Czech Metrology Institute  
Okružní 31,  638 00 
Brno 
1. ------IND- 2012 0116 CZ- EN- ------ 20120301 --- --- PROJET 
 
The Czech Metrology Institute (CMI), being the competent body for establishing metrological and 
technical requirements for legal measuring instrume nts and for establishing testing methods for type 
approvals and for verifications of  legal measuring instruments pursuant to Section 14(1) of Act No 
505/1990 Coll. on metrology, as amended, and pursuant to the provisions of Section 172 et seq. of Act 
No 500/2004 Coll., the Rules of Administrative Pro cedure, as amended, initiated on 13 December 
2011, by virtue of office, administrative pro ceedings pursuant to Section 46 of the Rules of 
Administrative Procedure, and on the basis of its information, issues the following: 
 
 
I 
GENERAL MEASURE  
number: 0111-OOP-C024-11 
ref.: 0313/024/11/Pos., 
 
laying down the metrological and technical re quirements for legal measuring instruments, 
including methods for the testing and verification of the legal measuring instruments: 
‘refractive index measuring instruments—prism refractometers’ 
1   Basic concepts 
For the purposes of this General Measure, th e terms and definitions given in the VIM1) and those listed 
below shall apply: 
1.1   refractometer: measuring instrument used to measure the relative refractive index n of liquids or 
solids and their dispersion, and to determine quan tities that are functionally linked to the refractive 
index (e.g. the proportion by mass of sucrose in aqueous solution) 1.2   digital refractometer: refractometer equipped with an in dication device showing numerical 
measured values on a display  
1.3   visual (analogue) refractometer: refractometer in which indications are read off a scale in the 
eyepiece 
1.4   measuring prism: prism on which a test sample (i.e. test prism or test liquid) is placed and 
through which a beam passes that is refracted by the sample 
                                                     
 
1)   International Vocabulary of Metrology—Basic and General Concepts and Associated Terms (VIM). Draft General Measure No 0111-OOP-C024-11 
1.5   immersion liquid: liquid that creates optical contact between the contact surfaces of a measuring 
prism and a test prism 
1.6   dispersion: dependence of the refractive index on wavelength  
1.7   proportion by mass of sucrose in distilled water WB: ratio of the mass of chemically pure 
sucrose in solution m1 to the mass of aqueous solution m2 in percent 
NOTE   The term Brix is used for this proportion. 
The proportion by mass of sucrose in aqueous solution WB in the interval from 0% to 85% may be 
converted into the refractive index value relative to standard air using the following relationship: 
n = A0 + A1.WB + A2.WB2 + A3.WB3 + A4.WB4 + 
A5.WB5 
1.000 271 91 
 
where A0 = + 1.333 348 8 A1 = + 1.428 372 × 10-3 
 A2 = + 5.440 473 × 10-6 A3 = + 1.306 219 × 10-8 
 A4 = + 1.203 625 × 10-10 A5 = – 8.977 840 · 10-13 
1.8   relative refractive index n: the ratio of the speed of light in a vacuum to the speed of light in a 
medium; the refractive index in air di ffers from the refractive index in a vacuum only by a value close to 
3 × 10-4 
1.9   basic error (of a measuring instrument): a measurement error of a measuring instrument 
ascertained under reference conditions before the st art of electromagnetic compatibility (EMC) tests 
1.10   serious error (during EMC tests): a state found in EMC tests in which the difference between a measurement error found in EMC tests and the basic error (of a measuring instrument) is greater 
than the maximum permissible error value 
2   Metrological requirements  
2.1   Specified working conditions 
2.1.1   Working temperature  
Prism refractometers must meet the metrological requirements within the temperature range specified 
by the manufacturer, which shall be at least +15°C to +30°C.  
2.1.2   Reference conditions for refractometer tests  
The ambient reference temperature for refractometer tests shall be (20 ± 2)°C. The reference pressure 
shall be normal atmospheric pressure in the range from 98.66 kPa to 103.98 kPa. 
2.1.3   Reference conditions for specifying the refractive index 
In accordance with convention, the refractive index of  a substance is determined relative to standard 
air in monochromatic light from a sodium vapour lamp, i.e. at wavelength λ = 589.3 nm. According to 
the ICUMSA ( International Commission for Uniform Methods of Sugar Analysis ), the reference 
conditions of standard air are defined as follows: 
a) temperature  20.0°C, 
b) atmospheric pressure 101.325 kPa, 
c) relative humidity 50%, 
2 Draft General Measure No 0111-OOP-C024-11 
d) CO 2 content 0.03 vol.%, 
e) refractive index of standard air relative to vacuum 1.000 271 91. 
2.2   Measurement interval and units 
The scope of measurement and type of test liquid shall be specified by the manufacturer.  
The measurement interval must be expressed in refractive index values or in units that can be 
converted into refractive index values. It may th erefore be expressed in the following values and 
appropriate units of measurement: 
a) refractive index; 
b) proportion by mass of sucrose in aqueous solution, in percent (Brix);   
c) the angle from which the refractive index can be calculated; 
d) quantities that are functionally linked to the refractive index (e.g. sugar concentration). 
In the case of c) and d), the technical documentation of the refractometer must give the conversion 
relationship or a table for the conversion of th e given units into the units in a) or b). 
2.3   Maximum permissible error  
The maximum permissible errors of prism refractometers at the reference temperature of 20°C are 
given in Table 1 together with the applicable classes of accuracy: 
Table 1—Maximum permissible errors 
Accuracy class Maximum permissible error in 
refractive index units  
I ±5 × 10-5 Prism refractometers w ith a refractive index 
measurement error less than or equal to  
±5 × 10-5 
II ±1 × 10-4 Prism refractometers w ith a refractive index 
measurement error less than or equal to  ±2 × 10-
4 III ±2 × 10-4 
IVa ±5 × 10-4 Prism refractometers w ith a refractive index 
measurement error less than or equal to  
±1 × 10-3 Va ±1 × 10-3 
a   Requirement for prism refractometers of accuracy classes IV and V will enter into force after the 
classification of these measuring instruments as legal measuring instruments. 
 
2.4   Corrections for the effect of heat  2.4.1   Digital refractometers 
Correction for the effect of heat of the su rroundings to the value at a temperature of 20
oC must (for 
digital refractometers of accuracy class I or II) or  may (for digital refractometers of other accuracy 
classes) be carried out by an automatic temperatur e correction device using suitable software. It must 
be clear from the indication of the result that the result has been corrected.  
2.4.2   Visual refractometers 
For visual refractometers, correc tion for the effect of heat of the surroundings to the value at a 
temperature of 20oC shall be carried out automatically by th e refractometer or by conversion of the 
measured values or using suitable agreed tables. 
3 Draft General Measure No 0111-OOP-C024-11 
3   Technical requirements 
3.1   Digital refractometers  
Digital refractometers must be equipped with: 
a) an indication device; 
b) an automatic heat correction device; 
c) a zeroing device. 
3.1.1   Indication devices 
An indication device must indicate the measured value: 
– of the refractive index with a scale interval of 1 × 10n, 2 × 10n or 5 × 10n, where n = –5, –4 or 
–3; 
– of the proportion by mass of sucrose in aqueous solution (Brix) with a scale interval of 0.01%, 
or 0.1%, or 0.2%, or 0.5%. 
The digits on the display must be at least 5 mm high.  
An indication device must not indicate any value if it  is not in contact with the optical surface of the 
test substance. 
3.1.2   Devices for automatic correction for ambient temperature 
Digital refractometers of accuracy class I and II must have a display temperature resolution of at least 
0.1°C.  
Digital refractometers of accuracy class I and II must be equipped with an automatic ambient temperature correction device, and the indication de vice then gives a measured refractive index value 
converted into the refractive index valu e at a reference temperature of 20°C. 
Data on the corrections made, including the subs tance type, conversion relationship and working 
temperature range must be given in the tec hnical documentation accompanying the measuring 
instrument. 
3.1.3   Zeroing devices 
Digital refractometers must be equipped with a zeroing device. It must always be clear when an 
adjustment is being made and when a measurement is being taken.  
Digital refractometers are reset to zero using distilled water. They may, however, be equipped with a 
device for adjusting to a value other than zero. 
Under normal conditions, the movement of the zero over four hours must be less than half a scale 
interval. 
Access to a zeroing device must be ensured during operation. 
3.1.4   Printing devices 
Digital refractometers must be equipped with devices for printing the indicated results of 
measurements, including their measurement units. The measurement results may be converted and 
printed in other units. 
3.2   Visual refractometers  
Visual refractometers must be equipped with: 
a) a measuring prism; 
b) an indication device; 
4 Draft General Measure No 0111-OOP-C024-11 
c) a temperature measuring instrument. 
3.2.1   Measuring prisms  
An optical-mechanical system must ensure that  the results from various operating positions do not 
differ by more than half the maximum permissible error.  
The design of the prism of a refractometer dispersion compensator must be such that the results of 
refractive index measures using the compensator in white light, or without it but in monochromatic 
light from a sodium vapour, do not differ by more  than half the maximum permissible error. 
Optical parts must not have coarse scratches, melting, black spots or other defects hindering 
observations. 
Measuring prisms must be fixed in a metal frame using an adhesive that is resistant to acids, alkalis 
and organic solvents. 
3.2.2   Indication devices 
Visual refractometers have analogue indication devi ces with an eyepiece for reading values off a scale. 
The unit of measurement must be indicated on the scale. 
An indication device must indicate the refractiv e index value with a scale interval of 1 × 10n, 2 × 10n 
or 5 × 10n, where n = –5, –4 or –3.  
Refractometer scales may be linear or non-linear. The division size must be such that a movement of 
the dividing line between two neighbouring divisions shows clearly in the field of view of the 
eyepiece.  
The measured value is a mark on a scale corresponding to the boundary between the dark and the clear 
parts of the field of view. The field of view must be well lit. The dividing line must be sharp and 
parallel to the scale divisions or the line of sight mark. 
The dioptre setting of the eyepiece must be within the range of at least ±3 dioptre. 
3.2.3   Temperature measuring instruments 
Visual refractometers must be equipped with a bu ilt-in temperature measuring instrument for making 
corrections for the effect of temperature on measured values. 
A thermometer must have a scale interval of at least 1°C. The tempering chambers of a refractometer must be  sealed, with an opening for the thermometer.  
3.2.4   Zeroing devices 
A visual refractometer may be equipped with a scale setting screw.  
3.3   Materials 
A measuring instrument must be made of materials that ensure reliability and constancy during use. 
The parts of a refractometer that come into contact with the test substances must withstand the effects 
of the substances that the refractometer is intended to measure. The metal parts of a refractometer must be protected with a coating of chrome, nickel, etc. The edges 
of a refractometer must be rounded. 
3.4   Power supply  
Digital refractometers connected to mains must be supplied with alternating current 
UN within the range 
UN –15% and UN +10%, where UN is the nominal voltage specif ied by the manufacturer of the 
measuring instrument, with a frequency of ±2%. 
5 Draft General Measure No 0111-OOP-C024-11 
For reference purposes, a voltage of UN ±2% shall be used, with a frequency of ±0.4%. 
The limiting values of the alternating supply current Umin and Umax shall be specified by the 
manufacturer of the measuring instrument. 
3.5   Resistance of measuring instruments to external effects 
3.5.1   Mechanical resistance  
The construction of a refractometer and the materials used must guarantee adequate strength, stability 
and resistance to mechanical shocks.  
3.5.2  Tempering of the place of measurement of a refractometer 
The effect of external temperatures can be compensated for by the tempering system of a 
refractometer. If an external medium is used for tempering, then the whole system must be sealed.  
3.6   Electromagnetic compatibility (EMC) 
Refractometers that contain electronic components must not be affected by electrical or 
electromagnetic interference, or they must react to such interference in a defined manner (for example, 
by reporting an error, blocking measurement, etc.). Furthermore, they must not emit unwanted electromagnetic fields. 
In EMC tests, a refractometer must show normal functioning within the limits of the maximum 
permissible errors pursuant to section 2.3 or, if the li mits are exceeded, the refractometer must react in 
a defined manner. 
3.7   Security of measuring instruments against fraud 
A refractometer must not have characteristics th at would facilitate its fraudulent use, and the 
possibility of its unintentional defective use must be minimal. Components that the user must not 
dismantle must be secured against such activities. 
4   Marking of measuring instruments 
4.1   Markings on a measuring instrument 
Refractometers must be clearly and visibly marked  with the following information as a minimum:  
a) the mark or name of the manufacturer; 
b) the type of refractometer; 
c) their serial number. 
4.2   Placing of official marks 
A space must be prepared on a measuring instrument for the placing of an official mark. 
5   Type approval of measuring instruments 
5.1   General 
The type approval process for a refractomet er shall include the following tests: 
a) an external inspection; 
b) accuracy tests; 
c) tests of resistance to external effects; 
d) tests of resistance to external disturbances. 
6 Draft General Measure No 0111-OOP-C024-11 
5.2   External inspection   
An external inspection shall assess 
a) the completeness of the required technical docum entation, including operating instructions; 
b) the conformity of the metrological and technical characteristics specified by the manufacturer 
in documentation with the requirements of this regulation set out under headings 2, 3 and 4; 
c) the completeness and state of functioning of th e refractometer in accordance with the required 
technical documents; 
d) for a digital refractometer, the compatibility of th e software version with the version specified 
by the manufacturer. 
The state of functioning of the refractometer shall be checked by testing the operation of the moving 
parts, if the refractometer has any. The refractomet er scale must be well lit, or the display readings 
must be clear and unambiguous. 
With the thermostat switched on, the tightness of hose and tempering chambers shall be checked, if the 
refractometer is so equipped. 
If the visual refractometer is equipped with an adju stment screw for the scale, the screw must rotate 
lightly, but not freely.  
5.3   Testing equipment  
5.3.1   Reference materials  
In refractometer tests, the following reference materials shall be used:  
a) optical glass certified reference materials (CRM) with a constant refractive index in the form 
of right-angled prisms, cubes or tablets;  
b) organic liquid certified reference materials ( CRMs), for example n-butyl alcohol, p-xylene, 
mono-bromobenzene and mono-bromonaphthalene, the stability over time of the refractive 
index of which is ν ≤ 5 × 10-5/year. Their expanded uncertainty U (k = 2) must be at least three 
times smaller than the maximum permissible error of the refractometer pursuant to section 2.3; 
c) aqueous solutions of sucrose, where it is necessar y to take account of their stability over time 
and the correct procedure for their preparation. 
5.3.2   Specific equipment 
The following equipment inter alia shall also be used: 
a) thermostats ensuring set temperature fluctuations of ±0.1°C and/or ±0.02°C; 
b) a sodium vapour lamp with λD = 589.3 nm or a mercury vapour lamp with λe = 546.1 nm; 
c) a barometer; 
d) a thermometer with a scale interval of at least 0.5°C for monitoring temperatures in the 
laboratory; 
e) a set of immersion liquids for sealing the gap be tween the test object and the measuring prism. 
5.4   Preparation of measuring instruments for testing 
5.4.1   A refractometer must be stabilised to the laboratory temperature while switched on and with a 
power supply pursuant to section 3.4 for at least six hours prior to testing in the laboratory. 
5.4.2   A digital refractometer must be stabilised for at least six hours prior to testing in the laboratory 
with a supply voltage UN ±2% and, in the case of alte rnating current, with a frequency fN ±0.4%, 
7 Draft General Measure No 0111-OOP-C024-11 
where UN is the nominal supply voltage specified by the manufacturer of the measuring instrument 
and fN is the nominal frequency of the supply voltage specified by the manufacturer of the measuring 
instrument. In the case of a battery-supply refractometer, the UN value shall equal the value of the 
nominal voltage of the battery. If the supply voltage  is determined by a range of nominal voltage 
values, the UN value must be specified by the manufacturer of the measuring instrument.  
5.4.2   All optical glass CRMs used for testing a refractometer must be clean and dry before each test. 
Prisms shall be cleaned with distilled water and a mixture of ethanol and diethyl ether. 
When using a standard prism, its contact with the hand of the tester must be limited to the shortest 
possible time.  
5.4.3   Immersion fluid used must be applied to glass prisms with a glass rod with a round end in order 
to avoid damage to the prism surface in the event of contact. Organic liquid CMRs are applied with a 
pipette.  
5.4.4   The area around a measuring prism must be stabilised  prior to the test itself for one hour with a 
thermostat set to a temperature of 20.0°C. The temperature of the measuring prism may vary within a 
range that can change the refractive index that is 10 times smaller than the maximum permissible error 
of the refractometer pursuant to section 2.3. 
5.4.5   A refractometer may be adjusted using distilled water or by another means in accordance with 
the instructions of the manufacturer. 
5.4.6   After the adjustment of a refractometer, the place used for placing organic liquid CRMs on the 
prism shall be thoroughly cleaned and dried. 
5.5   Accuracy tests for refractive index indications 
5.5.1   Measurement of the refractive index of an organic liquid CRM 
The quantity of an organic liquid CRM specified by  the manufacturer shall be placed on the measuring 
prism of a digital refractometer or in the measuring area of a visual refractometer and allowed to 
stabilise thermally. 
The measured value of the refractive index of the organic liquid CRM shall be calculated as the 
arithmetic mean of five indications. After cleaning and drying the prism, measurement is repeated using the same organic liquid CRM. 
The resulting measured value is calculated as the arithmetic mean of two measured values. 
The measurement error, which is equal to the re sulting measured value minus the refractive index 
value of the organic liquid CRM, must be less than or equal to the maximum permissible error 
pursuant to section 2.3. 
5.5.2   Measurement of the refractive index of other organic liquid CRMs 
The procedure under section 5.5.1 shall be repeated with other organic liquid CRMs. The separation of 
the points on the scale used for the testing of the re fractometer must be less than or equal to 1 × 10
-1 of 
the refractive index. 
Measurement errors must be less than or equal to the maximum permissible error pursuant to section 
2.3 at all tested scale points. 
5.5.3   Adjustment checks 
After completing an accuracy test, an adjustment check of the refractometer must be carried out using 
distilled water. The zeroing requirements pursu ant to section 3.1.3 must be fulfilled. 
8 Draft General Measure No 0111-OOP-C024-11 
5.5.4   Accuracy tests of refractive index indications of a digital refractometer using prisms 
If allowed by the manufacturer, refractive index indica tion accuracy tests of digital refractometers may 
be carried out using optical glass CRMs in the form of a prism, where the expanded uncertainty U (k = 
2) of the prisms used must be at least three time s smaller than the maximum permissible error of the 
refractometer. 
5.5.5   Accuracy tests of a visual ref ractometer with a dispersion compensator  
5.5.5.1   General 
If the visual refractometer is equipped with a disp ersion compensator, tests must be carried out to 
identify pyramidal errors (see secti on 5.5.5.2) and prisma tic errors (see section 5.5.5.3) of the 
dispersion compensator. 
For a visual refractometer with a dispersion comp ensator, the sum of the measurement errors (see 
5.5.1 or 5.5.2) and the refractometer dispersion compen sator errors (5.5.5.2, 5.5. 5.3) in all tested scale 
points must be less than or equal to the maximum permissible error of the refractometer pursuant to 
section 2.3. 
5.5.5.2   Testing dispersion co mpensators for pyramidal errors 
5.5.5.2.1   The tested refractometer shall be connected to a thermostat and tempered to a temperature 
of (20.0 ± 0.1)°C. 
5.5.5.2.2   The required quantity of distilled water shall be placed in the measurement area and lit with 
white light, for example from a table lamp. The re fractometer shall be allowed to temper for a 
minimum of five minutes. After setting the lighting, it  shall be rotated by connected prisms until dark 
and light fields appear in the eyepiece.  
5.5.5.2.3   A colourless boundary is obtained by rotati ng the compensator, which shall be set as the 
line of sight mark, and the refractive index shall be  read. The colourlessness of the boundary shall be 
checked and reset by gently rotating the compensat or, and the boundary is reset as the line of sight 
mark and the refractive index read again. This pro cedure shall be repeated five times and the measured 
value of the refractive index shall be calcula ted as the arithmetic mean of the indications. 
5.5.5.2.4   The compensator shall be rotated into the s econd position in which it is possible to obtain a 
colourless boundary, and the whole procedure pursu ant to section 5.5.5.2.3 shall be repeated. 
5.5.5.2.5   The difference between the measured refrac tive index values from measurements in two 
positions of the compensator with the same dispersion shall be taken into acco unt in the accuracy test 
of a visual refractometer. 
5.5.5.3  Tests of dispersion co mpensators for prismatic error 
5.5.5.3.1   The required quantity of distilled water shall be placed in the measurement area and lit with 
monochromatic light from a sodium vapour lamp. Af ter setting the lighting, it shall be rotated by 
connected prisms until dark and light  fields appear in the eyepiece. This boundary shall be set as the 
line of sight mark. The compensator is then slowly  rotated and the movement of the boundary relative 
to the line of sight mark is observed. 
5.5.5.3.2   From the movement of the boundary, two co mpensator setting positions are determined in 
which the boundary positions are at their greatest separation. Each of these positions of the 
compensator is checked by gently rotating the comp ensator, and the boundary is reset as the line of 
sight mark and the refractive index read again. In each of these compensator positions, the five 
refractive index indications shall be  read and the measured refractive index value shall be calculated as 
the arithmetic mean of the indications. 
9 Draft General Measure No 0111-OOP-C024-11 
5.5.5.3.3   For immersion refractometers, where the disp ersion compensator is rotated only within a 
certain range, the measurement positions are the ex treme positions of the dispersion compensator. 
5.5.5.3.4    The difference in the measured refractiv e index values from the measurements in two 
positions of the compensator with the same dispersion  shall be taken into acco unt in a correctness test 
of a visual refractometer. 
5.6   Tests of resistance to external effects 
5.6.1   Test of resistance to mechanical shock 
Resistance to mechanical shock pursuant to section 3.5. 1 shall be tested in a refractometer that is not 
switched on by dropping the refractometer on its side edge and overturning it onto its face from a 
height of 50 mm. 
After the test, the refractometer must show no da mage and, in the subsequent accuracy test, the 
measurement error must not exceed the maximu m permissible error stated in section 2.3. 
5.6.2   Resistance tests of digital refract ometers to limiting supply voltage values 
5.6.2.1   Test of resistance to limiting alternating current supply voltage values 
Resistance to limiting alternating current supply voltage  values shall be tested on a refractometer that 
is switched on at the limiting voltage values UN –15% and UN +10%, where UN is the nominal voltage 
specified by the manufacturer of th e measuring instrument. If the supply voltage is found to be within the 
range of values of the nominal voltage, then the te st shall be carried out at the lowest and highest 
voltages in the range.  
Measurement errors at the limiting supply voltage  values must not exceed the maximum permissible 
errors pursuant to section 2.3. 
5.6.2.2   Test of resistance to direct current frequency changes 
Resistance to direct current frequency changes shall be  tested on a refractometer that is switched on at 
the limiting frequency values fN ±2%, where fN is the nominal supply voltage frequency. 
Measurement errors at the limiting supply voltage  frequency values must not exceed the maximum 
permissible errors pursuant to section 2.3. 
5.6.2.3   Test of resistance to limiting values of direct current supply voltage 
Resistance to limiting direct current supply voltage values shall be tested on a refractometer that is 
switched on at the limiting voltage values Umin and Umax, where Umin and Umax are the limiting supply 
voltage values specified by the manuf acturer of the measuring instrument. 
Measurement errors at the limiting supply voltage  frequency values must not exceed the maximum 
permissible errors pursuant to section 2.3. 
5.7   Electromagnetic compatibility (EMC) tests 
Electromagnetic compatibility tests are carried out only for digital refractometers. 
5.7.1   Resistance to electrostatic discharges 
Resistance to electrostatic discharg es shall be tested on a refractometer that is switched on with a 
voltage of ±6 kV for a contact discharge and ±8 kV  for an air discharge if a contact discharge cannot 
be used. Discharges are applied to the casing of the re fractometer and to coupling planes in the vicinity 
of the refractometer. 
10 Draft General Measure No 0111-OOP-C024-11 
In this test, the refractometer must show norma l functioning within the limits of the maximum 
permissible errors pursuant to section 2.3, or the re fractometer must identify a serious error and react 
to it in a defined manner. 
5.7.2   Resistance to an emitted high-frequency electromagnetic field 
Resistance to an emitted high-frequency electromagnetic field shall be tested on a refractometer that is 
switched on in the following frequency ba nds and test field intensities: 
– frequency 80 MHz to 800 MHz, intensity 3 V/m; 
– frequency 800 MHz to 960 MHz, intensity 10 V/m; 
– frequency 960 MHz to 1,400 MHz, intensity 3 V/m; 
– frequency 1,400 MHz to 2,000 MHz, intensity 10 V/m; 
The test field intensity values are given for meas urements without modulation. The test field is 
amplitude modulated with a depth of 80% and the modulation signal is sinusoidal with a modulation 
frequency of 1 kHz. The frequency step for a frequency sweep of the test field shall not be more than 
1%. The time lag for each frequency must not be less th an the period needed to test the thermometer, 
including its reaction time. It may never be less, however, than 0.5 seconds. A test field shall be applied to all sides of the refractometer casing. 
In this test, the refractometer must show norma l functioning within the limits of the maximum 
permissible errors pursuant to section 2.3, or the re fractometer must identify a serious error and react 
to it in a defined manner. 
5.7.3   Resistance to rapid electrical transients/pulse groups 
The resistance of a refractometer to rapid elect rical transients/pulse groups shall be tested on a 
refractometer that is switched on using the following voltages: 
– ±1 kV at terminals for connection to an alternating current mains; 
– ±0.5 kV at terminals for connection to an ex ternal direct current supply voltage if the 
connecting cable may be longer than three metres; 
– ±0.5 kV at terminals for connect ion to signal, communications and control cables longer than three 
metres. 
The repeat frequency for pulses shall be 5 kHz, th e repeat period for pulse groups shall be 300 ms, and 
the overall length of tests on each cable and with one pulse polarity shall be at least one minute. 
In this test, the refractometer must show norma l functioning within the limits of the maximum 
permissible errors pursuant to section 2.3, or the re fractometer must identify a serious error and react 
to it in a defined manner. 
5.7.4   Resistance to surge electrical pulses 
Resistance to surge electrical pulses shall be tested on a refractometer that is switched on with a surge 
pulse of 
tr/th = 1.2/50 (8/20) µs at a voltage of: 
– ±1 kV asymmetric or ±0.5 kV symmetric on si gnal, communications and control cables longer 
than 30 m; 
– ±1 kV asymmetric or ±0.5 kV symmetric on exte rnal alternating current and direct current 
supply cables. 
This test shall not apply to terminals for connecti on to an internal supply battery of a refractometer. 
When testing at terminals for connection to an alte rnating current supply mains, the surge pulse shall 
be applied synchronously with th e voltage, and gradually in phase angles of 0°, 90°, 180° and 270°. 
11 Draft General Measure No 0111-OOP-C024-11 
For each polarity, the level of the test voltage and, in case of an alternating current supply voltage, for 
each phase angle, three pulses shall always be app lied. The pulse repetition period shall be one minute 
or longer. 
In this test, the refractometer must show norma l functioning within the limits of the maximum 
permissible errors pursuant to section 2.3, or the re fractometer must identify a serious error and react 
to it in a defined manner. 
5.7.5   Resistance to interference emanating from cables or induced high-frequency fields 
Resistance to interference emanating from cables or induced high-frequency fields shall be tested on a 
refractometer that is switched on in the freque ncy band from 150 kHz to 80 MHz at an open test 
voltage of 3 V. Interference applies to: 
– signal cables that are longer than three metres, 
– all inputs and outputs of external direct curre nt supplies that are longer than three metres, 
– all inputs and outputs of the alternating current mains, 
– all connections to functioning earthing. 
The value of the open test voltage is given for me asurement without modulation. The test voltage is 
amplitude modulated with a depth of 80% and the modulation signal is sinusoidal with a modulation 
frequency of 1 kHz. The frequency step for a frequency sweep of the test field shall not be more than 
1%. The time lag for each frequency must not be less than the period needed to inspect the tested 
measuring instrument and/or the time for any r eaction of the test measuring instrument to the 
interference; it may never be less, however, than 0.5 seconds.  
In this test, the refractometer must show norma l functioning within the limits of the maximum 
permissible errors pursuant to section 2.3, or the re fractometer must identify a serious error and react 
to it in a defined manner. 
5.7.6   Resistance to short-term drops in the alternating current supply voltage, brief 
interruptions, and slow changes to voltage  
Resistance to short-term drops in the alternating current supply voltage, brief interruptions, and slow 
changes to voltage shall be tested on a refractom eter that is switched on at all inputs from the 
alternating current supply mains with an input current of <16 A by the application of a voltage drop:  
– to 0% UT for a period of 0.5 of the period of th e alternating current supply voltage;  
– to 0% UT for a period of 1 period of the alternating current supply voltage;  
– to 70% UT for a period of 25 periods of the alternating current supply voltage;  
and an interruption to the voltage si mulated by a voltage drop of > 95% UT for a period of 250 periods 
of the alternating current supply voltage, where UT is the nominal voltage of the device. 
For the test device, the value of UT shall be according to the means of specification of the supply 
voltage, where: 
– for a single value of the nominal supply voltage, this value shall be used; 
– for a range of nominal voltages that do not exceed 20% of the lower limiting value of the 
voltage range, any voltage value from the specified voltage range shall be used; 
– for a range of nominal voltages that exceed 20%  of the lower limiting value of the voltage 
range, the test procedure musts be applied to the lower and upper limits of the voltage range. 
For each combination of test voltage and duration, th ree interruptions shall be applied at intervals of 
10 seconds or longer. Each series of interruptions must begin gradually in phase angles of 0°, 90°, 
180° and 270°, except for the interruption of duration 250 T, where the test may be carried out at an 
angle of 0°. 
12 Draft General Measure No 0111-OOP-C024-11 
In this test, the refractometer must show norma l functioning within the limits of the maximum 
permissible errors pursuant to section 2.3, or the re fractometer must identify a serious error and react 
to it in a defined manner. 
6   Initial verifications  
6.1   General 
The following tests shall be carried out in an initial verification: 
a) a visual inspection; 
b) accuracy tests. 
6.2   Visual inspection  The following shall be assessed during visu al inspections of refractometers: 
a) the conformity of the measuring in strument with the approved type; 
b) the appearance (including a description) and state of functioning of the measuring instrument. 
6.4.2   Accuracy test of a refractometer 
An accuracy test of a refractometer shall be carried out pursuant to section 5.5 with regard to the 
refractometer type.  
7   Subsequent verifications 
Subsequent verifications shall be carried out in the same manner as the initial verifications under heading 6.  
8   Notified standards 
The CMI shall, for the purposes of specifying metrological and technical requirements for measuring 
instruments and for the purposes of specifying tes ting methods for verifications stemming from this 
General Measure, provide notification of Czech technical standards, other technical standards or 
technical documents of international or foreign orga nisations, or other technical documents containing 
detailed technical requirements (hereinafter referred to  as ‘notified standards’). A list of these notified 
standards with their assignment to the applicable me asures shall be notified by the CMI, together with 
the General Measure, in a publicly accessible manner (on the website www.cmi.cz). 
Compliance with the notified standards or parts thereof shall be considered, within the scope and 
under the conditions set out in the General Measure, to be compliance with the requirements laid down 
in such measures to which the st andards or parts thereof relate. 
 
 
13 Draft General Measure No 0111-OOP-C024-11 
14 II 
SUBSTANTIATION   
The CMI issues this General Measure laying down the metrological and technical requirements for 
legal measuring instruments and testing methods for verifications of legal measuring instruments, implementing Section 24c of Act No 50 5/1990 Coll. on metrology, as amended. 
Regulation No 345/2002 Coll. specifying measuring instruments that are subject to mandatory 
verification and type approval, as amended, incl udes refractometers among the measuring instruments 
that are subject to verification in item 7.2.1 Prism refractometers with refractive index measurement errors less than or equal to ±2 × 10
-4 and in item 7.2.2 Prism refractometers with refractive index 
measurement errors less than or equal to ±5 × 10-5 of the annex ‘List of Legal Measuring Instruments’. 
In respect of the specific measuring instrument type ‘refractive index measuring instruments—prism refractometers’, the CMI therefore issues this General Measure laying down the metrological and 
technical requirements for refractive index measuring instruments—prism refractometers and testing 
methods for type approvals a nd verifications of such legal measuring instruments. 
This regulation (General Measure) has been notif ied in accordance with Directive 98/34/EC of the 
European Parliament and of the Council of 22 June 1998 laying down a procedure for the provision of information in the field of technical standards a nd regulations and of rules on Information Society 
services, as amended by Directive 98/48/EC. 
 
III 
NOTICE  
No legal remedy may be sought against this  General Measure (Section 173(2) of Act No 
500/2004 Coll., Rules of Administrative Procedure, as amended). Under to the provisions of Section 172(5) of the Ru les of Administrative Procedure, no appeal may be 
lodged against decisions on objections. 
The conformity of the General Measure with legal regulations may be assessed in review proceedings 
under the provisions of Sections 94 to 96 of the Rules of Administrative Procedure. A party may submit a petition for review proceedings to the admi nistrative body that issued this General Measure. 
If the administrative body finds no grounds for in itiating review proceedings, it shall notify the 
petitioner of this fact, stating reasons, within thirty  days. A resolution to initiate review proceedings 
may, pursuant to the provisions of Section 174(2) of the Rules of Administrative Procedure, be issued within three years of the entry in to effect of the General Measure. 
 
IV 
ENTRY INTO FORCE 
This General Measure shall enter into force on the fifteenth day after the date of its publication 
(Section 24d of Act No 505/1990 Coll. on metrology, as amended). 
 
 ...…………………………..............  RNDr. Pavel Klenovský 
  general director