Understanding Refraction

This pencil appears to bend when it enters
the water because of the change in the light
ray speed as the medium changes.

Refraction is the directional change of wave propagation caused by a change in the light beams transmission medium.

Light rays travel through space in a straight line at approximately 300,000 km/s. As light passes through a transparent medium, such as water or glass, its speed is decreased.

For glass, its reduced to 200,000 kilometers per second, and for water the speed is 225,000 kilometers per second.

If the light enters into a medium perpendicular to the surface, it passes straight through but at a slower speed. However if the light beam arrives at the medium surface at an angle, not only will it speed be reduced, but it will bend due to a process called refraction.

As a beam of light reaches the surface of a medium the lower portion enters first and is slow down. However, the upper portion is still traveling at the speed of light until it arrives at the surface and enters. This speed difference at the top and bottom aspects of the light path causes it to pivot, bending toward what is referred to as the normal. This is an imaginary line drawn perpendicularly to the surface of the material.
 
Transparent materials have what is called a refractive index. This is the speed at which light travels in a medium compared to like traveling in a vacuum.
   
For example, typical glass has a refractive index of 1.33. This is calculated by dividing the speed of light in a vacuum (300,000 km/s) by the speed of light in glass (225,000 km/s).
   
The refractive index of air is 1.0003. Anytime a light beam travels from a medium with a low index of refraction, like air, to a medium with a higher index of refraction, like glass, the beam of light will bend toward the normal.
   
Likewise when the beam of light exits a highly refractive medium into a medium with the low index of refraction, the process is reversed.
   
The bottom portion of the beam of light exits first, and resumes at the speed of light, with the top portion still at the speed determined by the medium. This causes the beam to pivot away from the normal line.

Instruments used to measure the refractive index are called refractometers. Refractometers used in industrial automated systems are referred to as inline refractometers.

Some Recent Literature Updates for Electron Machine Corporation

MPR E-Scan is a rugged, industrialized
in-line process refractometer.
Image courtesy Electron Machine Corp.

Electron Machine Corporation, manufacturer of industrial process refractometers, recently updated some of their product, application and support literature. The new documents are described and linked below. Share your process measurement challenges, and any questions you may have about the Electron Machine process refractometers, with a product specialist. Leverage your own knowledge and experience with their product application expertise to develop effective solutions.

Operating and Service Manual for MPR E-Scan
Service manual for the MPR E-Scan, a hybrid-digital critical angle in-line process refractometer. It is used to measure the refractive index of process fluids.

MDS (Monitor Divert System) Color Manual
Service manual for the Monitor Divert System, a BLRBAC (Black Liquor Recovery Boiler Advisory Committee) compliant Black Liquor solids monitoring system designed specifically for Black Liquor recovery boilers.

Refractometers for Food Industry

Brochure for refractometers used to detect sugar levels and properties of jams juices, beverages, dairy products and much more.

Refractometers for Chemical Industry

Brochure for the MPR E-Scan used for measuring the strength of a chemical when diluted with water or with another chemical.

MPR E-Scan Sales Brochure

The MPR E-Scan is a rugged, industrialized, in-line process refractometer. It directly measures the refractive index of process fluids and then displays the reading in any number of customer-desired units (Brix, Percent Solids, Dissolved Solids, SGU, R.I., etc.).

Rugged Benchtop Refractometer

The DSA E-Scan is a benchtop refractometer
rugged enough for portable field use.
Image courtesy Electron Machine Corp.

Refractometry is a widely employed analytical technique used to indirectly measure dissolved solids content of subject liquids. The process employs a refractometer, a device or instrument, to determine the refractive index for a test sample. The measurement is employed throughout science and industry to assess a material's composition or purity.

The refractive index of a substance is dependent, in part, upon temperature and the wavelength of light used in the measurement. Common applications include Brix testing for sucrose level, along with others in the beverage, pulp and paper, chemical, flavor, and fragrance industries. Refractometry is used as a quality control measurement, to assure uniformity among product batches.

Manual refractometers have been available for many years and require human observation and interpretation of a scale reading to obtain a refractive index. Automatic, as well as in-line units are available today that provide uniform accuracy and faster sample processing.

The DSA E-Scan, manufactured by Electron Machine, is an automatic, bench-top critical angle refractometer with a digital readout and temperature-controlled sample chamber. Its compact size and rugged design permit operation in the field and in areas with limited space. The unit provides fast and accurate refractive index measurements of sample liquids.

Share your process analytical measurement challenges with liquid process analytics experts, leveraging your own knowledge and experience with their application expertise to develop effective solutions.

Dissolved Solids Analyzer Refractometer from Alliance Technical Sales, Inc.

Applying Process Refractometers in Sugar Cane Processing

In-line process refractometer
Image courtesy Electron Machine Corp.

Sugar cane, after harvesting, requires processing within a limited time window to avoid sugar loss by inversion to glucose and fructose. The traditional two stage process, milling and processing, may be combined in a single modern production facility. Process refractometers can be found in both operations, making an optical measurement of a solution’s refractive index used to determine the concentration of dissolved solids.

To achieve high quality liquid and crystal sugars and contain production cost, refractometers are employed to deliver accurate in-line Brix and other measurements in the cane sugar refining and milling processes.

Specific uses of refractometers in sugar production are:

• Product flow adaptation to evaporator capacity to achieve energy savings.
• Extraction process optimization, minimizing the use of water that will need to be removed at the evaporator.
• Separation column feed juice control to adjust concentration to match capacity.
• Quality assurance check on liquid bulk sugar and molasses.
• Vacuum pan automatic and accurate seeding.
• Monitor supersaturation over complete strike of crystallization.

Share your process analytic and measurement challenges with the experts at application specialists, leveraging your own process knowledge and experience with their product application expertise to develop an effective solution.