 Okružní 31, 638 00 Brno  
legmet@cmi.cz  
+420 545 555 414  
 
1. ------IND-  2019 0288 CZ-  EN- ------ 20190628 --- --- PROJET 
Executive summary for the EC (not part of this legislation)  
'Support medium flow sensors with a nozzle' may be placed on the market and put into use in the 
Czech Republic as specified measuring instruments  pursuant to Act  No 505/1990 on metrology, as 
amended.According to the Act, specified measuring instruments are instruments which are included 
in the list of the types of specified measuring instruments (Implementing Decree No  345/2002) and, 
at the same time, intended (by the manufacturer/importer) for measurements of relevance to the 
protection of public interests  in consumer protection, contractual relations, imposition of sanctions, 
fees, tariffs and taxes, health protection, environmental protection, occupational safety  or the 
protection of other public interests protected by separate legislation.This means that  their purpose is 
similar to that used for defining specified products – measuring instruments and non- automatic 
weighing instruments –  under Directives 2014/31/EU and 2014/32/EU.The requirements of this 
regulation do not apply to measuring instruments pla ced on the market in the Czech Republic for 
purposes other than the above purposes defined by Act No 505/1990 on metrology. 
The subject matter of this notified regulation is to lay down the metrological and technical 
requirements for specified measuring in struments of this type.This regulation also lays down the tests 
for the purposes of type approval and verification of specified measuring instruments of this type.  
(End of executive summary)  
 
 
 
P U B L I C  N O T I C E 
 
As the authority with substantive and territorial jurisdiction for stipulating metrological and technical 
requirements for specified measuring instruments and stipulating test methods for type approval and 
verification of legally specified instruments pursuant to §  14(1) of Act No  505/1990, on metrology, as 
amended (hereinafter the ‘Metrology Act’), and in accordance with the provisions of § 172 et seq. of 
Act No  500/2004, the Code of Administrative Procedure (hereinafter the ‘CAP’), the Czech Metrology 
Institute (hereinafter the ‘CMI’) com menced ex officio proceedings on 15 April2016 pursuant to § 46 
of the CAP, and, based on supporting documents, issues the following:  
 
 
I. 
DRAFT MEASURE OF A G ENERAL NATURE  
number:0111- OOP -C092 -18 
 
laying down metrological and technical requirements for leg ally controlled measuring 
instruments, including the testing methods for type approval and verification of legally 
controlled measuring instruments:  
'transfer medium flow sensors with a nozzle'  Measure of a General Nature No  0111- OOP -C092- 18 
2 The specified metrological requirements are on a level comparable with the relevant requirements of the 
European standards and apply to the basic design of transfer medium flow sensors with a nozzle.  
 
1   Basic definitions  
For the purposes of this general measure, terms and definitions pursuant to VIM and VIML1 as we ll as 
the terms and definitions stated below shall apply:  
1.1    
transfer medium  
a liquid used for heat transfer; for the purposes of this measure of a general nature, water vapour is 
considered, i.e. the gaseous phase of water and/or condensate  
1.2    
measurement system for measuring the flow quantity of the transfer medium  
an assembly of one or more measuring devices (measuring device components), frequently including 
additional equipment, arranged and adapted to provide information on the qualitative and quantitative 
characteristics of the transfer medium  
1.3   
transfer medium flow sensor with a nozzle 
a transfer medium flow sensor based on the principle of measuring differential pressure before a nozzle 
and inside its throat, inserted in a defined manner into pipes with specified geometric parameters  
1.4    
ISA 1932 nozzle  
a primary element comprising a convergent section consisting of a confuser with a rounded profile, and 
a cylindrical throat  
1.5    
long radius nozzle  
a primary element comprising a convergent inlet with a quarter -ellipse shape and a cylindrical throat  
1.6    Venturi nozzle  
a primary element comprising a convergent inlet, which is a standardised ISA 1932 nozzle connected to 
a cylindrical section (the 'throat') and an expanding conical section (the 'diffuser')  
1.7   
pressure tap (in wall)  
an annular or circular cavity drilled in the wall of a pipe using such a method that the edge of the cavity 
fits with the interior surface of the pipe  
                                                      
1 TNI 01 0115 International Vocabulary of Metrology – Basic and General Concepts and Associated Terms 
(VIM) and International Vocabulary of Terms in Legal Metrology (VIML) are part of the technical 
harmonisation compendium ‘Terminology in the Area of Metrology’, which is publicly accessible at 
www.unmz.cz  Measure of a General Nature No  0111- OOP -C092- 18 
3 1.8    
static pressure of the transfer medium flowi ng through the pipe  
pressure that can be measured by connecting a pressure gauge to the pressure tap in the wall  
1.9    differential pressure 
the difference between (static) pressures measured in pressure taps in the wall, one being in front of the 
nozzle and the other in the throat of a nozzle inserted in a straight pipe through which the transfer 
medium flows, taking into account all differences in tap height in front of the nozzle and in its throat  
1.10    
ratio of diameters β  
the ratio of the diameter of the aperture in the nozzle throat to the internal diameter of the pipe in front 
of the nozzle  
1.11   
Reynolds pipe number ReD 
a dimensionless parameter expressing the ratio between the inertial forces and the frictional forces in 
the pipe in front of th e nozzle 
1.12    
flow coefficient C  
a coefficient defined for a flow of incompressible liquid; it indicates the ratio of the actual flow through 
the nozzle to the theoretical flow  
1.13    
expansion coefficient  
a coefficient characterising the degree of com pressibility of the liquid in question  
2   Metrological requirements  
Metrological requirements decisive for the placement of transfer medium flow sensors with a nozzle on 
the market are applied during verification.  
2.1   Operating conditions  
The operating conditions are specified by the manufacturer in consideration of the range of anticipated ambient temperatures during operation and in consideration of range of temperatures of the transfer 
medium being measured.If there are significant temperature differe nces between the ambient 
temperature and the temperature of the flowing transfer medium, then the transfer medium flow sensor 
must be thermally insulated by suitable means.  
For transfer medium flow sensors with a nozzle, the following conditions apply to t he use of individual 
nozzle types:  
 ISA 1932 nozzle:  for 0.30 ≤ β < 0.44:7x10
4 ≤ ReD ≤ 107 
for 0.44 ≤ β ≤ 0.80:2x104 ≤ ReD ≤ 107 
 long radius nozzle:  for 0.20 ≤ β ≤ 0.80:104 ≤ ReD ≤ 107 
 Venturi nozzle:  for 0.316 ≤ β ≤ 0.775:1.5x105 ≤ ReD ≤ 2x106 Measure of a General Nature No  0111- OOP -C092- 18 
4 2.2   Limits of use  
Transfer medium flow sensors with an ISA 1932 nozzle may only be used for:  
 internal pipe diameter D:50 mm to 500 mm  
 ratio of diameters β  (d/D):0.30 to 0.80  
 the roughness of the inside surface of the nozzle and pipe must comply wit h stipulated 
requirements  
Transfer medium flow sensors with a long radius nozzle may only be used for:  
 internal pipe diameter D:50 mm to 630 mm  
 ratio of diameters β  (d/D):0.20 to 0.80  
 the roughness of the inside surface of the nozzle and pipe must co mply with stipulated 
requirements  
Transfer medium flow sensors with a Venturi nozzle may only be used for:  
 internal pipe diameter D:65 mm to 500 mm  
 minimum throat aperture diameter d:50  mm 
 ratio of diameters β  (d/D):0.316 to 0.775  
 the roughness of the inside surface of the nozzle and pipe must comply with stipulated 
requirements  
2.3   Relative uncertainty of the nozzle flow coefficient  
The following relative uncertainties for the flow coefficient C apply to individual nozzle types during 
compliance with all technical requirements and installation requirements within the limits of undesired 
increases in the relative uncertainty of the flow coefficient by additional uncertainty:  
 ISA 1932 nozzle:  for β ≤ 0.6:0.8 %  
for β> 0.6:(2β  − 0.4) %  
 long radius  nozzle:  for 0.20 ≤ β ≤ 0.80:2.0 % 
 Venturi nozzle:  for 0.316 ≤ β ≤ 0.775:(1.2 + 1.5β4) % 
If a straight length of pipe with additional uncertainty is used, then this uncertainty must be added to the 
uncertainty of the flow coefficient.The use of a straight length of pipe with additional uncertainty is 
limited to either only the section before the nozzle or only the section after the nozzle. 
Compliance with technical requirements is ascertained during the verification of the individual parts of 
the transfer  medium flow sensor.  
2.4   Relative uncertainty of the expansion coefficient  
The following relative uncertainties for the expansion coefficient ε  apply to individual nozzle types 
during compliance with all stipulated technical requirements:  
 ISA 1932 nozzle and long radius nozzle: 2∆𝑝𝑝
𝑝𝑝1% 
 Venturi nozzle: (4+100𝛽𝛽8)∆𝑝𝑝
𝑝𝑝1% 
where Δ p is the differential pressure and p1 is the absolute static pressure of the transfer medium in front 
of the nozzle.  
Compliance with technical requirements is ascertained during  the verification of the individual parts of 
the transfer medium flow sensor.  Measure of a General Nature No  0111- OOP -C092- 18 
5 3   Technical requirements  
Technical requirements decisive for the placement of transfer medium flow sensors with a nozzle on the 
market are applied during verification.  
3.1   De sign 
The basic design of a transfer medium flow sensor with a nozzle includes the following parts:  
 a nozzle (ISA 1932, long radius nozzle or a Venturi nozzle);  
 pressure taps;  
 a stabilising straight length of pipe before the nozzle with total minimum length of 10D , or a 
shorter length if measuring system installation requirements allow;  
 a stabilising straight length of pipe after the nozzle of minimum length 2 D from the front side of 
the nozzle.  
The design and installation of the nozzle must ensure that the orifice plate is not subject to plastic or 
elastic deformation during operation under the pressure of the flowing transfer medium, or that said deformation is within specified limits.  
3.2 ISA 1932 nozzle  
Part of the nozzle inside the pipe is circular and concentric with the pipe axis.The nozzle comprises a 
confuser with a rounded profile and a cylindrical throat.The profile of an ISA 1932 nozzle comprises:  
 a straight inlet section A, perpendicular to the axis;  
 a convergent section (confuser) defined by two arcs of length B and C;  
 a cylindrical throat E;  
 mount F (used to protect edge G from physical damage).  
3.2.1 Straight inlet section A  
The straight inlet section is limited by the circumference of a circle concentric with the rotationa l axis 
of diameter 1.5d and the inner circumference of the pipe of diameter D . 
If d = 2 D/3, the radial width of this straight section is zero. 
If d > 2 D/3, the front section of the nozzle does not have a straight inlet section inside the pipe.  
The surface of the front straight inlet section must have a roughness parameter of Ra ≤ 10-4 d. 
3.2.2  Convergent section of the nozzle (confuser)  
Arc B is tangential to the straight inlet section A if d < 2D/3, and its radius R1 equals 0.2 d ± 0.02d for β 
< 0.5 and 0.2d ± 0.006d for β  ≥ 0.5.Its centre is 0.2d from the inlet plane and 0.75 d from the axis.  
Arc C is tangential to arc B and throat E. Its radius R 2 equals d/3 ± 0.033d for β < 0.5 and d /3 ± 0.01 d 
for β ≥ 0.5.Its centre is at a distance d/2 + d /3 = 5d /6 from t he axis and a distance of 0.3041d from the 
straight inlet section A.  
The convergent inlet profile must comply with specific geometric requirements.Two diameters of the 
convergent inlet in the same plane perpendicular to the axis must not differ from each other by more 
than 0.1 % of their mean value.  
3.2.3 Nozzle throat E  
The throat E has diameter d and length b n = 0.3d, where the nozzle opening diameter d must comply 
with requirements specified in Article  2.2. Measure of a General Nature No  0111- OOP -C092- 18 
6 3.2.3.1   Throat diameter  
The diameter of the throat opening d is the mean value of at least four diameter measurements distributed 
along axial planes and at approximately the same angles to each other.  
3.2.3.2   Throat cylindricity  
The nozzle throat must be cylindrical, and no diameter in any cross- section measured in the cylindrical 
section of the throat may differ by more than 0.05 % of the mean diameter.  
3.2.3.3   Throat exit edge G  
The throat exit edge G must be sharp.  
3.2.3.4 Throat surface roughness  
The inner surface of the nozzle must have a roughness parameter Ra  ≤ 10-4 d. 
3.2.4 Mount F  
The mount F must have a diameter c n equal to at least 1.06d and a length less than or equal to 0.03d.Ratio 
of the height of the mount ( cn – d)/2 to its axial length must not be greater tha n 1.2.  
3.2.5 Nozzle length  
The total length of the nozzle without mount F equals 0.6041d for 0.3 ≤β≤ 2/3 and 
d



−−+ 5225,025,0 75,04041,02ββ for 2/3 <β≤ 0.8. 
3.2.6 The back side of the nozzle  
The thickness of the nozzle walls H (the straight inlet section) must not  exceed 0.1 D.No other 
requirements are specified for the back side of the nozzle.  
3.2.7 Nozzle material  
An ISA 1932 nozzle may be made of any kind of material with a known longitudinal expansion 
coefficient, under the condition that it will continuously me et all of the relevant requirements of this 
regulation under operating conditions.  
3.2.8 Differential pressure taps for the ISA 1932 nozzle  
Fillet pressure taps (spot taps or annular slots) must be used in front of the nozzle.Both tap types can be 
located either in the pipe or in its flanges or in the chamber rings. 
The pressure taps downstream of the nozzle should preferably be chosen as fillet type, unless the other relevant requirements of notified standards specify otherwise for this measure of a general nature.  
The diameter of the pressure taps must be less than 0.13 D and less than 13 mm.The pressure taps must 
be circular and cylindrical over a length of at least 2.5 times the inner diameter of the tap (measured from the inner wall of the pipe).The axis  of the pressure tap must intersect the pipe axis at an angle of 
90° ± 3°. 
Other technical requirements for tap design are specified by requirements of notified standards relevant 
to this measure of a general nature.  Measure of a General Nature No  0111- OOP -C092- 18 
7 3.3 Long radius nozzle  
There are two types of long radius nozzles – nozzles with a large ratio of diameters (usable for 0.25 ≤β≤ 
0.8) and nozzles with a small ratio of diameters (usable for 0.20 ≤ β≤ 0.5).Both types of nozzles comprise 
a convergent inlet with a quarter -ellipse sh ape and a cylindrical throat.Part of the nozzle inside the pipe 
must be circular and concentric with the pipe axis.The profile of a long radius nozzle comprises:  
 convergent part A (confuser);  
 cylindrical throat B;  
 straight end C.  
3.3.1  Straight part of the nozzle A (confuser)  
In the case of a nozzle with a large ratio of diameters, the profile of convergent part A has the shape of 
an ellipse with its centre located a distance D /2 from the axis.The major axis of the ellipse is parallel to 
the longitudinal axis of the nozzle.The length of the semi -major axis is D/2, the length of the semi -minor 
axis is ( D − d)/2. 
In the case of a nozzle with a small ratio of diameters, the profile of convergent part A has the shape of 
a quarter -ellipse with its centre lo cated at a distance of d/2 + 2d /3 = 7d /6 from the axis.The major axis 
of the ellipse is parallel to the longitudinal axis of the nozzle.The length of the semi -major axis is d; the 
length of the semi -minor axis is 2 d/3. 
The profile of the convergent section must comply with specific geometric requirements.Two diameters 
of the convergent section in the same plane perpendicular to the axis must not differ from each other by 
more than 0.1 % of their mean value.  
3.3.2  Nozzle throat B  
The throat E has diameter d and length 0.6d , where the nozzle opening diameter d must comply with 
requirements specified in Article 2.2.  
3.3.2.1   Throat diameter  
The diameter of the throat opening d is the mean value of at least four diameter measurements distributed 
along axial planes and at approximately the same angles to each other.  
3.3.2.2   Throat cylindricity  
The nozzle throat must be cylindrical, and no diameter in any cross -section measured in the cylindrical 
section of the throat may differ by more than 0.05 % of the mean diameter.  
3.3.2.3 Throat surface roughness  
The inner surface of the nozzle throat must havea roughness parameter Ra  ≤ 10-4 d. 
3.3.2.4   Throat position  
The distance between  the pipe wall and the outer surface of the nozzle must be greater than or equal to 
3 mm.  
3.3.3 Nozzle wall thickness  
The thickness of the nozzle wall H must be greater than or equal to 3  mm and less than or equal to 
0.15D .The thickness of the wall of the cylindrical throat F must be greater than or equal to 3 mm, except 
for D ≤ 65 mm, in which case the thickness F must be greater than or equal to 2  mm.  
3.3.4  Back side of the nozzle  
The shape and quality of the outer surface on the back side of the nozzle ar e not specified.  Measure of a General Nature No  0111- OOP -C092- 18 
8 3.3.5  Nozzle material  
A long radius nozzle may be made of any kind of material with a known longitudinal expansion 
coefficient under the condition that it continuously meet all of the relevant requirements of this 
regulation under operating conditions.  
3.3.6  Differential pressure taps for a long radius nozzle 
The front tap axis must be D
D D2,0
1,0 1+
−  from the inlet side of the nozzle. 
The rear tap axis must be a distance 0.50 D ± 0.01D  from the front side of the nozzle, excep t in the case 
of a nozzle with a small ratio of diameters β < 0.3188, for which the rear tap axis must be 0
02,06,1D d−  
from the inlet side of the nozzle. 
The diameter of the pressure taps must be less than 0.13 D and less than 13 mm.The pressure taps must 
be circular and cylindrical over a length of at least 2.5 times the inner diameter of the tap (measured 
from the inner wall of the pipe).The axis of the pressure tap must intersect the pipe axis at an angle of 
90° ± 3°.  
Other technical requirements for tap design are specified by requirements of notified standards relevant to this measure of a general nature.  
3.4   Venturi nozzle  
A Venturi nozzle comprises a convergent section with a rounded profile, a cylindrical  throat, and a 
divergent section (of the diffuser).The profile of this nozzle is axially symmetrical and can be 
characterised as follows:  
 a straight inlet section A, perpendicular to the axis;  
 a convergent section (confuser) defined by two arcs of leng th B and C;  
 a cylindrical throat consisting of sections E and F;  
 a divergent section (diffuser).  
3.4.1  Straight inlet part A  
The front side of a Venturi nozzle is identical to an ISA 1932 nozzle.The straight inlet section is limited by the circumference of a circle of of diameter 1.5 d centred on the axis of rotation, and the inner 
circumference of the pipe of diameter D . 
If d = 2 D/3, the radial width of this straight section is zero. 
If d > 2 D/3, the front section of the nozzle does not have a straight inlet section inside the pipe.  
The surface of the front straight inlet section must have a roughness parameter of Ra ≤ 10
-4 d. 
3.4.2  Convergent section of the nozzle (confuser)  
Arc B is tangential to the straight inlet section A if d < 2D/3, and its radius R1 equals 0.2 d ± 0.02d for β 
< 0.5 and 0.2d ± 0.006d for β  ≥ 0.5.Its centre is 0.2d from the inlet plane and 0.75 d from the axis.  
Arc C is tangential to arc B and throat E. Its radius R 2 equals d/3 ± 0.033d for β < 0.5 and d /3 ± 0.01 d 
for β ≥ 0.5.Its centre is at a distance of d/2 + d/3 = 5 d/6 from the axis and a distance of 0.3041d from 
the straight inlet part A.  
The convergent inlet profile must comply with specific geometric requirements.Two diameters of the 
convergent inlet in the sam e plane perpendicular to the axis must not differ from each other by more 
than 0.1 % of their mean value.  Measure of a General Nature No  0111- OOP -C092- 18 
9 3.4.3   Nozzle throat  
The nozzle throat comprises section E of length 0.3d and section F of length 0.4d to 0.45d.The diameter 
of the nozzle aperture d must meet the requirements specified in Article 2.2.  
3.4.3.1   Throat diameter  
The diameter of the throat opening d is the mean value of at least four diameter measurements distributed 
along axial planes and at approximately the same angles to each other.  
3.4.3.2   Throat cylindricity  
The nozzle throat must be cylindrical, and no diameter in any cross -section measured in the cylindrical 
section of the throat may differ by more than 0.05 % of the mean diameter.  
3.4.3.3   Nozzle inner surface roughness  
The i nner surface of a Venturi nozzle must have a roughness parameter of Ra  ≤ 10-4 d. 
3.4.4  Divergent section of the nozzle (diffuser)  
The divergent section of the nozzle must be connected with the cylindrical section of the throat F past 
the pressure tap witho ut the rounded section; nevertheless, the transition must be free of manufacturing 
defects and burrs.The apex angle of the divergent section (diffuser) must be less than or equal to 30°.  
A Venturi nozzle is called 'shortened' if the outlet diameter of the divergent section is less than the inner diameter of the pipe D , and 'unshortened' if the inlet diameter is equal to the inner diameter of the pipe 
D. 
3.4.5   Nozzle material  
A Venturi nozzle may be made of any kind of material with a known longitudinal expansion coefficient, 
under the condition that it continuously meet all of the relevant requirements of this regulation under 
operating conditions.  
3.4.6  Differential pressure taps for a Venturi nozzle 
Fillet pressure taps (spot taps or annular slots) must be used in front of the nozzle.Both tap types can be 
located either in the pipe or in its flanges or in the chamber rings. 
Pressure taps in the throat must contain at lest four separate pressure taps inserted in the ring chamber, 
a circular tap  or three T tap configurations. Annular or dashed slits may not be used.The axes of the 
pressure taps must intersect the axis of the Venturi nozzle, must be at identical angles to each other, and must be located in a plane perpendicular to the axis of the Venturi nozz le on the imaginary border 
between sections E and F of the cylindrical throat.The mean of point pressure taps in the throat of a 
Venturi nozzle must be less than or equal to 0.04d, as well as being between 2  mm and 10 mm.  
The pressure taps must be circular  and cylindrical over a length of at least 2.5 times the inner diameter 
of the tap (measured from the inner wall of the Venturi nozzle). 
Other technical requirements for tap design are specified by requirements of notified standards relevant 
to this measur e of a general nature.  
3.5   Straight lengths of pipe before and after the nozzle  
3.5.1   Design  
The minimum straight length of pipe before the orifice plate that must be complied with in the specific application is determined based on the ratio of diameters β  and according to the type and mutual 
arrangement of at least two fittings situated in front of the nozzle. Measure of a General Nature No  0111- OOP -C092- 18 
10 The straight part of the pipe between the first fitting in front of the nozzle and the nozzle itself may be 
made of one or more pieces, but the piece of piping of length 2D  in front of the nozzle must always 
consist of a single section.  
The design and execution of the straight lengths of pipe must facilitate the performance of the tests 
defined in Article  5.2.4 or Article  6.2.4.  
3.5.2   Pipe straightness  
The straightness of the stabilising minimum straight lengths of pipe is deemed adequate i f the surface 
deviation of the pipe from a straight line running parallel to the axis of the pipe does not exceed 0.4  % 
of its length before and after the nozzle.  
3.5.3   Mean value of the inner diameter of the pipe  
The inner diameter D  of the pipe is the arithmetic mean of at least 12  measured diameter values, i.e. four 
diameters situated at approximately the same angles to one another at each of at least three cross- sections 
evenly distributed over a length of 0.5D  before the pressure tap at the nozzle in let.Two of these cross-
sections must be situated at distances 0 D and 0.5D  from the front pressure tap and one at the plane of 
the weld in the case of a design using a welded- on throat.If a chamber tapping is used, this value of 0.5D  
must be measured from t he front edge of the chamber ring.  
3.5.4   Pipe circularity and cylindricity  
The internal shape of the pipe must be circular along the entire minimum straight length of the pipe.  
No inner pipe diameter may differ from the mean value of inner diameter D  by more than 0.3 % in any 
plane in the part of the straight length of pipe up to a distance of 2D  before the nozzle. 
The difference between inner pipe diameters of two arbitrary sections of pipe may not exceed 0.3  % of 
the mean value of inner diameter D along  the straight section of pipe between 2 D and 10D  before the 
nozzle.At the same time, the overlap of the inner diameters of parts of the pipe connected to one another, 
caused by a deviation and/or change in diameter D , may not exceed 0.3 % of the mean value  of the 
internal diameter D  at any point along the inner circumference of the pipe.  
No inner diameter of a straight length of the pipe past the nozzle may differ by more than 3  % from the 
mean internal diameter D  of the pipe before the nozzle along a distance of at least 2D  from the front 
side of an ISA 1932 nozzle or a long radius nozzle.In the case of a Venturi nozzle, the inner diameter of the connected pipe must not be less than 90 % of the inner diameter of t he end of its divergent section 
(diffuser).  
3.5.5   Quality of the inner surface of the pipe  
The internal surface of the pipe must be clean and free of any visible defects.  
Along at least the minimum straight length in front of the nozzle stipulated by the  basic version of the 
transport medium flow sensor (see Article  3.1), the internal surface of the pipe must comply with 
requirements for surface roughness Ra . 
3.6 Installation requirements  
The installation position of the nozzle must be clearly defined by its design, or it must be schematically 
marked directly on the nozzle.  Measure of a General Nature No  0111- OOP -C092- 18 
11 4   Measuring instrument markings  
4.1   General  
All inscriptions and markings must be easily visible, legible and indelible, and must provide the 
information needed for the trouble -free installation of the transfer medium flow sensor with a nozzle 
into the measurement system in relation to its other components.  
4.2   Markings  
4.2.1 Markings on the nozzle  
The following information must be on the nozzle:  
a) serial number;  
b) the value of the inner diameter of the nozzle throat opening d 20 in relation to a reference 
temperature of 20  °C; 
c) type approval mark;  
d) suitable markings to identify type and placement of differential pressure taps, if pressure taps are 
a permanent par t of the nozzle's design. 
If after the nozzle is installed in the pipe the above information is not visible, the nozzle must have a 
separate auxiliary plate with the given information, which will be part of the apparatus used to secure 
the nozzle from unauthorised removal or replacement.  
In cases where the nozzle could be installed incorrectly with regards to the direction of transfer medium flow, the nozzle must have a marking clearly indicating flow direction.  
4.2.2 Markings on transfer medium flow sensors with a nozzle  
The following information must be placed on transfer medium flow sensors with a nozzle:  
a) name of the manufacturer and type (design variant);  
b) serial number and year of production;  
c) value of the internal diameter D
20 of the pipe in rel ation to a reference temperature of 20  °C; 
d) type approval mark;  
e) nominal size DN/nominal pressure PN;  
f) indication of the direction of flow;  
g) suitable marking for type identification and placement of differential pressure taps, if pressure taps are a permanent part of the design of straight lengths of the pipe;  
h) the measured flow range or the maximum flow value.  
This information must be placed on a part of the transfer medium flow sensor that is inseparably joined 
to a straight pipe section 0.5D  in front of the nozzle (installation chamber, connector flange in front of 
the nozzle, a straight length of pipe at most 2D  in front of the nozzle).  
The following information must be specified on the connection flange or in another location along the 
straigh t length of the pipe past the nozzle (at most 2 D past the nozzle):  
i) name of the manufacturer;  
j) serial number and year of production;  
k) type approval mark;  
l) indication of the direction of flow (if reverse installation is possible).  
If in the basic configuration of the transfer medium flow sensor the straight length of the pipe before the 
nozzle is made up of multiple pieces of piping, then all of these pieces must bear a type approval mark.In 
general, all major separate parts of gas flow sensors wit h a nozzle must bear a type approval mark. Measure of a General Nature No  0111- OOP -C092- 18 
12 4.3   Marking with official marks  
Suitable areas for placement of the type approval mark and official mark(s) must be provided.  
It must be possible to safeguard the nozzle against unauthorised removal or replacement.  
5   Type approval of measuring instrument  
The type approval process for a transfer medium flow sensor with a nozzle includes the following tests 
and activities:  
a) an external inspection;  
b) a check of geometric parameters.  
5.1   External insp ection  
The following are checked during external inspection:  
 completeness of the required technical documentation;  
 the conformity of the metrological and technical characteristics specified by the manufacturer in 
the documentation to this regulation's technical and metrological requirements specified in 
Chapters  2 and 3;  
 the nozzle, pressure taps and straight lengths of pipe for any physical damage or traces of 
corrosion that would preclude further testing; and  
 places for indicating the basic geomet ric parameters of the transfer medium flow sensor with a 
nozzle and locations for placing official marks are determined.  
5.2 Check of geometric parameters  
5.2.1   Test equipment  
Suitable equipment with valid metrological traceability must be used during the check of geometric 
parameters.  
5.2.2   Reference ambient temperature for tests  
5.2.2.1   Nozzle  
During the test, the ambient temperature must be between 18 and 22  °C and must not change by more 
than 2 °C.  
5.2.2.2   Straight lengths of pipe  
Pipe ≤ DN  300:  During the test, the ambient temperature must be between 15 and 25 °C and must 
not change by more than 2 °C. 
Pipe ≤ DN  300:  During the test, the ambient temperature must be between 10 and 30 °C and must 
not change by more than 5 °C. 
5.2.3  Check of the nozzle's geometric parameters  
The internal diameter d20 of the nozzle aperture must be established in accordance with the requirement 
of Articles  3.2.3.1, 3.3.2.1 or 3.4.3.1, and must relate to a reference temperature of 20 °C.  
5.2.3.1  Check of the geometr ic parameters of an ISA 1932 nozzle  
In the case of ISA 1932 nozzles, the following geometric parameters are also checked:  
 surface finish and roughness of the front flat inlet section (see Article  3.2.1);  Measure of a General Nature No  0111- OOP -C092- 18 
13  the shape of the convergent inlet profile (see A rticle  3.2.2);  
 the length of the nozzle throat (see Article  3.2.3);  
 the cylindricity of the nozzle throat (see Article  3.2.3.2);  
 the sharpness of the throat inlet edge (see Article  3.2.3.3);  
 the roughness of the internal surface of the throat (see Article  3.2.3.4);  
 the mount on the outlet side of the throat (see Article  3.2.4);  
 the total length of the nozzle (see Article 3.2.5);  
 the thickness of the nozzle wall (see Article 3.2.6).  
5.2.3.2  Check of the geometric parameters of a long radius nozzle  
In the case of long radius nozzles, the following geometric parameters are also checked:  
 the shape of the convergent inlet profile (see Article 3.3.1);  
 the length of the nozzle throat (see Article  3.3.2);  
 the cylindricity of the nozzle throat (see Article 3.3.2.2);  
 the roughness of the internal surface of the throat (see Article  3.3.2.3);  
 throat position (see Article 3.3.2.4);  
 the thickness of the nozzle wall (see Article 3.3.3).  
5.2.3.3  Check of the geometric parameters of a Venturi nozzle  
In the case of Venturi nozzles, the following geometric parameters are also checked:  
 surface finish and roughness of the front flat inlet section (see Article  3.4.1);  
 the shape of the convergent inlet profile (see Article 3.4.2);  
 the length of  the nozzle throat (see Article  3.4.3);  
 the cylindricity of the nozzle throat (see Article  3.4.3.2);  
 the roughness of the internal surface of the nozzle's throat (see Article 3.4.3.3);  
 the finish and apex angle of divergent parts of the nozzle (see A rticle  3.4.4).  
5.2.4   Inspection of the geometric parameters of straight lengths of pipe  
The mean internal diameter value D 20 of the pipe must be established in accordance with the requirement 
of Article  3.5.3 and must relate to a reference temperature of 20  °C. 
The following geometric parameters are checked for straight lengths of pipe:  
 straightness of the pipe (see Article 3.5.2);  
 mean value of the internal diameter of the pipe (see Article 3.5.3);  
 the circularity and cylindricity of the pipe (see Article  3.5.4);  
 the roughness of the pipe's internal surface (see Article 3.5.5).  
5.2.5   Check of the geometric parameters of pressure taps  
Compliance with requirements for differential pressure taps is determined depending on nozzle type 
pursuant to Articles  3.2.8 (ISA 1932), 3.3.6 (long radius nozzle) or 3.4.6 (Venturi nozzle) and the 
manufacturer's specifications.  Measure of a General Nature No  0111- OOP -C092- 18 
14 6   Initial verification  
The following tests and activities are carried out during the initial verification of transfer medium flow 
sensors with nozzles and parts thereof:  
a) visual inspection;  
b) test of metrological characteristics;  
c) indication of the basic geo metric parameters on the relevant parts of a transfer medium flow 
sensor with a nozzle.  
6.1   Visual inspection  
The purpose of a visual inspection is to check that:  
 the execution of the transfer medium flow sensor with a nozzle matches the approved type;  
 the nozzle, pressure taps and straight lengths of pipe are not physically damaged and do not bear 
traces of corrosion that would preclude further testing;  
 the content and implementation of markings and inscriptions correspond to the information and 
requirements specified in the type approval certificate for the measuring instrument.  
If the transfer medium flow sensor with a nozzle does not pass the external inspection, it is not tested 
further.  
6.2   Geometric parameter inspection  
6.2.1   Test equipment  
Suitable equipment with valid metrological traceability must be used during the check of geometric 
parameters.  
6.2.2   Reference ambient temperature for tests  
The ambient temperature requirements pursuant to Article  5.2.2 apply to the testing.  
6.2.3  Check of the nozzle's geometric parameters  
The internal diameter d20 of the nozzle aperture must be established in accordance with the requirement 
of Articles  3.2.3.1, 3.3.2.1 or 3.4.3.1, and must relate to a reference temperature of 20 °C.  
6.2.3.1  Check of the geometric parameters of an ISA 1932 nozzle  
During initial verification of ISA 1932 nozzles, the following geometric parameters are also checked:  
 surface finish and roughness of the front flat inlet section (see Article  3.2.1);  
 the shape of the convergent inlet profile (see Article 3.2.2);  
 the length of the nozzle throat (see Article  3.2.3);  
 the cylindricity of the nozzle throat (see Article  3.2.3.2);  
 the sharpness of the throat inlet edge (see Article  3.2.3.3), if a mere visual check i s not accepted;  
 the roughness of the internal surface of the throat (see Article  3.2.3.4);  
 the mount on the outlet side of the throat (see Article  3.2.4);  
 the total length of the nozzle (see Article 3.2.5);  
 the thickness of the nozzle wall (see Art icle 3.2.6).  
6.2.3.2  Check of the geometric parameters of a long radius nozzle  
In the case of long radius nozzles, the following geometric parameters are also checked:  
 the shape of the convergent inlet profile (see Article 3.3.1);  
 the length of the nozzle throat (see Article  3.3.2);  Measure of a General Nature No  0111- OOP -C092- 18 
15  the cylindricity of the nozzle throat (see Article  3.3.2.2);  
 the roughness of the internal surface of the throat (see Article  3.3.2.3);  
 throat position (see Article 3.3.2.4);  
 the thickness of the nozzle wall (see Article  3.3.3).  
6.2.3.3  Check of the geometric parameters of a Venturi nozzle 
During initial verification of Venturi nozzles, the following geometric parameters are also checked:  
 surface finish and roughness of the front flat inlet section (see Article  3.4.1);  
 the shape of the convergent inlet profile (see Article 3.4.2);  
 the length of the nozzle throat (see Article  3.4.3);  
 the cylindricity of the nozzle throat (see Article  3.4.3.2);  
 the roughness of the internal surface of the nozzle's throat (see Article  3.4.3.3);  
 the finish and apex angle of divergent parts of the nozzle (see Article  3.4.4).  
6.2.4   Check of the geometric parameters of the straight lengths of pipe  
The mean internal diameter value D 20 of the pipe must be established in accor dance with the requirement 
of Article  3.5.3 and must relate to a reference temperature of 20  °C. 
During initial verification, the following geometric parameters of the straight lengths of pipe are also 
checked:  
 straightness of the pipe (see Article  3.5.2);  
 the circularity and cylindricity of the pipe (see Article  3.5.4);  
 the roughness of the pipe's internal surface (see Article 3.5.5).  
6.2.5   Check of the geometric parameters of the differential pressure taps  
During initial verification,  compliance with requirements for differential pressure taps is determined 
depending on nozzle type pursuant to Articles  3.2.8 (ISA 1932), 3.3.6 (long radius nozzle) or 3.4.6 
(Venturi nozzle), and the manufacturer's specifications.  
6.2.6   Indication of th e basic geometric parameters on the measuring device  
The resultant internal diameter value d 20 of the nozzle throat aperture determined pursuant to 
Article  6.2.3 must be marked in a legible and indelible manner in a suitable location on the nozzle in 
accor dance with Article  4.2.1. 
The resultant internal diameter value D 20 of the pipe determined pursuant to Article  6.2.4 must be 
marked in a legible and indelible manner in a suitable location on the transfer medium flow sensor in 
accordance with Article  4.2.2. 
7   Subsequent verification  
The procedure for subsequent verification of the nozzle is identical to the procedure for initial verification pursuant to Article  6.2.3.  
Subsequent verification of straight lengths of pipe of transfer medium flow sensors with nozzles is not 
performed. 
The user of the measuring device is responsible for long -term compliance with operating conditions, 
including keeping it in good working order and keeping the inner surface of the pipe clean.For this 
purpose, the user of the meas uring device performs (or ensures) a visual inspection of the internal surface 
of the pipe at intervals that take into account operating conditions and the type of transfer medium being 
measured.This inspection must also always be performed prior to the in stallation of the nozzle.  Measure of a General Nature No  0111- OOP -C092- 18 
16 8 Measuring instrument check  
When checking measuring instruments pursuant to § 11a of the Metrology Act at the request of an entity 
that could be affected by its incorrect measurement, the procedure set out in Chapter  6 is followe d.The 
last sentence of Article  6.1 does not apply. 
9   Notified standards  
For the purposes of specifying the metrological and technical requirements for measuring instruments 
and specifying the testing methods for their type approval and verification arisi ng from this general 
measure, the CMI shall notify Czech technical standards, other technical standards or technical 
documents of international or foreign organisations, or other technical documents containing more 
detailed technical requirements (hereinaf ter referred to as ‘notified standards’).The CMI will publish a 
list of these notified standards attached to the relevant measures, together with the general measure, in 
a manner accessible to the public ( on www.cmi.cz ). 
Compliance with notified standards or parts thereof is considered, to the extent and under the conditions stipulated by a general measure, to be compliance with the requirements stipulated by this measure to 
which these standards or parts thereof apply.  
Compliance with notified standards is one way of demonstrating compliance with the 
requirements.These requirements may also be met by using another technical solution guaranteeing an 
equivalent or higher level of protection of legitimate interests.  
II. 
G R O U N D S 
The CMI issues, pursuant to §  14(1)(j) of the Metrology Act, for the implementation of § 6(2), §  9(1) 
and (9) as well as §  11a(3) of the Metrology Act, this measure of a general nature, stipulating 
metrological and technical requirements for specified measuring devices and test methods for type 
approval for verification of the following specified measuring devices: 'transfer medium flow sensors 
with a nozzle'.  
Decree No  345/2002 stipulating measuring instruments for mandatory verification and measuring 
instruments subject to type approval, as amended, classifies the measuring instruments under item 3.1.2(b) in the annex entitled ‘List of specified measuring instruments’ as measuring instruments 
subject to type approval and mandatory verificatio n. 
This legislation (Measure of a General Nature) will be notified in accordance with Directive (EU) 
2015/1535 of the European Parliament and of the Council of 9 September  2015 laying down a procedure 
for the provision of information in the field of technical regulations and of rules on Information Society 
services.  
III. 
I N S T R U C T I O N S  
In accordance with §  172(l) APC in conjunction with §  39(l) APC, the CMI has stipulated a time limit 
for comments of 30 days as of the date of posting the draft on the official notice board.Comments 
submitted after this time limit will not be considered.  
The persons concerned are hereby invited to comment on this draft Measure of a General Nature.With 
regard to the provisions of §  172(4) APC, comments are to be submi tted in writing.  Measure of a General Nature No  0111- OOP -C092- 18 
17 Pursuant to the provisions of § 174(1) APC, in conjunction with the provisions of § 37(1) APC, it must 
be clearly stated who is submitting the comments, which general measure the comments concern, how 
the draft contradicts legislation or h ow the general measure is inaccurate. The comments must also 
contain the signature of the person making the comments.  
The supporting documents for this draft general measure may be consulted at the Czech Metrology 
Institute, Legal Metrology Department, Okr užní 31, 638 00 Brno, after making arrangements by 
telephone.  
This draft general measure shall be posted for 15  days.  
 
 
Czech Metrology Institute  
Director General  