Czech Metrology Institute  
Okružní 31,  638 00 
Brno 
                                                     1. ------IND- 2011 0011 CZ- EN- ------ 20110126 --- --- PROJET 
 
The Czech Metrology Institute (CMI), as the comp etent local body for stipulating metrological and 
technical requirements for a specified measuring device and for the stipulation of test methods for type 
approval and for verification of a specified measur ing device pursuant to Section 14(1) of Act No. 
505/1990 Coll., on Metrology, as amended, and pursuant to provisions of Section 172 et seq. of Act No. 500/2004 Coll., the Administrative Code, as amended (hereinafter the "AC"), has on 29 November 
2010 commenced ex officio proceedings pursuant to Section 46 of the AC, and based on supporting 
documents issues this: 
  
I. 
M E A S U R E  O F  A  G E N E R A L  N A T U R E 
number:  0111-OOP-C018-10 
reference no. 0313/011/10/Pos., 
publication date: 29 November 2010 
 
stipulating metrological and technical requirements for specified measuring devices, 
including test methods for verifying specified measuring devices: 
 "process gas chromatographs for determination of the energy content of natural gas " 
 
1   Basic definitions 
For the purposes of this measure of a general natu re, terminology and defini tions contained in the 
VIM1) and the following apply: 
1.1   process gas chromatograph: a measuring device that determines energy values (heat of 
combustion and heating value) of natural gas based on an analysis of its chemical composition 
1.2   heat of combustion: the amount of heat that can be gained through complete combustion of a 
certain amount of gas with air in such a way that the pressure p1 under which the reaction occurs 
remains constant, and all combustion products  are returned at the same temperature t1 as that of the 
reactants, and all these products are in a gaseous state except for water that is created during 
combustion, and which condenses into a liquid state at temperature t1 
1.3   heating value: the amount of heat that can be gained through complete combustion of a certain 
amount of gas with air in such a way that the pressure p1 under which the reaction occurs remains 
constant, and all combustion products ar e returned at the same temperature t1 as that of the reactants, 
and all these products are in a gaseous state 
 
1)   International Vocabulary of Metrology - Basic and General Concepts and Associated Terms (VIM). Draft Measure of a General Nature No. 0111-OOP-C018-10 
1.4 internal calibration gases: a calibration gas that is part of the measuring device and serves for 
periodic operational calibration 
1.5   external calibration gas: calibration gas – a certified reference material that is not part of the 
measuring device, and is used to verify the measu ring device, or for calibration or testing of the 
measuring device's metrological characteristics 
2   Metrological requirements 
2.1   Stipulated service conditions 
The range of service conditions is stipulated by the manufacturer. Reference conditions for process gas chromatographs are as follows: 
– pressure:   101,325 kPa, 
– measurement temperature:  15 °C, 
– combustion temperature:  15 °C. 
The nominal power voltage value is specified by the manufacturer of the measuring device. 
2.2   Measurement range The measurement range must perm it determination of all 11 compone nts of natural gas during one 
analysis. Table 1 lists usable ranges of natural gas components. 
Table 1 – Usable ranges of natural gas components 
Component Range  
(% mol) 
Hydrogen 0.001 to 0.05 
Helium 0.001 to 0.05 
Oxygen 0.001 to 5 
Nitrogen 0.001 to 60 
Carbon dioxide 0.001 to 35 
Methane 40 to 100 
Ethane 0.02 to 15 
Propane 0.001 to 25 
Butanes 0.0001 to 5 
Pentanes 0.0001 to 1 
Hexanes 0.0001 to 0.5 
 
2.3   Measurement precisions 
The precision of measurement of heat of combustion, expressed as relative error, must be δr < 0.2 %. 
2.4   Measurement repeatability The repeatability of measurement of heat of com bustion, expressed as relative standard deviation, 
must be as follows: 
a) during type approval ≤ 0.05 %; 
2 Draft Measure of a General Nature No. 0111-OOP-C018-10 
b) during measuring device verification ≤ 0.1 %. 
2.5    Measuring device calibration 
Calibration with internal calibration gas must take  place regularly, usually once per day, however at 
least once a week (i.e. no more than 168 h after the previous calibration). 
3   Technical requirements 
3.1   In general A process gas chromatogra ph usually consists of: 
a) an analytical portion, 
b) an electronic control and integration unit, 
c) a pneumatic portion, 
d) a switching system. 
A process gas chromatograph must work continually , which means that it performs at least one 
analysis per hour for each sample being tested. 
3.2   Analytical portion 
The dispenser provides the analyzer with a constant  or measured amount of natural gas sample to be 
analyzed. The dispenser may be a multi-path valve containing an isolated fixed volume of calibration 
gas or sample. 
The separation unit consists of one or more chro matic columns through which the carrier gas into 
which the samples or calibration gas have been introduced flows. 
The detector may be a thermally conducting detect or (TCD) or a flame ionization detector (FID). 
3.3    Electronic control and integration unit The electronic portion may be built into the analytical portion, or can be located separately as an 
independent unit. 
The electronic control and integration unit must inte grate the signal from the detector, store calibration 
data, evaluate and calculate energy or other valu es from the composition of the natural gas. It must 
store the calculated data in electronic form or export it to a recording device. 
3.4   Pneumatic portion 
The pneumatic portion ensures stabilization and regulation of: 
– the carrier gas, which is most often helium, 
– service gases, e.g. hydrogen, air or nitrogen, which are necessary for functionality of the 
detectors used, 
– the internal calibration gas. 
 
The switching system connects samples and the inte rnal calibration gas to the dispenser, and must 
enable switching between them. The internal calibrati on gas must not be disconnected form the device. 
If multiple sample inputs are used, the analysis duration and dosage frequency must be set so that at 
least 24 analyses can be made from each input gas stream every 24 hours. 
If sampling takes place outdoors, the sampling capillary must be tempered so that the gas temperature 
does not sink below 10 °C. Sample flow must be arranged  in such a way that the gas sample delay, i.e. 
the time from when the sample to when  its analysis results are issued, is shorter than the dosage cycle. 
3 Draft Measure of a General Nature No. 0111-OOP-C018-10 
For measurement in contractual relationships, perm anent sampling tubing must be provided; samples 
in sample containers can only be used justified cases and with the agreement of both parties to the 
contractual relationship. 
3.5   Software (SW)  
The process gas chromatograph must be equipped with SW to calculate energy values and other 
quantities under applicable reference conditions a nd in measurement units under real and dry gas 
conditions, and under refe rence conditions in accordance to Article 2.1. 
Heat of combustion for higher-order hydrocarbons designated as  ∑C6+ is calculated from the heat of 
combustion of n-hexane. 
3.6   Internal calibration gas 
Internal calibration gas is usually a synthetica lly prepared gaseous mixture, whose composition 
approximates the expected characteristics of th e samples under analysis. The calibration gas must 
contain eleven components of natural gas: methane,  ethane, propane, n-butane, i-butane, n-pentane, i-
pentane, neo-pentane, n-hexane, carbon dioxide and nitrogen. 
Calibration gas can also be a real sample of natu ral gas, whose heat of combustion and chemical 
composition are certified. A calibration gas certificate must contain: 
a) information regarding the container in which it is kept, 
b) filling pressure/amount, 
c) required and actual admixture values and their measurement uncertainties, 
d) minimum service pressure, 
e) manufacture date, 
f) date to which it can be used for calibration. 
Table 2 lists requirements for base gases: 
Table 2 – Base gases for internal calibration gases 
Component Purity grade Gas purity 
% 
Methane 4.5 99.995 
Ethane 3.5 99.95 
Propane 3.5 99.95 
Butane 3.5 99.95 
Nitrogen 5.0 99.999 
Carbon dioxide 5.0 99.999 
3.7   Electromagnetic compatibility 
Measuring devices must not be affected by ambient electrical and electromagnetic interference, and 
must meet the requirements of the relevant special legislation2). 
                                                      
2) Government Order No. 616/2006 Coll., on technical product requirements with respect to their 
electromagnetic compatibility. 
4 Draft Measure of a General Nature No. 0111-OOP-C018-10 
3.8   Protection from fraud 
A process gas chromatograph must not have characte ristics that would facilitate is fraudulent use, 
while minimizing the possibility of its unintentional erroneous use. Components that the user must not 
disassemble or adjust must be protected from such activities. 
The structural element of the measuring device that contains internal calibration gas and its entry must 
be sealed in a manner that prevents it from being di sconnected from the device, and the integrity of the 
connection to the measuring device must be secured by an official mark. 
4   Markings 
4.1   Markings on the measuring device 
A process gas chromatograph, which can consist of several separate parts, must have the following 
information listed on each part: 
a) manufacturer identification, 
b) chromatograph type, 
c) serial number of each part of the chromatograph, 
d) heat of combustion measurement range, 
e) type approval mark. 
All markings and labels must be legible, perm anent, unambiguous and impossible to remove in a 
normal fashion. 
4.2   Verification mark 
If the measuring device has met all requirements dur ing testing, verification marks are affixed in 
locations specified in the type approval certificate, and a verification sheet is issued for the measuring 
device, with a "Measurement Record" attached that lists certified external gas parameters and data 
measured by the verified measuring device. 
Verification marks are affixed to all separate parts of the measuring device in accordance with the type 
approval certificate (e.g. to the cabinet housing the chromatographic columns, the internal calibration 
gas input, control elements, and the structural element of the measuring device containing the internal calibration gas). 
5   Type approval 
5.1   In general 
The type approval process for a process gas chro matograph consists of the following tests: 
a) external inspection, 
b) measurement accuracy test, 
c) measurement repeatability test. 
Type approval requires passing an electrical safety test. 
5.2   External inspection 
The following is assessed during an external inspection of a process gas chromatograph: 
a) that prescribed technical documentation is complete, 
b) that metrological and technical characteristics specified by the manufacturer in documentation 
conform to requirements of this re gulation listed in sections 2 and 3, 
5 Draft Measure of a General Nature No. 0111-OOP-C018-10 
c) that functional wholes of the process gas ch romatograph are complete and correspond to 
prescribed technical documentation, 
d) the calibration table in the tested device co rresponds with the internal calibration gas 
certificate, including cylinder number and certificate validity, 
e) the SW version of the process gas chromat ograph is the same as specified by the 
manufacturer. 
5.3   Functional tests 
Prior to functional tests, the process gas chromatogra ph is calibrated with inte rnal calibration gas, if 
necessary. 
5.3.1   Accuracy test 
An accuracy test involves analysis of two differe nt external calibration gases with known chemical 
composition and heat of combustion. During analysis, three sequential measurements of each gas are performed. The first measurement is 
not counted (it could be influenced by a previous ly measured sample). The second measurement is 
considered acceptable if the heat of combustion value does not differ from the third measurement by 
more than 0.025 kWh/m
3 (in practice, the difference between all three measurements should not be 
greater than to the third decimal point). If this me asurement difference is not achieved, the test is 
considered to be unsuccessful. 
The heat of combustion of natural gas is given by its composition according to the formula: 
 [][]
) , () , ( , .
) , ( ,
2 212 2 10
2 2 1p t Zp t V t H x
p t V t H
mixN
jsj i
s∑
==
 
where  Hs is the total heat of combustion of the natural gas, 
  Hs°
j  heat of combustion of the j-th component, 
  Zmix  compressibility factor for conversion to real-world gas (at reference  
    temperature and pressure – measurement and combustion). 
The following parameters are used to compare me asured and certified heat of combustion values: 
absolute error:  certx x− =měř δ , 
relative error: 
certcert) (
xx x
r−=měřδ ,  
and equivalent: 
) (2
cert2cert
U Ux xEn+−=
měřměř where 1<nE  
The uncertainty U is individually chosen as double the devi ce's reproducibility parameter (0.05% for 
heat of combustion expressed in kWh/m3). 
Heat of combustion measurement accuracy expressed as relative error must meet the requirements of 
section 2.3. 
5.3.2   Repeatability test 
The repeatability involves making 20 measurements of  a selected gas sample, usually a gas (from a 
gas cylinder) with a known heat of combustion, and the calculation of the sample standard deviation 
from the measured values. 
6 Draft Measure of a General Nature No. 0111-OOP-C018-10 
 
The following are calculated from the measured values: 
arithmetic mean: nx
xn
ii∑
==1 
sample standard deviation: ()
()1) (12
−−
=∑
=
nx x
x sn
ii
i  
and the relative standard deviation is calculated: 100 % × =sxRSD  
where n is the number of measurements and x is the concentration of the i-th component. 
Heat of combustion measurement repeatability expr essed as a relative standard deviation (%RSD) 
must meet the requirements of section 2.4 a). 
6   Initial verification 
6.1   In general 
The verification process consists of the following tests: 
a) visual inspection, 
b) measurement accuracy test, 
c) measurement repeatability test. 
6.2   Visual inspection 
The following is assessed during a visual in spection of a process gas chromatograph: 
a) that the measuring device is the same as the approved type, 
b) that the process gas chromatograph is complete  according to the type approval certificate, 
c) that individual parts of the process gas ch romatograph are undamaged and the measuring 
device as a whole is functional, 
d) that the SW version of the measuring devi ce is the one approved during type approval. 
6.3   Functional tests 
6.3.1   Accuracy test 
An accuracy test is performed according to section 5.3.1. 
6.3.2    Measurement repeatability test 
A measurement repeatability test is  performed according to section 5. 3.2, with the difference being 
that only three measurements are performed. 
Heat of combustion measurement repeatability expr essed as a relative standard deviation must meet 
the requirements of section 2.4 b). 
7 Draft Measure of a General Nature No. 0111-OOP-C018-10 
6.4   Assessment of tests 
If the measuring device met all requirements during tests, verification marks are affixed to the 
measuring device in places specified in the type approv al certificate, and a verification sheet is issued 
for the measuring device, with a Measurement  Record according to section 4.2 attached. 
Table 3 – Measurement Record 
Component Calibration gas A 
concentration (% mol ) Calibration gas B 
concentration (% mol ) 
certified value measured value certified value measured value 
Methane     
….     
Heat of combustion*) 
kWh/m3     
  M J / m3     
Uncertainty kWh/m3     
Absolute error      
Reproducibility (%)     
Relative deviation (%)     
Equivalence (ratio)     
*)   Under reference conditions (heat of combustion / measurement:  15 °C/15 °C, pressure 101.325 kPa). 
 
7   Subsequent verification 
7.1   In general 
During subsequent verification, the same tests are performed as during initial verification according to 
sections 6.1 to 6.4. 
7.2    Verification of a measuring device with limited test scope 
If, during service that has no influence on the metrol ogical characteristics of the measuring device or 
during replacement of a gas cylinder with internal calibration gas, one of the verification marks was 
damaged, except for the main verification mark, instead of verification according to section 7.1, the 
measuring device can be tested with limited test range to confirm that it meets given requirements 
during the validity period of the original verification. If not stated in the type approval certificate, the 
main verification mark is considered to be the ve rification mark with the verification sheet number, 
located on the analyzer housing. 
Verification of a measuring device with limited test scope is allowed only if, immediately after the 
damage to the verification marks occurs, marks of a registered repair facility for these measuring 
devices are affixed in those locations, and if the user immediately requests verification of the 
measuring device. Until a new verification mark has been affixed, the measuring device must not be 
used as a specified measuring device, unless a permit  pursuant to Section 14(2)  of Act No. 505/1990 
Coll., on metrology, has been issued. 
Verification of a measuring device with limited test sc ope is performed on a sample of real natural gas, 
where the characteristics of the g as must be corroborated via a natu ral gas analysis record with a 
declaration of metrological relationship to valu es of primary and certified reference materials. 
An accuracy test by measurement of real natural g as is performed using the pr ocedure in section 5.3.1. 
8 Draft Measure of a General Nature No. 0111-OOP-C018-10 
If the measuring device meets requirements, verificati on marks are affixed in locations specified in the 
type approval certificate where they were removed in order to perform the aforementioned service, 
and a verification sheet is issued for the measuring de vice, with a verification expiry date that is the 
same as the expiry of the original verification; a ttached to this verification sheet is a Measurement 
Record pursuant to section 4.2. 
8   Notified standards 
To specify metrological and technical requirements for measuring devices and to specify verification test methods stemming from this measure of a general nature, the CMI notifies Czech technical 
standards, other technical standards or technical docum ents of international or foreign organizations or 
other technical documents containing detailed technical requirements (hereinafter "notified standards"). The CMI shall publish a list of these no tified standards, with their assignation to relevant 
measures, along with the measure of a general natu re, in a manner available to the public (on the 
website www.cmi.cz). 
Compliance with notified standards or parts thereof is considered to be, to the extent and under the 
conditions stipulated by a measure of a general nature, to be compliance with those requirements 
stipulated by this measure to which these standards or parts thereof apply. 
 
 
II. 
J U S T I F I C A T I O N 
The CMI issues, towards the implementation of Section 24c of Act No. 505/1990 Coll., on metrology, 
as amended, this measure of a ge neral nature, stipulating metrologi cal and technical requirements for 
specified measuring devices and test methods for verification of these specified measuring devices. 
In Decree No. 345/2002 Coll., specifying measuring devices for mandatory verification and measuring 
devices subject to type approval, as amended, the annex "List of Specified Measuring Device Types" 
classifies process gas chromatographs for determinat ion of the energy content of natural gas under 
item 7.4.1 as measuring devices subject to type approval and verification. 
The CMI thus issues, towards the implementation of Section 24c of Act No. 505/1990 Coll., on 
metrology, as amended, for the measuring device type specified as " process gas chromatographs for 
determination of the energy content of natural g as", this measure of a general nature, stipulating 
metrological and technical requirements for  process gas chromatographs for determination of the 
energy content of natural gas and test methods fo r type approval and verification of these specified 
measuring devices. 
  
III. 
N O T I C E 
A measure of a general nature cannot be appeal ed (Section 173 (2) of Act No. 500/2004 Coll., the 
Administrative Code, as amended (hereinafter the "Administrative Code"). Pursuant to provisions of Section 172 (5) of the Administrative Code, a decision on objections cannot 
be appealed in any manner. The conformance of a measure of a general nature with legislation can be assessed in review 
proceedings pursuant to Section 94 to 96 of th e Administrative Code. A participant may submit a 
request for a review to the administrative body that issued this measure of a general nature. If the administrative body does not find reasons for co mmencing review proceedings, it shall notify the 
9 Draft Measure of a General Nature No. 0111-OOP-C018-10 
10 applicant within thirty days of this fact along w ith its reasons. A decision on commencement of review 
proceedings can, according to Section 174 (2) of the Administrative Code, be issued within three years 
of the effective date of the measure of a general nature. 
 
IV. 
E F F E C T I V E  D A T E 
This measure of a general nature takes effect on th e fifteenth day following the day of its publication 
(Section 24d of Act No. 505/1990 Coll., on metrology, as amended). This measure of a general nature sha ll be published for a period of 15 days.