1 
  Technical Specification for 
Verification and Inspection of 
Diaphragm Gas Meter s S/N CNMV 137 
Rev. 1 
1. This Technical Specification is developed  pursuant to the stipulations in Paragraph 2 of 
Articles  14 and Paragraph 2 of Articles  16 in the Weights and Measures Act.  
2. The date of promulgation, document number, date of enforcement and content of 
amendment are listed as follows:  
Rev. Date of 
Promulgation  Document N o. Date of 
Enforcement  Content of Amendment  
1 Jun. 2, .2003  No. 09240005160  Jul. 1, 2003  
2 May 1, 2006  No. 0954000 1570  Jul. 1, 2007  Revised according to related OIML 
requirements . 
3 Nov. 18, 2010   No. 09940005810   Jan. 1, 2011  
1. When conducting  re-verification 
on meters that passed initial  
verification before the 
implementation of  type approval, 
meters shall be sampled and tested 
for their errors at flow rate 3 Qmin as 
required for meters that ha ve been 
subject to type approval . 
2. Amending the requirements of 
errors for f low rates between 0.1 
Qmax and Qmax with same positive or 
negativ e signs of errors . 
4 Sep. 2, 2014  No. 10340007390  Sep. 2, 2014  1. For gas meters with Qmax greater 
than 16 m3/h that are not subject to 
type approval , the test  for errors at 
flow rate 3 Qmin is no longer 
conducted . 
2. For gas meters with Qmax not 
greater  than 16 m3/h that passed 
initial verification before the 
implement ation  of type approval, the 
test for errors at flow  rate 3 Qmin is 
maintained. For gas meters with Qmax 
greater  than 16 m3/h, the test  for 
errors at flow  rate 3 Qmin is no longer 
conducted w ith reference to those 
procedures for gas  meters that are not 
subject to type approval.  
5 Feb. 21, 201 8  No. 10740000820  July 1,  2018  1. For effective management , year of 
manufacture and history of repair are 
added  as mandatory marking items.  
2. To regula te the external airtight 
test in accordance with the claimed 
maximum working pressure  of gas 
meters , the leakage rate of external 
airtight and the submitted documents 
required for verification are revised.  
3. For effective use of verification 
resources, the determination of pass 
or fail for errors at flow  rate 3 Qmin is 
revised.  
 
2 
  
4. In consideration  of the material of 
seal may change with the progress of 
technology and the requirement of 
environmental protection, the 
material of seal is widened and no 
longer  limited to lead . 
6 To be 
determined  No. ○○○  July 1, 2024  1. Referring to the specification for 
type approval of diaphragm gas 
meters ( CNPA  137) promulgated on 
Feb. 6, 2023, amending the existing 
CNMV 31. 
2. Changing the serial number and 
the revision of this specification from 
CNMV 31, rev. 5 to CNMV 137, 
rev.1.  
3. This specification  is formulated with reference to the following international 
specifications : 
OIML R6  General provisions for gas volume meters  （1989（E）） 
OIML R31  Diaphragm gas meters  （1995（E）） 
OIML R 137-1&2  G as meters                              （2012（E）） 
 
 
Date of Promulgation   
(To be determined ) Bureau of Standards, Metrology and 
Inspection, Ministry of Economic Affairs  Date of Enforcement  
July 1, 2024 
 NO GUARANTEE ON THE TRANSLATION  
In case of discrepancies  between the English translation and Chinese text, the Chinese text shall govern.  
 
  
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1. Scope: This technical  specification applies to  diaphragm gas meters ( hereinafter 
referred "gas meters") subject to verification and inspection in which the 
volume of gas flow is measured by means of measuring chamber s with 
deformable films , including any other (electronic) devices that may be 
attached to the gas meter s. 
 
2. Definition  
2.1 Cyclic volume  
     The volume of gas corresponding to one full revolution of the moving part(s) 
inside the gas meter . 
 
2.2 Error  
The quantity value of a measurand minus quantity value  of a reference  (relative 
error) . 
 
  2.3 M aximum permissi ble error (MPE)  
 The extreme value of measurement error, with respect to a known reference 
quantity value, permitted by specifications or regulations fo r a given measuring 
instrument . 
 
  2.4 Accuracy class  
 The class of gas meter  that meet s stated metrolog ical requirements  to keep 
measurement errors within specified limits under specified operating 
conditions . 
 
 2.5 Rated operating conditions  
The conditions of use giving the range of values of the measurand and the 
influence quantities, for which the errors  of the gas meter are required to be 
within the limits of the maximum permissible error . 
 
 2.6 F low rate, Q 
The q uotient of the actual quantity of gas passing through the gas meter and 
the time taken for this quantity to pass through the gas meter.  
  
 2.7 Maximum flow rate, Qmax 
The highest flow rate at which a gas meter is required to operate within the 
limits of its maximum permissible error, whilst operated within its rated 
operating conditions . 
 
 2.8 Minimum flow rate, Qmin  
4 
  
The low est flow rate at whic h a gas meter is required to operate within the limits 
of its maximum permissible error, whilst operated within its rated operating 
conditions . 
 
 2.9 Transitional flow rate, Qt 
The flow rate which occurs between the maximum flow rate Qmax and the 
minimum f low rate Qmin that divides the flow rate range into two zones, the 
"upper zone" and the "lower zone", each characterized by its own maximum 
permissible error . 
 
2.10 Flow rate range  
The range of the flow rate of gas that is limited by the maximum flow rate 
Qmax and the minimum flow rate Qmin. 
 
2.11 Minimum and maximum working temperature, tmin and tmax 
    The minimum and maximum gas temperature that a gas meter can withstand, 
within its rated operating conditions, without unacceptable deterioration of its 
metrological performance . 
 
2.12 Working temperature range, tm 
The temperature range that is allowed when a gas meter works within the 
maximum permissible error . 
 
2.13 Minimum and maximum working pressure, Pmin and Pmax 
The minimum and maximum internal press ure that a gas meter can withstand, 
within its rated operating conditions, without deterioration of its metrological 
performance . 
 
2.14 Working pressure range , Pm 
The range that is between the maximum working pressure and the minimum 
working pressure.  
 
2.15 Static pressure loss or pressure differential, ∆P 
The pressure difference between the inlet and the outlet of a gas meter  when 
gas is flowing.  
 
2.16 Pressure  absorption  
The difference between the pressures at the inlet and outlet of the gas meter 
while the gas is flowing. Using air with density about  1.2 kg/m3 as the medium, 
the average pressure loss in one measurement cycle at flow  rate Qmax is taken 
as the total pressure absorption.    
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2.17 Value of a given air volume quantity  
The specified air volume that has been passing through the gas meter to 
measu re the error.    
 
3. Check of e xternal appearance  
3.1 Gas meter s shall be clear ly marked with the following items on easy scrutiny  
spot: 
(1) Type approval number . 
(2) Name of the manufacturer .  
(3) Type number  and serial  number.  
(4) Metrological gas name . 
(5) Accuracy class  (other than class 1.5).  
(6) Maximum flow rate : expressed  as Qmax = …m3/h. 
(7) Minimum flow rate:  expressed  as Qmin = …m3/h 
(8) Transitional flow rate:  expressed  as Qt = … m3/h for which is  not e qual to 
0.1 Qmax. 
(9) Working temperature range: expressed  as tmin – tmax =… - … ℃ or  tm= … - … 
℃ 
(10) Working pressure  range:  expressed  as Pmin – Pmax = … - … kPa or  Pm =… 
- … kPa. 
(11) Pulse values of HF and LF outputs : expressed  as L / pulse (dm3 / pulse or 
m3 / pulse) or pulse / L (pulse / dm3 or pulse / m3) for gas meters equipped  
with pulse generators . 
(12) Indication of flow direction : expressed  by an arrow  symbol.  
(13) Year of manufacture : expressed by 4 digits of the year of C.E., or year of 
the Republic Era . 
(14) Value of the cyclic volume: expressed as V = …dm3 (or m3) 
(15) Maximum permissible pressure difference between inlet and outlet : 
expressed as  ΔPmax =…Pa (or kPa). 
(16) Nominal diameter ( inside diameter of inlet and outlet): expressed by mm.   
(17) History of repair: expressed by trademark of manufacturer and year of 
repair.  
 
In addition to the above -mentioned markings, the software identification  of the 
firmware  should be displayed as required for gas meters with electronic indicating 
devices . Besides the nominal voltage and nominal frequency, expressed as Unom 
= …V and fnom = …Hz separately, should be marked  for gas meters with external 
power sup ply; the operational lifetime should be marked or the remaining battery 
capacity should be displayed as required for gas meters with  non-replaceable  
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power source ; the latest date by which the battery is replaced should be marked  
(In case an automatic alarm  indicates when the battery life is below 10 %, the 
above markings are not required) or the remaining battery capacity should be 
displayed as required for gas meters with replaceable battery . 
 
In case of the application for  re-verification Subparagraph 1, 9, 10, 13,  15 and 17, 
Paragraph 1 nee d not to be marked for gas meters not subject to type approval or 
that passed initial verification before  the implement ation  of type approval . 
 
In case of the application for  re-verification Subparagraph 13, Paragraph 1  is not 
applicable  to gas meters with Qmax not greater than 16 m3/h that passed initial 
verification before June 30, 2018 . 
 
3.2 Indicating devices  
The mechanic  indicating device of a gas meter should  be provided wit h scale 
marks which stand out in contrast  to the scale  (i.e. the silver line)  and the 
electronic indicating device should be provided with function to  display test  
mode.  
 
In case the gas meter has a combination of mechanic and electronic indicating 
devices and both indicating devices can show the  consumed gas volume 
synchronically, their indicated quantities should be identical . 
 
3.3 Characteristics of flow rate  
The maximum flow  rate, the upper  limit s of the corresponding transitional flow 
rate and the minimum flow  rate for a gas meter are given i n Table 1.  
Table 1 
Qmax 
m3/h Upper limit of Qt 
m3/h Upper limit of Qmin 
m3/h 
1 
1.6 
2.5 
4 
6 
10 
16 
25 
40 
65 
100 
160 
250 
400 
650 
1000  0.10 
0.16 
0.25 
0.40 
0.60 
1.0 
1.6 
2.5 
4.0 
6.5 
10 
16 
25 
40 
65 
100 0.016  
0.016  
0.016  
0.025  
0.040  
0.060  
0.100  
0.160  
0.250  
0.400  
0.650  
1.000  
1.600  
2.500  
4.000  
6.500   
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4. Verification, inspection and maximum permissible errors 
 
4.1 The traceability  of the equipment for verification and inspection is required.  
 
4.2 Prior to  verification or inspection , gas meter s shall be placed at leas t 12 hours in 
the place where  the verification is implemented . 
 
4.3 External airtight test  
4.3.1 For gas m eter with maximum working pressure not greater than  10 kPa : 
block the outlet of gas meter; conduct the test with air pressure of 10  kPa, 
and hold for  3 minutes ; the leakage  rate shall be less than 67 Pa  / min. 
4.3.2 For gas m eter with maximum working pressure greater than 10 kPa: b lock 
the outlet of gas meter; conduct the test with maximum working pressure , 
and hold for  3 minutes ; the leakage  rate shall  be less than 2%. 
4.3.3 In case of application for verification , the applicants and the measuring 
instrument enterprises entitled to conduct self -verification  shall  submit or 
prepare quality report/certificate , which shall be  in compli ance with the 
require ments of Section 4.3.1 or 4.3.2  and issued by testing labs accredited 
by accreditation bodies of ILAC MRA, original manufacturers of said gas 
meters or enterprises holding business license of repair  for measuring 
instruments , and relevant supporting docume nts in accordance with the 
quantity of gas meters to be tested. If necessary, the dedicated weights and 
measures authority should check the external airtight of these gas meters.  
4.4 Pressure absorption test  
The total pressure absorption of a gas meter, av eraged over a measuring cycle, at 
flow rate of air  with density about  1.2 kg/m3 as Q max, shall not exceed the value 
given in Table 2.  
Table 2  
Maximum flow rate 
 
m3/h Maximum permissible average value 
for total pressure absorption  
(including safety refere nce detection 
control unit ) 
Verification  
Pa Maximum permissible average value 
for total pressure absorption  
(including safety reference detection 
control unit ) 
Inspection  
Pa 
 
1 to 10 (inclusive)  
 
16 to 65 (inclusive)  
 
 
100 to 1000 (inclusive ） 200 
(242)  
 
300 
(330)  
 
400 
(440)  220 
(242)  
 
330 
(363)  
 
440 
(484)  
 
4.5 Flow rates of verification , inspection, and collected gas volume for error  test  
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The error  test of a gas meter  for verification and inspection  is conducted  at 
specified flow  rates and m inimum collected volume s listed in Table 3. The 
difference  between the actual  flow rate and the flow  rate listed in Table 3 shall 
not be greater  than 5%.  
For gas meters with Qmax not greater than 16 m3/h that  are subject to type 
approval , the error test shall be conducted one by one at flow  rate Q max and 0.2 
Qmax. Besides , 5% of the gas meters applied for verification shall be sampled 
and tested for error at flow  rate 3 Q min. If the quantity  of the gas meters applied 
for verification is less than 100, it is  counted as 100. In case any one of the 
samples failed the test, the original samples should be re -tested. If any one of 
them failed the test again, the whole batch of gas meters shall be rejected . 
For gas meters with Qmax greater  than 16 m3/h that are not s ubject to type 
approval , all meters shall be verified one by one  for error test at flow  rates Qmax 
and 0.2 Q max. 
For gas meters with Qmax not greater  than 16 m3/h that passed initial verification 
before the implement ation  of type approval, all meters  for re-verification shall 
be conducted error test one by one at  flow rate Qmax and 0.2 Q max. Besides, 5% 
of the gas meters for re-verification shall be sampled and tested for error at flow  
rate 3 Q min. If the quantity  of meters applied for re-verification is le ss than 100, 
it is counted as 100. In case any one of the samples failed the test, the original 
samples should  be re -tested. If any one of them failed the test again, the whole 
batch of gas meters s hall be rejected .  
For gas meters with Qmax greater  than 16 m3/h that passed initial verification 
before the implement ation  of type approval, all meters  shall be conducted error 
test one by one at  flowrate Qmax and 0.2 Q max when apply for re -verification.  
Table 3 
Maximum 
flow rate 
(m3/h) Verification  and inspection  flow rate 
 
m3/h Minimum collected gas volume for 
verification  and inspection   
dm3 
Qmax 0.2 Q max 3 Q min  Qmax 0.2 Q max 3 Q min  
1 1 0.20 0.048  50 20 10 
1.6 1.6 0.32 0.048  50 20 10 
2.5 2.5 0.50 0.048  50 30 10 
4 4 0.80 0.075  70 50 20 
6 6 1.20 0.120  120 70 30 
10 10 2.00 0.180  200 100 50 
16 16 3.20 0.30 500 300 100 
25 25 5.00 0.48 800 400 200 
40 40 8.00 0.75 1200  600 300  
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65 65 13.00  1.20 2000  1000  500 
100 100 20.00  1.95 4000  2000  1000  
160 160 32.00  .300 8000  4000  2000  
250 250 50.00  4.80 12000  6000  3000  
400 400 80.00  7.50 20000  10000  5000  
650 650 130.00  12.0 32000  16000  8000  
1000  1000  200.00  19.5 60000  30000  15000  
 
4.6 Calculation of error  
The error of a gas meter shall be expressed by percentage , i.e., the ratio of the 
difference  between the in dicated value  as volume of air flowing through the gas 
meter and the value  as volume of air flowing  through  the standard divided by 
the value  of air flowing  through  the standard . 
   (Indicated value – standard value)  
Error (%) =         x 100 (%)  
                  Standard value          
(1) When a wet gas meter is used as standard , the standard value 
sV  is defined as 
follows.   
P T WG s C C QCF V V  )( )(
 
VWG：Volume of air flowing through wet gas meter  
CF(Q)：Correction function of instrument error for the wet gas meter  
CT：Temperature correction quantity between standard  and gas meter  
Cp：Pressure correction quantity between standard  and gas meter  
 
 (2) When  sonic nozzle is used as standard , the standard value 
sV  is defined as 
follows.  
 
 
 
 
Cd：Discharge coefficient of sonic nozzle  
A*：Cross -section al area at throat  
C*：Critical flow function of sonic nozzle  
P0：Stagnation pressure at the upstrea m of sonic nozzle  
T0：Stagnation temperature at the upstream of sonic nozzle  
t： Collection time of air volume for verification   
R
：Universal gas constant  
M：Molecular mass of air   
),(m mPT
：Air density at Tm and Pm, in whic h Tm and Pm stand for the 
temperature and pressure of the meter under test respectively  
 
),()(0* *
m m od
sPT MTRtP CA CV
 
10 
  
4.7 Maximum permissible error s for v erification  and inspect ion of a gas meter  
When tested with  air whose density is about 1.2 kg/m3, the m aximum 
permissible  error s for  verification and inspection shall conform to the 
stipulations given in Table 4.  
Table 4  
 
 
 
 
 
4.8 The period of validity for verification, unless otherwise specified,  is from the 
day of a verification compliance  mark  affixed to the gas meter to the firs t day of 
the following month of the next 10 years.  
In case of verification for gas meters with Qmax not greater than 16 m3/h that 
passed initial verification before the implement ation  of type approval,  the period 
of validity for verification  is from the day of a verification compliance  mark  
affixed to the gas meter to the first day of the following month of the next 5 
years, and will be implemented from July 1, 2026.  
 
5. Verification compliance marks  
5.1  The verification compliance mark  shall be attached w ith metal wire (plate)  and 
sealed at the opening of the shell on the body of a gas meter.  The duration of 
validity for verification shall also be clearly mark ed on the front of the meter .  
 
6. Implementation date ：This specification will come into effect fr om July 1, 2024. 
However, if the correction according to the technical specification for type 
approval of diaphragm gas meters has not been completed before December 31, 
2027, the specification before the amendment is implemented will be applicable  to 
gas meters with Qmax not greater than 16 m3/h that  are subject to type approval . Flow rate  
m3/h  Verification  
 (Inspection)  
Accuracy class  
1.0 1.5 
Qmin ≤ Q < Qt ± 2 % 
(± 4 %) ± 3 % 
(- 6 %, + 3 %) 
Qt ≤ Q ≤ Qmax ± 1 % 
(± 2 %)  ± 1.5 % 
(± 3 %)