Refractometry or Refractive Index Measurement uses refractive index to characterize liquid or solid samples for concentration or purity determination. Every material or substance with which light interacts has a refractive index also referred to as refraction index or index
of refraction.
Refractive index is equal to the velocity of light of a given wavelength in space divided by its velocity in a substance. The velocity of light in a medium varies depending on the properties of the medium. In electromagnetic waves, the speed is dependent on the optical density of the medium where optical density is the tendency of the atoms in a material to restore the absorbed electromagnetic energy. The more optically dense a material is, the slower the speed of light. The refractive index is an indicator of the optical density of a medium.
A refractive index is a number that indicates the number of times slower than a light wave would be in the material than it is in a vacuum. The refractive index (RI, represented by its symbol n),
is the velocity of light in a vacuum divided by the velocity of light in
a medium:

Refractive Index Equation

Where,
n is the refractive index
c is the velocity of light in a vacuum (3 × 108 m/s)
v is the velocity of light in a substance

Refractive index is a measure of the bending of a ray of light when passing from one medium into another. With i being the angle of incidence of a ray in vacuum (the angle between the incoming ray and the perpendicular to the surface (normal) of a medium and r being the angle of refraction (angle between the ray in the medium and the normal), the refractive index n is defined as the ratio of the sine of the angle of incidence to the sine of the angle of refraction:

Refractive Index Graphic

Refractive index is temperature-dependent. The higher the temperature of a medium, the higher the speed of light in the medium and the lower its refractive index as shown in the graph on the right. The speed of light depends as well on its wavelength. The shorter the wavelength of the light, the higher its speed. This frequency dependency is known as dispersion. Thus refractive index is always stated together with the temperature of the medium and the wavelength of light used for the measurement. Refractive index is normally measured at a temperature of 20°C using light with a wavelength of the yellow line of sodium (D-line, 589.29 nm) and is therefore expressed as nD20.

Refractive Index Chart

How a Schmidt+Haensch Digital Refractometer Works

A modulated, high-intensity LED light source specifically designed to provide light energy at precisely 589.3 nm, the sodium D-line, the most common reference wavelength for refractive index measurements, focuses the light energy on the measuring surface of a prism. Most commonly a sapphire or YAG prism. In the absence of a fluid sample on the measuring surface, the total light energy is reflected internally toward a linear CCD array. With a fluid sample on the measuring surface, some of the light energy from the LED is predictably lost into the test fluid. Past the critical angle, all light energy is reflected internally from the measuring surface where a shadow line is projected on a high-definition CCD array.

Refracted Light Graphic

Which Refractometer Is Right For You?

Determining which refractometer is right for you will depend on your need for precision, temperature control, your measuring range, sample throughput and location, and modularity. Following are the specifications for our line of Schmidt+Haensch refractometers and inline process refractometers.

Inline Process Refractometers

Inline Process Refractometers measure the refractive index continuously and in real-time, thus determining the concentration of liquids or the mixing ratios of binary or quasi-binary mass ratios.

The measurement is independent of turbidity, color, absorption, and viscosity, which ensures maximum precision and better process control.

Applications for iPR Refractometers:

  • Concentration monitoring
  • Product interface detection
  • Quality Control (Deviation from the target value)
  • Crystallization monitoring
  • Dosage control
Inline Process Refractometers Comparison

Refractometer Model Comparrison

VariRef RefractometerVariRef RefractometerVariRef RefractometerATR-L Dispersion RefractometerATR-P Touch RefractometerATR-BR Refractometer
VariRef AVariRef BVariRef CATR-LATR-P TouchATR-BR
Refraction MethodCritical AngleCritical AngleCritical AngleCritical Angle/DispersionCritical AngleCritical Angle
Measuring Range1.32000 – 1.58000 RI /
100 °Brix
1.32000 – 1.70000 RI / 100 °Brix (VariRef B1)
1.29000 – 1.58000 RI / 100 °Brix (VariRef B2)
1.29000 – 1.58000 RI / 100 °Brix
(VariRef C)
1,33200 – 1,70000 RI
/ 100 °Brix
1,32000 – 1,54000 RI /
100 °Brix
1,32000 – 1,54000 RI /
0 – 100 °Brix
Resolution0.000001 RI / 0.001 °Brix0.00001 RI / 0.01 °Brix0.00001 RI / 0.01 °Brix0,00001 RI / 0,01 °Brix0,00001 RI / 0,01 °Brix0,00001 RI / 0,01 °Brix
Precision± 0,00002 RI* /
± 0.02 °Brix*
± 0,00002 RI* /
± 0.02 °Brix*
± 0,0001 RI* /
± 0.05 °Brix*
± 0.00004 RI* /
± 0.03 °Brix
± 0,00002 RI /
± 0,02 °Brix
± 0,00002 RI / ± 0,01 °Brix (measurement range 1,32 – 1,44) and ± 0,00003 RI / ± 0,01 °Brix (measurement range 1,44 – 1,54)
Repeatability± 0.000005 RI /
± 0.006 °Brix
± 0.00002 RI /
± 0.02 °Brix
± 0.0001 RI /
± 0.05 °Brix
± 0.00004 RI* /
± 0.03 °Brix
± 0,00001 RI /
± 0,01 °Brix
0,00001 RI / 0,01 °Brix
Measurement ModeSingle sample or flow through measurement (with optional compartment door)Single sample or flow through measurement (with optional compartment door)Single sample or flow through measurement (with optional compartment door)Single sampleSingle sample or flow-through measurementSingle sample
Ambient Temperature+ 10 °C to + 40 °C+ 10 °C to + 40 °C+ 10 °C to + 40 °C15 °C – 40 °C+10 – +40 °C+10 – +40 °C
Temperature MeasurementPt 1000 sensorPt 1000 sensorPt 1000 sensorNTC sensor for measurement of sample temperature placed inside the prismNTC sensor for measurement of sample temperature placed inside the prismNTC sensor for measurement of sample temperature placed inside the prism
Sample Temperature ControlDouble isolated
Peltier system
Double isolated
Peltier system
Double isolated
Peltier system
Double isolated
Peltier system
By external water bathNo temperature control
Temperature Control Range+ 20 °C
others upon request
+ 5 °C to + 100 °C+ 5 °C to + 80 °C10 °C – 80 °C+5 – +50 °CNo temperature control
Temperature Resolution0.01 °C0.01 °C0.01 °C0.01 °C0.01 °C0.01 °C
Temperature Precision± 0.03 °C*± 0.03 °C*± 0.03 °C*± 0.03 °C*± 0.03 °C*± 0.03 °C*
Temperature Reproducibility± 0.02 °C± 0.02 °C± 0.02 °C
Temperature Compensation Brix10 °C – 80 °C+5 bis +50 °C+5 – +50 °C
PrismSapphireYAGSapphireYAGSapphireSapphire
Light Source/WavelengthLED, interference filter
589 nm
LED, interference filter
589 nm
LED, interference filter
589 nm
LED, 7 discrete wavelength fixed
400, 450, 490, 545, 589, 660, 700 nm
(others available)
LED, interference filter
589 nm
LED, interference filter
589 nm
DisplayNone, or 7” Touchscreen,
800 x 480 Pixel
None, or 7” Touchscreen,
800 x 480 Pixel
None, or 7” Touchscreen,
800 x 480 Pixel
Back lit LCD, 16 x16 characters7″ touch screen, 800 x 480 Pixel, 16 Bit colorsBack lit LCD, 16 x16 characters
DHR 95 Refractometer
DHR 95
DHR Standard Model
Measuring scales: Sugar% (Bx) / Refractive Index (RI)
Measuring range: 0 - 95 Bx / 1.33 - 1.54 RI
Resolution: 0.1 Bx / 0.0001 RI
Precision: ± 0.2 Bx / ± 0.0003 RI
DHR Honey
Measuring scales: Sugar % (Bx) / Water in Honey (%)
Measuring range: 0 - 95 Bx / 10 – 30%
Resolution: 0.1 Bx / 0.1 %
Precision: ± 0.2 Bx / ± 0.2%
DHR Wine
Measuring scales: % Mass w/w (%)/Alcohol Probable (AP)
Measuring range: 0 - 35 % / 0 – 22 AP
Resolution: 0.1 % / 0.1 AP
Precision: ± 0.2 % / ± 0.2 AP
DHR Saline
Measuring scales: Sugar % (Bx) / Saline (NaCl)
Measuring range: 0 - 54 Bx / 0 – 28 NaCl
Resolution: 0.1 Bx / 0.1 NaCl
Precision: ± 0.2 Bx / ± 0.2 NaCl
DHR Aqua
Measuring scales: Seawater PPT (Part Per Thousand) / Seawater Specific Gravity (SG)
Measuring range: 0 - 180 Part Per Thousand / 1.000 - 1.070 SG
Resolution: 1 Part Per Thousand / 0.0005 SG
Precision: ± 1 Part Per Thousand / ± 0.001 SG
DHR PG
Measuring scales: Propylene Glycol % by volume (%) / Propylene Glycol °C Protection (°C)
Measuring range: 0 - 60 % / 0 to - 50 °C
Resolution: 0.1 % / 1 °C
Precision: ± 0.4 % / ± 1 °C
DHR EG
Measuring scales: Ethylene Glycol % by volume (%) / Ethylene Glycol °C Protection (°C)
Measuring range: 0 - 60 % / 0 to - 50 °C
Resolution: 0.1 % / 1 °C
Precision: ± 0.4 % / ± 1 °C
DHR DEF
Measuring scales: Sugar % (Bx) / For measuring AdBlue©
Measuring range: 0 - 54 Bx / 0 – 40
Resolution: 0.1 Bx / 0.1
Precision: ± 0.2 Bx / ± 0.2