User's Guide

Brix Refractometer

Models RF18

Introduction

Congratulations on your purchase of the Extech RF18 Brix Refractometer.

Precision optical instruments should be handled gently; avoid touching the

optical surface. Careful use of these instruments will provide years of

reliable service.

Specifications

Range

0 to 18% Brix

Resolution

0.1%

Dimensions

1.2 x 1.6 x 6.7" (30 x 40 x 170mm);

Weight

3.2 oz. (91g)

Description

1. Prism

2. Cover plate

3. Adjustment screw

4. Mirror tube

5. Eyepiece

Operation

This instrument measures the refractive index of a sample. The measurement

is displayed in % Brix.

1. Zero Adjustment

Cover the prism with distilled water (several drops will suffice). Close the

cover plate and rotate the adjustment screw until the light/dark boundary

(shadowline) lines up with the zero line. After the zero adjustment, clean

the prism with a soft cloth.

2. Sample Preparation and Reading

To take a sample reading, simply place a few drops of a sample liquid on

the measurement prism at the end of the instrument. Close the prism

cover plate so that the liquid spreads across the entire surface of the prism

without air bubbles or dry spots (see

diagram). Allow the sample to remain

on the prism for approximately 30

seconds.

While holding the instrument under a

light source, look through the

eyepiece. The sucrose concentration

is determined by the intersection of

the boundary of the light and dark

fields (known as the shadowline) on

the printed scale. If the scale appears out of focus, the eyepiece may be

adjusted by rotating the knurled portion of the eyepiece. The instrument

also features an eye-guard to prevent stray light from entering the

eyepiece and causing reflections.

It may be necessary to adjust the position of the light source to maximize

the contrast of the shadowline. Under normal conditions, optimal contrast

is obtained by holding the instrument underneath and perpendicular to a

light source.

Once a reading has been taken, wipe dry with a clean cloth (do not wash

or rinse) and place the instrument in the supplied plastic case. Store the

instrument in a safe, dry environment.

Note: The Distilled water temperature, used for zero adjustment, and the

sample liquid temperature should be the same. If the temperature of the

samples fluctuates, zero the refractometer every 30 minutes (RF10 only).

3. Temperature Compensation

Temperature is one of the single most important factors influencing

accurate refractometer readings and is one of the largest sources of

measurement error. Temperature compensation relieves the user of the

responsibility to measure temperature and apply a correction factor when

taking readings.

The RF18 Refractometer has been designed for use with a 20°C standard

temperature. Therefore, if the temperature of the measurement deviates

from 20°C, the reading must be manually compensated in accordance

with the Temperature Compensation Table below.

Example: A reading of 20% at 28°C is compensated thusly: 20% +

0.62%=20.62%.

Copyright © 2005 Extech Instruments Corporation.

All rights reserved including the right of reproduction in whole or in part in any form.

Temperature Compensation Table (Referenced To 20

%

5

10

15

20

25

30

35

40

45

50

55

60

65

70

o

C

Subtract the following from the measurement

10

0.58 0.59 0.61 0.64 0.67 0.69 0.71 0.72 0.74 0.74 0.74 0.75 0.76 0.77

11

0.51 0.54 0.55 0.58 0.61 0.63 0.65 0.65 0.67 0.67 0.67 0.68 0.68 0.69

12

0.47 0.49 0.50 0.52 0.55 0.57 0.58 0.58 0.60 0.60 0.60 0.60 0.61 0.61

13

0.42 0.44 0.44 0.45 0.49 0.50 0.51 0.51 0.53 0.53 0.53 0.53 0.53 0.53

14

0.37 0.38 0.39 0.40 0.42 0.43 0.44 0.44 0.45 0.45 0.45 0.45 0.45 0.46

15

0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.37 0.38 0.38 0.38 0.38 0.38 0.38

16

0.25 0.26 0.27 0.28 0.28 0.29 0.30 0.30 0.30 0.31 0.31 0.31 0.31 0.31

17

0.19 0.20 '0.20 0.21 0.21 0.22 0.22 0.23 0.23 0.23 0.23 0.23 0.23 0.23

18

0.13 0.13 0.14 0.14 0.14 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15

19

0.06 0.07 0.07 0.07 0.07 0.07 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08

Add the following to the measurement

21

0.07 0.07 0.07 0.07 0.07 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.08

22

0.14 0.14 0.14 0.14 0.15 0.15 0.16 0.16 0.16 0.16 0.16 0.16 0.16 0.15

23

0.21 0.21 0.22 0.22 0.23 0.23 0.23 0.23 0.24 0.24 0.24 0.24 0.23 0.22

24

0.28 0.29 0.29 0.30 0.30 0.31 0.31 0.31 0.31 0.31 0.32 0.32 0.31 0.31

25

0.35 0.36 0.37 0.38 0.38 0.39 0.39 0.40 0.40 0.40 0.40 0.40 0.39 0.39

26

0.43 0.44 0.44 0.46 0.46 0.47 0.47 0.48 0.48 0.48 0.48 0.48 0.47 0.47

27

0.51 0.52 0.53 0.54 0.55 0.55 0.56 0.56 0.56 0.56 0.56 0.56 0.55 0.55

28

0.59 0.60 0.61 0.62 0.63 0.64 0.64 0.65 0.65 0.64 0.64 0.64 0.64 0.63

29

0.67 0.68 0.69 0.70 0.71 0.72 0.73 0.73 0.73 0.73 0.73 0.72 0.72 0.71

30

0.75 0.77 0.78 0.79 '0.80 '0.81 0.81 0.81 0.82 0.81 0.81 0.81 0.80 0.79

Source: International Commission for Uniform Methods of Sugar Analysis (1966)

International Brix% Scale

Brix to Refractive Index (nD) Conversion Table

%

nD

%

nD

%

nD

%

nD

%

nD

%

nD

0

1.333

15

1.3557

30 1.3811

45

1.4097

60 1.4419

75

1.4778

1

1.3344

16

1.3573

31 1.3829

46

1.4118

61 1.4442

76

1.4804

2

1.3359

17

1.3589

32 1.3847

47

1.4138

62 1.4464

77

1.4829

3

1.3373

18

1.3605

33 1.3866

48

1.4159

63 1.4488

78

1.4855

4

1.3388

19

1.3622

34 1.3884

49

1.418

64 1.4511

79

1.4881

5

1.3403

20

1.3638

35 1.3903

50

1.42

65 1.4534

80

1.4907

6

1.3418

21

1.3655

36 1.3922

51

1.4222

66 1.4558

81

1.4933

7

1.3433

22

1.3672

37 1.3941

52

1.4243

67 1.4582

82

1.496

8

1.3448

23

1.3689

38

1.396

53

1.4264

68 1.4606

83

1.4987

9

1.3463

24

1.3706

39 1.3979

54

1.4286

69

1.463

84

1.5014

10 1.3478

25

1.3723

40 1.3998

55

1.4308

70 1.4654

85

1.5041

11 1.3494

26

1.374

41 1.4018

56

1.4329

71 1.4678

86

1.5068

12 1.3509

27

1.3758

42 1.4037

57

1.4352

72 1.4703

87

1.5096

13 1.3525

28

1.3776

43 1.4057

58

1.4374

73 1.4728

88

1.5123

14 1.3541

29

1.3793

44 1.4077

59

1.4396

74 1.4753

89

1.5151

Source: International Sugar Analysis Committee

Warranty

EXTECH INSTRUMENTS CORPORATION warrants this instrument to be free of defects in parts and

workmanship for one year from date of shipment (a six month limited warranty applies on sensors and

cables). If it should become necessary to return the instrument for service during or beyond the

warranty period, contact the Customer Service Department at (781) 890-7440 ext. 210 for

authorization or visit our website at www.extech.com (click on ‘Contact Extech’ and go to ‘Service

Department’ to request an RA number). A Return Authorization (RA) number must be issued before

any product is returned to Extech. The sender is responsible for shipping charges, freight, insurance

and proper packaging to prevent damage in transit. This warranty does not apply to defects resulting

from action of the user such as misuse, improper wiring, operation outside of specification, improper

maintenance or repair, or unauthorized modification. Extech specifically disclaims any implied

warranties or merchantability or fitness for a specific purpose and will not be liable for any direct,

indirect, incidental or consequential damages. Extech's total liability is limited to repair or replacement

of the product. The warranty set forth above is inclusive and no other warranty, whether written or oral,

is expressed or implied.

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