internal mechanisms.
  3. Replacement of the pivot point.
  4. Check the shaft and replacement if necessary.

All the actions taken should be recorded in the calibration and servicing certificate.

 

Calibration procedure for rotational type viscometer:
  1. Select the appropriate spindle and attach it to the viscometer.
  2. Transfer standard oil to clean test vessel.
  3. Insert and center the spindle in standard in standard until the level is at the immersion groove on the spindle shaft.
  4. Ensure that the temperature of the oil is noted.
  5. To take the viscosity reading, turn the viscometer motor on at the recommended speed and wait for the reading to stabilize.
  6. Use the recommended standard temperature and spindle speed.
  7. With disc-type spindles, tilt the spindle slightly while immersing to avoid trapping air bubbles on the disc under surface.
  8. You may find it more convenient to immerse the spindle in this fashion before attaching it to the viscometer.
  9. If necessary, calibration can also be checked at other points.
  10. Your instruments reading should be within 1% of the full-scale reading.
  11. Affix new calibration label.

 

The accuracy of a viscometer is dependent not only on the engineering of the instrument itself but also on how precisely temperature can be controlled. Normally many viscosity measurements are made which are then averaged to arrive at an accurate result.

 

e2b calibration provides calibration service for all types of instruments including viscometers. We are an ISO 17025: 2017 accredited facility. We can calibrate any type of viscometers to the highest industry standards. Our services are unmatched in the industry. Contact e2b calibration for more information about our on-site services.

 

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