EXTECH RF18 DATA SHEET

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

3

4

5

2

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

Bad

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

1

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 ©

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

2005 Extech Instruments Corporation.

Bad

Good

Temperature Compensation Table (Referenced To 20

% 5 10 15 20 25 30 35 40 45 50 55 60 65 70

o

C
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)

Subtract the following from the measurement

O

C)

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 [phone] 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 a ny 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.

www.extech.com

RF18 V1.1 3/05